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Tlib AVx.U;L>iOF

iiii .UliJuD FOxv T L L F O K & A T I O H

.AN I O N — P A I R B Y TLx, T O T A L AB-OIIFTIOK
O F l O O O V O L T i.L-CT'AOITL IN

.IR

By
Frederick A i l 1 1 am Kuether

_iN A B o T R a OT

ubm i fctca to the
S t ?<.1 e Co H e r e
in p a r t i a l

uciiool of dradufl.te 0t idies of L i d >
of A g r i c u l t u r e a n a Arno lie a Sc 1 o nc e
f\ilflll:ru nt of the r. - ao i rcrr.n t s
f o r the d e c r e e of
rOG lOu

OF

F A I L O ,..'0 1 'A Y

ijep- rl;.i'.nt o f
1951

-roved

Physics

x’xiL, iWjLiiu.Gii j_,•-.iuK-.fY U h
OF

,-.i; I O k - F A l u B Y

l'-Oti TILL FORk-VI'ION

1

i'ii

T O T A L .u3;_ O R F T I O F

O F l O O O VOl_T ^ L u C T n O f b
Frcderick

the

c o n s t r u e ted

ionization properties

Preliain&ry
totally

measurements

absorbed

average.

This

enei’ijy r e q u i r e d f o r
3 8 . 5 ev * 4 . 5 (. f o r
absorbed

of

indicate

of

ev e l e c t r o n s
on

the

the d e t e r m i n a t i o n of '.V, the a v e r a g e

the f o r m a t i o n of a n i o n - p a i r ,
the

particular

a c o m p s r i £o n of

r e m o v e u f r o m the
with

ionization

case of l O O O

chamber.

The

c a nnot be m e a s u r e u

to

ratio

to be

ev e l e c t r o n s

electron.

low eneryy

the

prouuces K ion-pairs
for

these

formeu

s i mple,

to p o s i t i v e

the e l e c t r o n s
of

--uite

suitable

entering

the

w h i c h of

y i e l d s K,

pe r i n i t i a l

ions

electric

currents,

simultaneously,

ion-pairs

r&^uircu

c u r r e n t due

ionization chamber by

the c u r r e n t uue

If

which appears

the

aver-.ye n u m b e r o f

enerjy

n:as.

in air.

consists

course

t h at 1 0 3 1

in

2 7 * 5 * 3,j i o n - p a i r s

The m e t h o d o f m e a s u r e m e n t ,

fields

-for the m e a s u r e m e n t

sl o w e l e c t r o n s

in air produce

allows

.iIR

'.Villiam K u e b h e r

nn instrument has been
of

IF

the

low cnerjy

e l e c t r o n w i t h e n e r g y L ev

per* i n i t i a l

electron,

the f o r m a t i o n of

an

;V, the

ion-pair

avers, ye
is y i v o n by

th e ra t.io h / K •
The

present

instrument

r- n_ c of e l e c t r o n s ,

as w e l l

t w e e n 200 e v anti. R O O O ev.
experimentally known
per unit
me a sure

track
s,

f u n c t i o n of

the

Initial

as

of m e a s u r i n g

.7 f o r e l e c t r o n s

'.Vith this

specific

l e nyth,
total

is c a p a b l e

of

information

ionization

ion—pair

electron

and

the

formation

m a y be d e t e r m i n e d

cnoru.

the

oneryy be ­

the e x p e r i m e n t a l l y d i f f i c u l t

track lenyth,

R,

to
as a

TABLE OP CONTENTS
Section

Pa^e

Ionization Processes

1

Ionization Measurements

0

The I m p o r t a n c e
Experimental

of d e l t a - r u y

Ionization

Observations on electrons

9

In Air

Design Considerations

19

V a c u u m R e q u i r e m e n t s of
Chamber

the

Vacuum Reruiremcats

the d u n C h a m b e r

of

Ionization
91

E l e c t r i c a l an d j^lectronic
the E l e c t r o n Gu n
Other electronic

14

25

Components for
97

and E l e c t r i c a l

Components

40

p r e s s u r e M e a s u r i n g ampul :.mv nt

51

Vacuum ^e-ls

51

Vapor Traps

52

Clcariin 0 of V a c u u m s u r f a c e s

52

Operational details

54

E v a c u a t i o n of I o n i z a t i o n aim G u n Chamber's

54

Care o f the

anu d i f f u s i o n P u m p s

55

P o s i t i o n i n g a n d F o c u s i n u of B e a m o n d m a l l
Orifice

56

d e t e r m i n e t i o n of the m t r ^ y d i s t r i b u t i o n
of e l e c t r o n s F a c s i n p t h r o u g h the dm a l l
O r i f i c e i n to the I o n i z a t i o n C h a m b e r

58

The

67

Pore p u m p s

. T u i t i o n of the

Aemoval

of

p t o p ; in 0 Gas

tn«, I o n i z a t i o n

d e t e r m i n e tion of

Products

the b a t u r n t i o n C o n d i t i o n

diffusion and ueconibimtion effects

68

77
80

Ice s u i t s

81

3u 20 ^£ited I m p r o v e m e n t s

86

Conclusion an^

90

Bibliography

acknowledgments

91

L I S T O F FIGUiUiS
I^ure

I'a^e
16

1
6

A

3

Interior

4

S e c t i o n of L o o r

5

Electron

G u n I.iounted o n A n d pi ate

28

6

electron

Gun

31

7

3 0 0 v Iie^ula ted T o w e r

S

The

o

Oeneral

Surface

Control

P] e u\'

—

View of

x - -

—

■*•

tlie Lqaixraent
of

the

20'
1 by

20
3 0 :t D o o r

S e al

23

and V o l t a j c

SuppGlea

Supply

32

iunel
\j

38

■ c • t: «nd
-

10

retail

11

An Ion C o l l e c t o r

12

C u r r e n t Lea c u r i n s

13

jj. c.

22

Oe r’no n 0j2 f'lce
—

of V a c u u m I n t e r f a c e

41
43
44

network

Curre.it ^ q l i l ' i c r
Curve

49

14

j_ncn-i_y

15

An

Io n C o l l e c t i o n Ca r ve

69

16

An

Ion C o l l e c t i o n C u r v e

72

17

An

Ion C o l l e c t i o n Curve

74

18

Liotribetion

47

63

78

LIST OF TABLES
Table
I
II
III
IV

Pa ^e
L e i ta — ray s rjtcocdi;\; l O O e v L n e r j y Prouu.ced
by e l e c t r o n a, P r o t o n s , anti Alp!ia-pa rtlclos

11

F r e q u e n c y of I o n - C l u s t e r s containing;
Various Numb e r s of Ion i z a t i o n s

12

Felc-itive I o n Y i e l d
Lxnerimental Values
of K

of

Clusters

13

in tbe Tietcnniiv: t i o n
• 84

THIi A V L R A G L
CF

aK

jA ^ R G T Y

R L JJlRLd F O R Tlid N O R k A T I O N

ION-P^IR BY ILL T OT A L ABSORPTION

O F l O O O V O L T L L jiO T R O N S

IN A I R

IONIZATION PAOCLSSrL
Various
protons,

pax*ticles,

electrons,

s u c h as

alpha-particlos,

gamma-rays,

x-rays,

etc.

neutrons,

are o f t e n

t h o u g h t o f as p o s s e s s i n g d i f f e r e n t o v e r - a l l p a t t e r n s
I o n i z a t i o n as
ences

the p a r t i c l e s

in t h e s e p a t t e r n s

their common features.
i ng

s e c t i on s ,

a very

i o n i z a t i o n c a u s e d bp
rays.

.delta-rays are

o r less)

electrons

fly

through matter.

are m o r e

frequently

As w i l l b e

indicated

significant

f r a c t i o n of

the

particle

initial

the l o w

ejected by

energy
the

of

T he d i f f e r ­

emphasized

than

i n the f o l l o w ­
the t o ta l

Is d u e

to d e l t a -

(a f e w h u n d r e d v o l t s

initial

particle from

the

m o l e c u l e s w i t h w h i c h It c o l l i d e s .
W h e n the
energy equal
there

initial particle
to

the

is a f i n i t e

all its

energy b y an inelastic

will be

e j e c t e d f r o m the

atom or molecule
grouna
have

that

the m e d i u m ,

the p a r t i c l e

will y i e l d

c o l l i s i o n and a n e l e c t r o n

target atom or molecule

with

It Is v a s t l y m o r e p r o b a b l e

t ha t

is m e r e l y e x c i t e d

state b y r a d i a t i o n .

It s k i n e t i c

a m e d i u m with

Ionization potential of

probability

negligible velocity.

traverses

The

and later

returns

the
to It s

a t o m o r m o l e c u l e m a y a l so

energy increased by

the

collision.

2
As the e n e r g y o f

the p a r t i c l e

ability of i o n i z a t i o n
Increases greatly.

(electron ejection,

W h e n the

the i o n i z a t i o n p o t e n t i a l
to be f o r m e u b y

the

initial

for

of the f i r s t
to cause

e n e r g y is i n c r e a s e d

particle.

Ion or more

i o n - p a i r m a y be

ionization by

and p a r t i c u l a r l y of

delta-ray which

contributes

n om ena,

e n e r g y of

the

to

the

the

the total

particle
second

the

electron

sufficient
I t Is n o t

energy

only
al s o

the
t h os e

slow e l e c t r o n or

incident

ray or p a r ti cl e becomes

the p o s s i b i l i t i e s

in Ionization become very numerous.

ionization

ion-pairs

the o b s e r v e d c o l l i s i o n p h e ­

l arge e n o u g h to f o r m m a n y I o n - p a i r s ,
the s e q u e n c e

the

the I n i t i a l p a r t i c l e b u t

of the p o s i t i v e

As

hence

twice

two

initial

probably

ejected with

collision,

b e h a v i o r In c o l l i s i o n o f

The

formation)

to

for

Involved In forming

the p o s i t i v e

the p r o b ­

Ion-pair

it b e c o m e s p o s s i b l e

is i t s e l f n o t n e c e s s a r i l y
ion-pair,

Is increased.,

can o nly be due

for

However

to the i o n i z a t i o n c a u s e d

b y the c o m p o n e n t s .
For an a l p h a - p a r t i c l e
phenomena must be due
positive

ions,

by attachment

etc.

Ions.

Ionization
ejected

Th e n e g a t i v e

electrons,

i o n is f o r m e d

o f a n e l e c t r o n to a n e u t r a l m o l e c u l e o r a tom.
e l e c t r o - n e g a t i v e ,25 the n e g a t i v e

air w o u l d b e Og,
are f u r t h e r

of m u l t i p l y

ai r the

to the a l p h a - p a r t i c l e ,

and negative

Since o x y g e n is

there

traversing

etc.

For

some

complicating

target atoms
effects

c h a r g e d Ions of mercury,

which m a y be

In

and molecules

s u c h as

Hg^,

Ions

the

creation

Hg"*"*, H g ’4'4'*, K g ’4"*"4”4,

formed b y relatively low energy

collisions.

Ionization by

electro-negative

u i ssociation of

the

target molecule,

secondary importance
i,ven in the

absence

constructed.
as the

The

to

following

is

<u i t c

effects of

secondary effects mentioned

sketch

f o r the

incid-nt particle.

oarticles

the

ar e

ionization,

cases,

remain complex.

account

ana to p r e s e n t a r oa l

of

multiple

etc#

e x c e p t in i s o l a t e d

the c o l l i s i o n p h e n o m e n a
f r o m the p r e s e n t

molecules,

the

H e n c e we d i g r e s s
physical

situation

instrument which has been

remarks

are

confined

The b e h a v i o r o f o t h e r

to e l e c t r o n s
incident

s i milar.
end

otart
t n e r y y l e s s th an
ionization notentinl
jinaioy V
total
The w a v i n g

track

e l e c t r o n ^0 s t a r t i n g
eiudrp

..-hen the

ion p a i r s .

The

is c h a r a c t e r i s t i c of

electi*on is no
rmye

of

longer

The

t r ac k o f

e-ual

to o r y r e a t e r

is of

course

and

£■• f o r

tali.,n as

the
than

considerable

electrons of

average
the

seme

ranye

d,

the

the

path of

is

statistical

the

s, is

election,

variation

and

electron.
always
There

in b o t h It

en c r y y ,

lienee A a n d

a n a av-. rape

track lonjth

enerjy.

an

t a k e n as the

track of

the

s

of p r o d u c i n g

electron,

the r a u y e o f

electrons of a yiven
the

carmole

the e l e c t r o n ,
the e nd s of

l e n g t h of

the

'.vith an one r jy of v e l e c t r o n v o l t s

linear distance between
total

track length,

s are
for many

4
H x p e r i m e n t a l l y i t is m u c h l e s s
than to m e a s u r e
fact

s for a particle

at the p r e s e n t

possible

state

to m e a s u r e

knowledge

of

L et

s.

the e l e c t r o n ,
formed along

the

However,

Ion-pairs

and let K be
the

of

tr a ck .

It d o e s n o t a p p e a r

n u m b e r of

T h e n d K * I ds,

of e n e r g y V e l e c t r o n v o l t s
g i v e n in

terns of

the

The p>roblem is
This
of

cannot

the

tne e n e r g y

I = f(V ).

Obviously

where
naiss

the

the

of

or for a par t i c l e

the u n k n o w n

accuracy

Let

o r we m a y w r i t e

F r o m tlx., fli-st i n t e g r a l

fox- the
above

s and

s » i (V ) = J (R ),

T * (R ) dR.

these

track

as a f u n c t i o n

relation exists between

energy

are

i o n i s a t i o n I ca n

electron,

s t a t e d in

average

ion-pairs

e x p r e s s i o n f o r Ky.

specific

d s ■ H f(V) u.V =

for K y can be

W is

the

experimental

some

track of

electron.

this

of tine e l e c t r o n .

ca n be d e n o t e d :

Integral

some

range of

anu

energy anu range
as

to i n t e g r a t e

However

be d e t e r m i n e d w i t h
of

energy of

generally be done b e c a u s e

electron.

the

The l i m i t s
V
the

some

obtained:

formed p e r cm of
total

Hence

the
then

the

forms:

f o r m a t i o n of an io na n u a kno vdod, e o f f(V),

o func 11o

ince
f ( V ) J * ( K ) L f (V)
V

R

In

in a n i n d i r e c t m a n n e r

s can be

the

to m e a s u r e

^ i v e n energy.

of k n o w l e d g e

the b e h a v i o r o f

I be

difficult

dV

5
P r o v i d i n g we write
T he g o a l o f
to m e a s u r e b o t h
ion-pair,

W,

energy of

the

the

d R = L*(V)

the e q u i p m e n t w h i c h is
the a v e r a g e

a n d the

aspects of

H = L(V);

range,

electrons#

energy Tor
R,

to b e d e s c r i b e d
the

the

discussion

returns

the m o r e

general

The

case

of

an

with

th e d e t e r m i n a t i o n o f

the f o r m a t i o n o f a n i o n - p a i r .

is

initial

The p r e s e n t w ork dea l s o n l y

energy for

p henomena of a particle.

formation of

as a f u n c t i o n o f

the f i r s t p r o b l e m ,

to

dV

the

following
the i o n i z a t i o n

6

I ON IZ AT I O N lu^ASUKALIhNTS
The a v e r a g e

energy,

has often b e e n assumed
energy of

W,

Tor

to b e

a c o n s t a n t i n d e p e n d e n t of

the i n c i d e n t p a r t i c l e .

c o n u i t l o n h o l d s o n l y as l o n g
is c o m p a r a b l e
electrons.

as

I n the c a s e

the v e l o c i t y o f the p a r t i c l e

to l O O e v e l e c t r o n s ,

relative numbers of e x c i t a t i o n
ization collisions

of

(in w h i c h

the

Below

theoretical

with electrons,

x:>r'°'ko n s

is n o t a c o n s t a n t b u t

c o l l i s i o n s and of l i g h t i o n ­

are p r a c t i c a l l y i n d e p e n d e n t

the m o v i n g p a r t i c l e .

but

the v e l o c i t y of o r b i t a l

guide.

Howev er ,

indicates

particle

the n u m b e r o f
into

t ha t W

i n c r e a s e s w i t h d e c r e a s i n g e nergy.

the

themselves

total

electrons

experimental work

and alpha-particles

k n o w l e d g e of

divide

The

this is r e l a t i v e l y u n i m p o r t a n t

. experimentally the d e t e r m i n a t i o n of W r e q u i r e s

for

t h at the

e n e r g y is u l t i m a t e l y d i s s i p a t e d i n l i g h t

collisions.

there is no

the

c o l l i s i o n s w i l l o f co u r s e d e p e n d

u p o n the p a r t i c l e v e l o c i t y ,
as n e a r l y a l l

a nd

the e n e r g y l o s s e s are o f the

and v e l o c i t y of

frequency of more violent

ionizing

theoretical result

ionization potential)

the n a t u r e

0,2 i.iev p r o t o n s ,

Y;/illiams^ p o i n t s ou t t h a t

c o n s t a n c y o f W is i m p l i e d i n the

the

It is n o w k n o w n t h a t t h is

t h a n the v e l o c i t y of o r b i t a l
_
18
o f air, this is a b o u t 6 x 1 0
c m / sec

alpha-particles.

o r d e r of

the

to o r g r e a t e r

which corresponds
0.8 Mev

the f o r m a t i o n of an i o n - p a i r

the

e n e r g y d i s s i p a t e d b y the m o v i n g
ions formed.

two g r o u p s .

The d e t e r m i n a t i o n s

Absol u te deteimiinations

in which the

n u m b e r

known f r o m w i t h i n
formou p e r

&rxcx

tine

ubsox-bed.

cloud c l u m b e r

e n e r g y

g> ^ x ^ t i c X o
ox*

(as In i o n i s a t i o n

c l ifu-abu r

determinations

v/liich

an ionizing a g e n t

i s

the moving particles are

e x p e i ' i : u f ' n t - and. the number of ion-pairs

s.tuuic; s )

in

of

is

s

observed directly (as in

can average of many particles

: .invicli c;s ) •

for*

Secondly, relative

ooco.mule, the effectiveness of

comi^aroo

with

the da G 1 al;ha-particle

ionization •
The 11a

G *

a.X p b a . - p a r t . i c l e

determinations •
ing to i..ano^°
rately k n o w n

Tire

anei
bo

a c c e p tod

*'7 • b G

oc

a c c u r a t e l y

the number o f

a 1 jplis.— p a r t i c l
1-cnovwrx

ization o f

waG*

calculated,

for
the

measured w h e n
wiae rzigc

to

tlie

"o e

e m it t ed per second per gram

b • 71

V • C3G

e n e r g y
tlie

xc l O ^

oc 10-^.

of*

ev

tlx ex

i n i t i a l
.0

monoenor^o t i c

e l e c t x"*o r* s

of* tlie

with c o n s i u e r a b l e
loo

is i.immured, V« may
alpha-particle.

jo u r t i c l e
o

Hence when the ion­
be

The variation

i n i t i a l particle is more easily

c n c r g i e s ,

be totally

Ida). G ’ is in equilibrium, and

al g )ha - p a r t i c l e s
a

The strength of a source

b e nun of tin. ja,mua-rsy activity

*.•s

of

It s h o u l o

ev.

in

with

of „ with

\vhich

Chadwick anu bills'''® is accu­

X 0°

of i.a (C -f D)

of rauium i s

e n e r g y of the particle accord­

R n t h c . r f o z*d ,

Too

may be m e a s u r e c i

i s. most suitable for absolute

iro

the

can be generated over a
case of electrons where

d o sired energy can bo formed

o r_» a o .
o m e d i a s 1 z e cl

absorbed

the sole, c r i t e r i o n
If total a b s o i ' p t i o n

if*
o f

ibex
brio

d o e s

fcixa t the initial particle must

initial
-w m ; r g y

n o t

u w r j is to be used as

dissipated by the particle.

occur,

some measurement of the

r e s i d u a l e n e r g y o f the pa rticle m u s t be made
the e n e r g y e x p e n d e d in ionization*

to d e t e r m i n e

The l a t t e r p r o c e d u r e

of c o u r s e i n t r o d u c e s error*

I

9

THii I M P O R T A N C E O F D E L T A - R A Y I O N I Z A T I O N
In 1 9 1 6 b y photogi*aphing
In h y d r o g e n

at a l o w p r e s s u r e

Bumstead® became

the f i r s t

electrons

radiating

estimated

2000e v

electrons

or delta-rays*

to b e

t r a c k s of* a l p h a - p a r t i c l e s

in a W i l s o n

to o b t a i n d e f i n i t e

to b e

to e m e r g e d i s t i n c t l y ,

edge*

In 1 9 2 2

C* T.

distribution of delta-rays
experiments

maximum range had

a nd n o t

along

theory w o u l a
o ut t h a t
the f i r s t
c au s e o f

to

a velocity

that

angle

40

that

about twice
to be

the l i n e o f m o t i o n
indicate*

In 1 9 2 6

small velo c­

studied

a f u n c t i o n of

however,

th e re

track giving

it a

the

angular

their energy.

the d e l t a - r a y o f
t h at o f

the

al p ha -

e j e c t e d n e a r l y at

the d i r e c t i o n o f m o t i o n o f the
as the
Chadwick

alpha-particle,

s i mp l e

collision
Q
and L m e l e u s 0 p o i n t e d

the r e s u l t s o b t a i n e d b y W i l s o n w e r e m i s l e a d i n g
0.2 m m

the

of delta-ray

ionization

In h y d r o g e n at n o r m a l
out

as

Wilson estimated

It a p p e a r e d ;

right a n g l e s

R. W i l s o n

s l ow

electrons

but

large numbers of delta-rays with

ragged

Bumstead

these

Only a few exceptional

w h i c h f o r m e d p r o j e c t i o n s o n the

particle*

evidence of

track*

the m a x i m u m e n e r g y o f

ities,

In h i s

cloud chamber,

f r o m an a l p h a - p a r t i c l e

had su ff ic ie nt v e l o c i t y
appeared

the

track cannot be obse r v e d b e ­

surrounding

temperature

the

alpha-particle

and pressure

than fortp

five degrees

o f a 2 m m d e l t a — r a y Is 0*V

a n d I n the

In

track*

they point

the m o s t p r o b a b l e n u m b e r of d e f l e c t i o n s

greater

since

t h r o u g h an

the f i r s t

0.2 m m

first 0*3 m m of a 0*6 m m

10

d e l t a — ray,

It Is 5.4.

a forward, d i r e c t i o n .
range o f

Hence
This

the l o n g e r

was o b s e r v e d .

should have

Since

in a i r the

a d e l t a - r a y o f a g i v e n e n e r g y is o n l y o n e - f i f t h

that i n h y d r o g e n ;

a nd the n u m b e r o f

and the

the n u c l e u s

great,

tracks

charge on
the

scattering electrons

are r o u g h l y

s e v e n t i m e s as

chances of d e f l e c t i o n t h r o u g h a large

so g r e a t l y i n c r e a s e d
the a l p h a - t r a c k

that

the d e l t a - r a y s w i l l

at r a n d o m .

argon w i t h

this

su m m a r y ;

emerge f r o m

Chadwick and Emeleus

their s t u d y o f a l p h a - t r a c k s in h y d r o g e n ,

a n g l e are

helium,

conclude
air,

and

9

MAs f a r as o u r o b s e r v a t i o n s go, the r e s u l t s are in
a c c o r d w i t h the v i e w t h a t the d e l t a - r a y a r i s e s f r o m
the c o l l i s i o n o f the a l p h a - p a r t i c l e w i t h a n e l e c t r o n
i n the a t o m s t h r o u g h w h i c h it p a s s e s .
We a s s u m e that,
f o r the d i s t a n c e s i n v o l v e d in t h e s e c o l l i s i o n s , the
a l p h a - p a r t i c l e a n d the e l e c t r o n b e h a v e as p o i n t charges,
a n a t h a t the l a w o f f o r c e b e t w e e n t h e m is that o f the
inverse square."
H ence i t h a s b e e n e s t a b l i s h e d
a straight forward manner
m at t e r .

t ha t d e l t a - r a y s

are f o r m e d in

as the i n i t i a l p a r t i c l e

traverses

H o w e v e r the i o n i z a t i o n p h e n o m e n o n o f p a r t i c l e s

n ot be p r o p e r l y u n d e r s t o o d u n t i l
tion d u e d i r e c t l y
established.

can­

the m a g n i t u d e o f the i o n i z a ­

to the d e l t a - r a y e l e c t r o n s h a s b e e n

The follo w i n g

s e c t i o n s w i l l d e a l w i t h this

po i n t .
There

appears

to b e l i t t l e

question

tha t a m a j o r p o r t i o n

of the i o n i z a t i o n c a u s e d b y

the i n c i d e n t p a r t i c l e

the s e c o n d a r y i o n i z a t i o n o f

the d e l t a - r a y .

series o f

experimental observations on

t i o n o n l i v i n g c e l l s L e a 25 r e p o r t s

is due

to

In an e x t e n s i v e

the e f f e c t s o f r a d i a ­

the f o l l o w i n g i m p o r t a n c e

11

TABLE

I 26

D j^ L T A - K A Y S E X C E L L I N G l O O e v iiUERGY P R O D U C E D B Y
ELECTRONS,

PROTONS,

Electron Energy
Kev

0.5
1.5
3.0
6.0
24.0
96.0
192.0
584.0

AND*ALPHA-PARTICLES
^ N u m b e r of Ions P r o d u c e d b y
Delta-rays per Primary Ionization

0.225
0.504
0.597
0.672
0.780
0.856
0.891
0.920

Alpha-particle Energy
Mev

1.0
4.0
5.0
6.0
8.0

0.718
0.907
0.925
0.939
0.959

Proton Energy
kev

1.0
2.0
5.0
4.0
6.0
8.0
10.0

0.905
0.956
0.978
0.981
1.006
1.013
1 .018

■H-Including t e r t i a r y e l e c t r o n s ,
delta-rays produced by deltarays

12
of d e l t a - r a y
Indicates

ionisation.

the

at the r i g h t
formed by

e n e r g y of

The
the

Indies-.'tes the

the d e l t a - r a y s

c o l u m n at

the l e f t o f T a b l e

incident particle.
ratio

of

of greater

t h a n 100 e v e n e r g y

Ion-pairs

particle.

f o r a 5 ilev a l p h a - p a r t i c l e

Ions are p r o d u c e d b^
as b y

the

delta-rays

and

all n u m b e r o f
g iv e s

less

formed directly by

At

the

same

t h a n 1 0 0 ev en e r g y .

0 . 9 2 5 as m a n y

These

experimental

low energy

increase

created by uelta-rays.

the f o l l o w i n g

the I n i t i a l

time m a n y d e l t a - r a y s

their ionization products
ions

compared

d e l t a - r a y s o f e n e r g y e x c e e d i n g 100 ev

alpha-particle.

are f o r m e d w i t h

column

the n u m b e r of I o n - p a i r s

to the n u m b e r o f
Hence

The

I

C. T.

the o v e r il. W i l s o n

data for a reasonably

42

fast

alpha-particle•
TABLL

II

OF ION-CLUSTANS
VAKIGoS
No. of I o n - p a i r s
Fre '.uoncy o f

tions in
shoals b e

N ’UIJBuRS O F I O N I Z A T I O N S

In the

Cluster of

Let us a ssume

t ha t

Cluster
this

Size

t e n is the

the g r o u p h a v i n g m o r e
aueouatel^r

particles because
of h i g h e n e r g y

of

large
the

1

2

3

4

>4

.43

.22

.12

.10

.13

average

than f o u r

for even

the

rapid decrease

ionizations.

Ioni ze t i o n y i e l d o f

CONTAINING

One

the v a r i o u s

can

Tota]
1.0C

n u m b e r of i o n i z a ­

ionizations.
fastest

Tills

initial

in the p r o b a b i l i t y

t he n agproximi'te

the

i o n - c l n sters •

I

13
TABLE III
RELATIVE ION YIKLi) OF CLUSTERS
No, of Ion-Pairs In the Cluster

1

2

3

4

>4

Relative Ion Y i e l d of this Cluster

,43

*44

,36

#40

1,30

Since a lOOev electron can on the average yield about
three ion-pairs,

approximately forty-two per cent of the

Ionization due to delta-rays is accomplished b y delta-rays
of lOOev energy or less.
their importance.

This is probably a lower limit of

One can tnen show that 1.5«5 ion-pairs

are formed by delta-rays for every ion-pair formed directly
by tne alpha-particle.

Hence a little more than sixty per

cent of the total ionization is due to delta-rays.

For

protons of the same energy this percentage is apparently
somewhat higher.

Thus the ionization due to moving electrons

is an important fact in the total ionization of heavy
particles•

14

iiJtPA AI hLI'lTi'iL O B S E R V A T I O N S ON L L e C T R O N S IN A I R
A great amount of work h a s b e e n done by m a n y o b s e rvers
with considerable d i s a g r e e m e n t b e t w e e n
investigators
1927;

PI
Johnson^* , 1917;

are:

S c h m i t z 5 1 , 1928;

son^,

1931;

K,

the n u m b e r of

Some o f

the

Lehmann and Osgood

B u c h m a n n 5 , 192 8;

F r e u n d 1 5 , 1 93 5 ;

and O s g o o d p r o p o s e d

them*

E i s l 1 4 , 1929;

a n d G e r b e s 1 6 , 19 3 5,

the f o l l o w i n g e m p i r i c a l

P7

,

Thom­

Lehmann

relation for

i o n - p a i r s f o r m e d i n ai r b y a n e l e c t r o n o f

energy V electron volts,
K = 0.0225
The a c c u r a c y of

(V - 17)

200ev - V - lOOOev

the d e t e r m i n a t i o n w a s p r o b a b l y of tlie o r d e r

of ten p e r cent.

In 1 9 3 1

this r e l a t i o n was c o n f i r m e d b y

T h o m s o n f o r 50 to 2 7 0 ev e l e c t r o n s ,
energy

electrons.

Thomson changed
K * 0.0270

and u p o n
of all

the a s s u m p t i o n

energies,

the e n e r g y f o r

with

In 1935,
following

(V - 17)
the l i n e a r i t y h o l d s

fo r e l e c t r o n s

the o b s e r v a t i o n s of F re u nd .

the f o r m a t i o n of an I o n - p a i r

57 ev f or 10 ev e l e c t r o n s ,
the v a l i d i t y of

to:

57
57
ev
(V - 1 7 ) / V
1-17/V

relations disagree

ae f o u n d

the c o n s t a n t

V* b e c o m e s :
W »

These

th at

as w e l l as f o r h i g h

however

th e re

is r e a s o n

to

this result.

G c r b e 3, a st u d e n t of eIsI,

empirical

r e l a t i o n f o r '-V:

7» = 5 1 . 6 2 -f 5.27

proposed

x

( V - V i ) “ a~ * O . O S e v

the

to be
question

15

Vi

Is

tlie I o n i z a t i o n p o t e n t i a l

relation upon
which he

in Kev.

the w o r k o f E i s l

theoretically

(9 to

corrected

Tor

collection potentials Eisl used,
P igge^-^ w i t h
The p l u s

200 ev

or minus

the a b s o l u t e

magnitude

error.

is

The

vary by

subject
Gerbes*

the o b s e r v a t i o n s

relation

of Freund.

o f ',Y f o r

1000 e v

technical

ports

earlier

of

instrument has
dividual

some

a c c u r a c y of

individual

determina­

c e nt .

Further,

to the

errors i f n o t

for W does

eouivalent

serious

not h o l d for

Apparently W has not yet
accuracy

improvements

so

an accuracy

expressions

Lehmann

anu

200 a n a

2000 ev.

this

investigators

b^en

will be

in

to d e t e r m i n e

absorbed
since

a

established
in air.

1955

as a g u i d e ,

constructed

and

the

a

.Yith
re­

the p r e s e n t

that ul ti ma te ly

in­

o f \Y as a f u n c t i o n o f V m a y b e

of p l u s

adequate

to

or minus one
ascertain

which have bten

Osgood,

thesis has

electrons

determinations

with

accuracy
the

the

in n i t r o g e n

sufficient

work described

the m a n y

made

in nitrogen.

r e l a t i o n b e t w e e n V/ a n d V.
The

value

the

large

th e w o r k o f

about five per

to l e a s t

been determined with
valid

and u p o n

for

the c o n v e r s i o n o f P i g g e 1s w o r k
in oxygen

the u n u s u a l l y

ev can h a r d l y be
o f W,

this

60 K e v e l e c t r o n s )

to l O O O e v e l e c t r o n s

0.08

tions of W b y Eisl

Gerbes based

cent.

This

the v a l i d i t y of

advanced by

for electrons

per

having

Gerbes

and

energies between

16

IZiiTiiOD O F oj-TLAi.I-inTIO:; 01” W
Tlie m e thou. u s e d
Vi will f i r s t
of

the

be

tills w o r k

explained

constructi-m

experiment,

in

which

will

in b r oau
be

appears

vtrj

f r o m ripurfc 1.

Tire b e a m o f

c h a m b e r is

through

where

the

sent
enerpy

of i o n - p a i r s
formeu

of

is m e a s u r e !

incoming

and

electrons

formed per

initial

the e n e r g y

of

the

the f o r m a t i o n o f
reli t i o n W = V / K .

is

electron,
initial

an

formed

into

K.

of

in

the g u n

v.ith the

ion-pairs
number of

n umber’ o f

.<ith tlie k n o w l o u ^ e
the

chamber

i n the f o r m a t i o n

avtr p t

71 m a y b e

tlie

seen readily

The n u m b e r o f

the

details

an i o n i z a t i o n

dissipated

e l e c t r o n V,

ion-pair

c a n be

is c o m p e r e d

to d e t e r m i n e

Lnter,

Tlie p r i n c i p l e

electrons

processes.
this

outline.

s im p l e ,

the o r i f i c e

the b e a m

and other

^ivtn.

for- the d e t e r m i n a t i o n o f

average

ion-pairs

of

h an d

energy

calculi, ted b y

tlie

for

17
T he
cathode

source

ray

r em o ve d .

of

tube

For

th e

from which

the

oi'ifice

so

The n u m b e r o f

th ey

them in a F a r a d a y
that it c o u l u b e
electrons
within

to

the

to f o r c e
stops

needed

age n u m b e r o f
the i n i t i a l

of i o ns
As
was

the

formed by

Faraday
these

taken

to m i n i m i z e
onttrinu

tion of Iv.
two

chamber.

positive

the

to

themselves

ion-pairs

removed

and

the v a r i a t i o n in

First,

Faraday

tlie c u r r e n t

was m e a s u r e d b y

not be made

Two

the a v e r ­

electron.
the

formed

potentials

the c o l l e c t o r .

o b s e r v a t i o n o f K,

wa s

so

incident

or negative

per initial

electrons

trapping

cagge w a s m o u n t e d

to d i s s i p a t e

i on s

the

the

collector.

simultaneously,

care

the n u m b e r of i n i t i a l

ionization chamber

curing; an o b s e r v a ­

determination

of K c o n s i s t e d of a. c o m p a r i s o n

currents

r e g i s t e r e d by

a h ’A r s o n v a l

apply

the

reoulreu

tions m u s t b e
suffer

initial

The

To
energy

the

the ggun

The

ionisation

was m ea su r e d b y

cage

could

o r loss.

The n u m b e r of

one

formed

current

t he s e m e a s u r e m e n t s

electrons

of

to c o m p l e t e

electron

ca0 e ; s e c o n d ,

electrons

or p o s i t i v e

s ou r ce ,

was determined by

chamber.

ion-pairs

the

the p a t h o f

applyin ~ small

electrons

the

Faraday

reiaoveu f r o m

ionization

we r e

into

The

these

a conventional

e l e c t r o n gyun t o w a r d

electrons

cage.

allow

w a s mo a s a re d b y

the

passed

initial

was

the gglass e n v e l o p e h a w b e e n

at 0 . 0 5 m i c r o n s

uirected by

that

electrons

p r o p e r o p e r a t i o n of

chamber was o p e r a t e d
electrons were

initial

so m a n y

in

r e l a t i o n IV = V / K
the

formation

satisfice..
collisions

wa l l

to d e t e r m i n e

of an ion-pair,

F ir s t ,

tie

initial

within

the p a s o f

jalvanomster•
the a v e r a g e
two

condi­

electrons must
the

ionization

18

chamber that the terminus of their track lies within the
limits of the gas in the chamber.

This condition,

total absorption, must apply as well
fonnea by the initial electrons.

called

to the delta-rays

S e c o n d the initial electrons

which enter the ionization chamber through the orifice

should

be identical, m o n o - e n e r g e t i c •

satis­

The first condition was

fied mainly by adjusting the pressure in the ionization
chamber.

The details of this will be given in a later

section.

The second c on dition cannot be satisfied exactly.

However,

as will be seen later,

it was possible to satisfy

this condition to a good approximation.

The energy d i s t r i ­

bution of the initial electrons was determined by applying
retarding p ot entials to the Faraday cage to prevent the
collection of electrons h a v in g an energy less than the
retarding potential.

unfortunately these retarding potentials

could not be appl ie d with the gas in the ionization chamber
at the normal pressure for total absorption,
discharge was formed in this case.

for a gaseous

This is a source of error

which cannot be removed f r o m this method for the determination
of W.

The pre se nt work has done mu c h to reduce this error;

it is now b e l i e v e d not to be

significant.

i
A

19

D E S I G N CONSIDERATIONS
For the Ionizat io n Chamber
The body of the Io n i z a t i o n cha mb er Illustrated In
Figure 2 was f a b r i c a t e d f r o m three-eigh ts -I nc h b oi l e r plate
and the thirty-by fo r t y - i n c h d o o r f r o m o n e - in ch h o t rolled
steel.

It was d e s i g n e d to w i t h s t a n d an external pressure

of five atmospheres w i t h safety.

A twelve-inch spherical

collector u se d in p re l i m i n a r y work is shown in p osition in
Figure 2.

The m a j o r dimensi on s of the i on iz a ti on chamber

were chosen to allow the tank to enter the l ab o ratory wi t h ­
out the removal of any walls.

While it is desireble to have

the tank as large as possible to reduce the pressure
differential b e t w e e n the io ni zation chamber and the gun
chamber,

it d id not appear feasible, for reasons of expense,

to go beyond a volume of one h u n d r e d cubic feet.

The u s e ­

ful volume of this tank is about fifty times as great as
has b e e n us e d in previous experiments.

The shape of the

ionization chamber was chosen to approximate the envelope
of the furthest p e ne tr at io ns of the initial electrons.
This envelope has an axis of symmetry along the line of
flight of these electronsj its di me ns io n should be greatest
in the forward direction.

For the large scattering angles

expected, the forw ar d p o r t i o n of the envelope would be
approximately a hemisphere.

Figure 2 .

A G eneral

V ie w

of

th e

E q u ip m e n t

21
The twenty- by thirty-inch door illustrated in Figure
3 allows access to the interior of the tank Tor cleaning.
This l ar g e door is p a rticularly essential for

of the large

the in se rt io n

sheet metal plates u s e d to collect ions.

V a c u u m Requirements of the Ionization Chamber
To obta i n a clean sample of air o n which to determine
W, it is nec e ss ar y that the ionization chamber first be ev a c ­
uated to at least on e -hundredth of the operating pressure of
fifty microns before

the introduction of the air.

Pressures

as low as 0.05 microns can be ob ta in ed within twenty-four
hours pumping time.
A potentially large source of leakage ma y be expected
along the one hundred twenty inches of v a c u u m seal required
for

the ionization chamber door.

The seal employed was

b a s e d upon recommendations very willingly furnished by R a ­
ni

Lions Laboratory, University of California.

is illustrated in Figure 4.

A section

A comparison of Figures 3 and 4

indicates that the seal consists of two rubber gaskets m o u n te d
in gi'ooves so machined into

the door that the max i mu m squeeze

applied to the rubber gasket is limited.

The major portion

of the eighteen thousand pound force exerted on the door
by a tmospheric pressure
tact.

is supported by metal to metal con­

Pump-out holes A and B allow the evacuation of the

volu me b e t w e e n

the

two

rubber gaskets

for the p u m p — out h o 1 es is
1 eaks the

pressure

two

fold;

u l f f erential

if d e s i r e d .

fi r st ,

across

tut

The r e a s o n

in the e v e n t of
inner seal could

F ig u re

3.

In te r io r S u r f a c e

of

th e

2 0 " by 3 0 "

Door

1

3 ^ X 4 5 * CHAMFERS
0 2 0 0 2 .001
l^^X.JlL-X

-------- !L

---

- 1

h
Z

£

HOLES

d r il l

* X

d

CEP

S HOLES
O . t O O *• .OOI
2 4
i

deep

jjD R IL L - THRU

PIPE T H R E A D

I DEEP
F ig u re

SEC TIO N

OF

A

DOOR

SEAL

b e re -uc e u and

i th It

•.^ n I tu do of

th e

in th e 1 oc a t io n. o f 1 e a k s It
of

tb.s. ^s.s kc t s r.s.y be

1 o c a ted

^ h i.ivt LS C h*l be

evacuates

ar.axj Z t - •

uooi*

r &si£c t is

The

-sea anu

Tne r a b n r

Is

anu

Seal is

tne

1 e ak ; s e c o n d .

r e a s o n e d thn t lr. k s I n t i th e r
if

the

th.e re _ I o n be t\ve e n

of

exhaust

the

punpin^s

so s s t i s f a c t o r v tllHt only

one

V

the pu: .p-out ho 1 c s have been sealed,

0 ss.:^ts sre fonaed f rom s i x t y - duromettr round

qu&rte r-inch h’eo; re ne rore by cutting the rope at a fortyfive deurce

&ryle and vulc ar.iziny at the corners •

maximum squeeze on the yasket was intcuueu
per cent of the d i & m e t - r of the u asket,
^reatvr than

to be

Tlie
twenty

s. factor of two

the ten per cent s -ueeze which is usu a l l y

£c: tiifactory for v a c u u m seals.
-er cunt squeeze was useu,

It. is fortunate

for in the process of v u l c a n ­

izing tne yaskct at the corners,
c„. scout ten per cent,

tnat a twenty

the uiameter was reduced

leaving ten pier c.nt for an aue uuite

.n
w c ux
•

.»elus of tne one h a n d l e d per Ct at p e n e t r a t i o n t^pe
widen are inaicateu in Figure

4 were useu throu6h o u t

ionization chamber w ith excellent results.
hundred per cent p e n e t r a t i o n weld,
in^ pieces are gro u n d
to both

surfaces,

the

For a one

one or both of the m a t ­

to a !fV M edye an-

the weld appliee

thus yreatly reducing tne possibility

thb t b l o w —holes extenu throuyh both w e h s

to form leaks.

iir.ee conr iu _r&ble h eat is yenera tea in the v,cl-i::c o p e r a ­
tion,

it is frequently di f f i c u l t

of t.ieces that are b e i n y

joined,

to prevent the warpiny
p a rticularly if tueir

25
thicknesses and hence
quite different*

thei r h e a t c arrying capacities are

The f a b r i c a t o r can overcome w a r p i n g

a considerable extent b y w e l d i n g at numerous

spots to

to
join

the two pieces w i t h litt le h e a t i n g and then pr o c e e d i n g w i t h
the running wela*

Some w e l d i n g strains are inevitable b u t

the warping is u s u a l l y not b o t h e r s o m e if the strains are
syrrmietrical to the weld*

The d e s i g n e r can do m u c h to I n ­

crease the symmetry of w e l d i n g

strains.

The twenty-four b o l t s at five and a ha l f - i n c h Inte rv al s
forced the door and the m a t i n g plate to yie ld to e ac h other*
The door and Its m a t i n g plat e
the unbolted condition,

are

quite x^la n e »

However,

In

there 'was a wedge between them of

about o n e - fo ur t h Inch at the g r e a t e s t point*

This was due

to lack of alignment of the h i n g e s of the door*
Vacu um liequirements of Gun Chamber
U p o n the a s s u mp ti o n that

the dimensions of the small

orifice connecting the g u n c h a m be r and the ionization
chamber were small c o m p a r e d to the m e a n free path on either
s

i

a

e

of

the orifice,

one m a y calculate

from the tank into the g u n chamber*

the net flow of gas

This assumption was

not strictly valid but c ould be relied upon to yield the
oruer of magnitude of the effusive flov; of gas*

At fifty

microns the mean free pa t h of an electron Is of the order
of 1 mm.

For a tank p r e ss ur e of fifty microns opposed b y

the _un chamber pressure of 0.05 microns on opposite
of an orifice

0

.

0

1

Inches

in radius,

a

c

c

o

r

d

i

n

g

sides

to equations

26

developed b y Dushmann,

the "conductance" o f the orif ic e

was 20*1 cm^/sec and he nce the effusive f low Into the gun
chamber was calculated to be 1,0 rnlcron-11 ter per second,
(The choice of an orifice 0,01 Indies in radius will be
uiscussed l a t e r , )
To remove this gas at a large rate co mpared to one
ralcron-liter per second a d i f f u s i o n pump was chosen w ith
a pumping speed of f i f t e e n m i c r o n - l i t e r s per second at
10 — lb mm. of mercury,
A m i c r o n - l i t e r is a unit p r oportional
to the number of ->as molecules;

one m i c r on -l it er equals a

liter of gas at a pressure of one micron,
gas at one -t en t h micron,

etc.

or ten liters of

The D is ti l la ti on Products

Inc, VMF-260 three-stage oil d i f f u s i o n pump was chosen
because it ha d an adequate p u m p i n g speed.

The choice of

pumps is restricted to oil d i f f u s i o n pumps because of the
slow pumping speed of m e r c u r y di f fusion pumps of comparable
co s t •
The V M F - 2 60 requires a forepressure or exhaust pressure
of one-tenth xmn, of m e r c u r y or l o we r for satisfactory o p e r a ­
tion.

The pum pi ng action stalls if the pressure differential

over the pump becomes too large.
chosen for this task.

The

A Cenco—Kyp er va c— 25 was

Cenco — Hyp':-rvac— n5 has a pumping

apeeu of about twenty-five m ic ron-liters per second at oxueb'.iijth mm. of mercury and hence it is capable of creating a
sufficiently low fox*epressure for the Vx.-F— 210 diffusion
pump,

Sullivan^*'1 (IP m B) gives a fine account of modern

p '.iLpin_ techniques.

27
The d e s i g n of a v a c u u m p u m p in g syst em is quite like
the design of a plum bi ng system except for the c o m p l i c a t i o n
caused by the c om pr es si bi l it y of the gas.

The tubing c o n ­

necting the gun chamber, d i f f u s i o n pump and f o r e p u m p must
be adequate to handle

the ex pected flow.

The g u n c h a m be r

ana a iffusion pump were connected b y f o u r -i nc h tubing; b e ­
cause of the co nsiderably h i g h e r pressure b e t w e e n the d i f ­
fusion pump and the forepump a one -i n ch tube was adequate
there.

A v a c u u m valve was inserted b e t w e e n the d i f f u s i o n

pump and the forepump so that the forepump., w h e n not in
operation,

could be returned to atmospheric p ressure with ou t

bringing the rest of the system to atmospheric pressure.
Thu gun chamber and pum pi ng system are shown at the right
of the tank in Figure 2.
Electrical and Electronic

Components for

the E l e c tr on Gun
The work of N i s l e 29 and particularly of Barnes4 h a d
indicated that the local facilities v.ere not adequate to
form high l y u n i f o r m electron guns.

This p r o b l e m was e lim­

i n a t e d b y the use of the electron gun from a conventional

3GF1 cathode ray tube,

a port i on of whose glass envelope

had been removed.

The 3GP1 tube wi t h its original socket was inserted
i i an e l e v e n — prong ceramic

socket which was m o u n t e d rigidly

on

chamber•

the

e, .dplate of

T'ig'.i.re b.

the

The e n d p l a t e

gun

seals

the

This

is

lijfit h a n d

illustrated

in

e n d of

T

tne

28

Figure 5.

Electron

Gun Mounted

on Endplote

59
shapee. pu-v'cinj ster; I l l u s t r a t e d
connector
is

s e e n fastt n e d

to

in Fi rare

the e n d p l s t e

:-n e ivi: t - c o n c u c tor c a b l e d e l i v e r i n g

vices

necessary

the

the j u n .
end l a t e

An o c t a l

the

cutsivle

the

end of

the

elght-conauctor cable

connection

and

-iscopj e c t i o n o f

the

oT

for

wall on
each

other- b y

a call

services

eight copper buss

f it tin-

the

the

the

sa m e

figure

electrical

ser­

socket m o u n t e d f r o m

an o c t a l

of

oiug

joinea

to

ellov.ed c o n v e n i e n t
electrical

services

bakelite

wes

such as polystyrene,
satisfactorily
Further,
to d r y

at the

in this

surface

exposer

the

q u a l i t y of

of

the

surface

to

In

service
x-.s is

Cot- one

raw

the

fire v a c u u m

a cracking

s e al i ng .

seal

depenas

s h o w n In F i g u r e
is b r o k e n

upon

fhe b a k e l i t e

S,

by melt­
ana

stand up
Flicene.

a tendency

crazing

very

of

the

troublesome
the

condition

insulator has be en

signs o f d e t e r i o r a t i o n .

the g l a s s

at a b o u t

that

insul: tors,

showed

T h is w a s

and

thrust

of b a k e l i t e

not

or

so

the

for melting

polystyrene

tv.o y e a r s w i t h o u t

Lube

will

temperature needed

develop

wires

was made

than b e t t e r

for polystyrene

snugly

the b a k e l i t e

supported

s ea l

from

holes

the b u s s

oints of c o n t a c t

used rather

tdoe v a c u u m

insulated

oakelite.

the b a k e l i t e

a vacuum

for

of

e a c h of

to the v a c u u m .

as

fo r

with

on

experiment,

in v a c u u m and

through

were ^.rillea t h r o u g h

pressure.

to c o v e r

passed

wires, v u d c h w e r e

was p l a c e d

in c o n t a c t

at wo s p h e r i c

metal.

wires

solder

I-licene

were

a quarter-inch wise

the b u s s

the- s o l d e r

ing

in

ran.
Tire e l e c t r i c a l

of

an d

Th e h e a v y

2.

envelope

o.

the- l e v e l o ± tne

^ne

30
deflection plates*
serves
after

The r e m a i n i n g p o r t i o n of

as a s u p p o r t fo r
removal

of

the

the g l a s s

tube e l e m e n t s .
envelope

o p e n to

the

appear

to b e

reason

to h u r r y

results

air of

are

lOOO

shown

can

th

was

t is,

voltages

regulating

change

If

aays

the

A well r e g u l a t e d v o l t a g e

t h an the n e c e s s a r y c ur r en t

t h i r t y p e r c e n t of n e w V R tubes are noisy;

w i t h i n the tube

VR

their o p e r a t i n g

It seems that the d i s ­
ca u s i n g the v a r i a t i o n in

tubes h a v e b e e n u s e d before,

complicated by

their b e ­

th eir p a st operat ion.

Th is

c a n u s u a l l y be a v o i d e d b y o p e r a t i n g the tubes at

should b e
to

the e l e c t r o n

this m a n n e r if the V R tubes are chosen

about

uesireu. l e v e l

tubes

tubes.

in a r andom manner.

is f u r t h e r

uifficulty

The a u t h o r ' s

A n e g a t i v e p o t e n t i a l of

t h e i r ’ c o n d u c t i o n p a t t e r n anu h e n c e

voltage.

the

About

moves

havior

a n e w tube.

s t a b i l i z e d in a s t r a i g h t f o r w a r d w ay b y a

b e obtained, i n

charge

6 anu 7.

c a p a b l e of providing more

carefully.

there was l i t t l e

c i r c u i t s eux>loyed to o p e r a t e

in Figures

of v o l t a g e

s u p p ly,

tubes w h i c h

a g r e e m e n t w i t h those of B ac h man^.

v or l e s s

series

Hence

the i n s t a l l a t i o n o f

The e l e c t r o n i c
gun

Ho w ev er ,

to a

the l a b o r a t o r y for two w ee k s d i d n o t

a p p r e c i a b l y effected.

are i n

envelope

The e l e c t r o n g u n

co u lu be r e t u r n e d

r e a s o n a b l e v a c u u m w i t h i n f iv e m i n u t e s *
were

the gl a ss

see i f

3<_st r e s u l t s

f o r a period, of a week or so.

o p e r a t e d at

u v e n ne w

the u e s i r e d level for several

t h e y will d e v e l o p a stable mode of discharge.

were

o b t a i n e d if the VR tubes are kept in

continuous operation.

jam

IIO V
AC

O -C O N TR O L ORK)
A ,-1s t ANODE

R7- 2 O H M P O T

V,- V# - VR 15 0
\^ - VR 105
V^- 2 X 2
RP-REGULATED

R * - 135 K
R * - IOO K P O T .

POWER SUPPLY
C ' 8m f

Dfc-DEFL. PLATE
T|“ 2 0 0 OV TRANSF

R ,J V 5 0 0 K

POT

Rt ,R4 - 5 0 K POT

R 8,R«

200

K

A ? 2 no ANODE
Di -D E F L . PLATE

ELECTRON GUN S VOLTAGE SUPPLIES
Figure

6

V

1

b*"
o

f /r

300V REGULATED POWER SUPPLY

°|.C,fii 8mf 400V

C,

•

Ct
L.L*

R, • I5K

«Y«

Rt* 470 K

Olmf 200V

•SJ7

R,* IO K

.Imf 300V

VR 105

.Ihf 2 0 0 V

C4 ’
C.

60

•
*

4«f 400V
12k

IOW

IOOK

2W
IW
IW

R| * IOOK

POT.

R.' IOOK

IW

33

An exc e l l e n t
Is g i v e n toy H u n t
negative

account of

and Hickman2 0 ,

voltage,

constant

exceedingly good,
work wi t h g o o d
measurement
o f 5 ma,
of

A

''mu” t y pe

success.

"mu"

tube n e t w o r k

regulator but has
quent v o l t a g e
of h i g h e r
regul

cl

voltage

ar e

for

somewhat

current

regul? ted.
ohms

C4 .

A series

supply

for

of

the o r d e r

sixty

of d r y

tubes.

capacity.

Subse­

made with equipment
the

"mu"

type

low voltage
This

impedance

cycles.
of

power

employed

of

the p o w e r

T he o u t p u t
of

impedance
the c o n —

sometimes used

plates

the

and v a r y i n g line

the p r e s e n c e

cells were

the d e f l e c t i o n

of

ten microamps.

regulated

The o u tp ut
at

currents

current requirements

the o r u e r o f
tne

in early

inferior voltage

i n v/hich c a s e

the

is f r e q u e n c y d e p e n d e n t b e c a u s e

voltage

a

for* the d e f l e c t i o n v o l t a g e s .

three

r e g u l a t i o n is

requirements on

r e g u l a t i o n in w h i c h v a r y i n g loads

supply w a s

uensor

currents

should be

impedance,

Figure V illustrates

gate-type

type

high

the m e t h o d o f v o l t a g e

excessive

shown makes

tion m a y be used,

supply u s e d

"mu"

regulation cannot deliver

of

is o f

the

required

measurements

the e l e c t r o n g u n

regulators

regulator was used

the n e c e s s a r y

internal

voltage

For low current,

However,

type

this o r d e r b e c a u s e

The V R

load

w h i c h was u s e d

The

electronic

to a v o i d

as a

sixty cycle

hum.
The

great

was n e c e s s a r y

stability

to o b t a i n

of c o n s t a n t m a g n i t u d e .

re u i r e d

in th e se

two p o w e r

supplies

a sufficiently mono-energetic beam
The

accelerating voltage,

of

co urse,

hau

to be

c o n s t a n t in time*

e n t e r i n g the

The m a g n i t u d e

ionization chamber from

u p o n the p o s i t i o n of
carbon orifice.

The p o s i t i o n o f

the

constant initial

t he

and

the b e a m

to

the

depends

the a c c e l e r a t i o n

accelerating voltage

the c u r r e n t
chamber depends

the b e a m w i t h r e s p e c t

the d e f l e c t i o n v o l t a g e
importance of

of

in

s ma l l
on bo t h

voltage.

The

maintaining

electron current i n c r e a s e s

a

with increasing

deflection voltage.
The d e f l e c t i o n

sensitivity of

celerating potential

(of

the o r u e r of

the p o s i t i o n of
cent o f
e rable

If

in

the

the m a g n i t u d e

as w a s f o u n d

to be

of

the

the

the case,

more

vdthout

small

s e c t i o n of the beam,

less c r i t i c a l
entering

the

f u n c t i o n of

small o r i f i c e ,
l e ss

the c u r r e n t

ionization chamber.

b e a m c o u l d be m a d e

woulu be

the p o s i t i o n

small

of

the

the r e q u i r e m e n t s o n the

comparable

to

the u i m e n s i o n s

which were

used

of

over

the w h o l e

electrons

if the

focus of

(dimen si o ns of

having

the o r i f i c u .

were not c a p a b l e of f o r m i n g

in

the b e a m is a m u c h

position

th a n in the ca s e of a b e a m

the f o c u s

density

Initial

Finally,

comporee. to

stream enter­

current

of

a consid­

carbon orifice

the e l e c t r o n b e a m is a p p r o x i m a t e l y c o n s t a n t
cross

t h a n a few p e r

o bluer h a n d

the

The

the b e a m is

electron

If o n the
to

of

inch.

blue small or i f i c e )

small o r i f i c e

the b e a m is U r u e c o m p a r e d

and if,

of

at 1 0 0 0 v a c­

per

foetus

the b e a m m a y n o t v a r y b y

ing the i o n i z a t i o n c h a m b e r .
of

the

the u i m e n s i o n s

the d i a m e t e r of
change

3GrPl

is a b o u t f o r t y v o l t s

d e f l e c t i o n is e l e c t r o s t a t i c .
sharp

th e

the

of the b e a m
a fo cus

Trie e l e c t r o n s
a focus

small

the

35
compared

to

w as p a r t l y
system.

the d i m e n s i o n s
aue

However,

centrations
mutual

to

quality of

to

radius

formed

in

certainly

electron optical
that

the b e a m o f
the

This

charge

the g u n

formation of

con­

such

that

a focus

small

the o r i f i c e .

According

to B a c h m a n 2 , the o u t ­

d e f l e c t i o n of

the

outer

electrons of

a b e a m of

rQ c m accele r a t e d by V volts

anu carrying

a current

I ampere3 along
1 ? ro ^ *

let L be
the

the

should he m e n tioned

could he

ward radial

of

it

the o r i f i c e .

repulsion would prevent

compared

V

the

of

For lOOOev

2 0 cm,

small

flection of
comparable

a distance

L c m is g i v e n b y 0 . 7 6 x 1 0 ^
electrons,

a n d let r0 be

0.005

carbon orifice),
the o u t e r

to r Q •

then

let
cm

10”^

if a h i g h

amperes,

( o n e - f i f t h the

the o u t w a r d

electrons becomes

Therefore

I be

0.002

radial
cm,

quality

I

radius
de­

w h i c h is

electron

optical
less
the

system were used, for lOOOev electrons, currents
ry
than 10
a m p e r e s s h o u l d b e u s e d to p r e v e n t m a s k i n g o f

quality

of

the

system.

If c u r r e n t s o f
at w h i c h m u t u a l

the o r d e r

r e p u l s i o n w o u l d no

current m u s t be r e a d

( f or o n e

10”^

in

amperes.

use d i n

t he

meet more

stringent

the v e l o c i t y
the

This

i s o l a t i o n of

cage n e t w o r k ,

wire re

re

per

l o n g e r be
cent

turn would
the

as h i g h

d i s t r i b u t i o n of

as

the

the

a leakage

wi r e a c o r r e c t i o n o f

to

in

this

about

insulation

carrying networks

For example

lOOO

a factor,

accuracy)

require

current

conditions.

ionization chamber,

ano would

of 10 ” 9 amperes were used,

the

to

Faraday

v is applied, to d e t e r m i n e

electron
current

stream entering
as small

as 1 0

the o b s e r v e d d a t a .

To

56

a conduction current

o b t a i n so s m a l l

the i n s u l a t i o n r e q u i r e d T o r
must be 10^ ^ ohms.
of m o i s t
glass

air b e c o m e s

conducts
For

these

reasons,

impedance
carrying

r e g i o n of 1 0 ^

oiims,

wood becomes

surface

all

of

network
the

conduction

a conductor,

even

f i l m of m o i s t u r e .

i n s t e a d of f o r m i n g

system and meeting

a high

the m o r e

quality

stringent

In­

requirements,

at c u r r e n t s o f
operated

the c u r r e n t

a factor,

through a

electron optical
sulation

I n the

the

about

a conventional electron g u n was used
O
5 x 10”
amperes.
The g u n was u s u a l l y

v.Ith a b r o a d f o c u s

to m i n i m i z e

deflection require­

ments •
It d i d
moved

in

through

not

appear

slightly

convergent

the o r i f i c e .

it \,o.du s e e m t h a t
e ra ble,

since

t he r e b y b e
As
the

the

to b e

special

a slightly

e n e r g y of

importance

study of

electrons

as t h e y p a s s e d
the p r o b l e m

c o n v e r g e n t b e a m w o u l d be

f r o m the w a l l s o f

of

the

incident

the m u t u a l

F o r tun-- te ly

tne u i f J'iC'dty o n e

expects

bhe. b is,

for l o w e r

energy

pressure

is

required

burn a l l o w s

the

inn l za t Ion c h a m b e r
effe.hve

or d i v e r g e n t paths

Without

scattering

the

the o r i f i c e

pref­
could

reduced.

came g r e a t e r •

in

important whether

for

use of
anu

flow beyond

electrons

r e p u l s i o n of

another
due

to

effect
the

tenas

tolerable

a b s o r p t i o n of

cancel
the

a lower

connecting

oe am;

ta? -a

the b e a m ;

chamber without
limits.

to

s p r e a d i n g of

a larger orifice

bile g u n

reduced,

the e l e c t r o n s b e ­

incident electrons
total

was

t h is
the

increasing

the

voltage Tor* the electron gun was supplied

2Sie

t*3 i u i s c n cell

'The voltage

1.1 v s teps -a iill s t ^.o o;
..stat::* w i t u i r these

was available

;ip. hi s tab 1 e re si s t v.rice for

cteps,

-■c.i^oi cells retain their

rge for a coasil-: nr lie length of tine with
In re p-lrei by

the electron

lity leal, storage
v^ge«

(C .6 amps).

the low current
A go o d

cell t o v .11 :;?.intain s. aore constant

Zhe ccr.etiv.ev cf the ever.ter voltage is Important,

any variation in erission of the filanent will cause a
lespoaliag v & r i c ti cv in the electron current passing
■u.g~ the snail orifice •
Ihe conti’o ls Tor the elecu'or. gun were centralised on
card illustre ted in Figure S •

The functions controlled

u this board include Tine and corrse vertical and horit&l deflection voltcges,

control grid bias Tor the gun,

hue 31F1 cathode ray tube shown in Figure 8 was
otrically in parallel vith the unit sounted vrithin the
chruber.

Its purpose was to simplify the problem of

iticr.ing the stream o f electrons o n the small orifice
.ecti.g one gun chamber and the ionisation chamber.

It

particularly useful to indicate the focus o f the gun
racing

ithin the gu n chamber.

. 11 sued by placing

This condition was ac-

the orifice in the gun chamber at tire

lcl:n formerly occupied by the fluorescent screen of the
here

ray tube.

,.hile the commercial cathode imy tubes

s.it _b cly in or crating con.itir:s,
r.tic tl,

tct; arc a:::hsi:nly

=nu one is never far frmi a shi rp focus condition

Figure

8.

The

C o n tro l

Ponel

39
on the gun in the g u n chamber if the monitoring
sharply focused.

tube is

As long as the focus on the g u n in the

Uun chamber was It rger than the orifice,

a sharper focus

could be accomplished by m i n i m i z i n g the deflec ti on voltage
required for the el ectron b e a m to sweep the orifice.

The

Faraday cage or the c o ll ection plate was used as a detector.
The m on itoring tube f ur nished a visual account of the
deflections applied to the gun;
beam on the orifice.

this aided in locating the

Once the orifice is located for a

particular gun inserted in the g u n chamber,

the location

of the image formed on the m o n i t o r i n g tube was used to return
the electron b e a m to the orifice as long as the gun had
not changed or been disturbed.

To compensate for the de­

terioration of the emission of the gun in the gun chamber
without burning the fluorescent screen of the monitoring
tube,

the monitoring tube was

supplied b y an independent

filament sup ply consisting of 6.3 V transformer whose primary voltage was controlled by a variac.

The emission of

the monitoring tube was set to correspond to that of the
0un in the gun chamber.
The use of the m o n i t o ri ng tube provided a means of
visualizing the operation of the g u n in the gun chamber
without the need of more complicated measures which might
be taken to view the o p e r a t io n of the gun directly.
was more

It

satisfactory than a bank of meters indicating the

voltages or currents delivered

to the gun.

The monitoring

tube was placed in a location convenient for continual
observation.

40
Other Electronic and Electrical Components
A Faraday cage. Figure 9, was used to determine the
magnitude and the energy distrib u ti on of the electron
stream entering the ionization chamber f rom the gun chamber*
The dimensions of the entrance to the Faraday cage were
such as to predict capture of 99*7 per cent of the charge

entering the cage*

The Faraday cage was adjustable f r o m

outside the v a c uu m system*

Hence the electron stream enter­

ing the ionization chamber coula be captured or allowed to
ujienu itself on the gas in the ionization chamber.
the position of the Faraday cage for capturing
s t r e a m w a s exactly reni'odu ceable •
electrical

circuit

F a r a d a y cage was
of

removing

Further,

the electron

The F a r a d a y ca g e a n d

the c h a r g e

collected from

the

the

shielded to prevent any charge from the gas

the tank to be included with le the current of the electrons

captured by the Faraday cage as they entered the ionization
chamber through the small orifice.
these

The system satisfying

conditions is shown in Figure 9*

The Faraday cage

rotated about a vertical axis; m o t io n was transmitted by a
flexible

solid spring brass rod.

This motion was transmitted

through the vac uu m wall b y use of an O-ring seal^^*
bearing

The large

surfaces and close tolerances used on the hinge on

v.'i'i cli the Faraday cage rotated maintained an accurate vertical

:-r•<:. horizontal position of the Faraday cage with respect to
Lai

small orifice.

Along the line of flight of the electron

stream enterin^ the ionization c h a m b e r ,
the

small o r i f i c e

m u

the F a r a d a y

the separation of

ca ge wa s a e t e r lined by a

Figure 9.

The Faraday

Coge 8

C arbon

O rific e

42
suitable

stop

against which

t e n s i o n f r o m the

spring brass

The p o r t i o n o f
i

s

it f r o m
the

the

stray

charge

stray

charge.

ionization
from

tential.

The

s ma l l g l a s s

entering

the

and

was

retarding

entering

th e

portance

to

..-gle

cage

the

to p r o t e c t

shield was

the

at g r o u n d

tubular

the

the

inch lengths

carbon orifice

C .100 i n c h e s .

capture

were

the

a

l

l

the

certainty

applied

f

and

this

the

the F a r a w a y

cage

o

r

w

a

s

i

f

i

the

■ ,

p.

l^von-inct

e

d

e

c

r

e

e

O
: ; u s ef u l

rs h^rlcal

.

tha t

im­
ioniza­

increased
c

e

w

a

i

f

large •

s

i i b

-

the

electrons

entering
th is

of

region

It w a s o f p r i m a r y

aoing

sm all

the o r i f i c e

to

the

s h o w n i n F i g u r e 10.

It is o v e r

electrons
o

as

the

r

1

to g i v e

to c a p t u r e

spacing of

cage was

ionization chamber.

c

po­

conductor was

in p o s i t i o n

tank,

Faraday

subtenaed by

;

that

shielded from

conductor

the

9

conductor carrying

also

in one-half

the

potentials

tion c h a m b e r j
: . i « c

of
The

tubular

c ag e w a s

into

The- s e p a r a t i o n of
cage

Faraday

in Figure

flexibility.

carbon orifice

Farauay

rested under

visible

cage was

inside

tubing broken

the F a r a u a y

electrons

the

ground.

a flexible

insulation

the n e c e s s a r y
hhen

chamber,

cage

rod.

The pote nt ia l

the F a r a d a y

charge by

Farauay

the F a r a d a y cage

shiela w h ich fitted over

a

of

the

t

e

n

u

■-

1

e

d

o•
o oil: c
■•2■

ssown

Oi
in Fi_

i

n

n

:

■_

r

e

--es

m i ’ 11.

colic ctor i l l u s t r a t e d

in F i g u r e

The
2

43

— e le c t r o n

s tb p a u

R^T
O R IFIC E OF FARADAY CAGE

CARBON
O RIFICE

S C A LE

!" • . 0 5 0 " -.1 2 7 c m

D E T A IL O F VACUUM IN TER FA C E
Figure

10.

Figure II.

An Ion

C o lle c to r

45
consisted

of

two

stainless

steel h e m i s p h e r i c a l

f r o m which. h a n d l e s

and base

supported by

insulated

a im

a roa

extending

through

as an e l e c t r i c a l

the

had been
f r o m the

to

the

collector

was useful

spherical

shape

calculate

to a O o o d

isting

in

any portion

of

collector

illustrated

in Figure

larger

surface

chamber

wall

chamber

at

the

the

ions

the

such

(an e l e c t r o n
time

the

fielas

J.

J.

fielus
by

became

a rate

are

assumption

mean free

that

path

the

are

ionization
lost by

within
that

these

the

is

anu

the

five

differed

recombination

This

the m e a n

is

fields

calculated

fr e e

centimeters*

p r e s sure

strongest

I«len s u r e m c n t s

at e l e c t r i c

twenty

ioniza­

conditions

electrons

at 0 * 6 m i c r o n s

such

the

that

path*

a nd

of f o r m i n g more

inuicated

free

recom­

ion);

removed with

a f a c t o r of one h u n d r e d •

v per mean

ex­

ionization

to

the

capable

satisfy both

for

then

The

a positive

gas molecules

collector

electron

in

T h o m s o n 38 discov e r e u

negligible

than 0*01

fields

the

normal

with

that

that

roughly

could

chamber.

that none

not be

th e

spherical

electrons

ions m u s t
they

serve

a considerably

formeu

recombining

almost

spherical

of a l O O O e v
of

approximately

to

the

One

i n s u l .teu f r o m

of

in m a g n i t u d e

the

11 h a s

collection
at

with

electric

ionization

incident

a nu w e a k e s t

on

was

the

the

tion chamber*

greater

It

collision with

..ith the

the

This

chamber*

of

high electric

losses

approximation

chamber

c h a m b e r wall

concentric

ionization

They were

ioniuetlan

sphere.

flight

same

ions b y

the

area.

must be

bination

if m o u n t e d

in a p l a n e

direction of
The

of

removed.

ionization

connection

colanders

path

Th e p r o a u c t

is a p p r o x i m a t e l y

a

46
constant,

increasing

The m e a n f r e e p a t h
tha t o f

an

slightly

of

an e l e c t r o n

ion-pairs

the c o l l e c t o r .

were

Since

collector

could not be

a nd

still

collect

The

electric

all

fields

must fall b e t w e e n

formed b y

the

fields

tion

than fifty

i n the

and only

everywhere

0.01

edge

fields

effects.

sheet

To

reduce

performance of

the

section on operation.

s cale

ion

these

the

a detectable

migrating
the

applied

to

ionization
to

ions being
ionization

in m a g n i t u d e

allows

the

formed.
chamber

sphere

these

edge

effects,

of

the

will be

currents

made

the

in F i g u r e

11

mainly due

to

the e d g e s o f
steel

rods.

described

in

f r o m the F a r a d a y

with h'Arsonval

read

c ag e

wall galvanom­

a s e n s i t i v i t y o f 1 0 ^amp,

is i n d i c a t e d

2

th i rt y ,

three— eighths— inch

collectors

two v a r i a ­

in F i gure

about

illustrated

i n the

by a factor

a factor of

The

d e f l e c t i o n f o r 1 0 “ 6a m p

system used

in

factor,

The g a l v a n o m e t e r h a d

electrical

charge

s a me

collector were

(25 cm)

path,

the

rolled over

T he m e a s u r e m e n t s

the

a factor of

differing by

The

eter.

times

a fa c t o r of one h u n d r e d

in

collector

sheet were

the

4/5

which uoes not f o r m fields

and hence

the

a nd

electron.

v and 1. 0 v per mea n free path.

differing by

steel

free

the

all

collector potential.

formed fields

formeu

the

approximately

developed

varied by

c o l l e c t o r is o n e

stainless

energy of

the v o l t a g e s

ionization chamber which differ
greater

Is

volt per mean

chamber were never uniform,

A usable

the

ion.

A t a field, o f o n e
number of

with

to * mm.

schematically

a full

The
in F i g u r e

12.

47

TO C O LLE C TO R —i

CURRENT

i~T O

MEASURING
F ig u re

12.

FARADAY

NETWORK

CAGE

48
The
at

collector or
th e

with
to

s am e p o t e n t i a l .

tnis

the

Faraday

arrangement

collector or

conventional
no u n u s u a l

cage
The

chan w i t h

Faraday

be

the

be

the

To e x t e n u
amps,
is

e a c h d i f f e r i n g bv

other

a m p l i f i e r was

the

grid of

the

known grid

the

the

of

limited

ten,

circuit for
five

and

The

of

the

the

Bince

the- r a t i o

ion co ll e c t i o n

current

could

also

of
the

the

amplifier
s c al e s,

consistent

calibration of

with
the

the d e f l e c t i o n o f

the v o l t a g e

applied

From

this

to

6SN7•

the

current generating

and
a

accompanying galvanometer

response

in

to 1 0 “

the

r e g i o n of o peration,

in

and n e g a ­

p e r m i t t e d m e a s u r e m e n t of

the arnxolifier w a s
of

the
could

amplication

scales were

cent.

triode

voltage

linearity

i n t e r e s t onlj'

potentials

electrons

that

of

the g a l v a n o m e t e r

The

resistances

c a u s e d no d l f f i c u l t ^ •

thu

of

The

per

the g a i n o f

the

either

as a f u n c t i o n o f
first

particular grid

cause

to v e r i f y

accomplished by determining

the g a l v a n o m e t e r

deflection,

in order

series of

range.

to o n e - h a l f

latter more

cage.

a fa c t o r of

currents of a wine
each

A

the

Retarding potentials

sensitivity

13.

simpler

applied only

the h i g h p o t e n t i a l

a DC amplifier was used*

shown in Figure

were

However,

and negative

io n s .

Farauay

the

to

c o l l e c t i o n of

ions or positive

apxjlied to

tried

exist due

Both positive

t iv e

the p o t e n t i a l

cage,

galvanometer.
applied for

the g a l v a n o m e t e r operated,

insulation problems

or ientation was

effects

and

small
this

the

of

ca l cu l i. t ed •
the

grid

tube o v e r

leakage

experiment

Faraday

accuracy

of

ca ge

Be­

currents

thore
current

is
to

axnplification

49

6SN7

6

G - D’ARSONVAL
R(- 9 8 9 4 .T l

±4 %

W A LL GALVANOM ETER
r 8- io k p o t .
R9- 4 0 Q A - POT.

R2- 9 8 9 . 4 A . i t 4 %

R^- IO O K A

4°/<

R 3- 9 8 9 4
R* - SHORT

R |i *

Rs - 9 8 . 9 4 K A = t 4 °/
*o

C, -lO O O ^ i , 15V DC

R6 - 9 8 9 4 K
R7 -

484A
DC

A ±4 %
DAMPING

B,

m

-ZZk V

DRY

CELL

RES. Ba - 6 V STORAGE CELL

CURRENT
Figure

A M P L IF IE R
13.

50
I'C -ire^ o_

the amplifier is satisfied by precision resistances

Rp t:.rouc h Eg, and the linearity of tiie amplifier.
from tube to tube nnu vari

1

1 ons in the operation of a

tube uurinj its life .:ie not affect tiu
scales

the

lifier

of tiie amplifier,
cii&:nta e x c e p t

rents ueveloreu.
lniv.c c n u n _ e s
to

Laip;e

in

the

because
v a n o m e ter,

of

the

!,- e r o !l o f

a nu

reduce

A

..ore i. .rort'v t :.;e a ss o f re d u c i n _

about
r

e

r

a

o

r

c

n

e

a

tines

as

full

s c al e

d

o

Y.

e

r

a s if

it

y la t e

resista/.ce

c

f

. ; r r - ~

-).•

: i t

t . ^ c

o

s

f

w

n

a

t h - :

l

v

n

=

u

o - . - .

o

f

b

e

t

Cr. t.,c; ot-i^r js. nu,
1
If

c i.
the

^r-_ ■ tly
of

—

t

h

e

v . a s

:

r

,

the

to

t

u

b

ih e

*

e

c

s

t

i

h

;

s

o

o

n

t

,

h

...icro

p

h

r

t

r

o

t

t if

lsrw e

c

^

y

;

u

e

u

b

o

a

,

.

t

b

c .induction. c a r re nt o f
s u ; :: l h u

to

the

were

tube

cer o

the

it

i

t

c

nois

c

i

u

j

f

r

acted

'

o

m

tt i e

o

e

t

c

a

’ u

.

t

e

r

e

excc

u

n

i

r

e

d

ive.

l.lie tioe m u s t be

iu<-- ja.lv no..:*. ter
not

(loss

to e h a n j e

of l i n e a r i t y

serve,, as f in e

walvunometer.

sensitive;

n

turn- cnn^Aic ti m

tiie ..-.icropiionic n o i s e

of

currents,

<w

to
h

sensi­

••••lvr none ter c u r r e n t

e

*.c si s t a n c e s d g a n d liQ

te .«_•<.rt t:re

cruuely shock-nounteu •

contcthn

as

t

o f tiie j a l -

to m i c r o yiionic n o i s e .

w '.lv‘Vi'..: t-.r deflection,

a., hast.n*..-,tc to

ui te

e

vciy

opera tin_ c onditions
.i th

l

currents

:.;r. h , r l l f i e r ) .

c o u u
•..as

r e .

f

^ eua.nee a

I

t

e

e

sci.le

.. I st u rb a nc e .

th a m i c r o p h n n i c

tube s at
r

t h is

sensitivity

a./ 1 ’ f i e r v/a s r a t h e r

hur.dreu
f

remedy

v, s s e n s i t i v e

a.a s to o_ u " te "both

0 riu cur­

v.ere nc co::r'anied by

current

To

tivity

t h i s , th-

lr.rje

tiie ^alv:r'o:r*eter f r o m

detect
~h

a.-lifier

proportional I t.y of

unusually

v;rid c u r r e n t s

the hi

iven

no matter h o w the jain of the

in case

It v.a s e a s y to

scale •

Variations

The

and

an l i f i e r

re -uired an h o u r

I

to e a r n ur

Pressure
Pressures
chamber
was
to

were

applieu
s er v e

surfaces

Measuring Equipment

in both

gun chamber

and

the

cieterruineu w i t h a M c L e o a g a u g e ,
to

either vacuum

system

to

ionization

A Pirani

Acetone

was

where

Because

of

leaks

were

at a f a s t e r

rate

there h a d b e e n
.oou

than

a

it c o o l e d
air ana

suuden

solvent

suspected,
the

of glyptal;

Pirani

the g a u g e

increase

in

acetone's
filament

registered

was

anu

sprayed, o n

gauge

pressure.

glyptal

gauge

check for vapors

sis a l e a k - h u n t i n g d e v i c e * ^ ^

high m o l e c u l a r weight,

is a

the

as if

As a c e t o n e

not u s e u

in

the

sy stem.
V a c u u m deals
Metal-to-metal
or* s of t

soldered.

maue using
recent

vacuum

Demountable

O-ring gaskets

article.

satisfactory

These

though

associateu with

the

a vapor

by wetting both

metal-to-metal

proven

pressure

by

p.

to b e
of

same m a n n e r

Fortunately

no

seals u s e d

IT, D,

temperatures,

soldered

Kurie

24

in a

exceedingly

about one

micron

7

is

c o n s i s t e d of grornu glass

counterparts,

surfaces

with

that vin y l

as P l i c e n e ,
seals

silver

joints were

The

Plicene

were

at w h i c h

has

acetate

which

allowing

'work b y
is

com—

is

operate

applied

at e l e v a t e d

a satisfactory

it

Cloud

a l o wer vapor pressure.

re -uireu to

glyptal

seal w a s

a nu

T h i s m e t h o d 'was r a p i d a n d u u r a b l e •

one. P h i l i p 7 i n d i c a t e s
the

welded,

gaskets.

parts mating machined metal

to c o ol .

were

as d e s c r i b e d

gaskets

The m e t a l - t o - g l a s s

pleteu

joints

s ea l a n t .

in

52
Vapor
The o i l

Traps

d i f f u s i o n piumps w e r e

equipped with

f l i g h t •' v a p o r b a f f l e s •

‘T h e s e w e r e

all

entering

the v a c u u m

system.

s y s t e m v;as u s e d

to i p r o v e

the p e r f o r m a n c e

tr a c e s of

oil

auxiliary baffle
of

vapor

not

"line o f

adenuate

to r e m o v e
An

the p u m p •
For removal

p ed w i t h a t h r e e
f r o m the
t hi m bl e

top of

liter
the

extended

filling port.

of v a p o r s ,

ionization

ice m i x t u r e

the t h i m b l e

exposeu

time

the

thimble

acetone-dry

acted

to

the

time

either for

was

the

tio n c h a m b e r

caused,

to

st eel

chamber.

usually

because

gas

of

of

tniou^h a gloss

vapor

mixture.

T he

as l i t t l e

as p o s s i b l e

pump-down

ti me

(roughly

tire l a r g e

Th e g a s

to r e t u r n

pressure

chamber

with

s e r v e d as a

surface

which from

the i o n i z a t i o n c h a m b e r

traps i m m e r s e d

ionization

the

the i o n i z a t i o n c h a m b e r ,

d e t e r m i n a t i o n o f 7/ o r

to a t m o s p h e r i c

suspended

T he n e c k of
ana

equip­

c h a r g e d w i t h an

conuenser.
enter

chamber was

thimble

v a c u u m w a ll

was

and,

as an e x c e l l e n t v a p o r
to

ionization

stainless

through

The

the

the

for repair's,
in a d r y

was e x p o s e u

-mite m a r k e d

ioniza­
passed

i c e - a c e tone
to i.ioist a i r

improvement

of

the

five hours).

Cleaning of Vacuum Surfaces
The

techniques

r e c oil e n e e u b y
witn a wire
C-rbon

J. L>. Strong*-'^.

bru s h or

tetrachloride

rinse w a s

with

which were

s teel

wool

used

hetal
anu

anu acetone,

acetone,

as

are

carbon

essentially

surfaces were

then washeu down

in t h a t o r u e r .
tetrachloride

those
scoured
..i t h

ihe f i n ^ l
leaves

a

53
slight
used

residue.

to h o l d

vapor

S a n d p a p e r w a s n o t used, b e c a u s e

the g r a i n s

pressure.

sanded.

u i c h r o m a te c l e a n i n g

speed

as i n

solution,

ca s e o f

frequently has a high
to the m e t a l

surfaces

cleaned with potassium

r in s e d ,

anu

thoroughly washed

the g l a s s w a s w e t w i t h a l c o h o l

Rubber

unless more

the

clings

Glass was

Frecuently

the u r y i n r .

acetone

abrasive

The b i n u e r

which hav e b e e n

with water.

of

the b i n d e r

wa s

washed

elaborate

rubber

with a solvent

precautions had

tubing

to b e

to be

to

s u ch as
taken

u s e d in c o n t a c t w i t h

mercury•
It w a s
obtained
cleaned
that
of

if

found

that

the m e t a l

considerably

surfaces

rather frequently

auliered o r w e r e

rough metal

exposed

to

(six m o n t h s o r

loosely

surface

cleaner vacuums

a v a c u u m were
so).

The v a p o r s

absorbeu on fifty

re.uired

are

considerable

square feet

time

to p u m p
*

out

(much l o n g e r

re u i r e d )•

than

the

rather

tedious

cleaning process

54

OirLRATIONAL D A T A I L S
e v a c u a t i o n of
The
quite

small

carbon orifice,

fragile.

a lar^e

I o n i z a t i o n anu

Because

pressure

of

two v a c u u m c h a m b e r s u n l e s s
rapidly.

V.Ith the

chamber,

the

mercury.

air was

chamber rapidly,
l o n L as

the

lar^e

air was

for f i f t e e n m i n u t e s
d i^

no t a f f e c t

duce

a i r at

the ^_.un chamber^eu^e

thinness was

t h r o u g h the

sma ll o r i f i c e

u lu n o t d e v e l o p b e t w e e n

the

allowed

the

ir e s s u r e w a s c h a n g e d v e r y

differentiul

f o r the

never exceeded

to r e e n t e r

Ionization
R5 c m o f

the I o n i z a t i o n

pressure differentials occured.

allowed

to

or lonper,

the o r i f i c e .

a more

of its

t w o - h o u r p u m — d o w n time

pressure

when

because

the l e a k

ulfferentisl

Gun Chambers

rapid

enter

the

the p r e s s u r e

If it was

rate,

ionisation

some

chamber

differential

necessary

air was

to e u a l i :,e tne p r e s s u r e ,

As

to

Intro­

i:itrouuceu to

asin0

tiie L c L e o d

n s a b uiue •
The

forepump

usual
on

technique

the

in evacuation

ionization chamber until

cha,,ibv;r px*essure h a d b e e n r e d u c e u
the f oreeu-.ip f o r
volume

of

was

the p u n

the p a n c h a m b e r

the

s t ar t ed .

the h i p h

the

ionization

to TO c m of m e r c u r y ,

chamber was
siu

to use o n l y

s p e e d of

then

'.Vith the

small

tiie p u m p ,

pl'f Jo ieX‘tp

Li

.e

xl-

forep'Ump

t i .ie •

f’

i.

n chamber

..ere tu r ne d o n

at

55
Care

of

tiie F o r e p u m p s

The V1.IF— 2 6 0
I' . f l u i u
a,.io nt
cue
in

of

re ;uired a b o u t 3 5 0 cc

which was
fluiu

is

cbv n g e d w h e n

not: v e r y

..,ip p a r t i c u l a r l y
'-a p map •

u.oes no t

The

tor for,
>

to

j.

the

the

upon use,

puinp •

ill ^ i s c o l o r s
th.

floor

of

..iO•itxis o f

continuous

its

ano

nunt

the
was

fluid

pump while
checked

the

>— >

Vhi-hSO.
p:.,v
^ 0

—

pwts

of

the

tiw

by

. pu.

a av u s e f u l

a safety fac­

ip is

on

the

u e f e a t e a by

the

re-

i t.

to

two

pui.ip f r o m
Tiie oi l

ionisation

sebacate,

was

claufxr

diffusion

this p u m p

chon.

as to

fluiu

and

the

the

c h a r r e d - i th a total o f 3 0 0 to
the

oil

relis. ole .
t the

a baffle

le v el

frequently.

re ;uireci ebovit

(C'.nco f D O u O ) •

not

layer

a y;.r.

at'-ply to

th-ui c h e c k

q> o i l

a

in o p e r a t l o o .

re ,.ov 1 ow

is r e l a t i v e l y

cost,

(/'win!

the oil )

six vw cks

x

it

a little

thin

it is

cc o f b u t y l

*•<->s i t .1o n o u
'<I r e s' .■i wiO v, x

era .ose w a s

too

iiyperv-'-c-35 f o r e p u m p s

li_ht

ics.tor o n
of

■_<t s m a l l

f l u i d rntli.m

cl of

crops

-■uino to u r n i n

techniques

T u t yl s e b a c a t e

xiHy b,, ,
cc of

s a me

serve

it g i v e s

a p :,.roxiw. t*-ly o n c e

s t e m ro w ireu. 530
The

n or

ev.up.

Tiie :...}-lG0 b o o s t e r p u m p u w e u

e -:.-p o i l .

th*-n 5 3 0 cc is p l a c e d

o:~ hue oil

onei" tion,

Lnvu r t l n

;.^wu c o m p l e t e l y

the

The
of

is v i r t u a l l y w a s t e d as

v e r y r&..iuly if

tiie oil

the o p e r a t i o n

n l. d w r<-• n: 1 c r a c k i n g o f

of

h ■ level

for

:.owevc,r,

the l e v e l

inn f f lc le '1. h p

on

of

of Octoil-S

the f l u i d d i s c o l o r e d .

critical

in excess

tine l i f e

in

(500 gm)

i f a l i t tie m o r e

oil

prolong

f'-uctl o n w u l l e

and D i f f u s i o n Pumps

me

oil

level

two
in—

The- i .i-..ica <_or co.idiots
p r o p e r oil

l e v e l j its

vmich presumably

p r e v u ted

56
tiie o il

foam,

which

from reachlng
als o

the

developed

aujuilea

ihe

s a t i s f a c t o r i l y by
unit

oi l d i r e c t l y
directions

of

the

while

the

are

electron gun

and

was

0un

considerably

o p e r a t i o n of

the

gun

v*as ^ at i n o p e r a t i o n
operation

tion

u an

the

for

s om e

operation.

attained,
in

the

Uun

sorvicv.. c a b l e
the

gun
If

the

the g u n

to

The

of
of

tiie
the

servicing

Company fop

the

reliable.
of B e a m

at

oressares below

for

power

electrical

Prior

a while
If

" w a r m up"

to

check

was

operating

receptacle

the

mounted

the
the
tube

the

the Vli t u b e s

services were

connecting

to

the m o n i t o r i n g

supply had not been

suitable

0.3

the o p e r a t i o n o f

pressures.

equipment.

a half hour

the

the l e v e l

chamber*,

ana observed

chamber by

the p u m p w a s

cover plate

though

at l o w e r

Whenever

away from

Orifice

results,

voltage

time,

quite

operated

electrical

accelerating

stable
ware

of

in

in

Scientific

Focusing

Small

reasonable

the o i l
the

th i s b a f f l e

toward or

in opera t i o n .

Central

..ticrons w i t h
Improved

was

apparently

on

oil

anu observing

pump

Positioning

The

of

removing

pump

furnished by

liypervac-25 p u m p

the

level

pump was operated,

Unfortunately

the m o v e m e n t of

indicator.

rressovac

the

I n d i cator glass.

1 ntc.rfereu w i t h

tne 0 l y s y

when

in

in o p e r a ­

required

for

conditions

supplied

to

the

eijit-coiuuctor
on

the

endplate

of

chamber.
the

stream from

gun hau been operated
the

a m

was

directed

at

previously,
the

small

the

electron

orifice

either

57
with

the

face o f

aid of

an

ink dot which had been placed on

the m o n i t o r i n g

tube w i t h a p e n or m o r e u s u a l l y by

the e x i s t i n g d e f l e c t i o n
unless

necessary.

tion v o l t a g e
return

the b e a m

field was
at

was

the

potentials which were

If b y

the
suite

If a n e w

was

form an image

3

the

independent

5 mm

swept

The p a s s a g e

electrons

e i t h e r by
lecting
s pe n t

of

themselves

form many

orifice
of

was

the

can be

stream passed

uirectea

accurately

toward

On

the

t he

included
was

cage,

or by col­

electrons

chamber.

as

The

they

latter

l o c a t i o n of

approximate

towsru

each

sharpened until

the g u n I n

o t h e r h a nd ,

if

without

t h e

the

location

tht- n the

the l e a s t

a butter

electron
use

the

experience

for

with

giving

the

electron

the g u n c h a m b e r

the o r i f i c e ,

the o r i f i c e ,

orifice

With

tiie o.tifice

to

indicated

the

to h a v e

the

the o r i f i c e .

as

through

tiie w a l l s o f

located

fox* a w e a k b e a m

in

and

the b e a m w a s

several minutes.

electron

distribution.

then

located

quite

contact with

and

the

to

gun chamber

determined.

airecteu

a guide

the m a g n e t i c

accurately

advantageous

deflec­

a c c e l e r a t i n g i>otential.

the F a r a a a y

the foc u s w a s

was

as

the o r i f i c e

ionisation

Once

the

ink dot

area w h i c h

formed by

sensitive

found,

It w a s

the

t he m in

ions.

the o r i f i c e

the o r i f i c e

in

the

changed

the g u n w a s d e f o c u s e d

through

ion products

iiiethod was m o r e
may

over

collecting

the

of

the

in d i a m e t e r

systematically

As

w i t h i n th e

tube,

in operation,

to

served

location.

same

not

necessity

ink aot

monitoring

small o r i f i c e
tube

the

the p r o p e r

approximately

site o f

a c c i d e n t or

altered,
to

the

velocity

s t r e a m was

of defle c t i o n

58
potential,

o ne

could, no t,

f r o m the o r i f i c e
by o p e n i n g

and

as w a s

and. r e i n s t a t e

closing

convenient,

tween a p a i r o f d e f l e c t i o n p l a t e s .
the

mad e b y

the p r o b a b i l i t y

eye,

recuired was

axis of

the

satisfyingly

have b e e n us e d e o u a l l y

the b e a m

the b e a m to i t s f o r m e r p o s i t i o n

a switch which

d irection of

remove

c o m p l e t e d a short b e ­

If

the

a d j u s t m e n t of

g u n m o u n t e d o n the

the

endplate was

t ha t n o d e f l e c t i o n v o l t a g e w a s

s mall.

.In a u x i l i a r y v o l t a g e c o u l d

sucessfully for

the

above

purpose.

0

As m e n t i o n e d

earlier

the

focus

ir.oijitorlng tube

a nu

tire U u n m o u n t e d

nearly

due

to

th e

orifice

i n the p l a n e

screen.
moanted

same

T he

exact

i n the g u n

tire v a r i a t i o n o f
tire b e a m a c r o s s
long

as

the

conditions

of

in

chamber wore

tire g u n

location of

the

small

formerly

occupied

by

conditions

for fine

focus

chamber were

the o r i f i c e

is

This

smaller

carbon

the f l u o r e s c e n t
of

the g u n

d e t e r m i n e d by minimizing

the d e f l e c t i o n v o l t a g e
the o r i f i c e .

the

than

re paired

technique
the

c ro s s

to d e f l e c t

a p p l i e s as
s e c t i o n of

the b e a m .
x > e t e r mi n at i on of

the A n e r g y d i s t r i b u t i o n o f

jilectrons P a s s i n g
Orifice
The

into

filament

a.y r o x i n a t o l y
sec 'nd u u o u e

of

of

l.he

faa e l e c t r o n s

I.i*•
-v... rra. u

the

field-free

with

Chamber

at

tin

respect
same

ci a.Tier,

leavin^
space

grnall

e l e c t r o n g i n v, s o p e r a t e d

-n w as
gun

the

Ionization

1O00 v ne_'tive

I'n.'iz- L I o n ci •• ebcr,
ice

the

through

the

to O r o u n u .

potential

o r i f ice;

as

namely,

The
tire
O ro .aid •
un

; <-c ui

o x c e L t fo e

at

tiro s-

59
fields due

to

uue

earth.

to

the

i'arauc.jf c a ^ e

the d e f l e c t i o n v o l t a g e s

escape

traveling

at

axis o f

t he y

the

v.icte t i g l e
tance

of

at a p r e s s u r e
at

The

consiuer

enter

the

small

average

free

to

the

tank
Of

the o r i f i c e
collisions
i -i t h e s e

lies

course
or

just

take

some

but

t ak e

into

in

the

the

tiie I o n i z a t i o n

transi­

chamber.

that

electrons

side

the

as

they

tiie i o n i z a t i o n
collision within

chamber but most

ionization

cage

error

chamber

reason

suffer

it s m e a n

Ionization
This

of deflection

Faraday

where

the g u n

the

ionization

angle

the

Inches.

i nch.

then

dis­

path of a lOOOev

inches within

the

further

uegrees,

may

uo

small

even in a gas

to

at

the

Such a

c a n v.ith s mall

place

electrons

the

the

0.1

0.1

one

O ne

0.08

within

collisions

tiia.n f o r t y - f i v e
Ir.eir e n t r y

p a th Is

c o l l i s i o n of

about

place

electrons,

2.5 meters,

carbon orifice.

they were

degrees with

the g u n chambex*,

continuous,

transition

electrons

the o r i f i c e .

The m e a n f ree

of

the

or have been

unlikely over

from

l o c a t i o n of f i r s t

chembei*.

If

its me an

course

of

cage,

Is a p p r o x i m a t e l y

oraer

the

of

gas molecules b e t w e e n

walls

50 microns;,

the

that

field

exceedingly unlikely unless

Ftraday

is v e r y

50 m i c r o n s

it. o f

t i o n is o f

the

the

electron passes

path

was

inch with lOOOev
of

cjii.iiibor w n e r e

of

from

so

the o r i f i c e

than forty-five

with
the

10

the m a g n e t i c

Fax'suay c a g e u n l e s s

This

ana

deflection

0.100

electron

the

a collision

scattered

situateo.

wreater

system.

carbon orifice

sharply

free

enterin0

an angle

suffered

small

shown in Figure

’was lsi*gc a n d

could not

the

As

and

will

chamber.
is g r e a t e r
not

register

If the p o s i t i o n of

60
the f i r s t

collision occurred further within

the

tank,

a n g u l a r r e f l e c t i o n m u s t "be e v e n g r e a t e r

to e s c a p e

ca0 e •

acceptance of

The

r rauay
the

experimental

cage

as a n e f f e c t i v e

ionization

chamber was

During periods
operation

(after
p.m.)

cage u i u

not vary

'.VIth

ionization

for

the

was

swung

After

t o ta l

th e

ten hours

the

current

collected

of hal f

the

electrons,

c h a m b e r w as

of d r i e u

air

to r a i s e

pressure

to f i f t y m i c r o n s

test w a s

i n t e r r u p t e d b y one

the b e a m c u r r e n t

obtained, in w h i c h
cage u i u

n ot v a r y b y

rurtherinore,
enc e f o r

the

they

these

of

of

current
one

per

variations

appeared

e l e c t i o n s by

to b e

the c u r r e n t b e i n g
Th e

ionization

pumping
and

collected by

many

Faraday

t hi s

which

runs were

the F a r a d a y

I ts o r i g i n a l

v alue,

show a pressure d e p e n d ­

random fluctuations.
that

a sample

chamber

Frequently

However,

aid not

electrons.

the I o n i z a t i o n

the m a n y v a r i a b l e s

verified
the

to f i f t y m i c r o n s

then closed

cent of

Faraday

■u i c k l y as p o s s i b l e

admitted.

to v a r y .

series of o b s e r v a t i o n s
capture

was

the

entering

t i me

the

usually

the F a r a d a y c a g e

c a g e w a s o ’o s e r v e u .

the i o n i z a t i o n
sufficient

as

which

stem for

cause

the

was measured,

during

stable

an h o u r o r l o n g e r .
adjusted

to 0 . 1 m i c r o n s

Farauay

the

entering

in u n u s u a l l y

collected by

to I n t e r c e p t

(about f i f t e e n m i n u t e s )

electrons

of operation,

chamber pressure

position

the

s y s t e m is

periods

evacuated

collected by

trap for

the

electron
for

current

chamber was

to

the

the F a r a d a y

as f o l l o w s :

a b s o r p t i o n of

into

the

when

eight

a f t e r 11

the

support for

the

This

the e f f i c i e n c y of

the

cac e was not pressure

61
uependent over
l e g i t i m s te

the

region

to a s s u m e

fer C,nt of

0.1

the t n o t m o r e

th-. e l e c t r o n s

c rbori o r i f i c e

an u

to 50 m i c r o n s .

in

u n a e r 0o in-

the

the

after

.rif ty n d c r o n s ,
u s f vi.i' 7

taut i n s beau

i.i r k e u

r rn- <ny c •..•w e •
t.sv c-

tiie i o n i z a t i o n

Gh

orally

e coo iiou eu
two

!n

L.I sr. ci,,.. h

*•
..:*

:. I- bu rnsii
!>’• ra.asy

-ulna teS

cc w e a i d n o t

.sea

re t o r n

the

ourreni

;,rt. ■; ure

by

the

the

tube

CU thouc •

ir- s

but

1
.1'Voi-, ••. ice bj

>m ium nnex*

A.-re s.ouro

value.

lo-est vrluc

the

The

ttaint.u v.-hile
Occssion-

as

the

1 n ni y.n t ion cha.-iber

cas e

e id

it a-, -roach its

in

current

ivc s «'iue to v a r i a t i o n

in

the e m i s s i o n of

tube w a s

po s i t i v t

fro-u; itly

collected

ion b o m b a ru.me nt oi

returned

ohe

to its o r i g i n a l

:,f la s h i n j " o r b y u s e o f o t h e r

activating

-ies.

lerhni

.Ji.'i u.^ i it 11 1:< s been. who v:n th' t the
raeuy
hhic

the F i*h-

t t-. .1 r i.'.to

its o r i g i n a l

in no

the

t. ie vsrii tios

.r-obabl j c a u s e d by
Th e

collecti- j b,,

to

there

t t .vo Iron -rsu .,iic r o n s •

-r,,. ■n r e . tly

Fa rs *:a y c a y c

returned

th e c u r r e n t colit e t u i 'ou

r t the

tiie

chamber,

IV,«. 1. ' 'i/a Liar' el'. •h e r

to

an u

c o l l e c t e d by

t fl

incr./.t: cd a l i t t l e

si s d e c r e e wed,
value .

initial

chamber

current

in a rntlu-r m u

tcrons,

euri**. .it u siia.11 j 1‘ei.t?.i n e d

-11,;

the

I'l-.an i.rs • to

to f i f t y

. 1 i-iza ii m

in

small

caye.

the i o n i z a t i o n

tiie c u r r e n t

v •

the

the o r i f i c e

c h a m b e r w ••s n o t

to b t c r - o we

•:f tel* th e

in

bo tro bandrcc-. m i c r o n s ,

uecrei. se

it w a s

t e n t h s of o n e

collisions

the F n r a u a y

tiie evacu;. t i o n o f

ia'CHsure o f

a few

rejion between

i-hruuay c n w e escaped, c a p t u r e by
If,

than

Hence

cuy's

capture

of

electrons

c Ire u m s te :ice uo o s not p r o v e

is n o t

that

all

e f " tcic nc^

o j one

.re s sure d e p e n d e n t ,
tile e l e c t r o ns

62
entering
Faraday
rather

the

tank

cage•
rapiu

the c a g e ,

from

On

the

about

cent

do

not

remain

orifice.

effectiveness
energy

curve

collected by

potentials

applied

variables being
F* r a u a y c a g e

held

with

electrons having
100 v r e t a r d i n g
ns

Faraday

the

to

currents

with

one

may

a retarding

uue

to

the

f or

t h a t matter-

i ng p o t e n t i a l
ficant, b u t n o t
collected.
by

to

the

th a t o f
o f 1 0 0 v,

not

8 0 0 v.

In

the

(two

per cent),

m a y be

of

primary

the

due

to

cage.

at

captured

none
to

are

lost

200 v o r

50 to 1 0 0 v r e t a r d ­

cage

there

decrease

was

in

with

a signi­

the c u r r e n t

s lo w e l e c t r o n s

electrons

o r i f i c e or w i t h

the

significantly

virtually

first

large

change

Faraday
cage

tiie r e t a r u i n 0 p o t e n t i a l

tire F a r a d a y

small

the

the

o f all

of o v e r c o m i n g

the e l e c t r o n s

to

tin. c o l l i s i o n

walls of

we re

nega­

collected by

the F a r a d a y

potential

plotting

all o t h e r

consists

to e n t e r

applied

This

at v a r i o u s

current

capable

collected by

of

14,

potential

energy

conclude

increase

ca ge

the

f r o m the

w a s o b t a i n e d by

T he

required

potential

concerning

the: F a r a d a y cage,

a kinetic

which enter

was obtained

Faraday

100 v negative

w al l o f

scatter b a c k out

in Figure

constant.

potential

electrons

curve

the

s c a t t e r i n g a nd

the i n s i d e

there b u t

shown

the

l O O v an-i 2 0 0 v negative;
oiffcrunt,

the

c a ge

captured, b y

random

information

energy distribution

current

tive

of

Further

the

distribution
T he

the

of

are

striking,

per

of

cage

after

0*3

cage

chamber

a s s u m p t i o n of

absorption

tiie F n r a u a y
the

the g u n

formed

the c a r b o n

the g a s m o l e c u l e s

through

63

20

—

CURRENT
FARADAY

FROM
CAGE

1 8 --

1 6- -

l4'-*'*o

o -----o--o— - o - --o--- O

O'

~or

12-

IO --

8- 6 ..

4-

-

2-

-

R ETA R D IN G
H
6
00
400

A

200

ENERGY

P O T E N T IA L
800

D IS T R IB U T IO N
F ig u re

IN ' VOLTS

1------- — £

14.

IOOO

CURVE

1200

64
which

the p r i m a r y

appear
the

to h a v e

electron

electrons
a

electrons

less

than 7 5 e v

stream.

may have

A

considerably more
to

slow electrons

tiian an a v e r a g e

u as m o l e c u l e s

in

the ,
1 constitute
ion-pairs

the p r e s e n t

to

these

of

the

of flight

conciuered

40 v to

tank.

This

work.

low energy

tun p u r

cent

of 0 . 0 1

per* c en t .

low energy

of

the

or* so,

The

ret'..ruin0 p o t e n t i a l ,
The

increase

too

in

can be

sm a ll
for

token
zero

as

c e n t of

vdiich are vsli*.'. to
the o r d e r
the

current with 100 v

retaiainw potential •

the c u r r e n t

collected by

retaruin0 pobenllals between

300 v

the

Farrday

and 1 0 0 0 v is

not clour] j uau t r st uoe •

Tiie e f f e c t m i ^ h t be vurioutily

described

in

as

a decrease

in

the >.h c tron
electron

an i n c r e a s e

the p o s i t i v e

the e l e c t r o n
ions

c u r r u n t lc a v i i p

the F -*r a n a y

f o r m a t i o n ) , or* a ... i n c r e a s e

formeu

v , i.rJuv/

within

CO -e

ana

the
the

Faraway
small

current collected,

collected,

in

e u n x i j t :..(.)viig a w a y f r o m t.io I*a r a u e y
are

the

considered

ie ent e r i n g

the

the

i o n i z a t i o n du e

e r r o r of

current

with

formed hy

to b e

the

maue

an absolute

electron

w it h

ion-pairs

t h a n 0. 1 p e r

Approximations

leaving

in c o l l i s i o n

the

error was

electrons

as a g r o u p h a d p r o b a b l y

spend

Hence

ioni z a t i o n c h a m b e r must be

ut

the d i r e c t i o n of4

than 75ev energy along

the li n e

c on si d e r a b l y less

formed.

in

ca ge

along

slow electrons

s tr e a m .

These
los s

energy

These

s m a l l percent'jge of* t h e s e

direction perpendicular

ulechon

traverse.

cape

carbon

a decrease

cag e

(s e c o n d a r y

the p o s i t i v e

cape

(positive

ion
io ns

and r e g i o n b e t w e e n
orifice

if

in

the

the v a c u u m v;as

55
not

icientlj

V:-.;-0^'S j

the

pri’t i c u l s r l y o f oil

—liere c ?ula h a r d l y b e

electron
as

cleiin,

current

passing

---tnr-iny

l u .'.3re« as f a r
c .r u cu .

the

and lOOC

f ew r u n s h a v e b e e n
"he i n c r e a s e

for

in c u r r e n t

e.n t e r i n w the

t. .c s. .a13

electrons

men

caue

densities of

cubic

t.-. nk.

A

the F n r a n a y

mrbon

orifice

thep

.ere

stronjl"

_oier_y d i s t r i b u t i o n

tat

600 v

a. : arent-ly c h a n g e

oi-ifice •

k c o n a t ry
ere

not

fi-

b i-a s a to

c arbon

p>.r

ecu l iar

effect

c .rr-. t- .v.f•.eur 1 1

u

e

c

u

r

s

re s -on.siblc
lips

■- ui

l

i

k

e

c.ue to

mot

the
l

not

formed
for

t

h

a

t

i

l

?

i ^n i -

appear

at

of

or

sharp

the

curve

to inntter

it ci ti-red

the l i p s of

the

t. x. c n/'cct - £ •• c u s n y e
in t h e

curve.

ti.e c u r r o u t - c a m y i r . y

or

rplf 'r i s ..a^:u,reu in

re u i r e s
o

a

s hape o f

- iv ~ru,e .•t as

for no

effect
y

th.

a

the h. ° t i ; n

ro ..need no v-ri: A ion

is n o t

crrut;
t

electrons

ithout

focus b e a m

-id

was conv.-rw e t o r

'•- re _ v v* c a n

I

It

v.

in

a bro-

to 1 0 0 C v r e g i o n .

m<_ tn<=r tne b e a m

ro

1'iie ci,0':pt

a e to

tiie

ce n ti m e ter v.ere

in ;u:.0 Atiaie

in tiie c u r v e .

f o c u s b .a m - i d n o t

.

of

A ve b ee n take n o f b e a m cur-i-e ots ..iff:i l n p b y

change

n

..ere co:v

tire e f f e c t w a s m i s . i n ^ .

charje

charges per

fic: n t

a

vhich

civ rpre tit.or j h

of n e a r l y one t h o s a n d

hack

the e x p e r i m e n t

inteu-it? beams

»h e n

-due e f f e c t w a s

c o l l e c t e d by

factor

in

carbon orifice

ener~y uistributio~

obtained

space

It., u *_h

dc-cclora twl

small

in the

e v v.as not a c c u r a t e l y k n o w n .

or-ci'- of 10 c e l e c t r o n i c
for.:xu

the

re s u i t s o f

V n f o r tun a t e 1 y the

.as r.o t .:ue to

an i n c r e a s e

;.otcntiil v.a s i n c r e a s e d ,

as

b et . t e n o'“0 ev

curves

ohroa. y h

and. n s r c u r v

o

r

m

e

the
r

c

u

r

pre-reocc
y

v

a

p

o

r

s

of
m

a

y

;ne
the
b

e

66
re s p o n s i b l e

for

conciensor In
the

of

the

1 on i z -al i o n

iov,tva'
Ihe

the u n u s u a l
Ionization

charaber

tiie v a p o r s

effect

s't-ricteu •

we re

The

of

V. r i n t i o n s

In

t he

a TOO

e l e c t r o n be a m

ev

i-uso-t

i i th;

r he

of

2„ro

•v

. r

.

of.

,.
: i -1

to

woula be

seriously

re­

c rve

n e n s - rn

to

i -t

I..- ; ’

v

m b .
c i.i. t

• X"'

c.j

c-.%

*

, ; of the

.

nc .

ev- :

■

re m ac e 1~

O •

l0 ,

o1
'

■-1

h o

r:

of

c re h.st.

'
•

a
ICO

ciory
ha.

c

th

re- sp-o n s i b l e •

the

voles

Faranay

spreau

'h-om

t tec .ua joi-lty
CXCOCU-

c n a -h. ;:in,
. 1"

to h - l f

is

this

the
s

than

its v a l u e

at I C O

•
.1 •.c t

'a c -i"- .it, c

t-

as

c

r ■

f -’
v.

r-

L measured.

i'l.

’•

r •■•

c

• 1 c L;-

:LCi

of

t' ; U i ’/'i.CO O'C

o : c.s

*•

small

th t th-. v a p o r s

are p r "'bably

1 u .I c • fos

ur

f h

;h.

the

wl »tch \v- s m-.u.e o n

c o l l e c t e d by

!;.r*)Vj:

h r

i n u i c a te

Tiie p r e s e n c e

chamber

this

to

indicate

current

;;■ i .1_

of

region
of

ch; r-p (abo.it fivo

’

the

operation

sensitivity

se_ns

the

o- . ' r ■etf '.

If

the

pressure.

c n o n t);

o'- *.h,. ,,1 cti'O I!

trap

•-i s t r i b n t i o n

..as ( . x c c t u h p l y

**

the

I" n i z a Lion

cut-off

../L.uiu to

1

oi* a b s o r b e d i n

in

p r e s s u r e - m e a c -nri n j , v a p o r - s e n s ! ti ve

the v a p o r

tiie ciiuipj

—

i.ibe-r removed, any v c o o r s

a.u s o r b eel

vapor

present

:h in : I n

lar^e vapor

v.1 t h i n a m a t t e r o f m i n u t e s .

opni^i.iunt o.i^ n o t xisve

•

ch

The

Fe.raa.ay c a 0 e anu. evolveu. uui*.inc

j u n , the

cr._s

behavior.

i

:•">.■ c

v

,ails

col

v is

to

.-r'•c i

>C 1 .=■. •1 s

rr-

c ;;o r the

-..I' C h . a '.'is.

f cm; h •v

a.

-c ,
tshcr

’m-a
b n

I'-ctro 1

^.xx.

0

as

an

„
the

67
scatterin^r

at v.i^e an^lc-s,

. ott:'.tials w o u l d

s-/ravate

c o 1 .> v C t c u

raradsy

cc. i w

by

cease

icurrent

Ihe
tne

all

s re

the

arplicatior. of* r e t s r a i n y

the

situation

caye

effect,

these

should
"but ir

and the cun-er.t

decrease.
the

Other

ab sence

con-i tions a u s t have

fac :ors

of* a d e c r e a s e

ce en s i m u l t a n e o u s l y

sa v1 s f i e d •
-he
e-.crj

measurements

distribution

beam on

and off

potvntii.l

comprisiny

curve)

the* s m a l l

2-ecorued.

Hence

bear, w e r e

recorued.

o

on of

electron

- r..lrw p o t e n t i a l s to

rommir.

one of

effects

_nn by

to

renuce

che

fli_;iny
for

only

of

use^

the

c h e c k s we r e

r« t u r n I n ^

the

1-i (the
electron

;r.ch re t a r d i n c
to

presence

ria^e of

tiie

to : r e v i c as re-

the

small

e . r b o n o r i f i c e bj

the d e f l e c t i o n volt-; _e s of

sto.-. iny yes

laboratory.

in T i u u r e

t h •, c o n s i s t e n c y of r e s u l t s .

The .addition of
The

aae

Treouont

check

b.c b e a m w a s flip, ed o f f

made b y

cordon, o r i f i c e

of' uhe

t;

were

di© c u r v e

the
was

dry

'The l a b o r s fcory h a s
_ossitiliti;

Sto.

an

in n

air

th<. y n .

las

taken

from

the

a ^e - a - te c i r c u l a t i o n

of c o nt a m i e -*•tio n uue

to

co.— .iO."x laboi-atory v a p o r s
cam b o n

te t r a c h l o r i a e ,

etc.

t-.-e •- -.. a cetori-.

t-rac o f

tine

a i th y e s

bran

filled

t; ... i T'izatior. ch r h r
hi-miu
ns

r e f ri

The

r-u c h

to

at

a i r v.as ^ r i e a in a u r y

a volu:..e, that
atmospheric

a areas .re o f

air o r l i - u i d r.iti-opa'- -re

e r a n t s f or

Ol* S

txie v o l u m e o f

.res sure f i l l e a
seventy-five
not

oo 1 .

microns.

satisfactory
or'

;ne

68

ni t rogen in tlie sample freezes out o n the walls of the
trap

anti the

sample

chamber* is n o t
of

of gas

air.

The

introduced

necessity

this ;:oint w a s d e m o n s t r a t e d b y

tion.
air

'.Then a

samj^le o f

(presumably

higher value

at

o f b,

by

remove

The

were

the

too

the

the

for

This

value

insul

of

the

lost

aue

energetic

consisted of

collector* w h o s e

to g r o u n d .

The

ra; -w e was

extended by

r e g i s t e r e d by
15

collectou;

of

the i o n s

times

the

c o u l d be

the

that f ew

none

were

formed

the c o l l e c t o r .

one,

the i o n ­

second,

an

varied

c o l l e c t e d by

the

with

second

v/ull g a l v a n o m e t e r w h o s e
The

current

is i n d i c a t e d

potential

'The u p p e r

of

cu rve,

(electrons

curves

required

such

towara

potential

the

were

electrodes;

galvanometer

c rrent

these

ar.u y et

and

the lower* curve, the

The o r d i n a t e s

at a r a t e

tire ±j0 a m p l i f i e r •

to O r o u n u •

trie e l e c t r o n

two

fields

potential

re^istereu by

the w a l l

of

currents

as a f u n c t i o n o f

v.1 til re s pe c t

electric

movement

were

_;ives

a p p r o x i m a t e l y 1.4

to r e c o m b i n a t i o n

electrode

figure

was

Ionization Products

c h a m b e r at g r o u n d

t ed

respect

a strikingly

the f o r m a t i o n o f a n ion-

ionization products

system used

ization

through liguid

temperature),

energy

control

an i n c i d e n t a l o b s e r v a ­

vzas i n t r o d u c e d

As h a s b e e n m e n t i o n e d ,

ions

for careful

air.
Removal

to

the i o n i z a t i o n

the o x y g e n

pair was measureu,
that of

gas

to

and

positive
differ by

the

in
collector

as i n d i c a t e d ,
negative

io n s

ions)

collected.

tire m a g n i t u d e

of

69

juA

C O LL E C T IO N
CURRENT

PRESSURE IQOjft

✓

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0

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Jt>'
0

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E LE C TR O N

CURRENT

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VOLTAGE BETWEEN COLLECTOR S TANK
VOLTS
Figure

15.

70
the

Initial

where
are

all

electron current

and only

all

the

voltage
e xist,

end of

the

region of

formeu by

impart

enough

In

so me

the p l a t e a u ,

the i n i t i a l

At v o l t a g e s
the

the

above

Ionization

energy

to

the

collision

excited molecules,

and

the c u r v e

(at

electrons

the l o w

a sufficient field does

parts of

may f o r m i o n - p a i r s b y

Ionization by

"knee” of

Ionization products

recombination*
parts of

the

the p l a t e a u )

at l e a s t

to r e m o v e

the y

ions

th e

collected#
At v o l t a g e s b e l o w

some

over

ionization

without

chamber,

some l o s s

d u e to

the p l a t e a u , at l e a s t

chamber have

fields which

i o n i z a t i o n -products
collision

in air

not

with

re u i r e s

so

that

the g a s m o l e c u l e s .

a b o u t 17 v f o r u n ­

c o r r e sponu.in._ly l o s s

if

the m o l e c u l e

is e x c i t e d *
T he
curves

wo re b a s e d ,

V'loclty
were

measurements

not ..ge

to

_i-oo mu. c u r r e u t ,

of"

we- re :naci e in

the

sa me m a n n e r

the o r i f i c e

plates*'

F ro - u c n t

fa c i,o r y o n

curves•

of

the b e a n of

switch

To r e m o v e

of

ration of
ti :C same

the

uric
LC it,

collection
as

v/ex-e i.nuo
electron
Used
.-I.-, n t

(back-

on cuxu'c; t
was

sv/i tci.ied

two c h n u b n rs w i t h

• p a i r of n P L
to uotoi-iifjo
j m •

which

electrons

iocid-. nt e l e c t r o n s
th -

the

effects

h ':c w a.1 v a no i,-ieter

separating

chocks

all

tne i n i t i a l

co-v'-: c toCi b.. tao-m

.i.o t h o d , -wnilc c o n v o
c r r o x*

Ionization

ze r o d r i f t

shorting

obt.Tu i.1^

the

the p r e s e n c e

,.:p l i f iei*, et c .)
on a

which

uistrtbutlon

on

a

chon
ane

satis—

utixcr notjiods of

to -'SC!U'tain
intro-■n e e

any

that this
systematic

I

71
,71 th the a i d
was p o s s i b l e
whe n f i e l d s

to

of*

e no u g h
was

everywhere
v

two f i e l u s

to p r e v e n t

just w e a k

that

of

tial,

30 v,

The

smaller

just c a p a b l e of r e m o v i n g i o n s fast
r e c o m b i n a t i o n and

collection

the l a r g e r f i e l d

the f o r m a t i o n of a n o t i c e ­

by

migration

this

the i o n i z a t i o n
the

Ion

the i o n s

and e l e c t r o n s in

to e i t h e r c o l l e c t o r .

Ko t i c e

plateau extends over a twelve­

collection plateau from approximately

occurred, u n u e r w h i c h

uevelooea

o b t a i n e d if t h e

of*

the

effect

chamber

troublesome

ionization products.

Figure

by

laaynitule

showiny
of

the e l e c t i o n

k e p t c o ns t a n t .

pear ed,

yocs

without pause

an d o n e

Lons are l o s t by
formed in

the

i-e c o m b i n e tlon

represents
pier stconu,

surface

This of c o u r s e
ten.

to a r e g i o n w h e r e
The

ion-pairs

r e j i o n s do no t
two m i c r o a m p s

of r o u y h l y 10^*^ e l e c t r o n i c
area of

r.ll

f r o m a r e g i o n in w h I c h

A c o l l e c t i o n c u r r e n t of

a collection
Tire

te n -folu.

The p l a t e a u h a s d i s a p ­

c o l l e c t i o n process.

t h e v, o v e r l a p ,

stream entering

current by a factor of

y/cji*o

13

the c o l l e c t i o n c ur v e

was i n c r e a s e d

collection

space ch a r g e

uotentials which were

other variables

join;

sh ould b e o b t a i n e d

1 v p e r m e a n free path.

to p r e v e n t

easily

collection

illustrates

are

It

a f o u r * — f o l u ranye.

concentrations

increased

2,

f r o m ap;_ r - o x i m a t o ly 5 v to 30 v c o l l e c t i o n p o t e n ­

Conditions

to the

was

their*

the p o s i t i v e

TO v to

that a p l a t e a u

ion-pairs

the- e l e c t r o n

fold r a n r e

and

enough

s h o w n In F i g u r e

i n the i o n i z a t i o n c h a m b e r w e r e w i t h i n

their

able p r o p o r t i o n o f
the c o u r s e

collector

calculate

the l i m i t s o f 0 , 0 1
of these

the

the c o l l e c t o r

charges

shown in

UA

C O LLEC TIO N
CURRENT

PRESSURE

IQ O ^ .

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O

ION C U R R EN T
ELECTRON

CURRENT

VOLTAGE B ETW EEN COLLECTOR S T A N K
140
160
80
IOO
120
60
20
40
VOLTS
Figure

16.

73
Figure

H

Is o f

collected, p e r
electronic

the o r d e r o f

square

charges

centimeter

per
0,1 v

of a few

centimeter

charge

to b e

density

oraer of 10^
high

the o r d e r o f
to m a s k
This

with

the

1 v

per

difficulty

rise

space
which
the

unmistakable

plateau

positive

Ions

eleven-inch

were

with respect
did not

to

develop

was

of

that
space

the

ion

on

the

the

charge

space

sphere•

charge

the

more

but

when

when

the

concentrations

the

Ion

ions

electrons

for

the a re a

tv/enty-five times

electron collection
symmetrical

ionisation

an

the

the p o s i t i v e

roughly

The

existed

surface of

chamber wall

was

electron

a result,

The p ositive

conditions

Ionization

of

conditions

small

electron.

collection become
areas

Initial

electrons,

the l o w m o b i l i t y o f

eleven-inch

surface

charge

formed for

cbambt.r w a l l

positive

The

f o r e l e c t r o n s , • As

of

the

In F i g u r e

s pa c e

the

t h at o f

the c o l l e c t o r *

taken

ww,re c o l l e c t e d o n
the i o n i z a t i o n

of

sufficient

17 w e r e

collector,

of

than

1 5 and IS,

collected

spherical

developed because

not

This

Figures

that

but

the

d e m o n s t r a t e d by

I n Figux*e 2,

I on s ,

Is o f

the

p o t e n t i a l s of

poteen tial

collector visible

for p o s i t i v e

the

centimeter.

is m o r e

the

so

the o r u e r

charges,

charge

simvm

reduceu

a positive

Assuming

cubic

collection carves

was

charge

is o f

collector

The

current

as

path

electronic

the

to

centimeter

clearly

the

mobility of

per

generated by

Is

hence

second.

single

charges

gives

fielus

as

per

charges near

electronic

concentration

T he

per m e a n free

transported

of pos i t i v e

cm^,

Is a p p r o x i m a t e l y 1 0 9

second.

i on I n a f i e l a o f
thousand

6000

to

c h a m b e r w a ll

and

each other
and

uhe

74

^

q

.u A

C O L L E C T IO N ______________ P R E S S U R E 7 0 ^
CURRENT

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ELECTRON

CURRENT— *

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OO

VOLTAGE B E T W E E N
20
40
60
80

Figure

COLLECTOR
IO O
120

17

ft T A N K
140
160
V O LTS

75
collector become
advantageous
f ac e
on

As l O O O e v

electrons

to ry c o l l e c t i o n

This

a fac t o r of

three

the

ization

u ield.

quired

for

c ^ n t of

T

and

For

t en p e r

c e n t of

an c x s q l e ,

the

for

the

potential
remain

the

t

c

.

i

sur­

themselves

i

I

s

the

v,

i

c

the

h

_

i

s

ionin

products

o

n

at

pressure
reauceu by

the

So

source

the

on

sm a ll

of

the

ion­

ores, are

re­

electrons,

the

order

i

used

l

n

c

i

d

e

of

n

ma y h a v e

\

o

r

of one

per

been

f

e

r

e

u

e

n

particle•

t

bOOOev

lOOO
that uisl

satisfac­

electrons,

of

i

the

a

this

could be

initial

the o n o r q y
t

at

potential

was o f

of

ionization

the p l a t e a u .

p r e s e n t v.ork,

enoiw;

the

a treacherous

collection

re m i r e d

t

on

abso rb
author believes

smaller

50 m i c r n n s ,

saturation

a b s o r p t i o n of

o

on

is j e n e r a lly

stepped, w i t h i n

removed

the

the o r i g i n a l

p

It

to n e u t r a l i z e

the o r d e r o f

still

of

pot*.." ti a l

collection

i l e

ions

collection

effect

total

collection

of

potential

e rr o rs

same.

electrons

were

potential

w a s 1 0 * 5 v*

the

c h a m b e r wall*

at p r e s s u r e s

a collection

the

the p o s i t i v e

ionization

chamber

nearly

to c o l l e c t

an d a l l o w

the

more

t

l

y

As

electrons

v potential
r e g u t red

to u s e

these

conui tion s

The n u m b e r o f
of

i

tiie

e l e c t i o n of

hi
v

i

e

o

ova

n

n

i

z;.,

t

i

o

n

mean

.free p a tth
h ss re

a yi v o n
the

- ' i * o d

u

tin r w y is

nu-.ber o f m e a n
c

ts m u s t

b

e

aired

for

r -» qhi.j

tne

a constant

f re c. p - th s o v o r

collected

i

s to tipi:iq,

.
c

for­

w 1cn

row i iri• t cl y

76
the

same n u m b e r o f m e a n f r e e

initial

electron.

p er m e a n

free

electrons
prouucts

to

Hence

p a t h the
the

paths

renuired

r atio o f

the e n e r g y o f

approximately

V/ithin b r o a d l i m i t s

of

the

(vdiich a f f e c t s
•therefore it

;alte

p o t e n t i a l s Y.ei'e w a ue
dote

th at

the

particle

the p r e s s u r e

is

thi: n v;e re re o u i r e d f o r
the

space

charge

appLimtly

moves

to

validity

of

per- c e n t Is

to the

ri^lrt

space

charge

the

is

v.

likely

collection

collection

conditions,

ion collection curve

more

potentials

coriultions.

"knee".
the

As

"knee"

th a t

emor

for lack of
tlie

fo r largge

in tlie k n o w l e d g e

potentials

is,

the t r i s l

dhatever

correction

absolute

small;

serious

It is p r o b a b l e

if lov/er c o l l e c t i o n
Is

absorption),

(higher potential s ) until

can be

used.

a c o r r e c t i o n of o •6

re u i r e d in U f o r 9 0 c O e v i n c i d e n t e l e c t r o xo.s

v;iioto I o n i z a t i o n p r o d u c t s w er e
of l O O C

sp ace c h a r g e

conuitlon becomes

G c r b e s » correction

t ot a l

at c o n s i d e r a b l y higgher f i e l d s

Gex-bes ’16 t h e o r e t i c a l

.* is r e d u c e d

is i n d e p e n d e n t

the e l e c t r o n c o l l e c t i o n

coltfcctton p o t e n t i a l s ,
of

for

the p o s i t i v e

.se iiig;ii c o l l e c t i o n

c o m i d e m tion of

roughly ecual

t h a t j^isl f s la r g e

tiit p l a t e a u f i n a l l y d i s a p p e a r s .
\/f l d r i v e n

thi s

rc u i r e d

n e c e s b u r y by

s h o w n in FIggure l b a p : e a r s

the i n c i d e n t

a n d d i m e n s i o n s of the c h a m b e r

probable

"knee" o f

the

fox- t h e i r i o n i z a t i o n

a constant,

to one h u n d r e d .
the onerggy of

stop

for a g i v e n c o l l e c t i o n voltage

collection potential

s h o u l d be

to

as

Gcrbes

was

t ha t _,isl w a s
potentials■

co l recteu.

a,, p s r e n t l y

conscious of

..Ith a po t e nt Lai

a s t u u c n t of m s l ,
the o b j e c t i o n

it

to higyh

77
lie t o r m i n a t io n o f tlie S a t u r a t i o n C o n d i t i o n
To

a s c e r t a i n the p r e s s u r e

tiuCC s p l a c e ,
well
in

below-

the

will

limits

of

may

coming

be

f o r m ; ition o f

cnei*w y
of

av n r

^e

should
the

with a net lo ss

in the u as,

fo r me d p e r
totally

i n it i al

ch-.r e units:

o 1t v a t e u

electron

the p re s su r e

expects

electron

total

f o r m e r per

until

absorption,
initial

the

electron

p re s.su re .
of i o n - p a i r s f o rm e d p e r i ni tial

p l o t t e d as a f u n c t i o n of

the pr e s s u r e of

the i o n i z a t i o n c n a m o e r p re ssure

rl with

( F i n ire 13).

tii>, a v e r a g e

the v a l u e of li r o a c h e s
a i c i p y of

is in a 0rceand others.

a li m it i ng v a l u e dote n n i n e d

the i n c i d e n t

u ;> r o c i a b l y f r o m this va l ue

the

The l i n e a r

tiie o b s e r v a t i o n s of .Lehmann s u e 0 s 0oou,‘^

*i.s i.rouic tod,

m e Vi: te

in the

s t opping yas •

l u c r e a sc o f

by

in the

the initial

in micro os

with

may

the n e t loss of

io t« Lz.&Lio n c h a m b e r

m c :;t

el ec­

s e c o n d a r y ef Cectc ore p r o d u c e d by

avcrf'jo number-, K,
is

ns

a b s o r b e d wi thin the

nu:.ibei- of i o n - p a i r s

The

el e ctrons

The i n it i al

in the e n e r g y expen d ed

p re s s a re re 'aired f or

not

the initial

d e c r e a s e d an a as a r e s u l t a n e t i n c r e a s e d n umber

are

the

e l e c t r o n s with

s e c o n d a r y electrons,

c h a m b e r is i n c r e a s e d one

ion-pairs

3cyonu

in itial

the i o n i z a t i o n c h a m b e r wall

may produce

ion-pairs

to b e

electrons

the

spent all of t h e i r energy.

in c o n t a c t w i t h

etc.

ionization

stop

the i o n i z a t i o n ch- mber,

neutralized,

s c !1L ter,

to

At p r e s s u r e s

at the i o n i z a t i o n c h a m b e r wall or o t h e r limit

•ithout having
tions

total a b s o r p t i o n

the f o l l o w i n g rco.sonln^ is usedj

t ha t r e o u i r e d

arrive

at w h i c h

olectx-ons a m

>oes not

..Itf. i n cr e as i ng ior.ization

78

K
30

HH

27

4- ION

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0

BEAM

---- O "

0

24

f*>

I
/
/
/

/

21

/
/

/

P
/

18

/

0
t

/

/

15

/

I
/

0
I
/
/

12

/

t
t

/

O

9-

/

/

/
/

0
6

t

/

3

O

TANK PRESSURE IN MICRONS
H -------50
75
25
Figure

18-

IOC

79
chamber pressure*

Notice the apinarent decrease in the ac­

curacy of the d e t e r m i n a t i o n s of K

V/ith

advancing pressure.

This scatter of o b s e r v a t i o n s resulted chiefly from the
increased i nstability of the electron 0un as the ionization
chamber pressure b e c o m e s large.

Since even with the in­

creased effusive flow,

the pressure of the gun chamber

remaineu satisfactory,

it is b e l i e v e d thst positive ions

foimieu in the region of the small carbon orifice follow the
trajectory of the el e c t r o n b e a m in the opposite uirection
to bombard

the filament of the wun,

cannot be removed in other ways,

If this difficulty

a magnetic ion ejector

such as used in mod e r n television tubes will certainly
remove the bombardment.

Vuithin the accuracy of measuremei it,

no variation has b een found in the value of K wlt.li increasing
pre s t.i.re •
If

the Incident electrons were

scattcreu upon entering

the io Isa tion chamber through such v.iue angles that an
appreciable n u m b e r of tnem collided with tlie ionization
chamber wall near
produced bj

the incident electrons

T-ois i'fcuuction
p.re s s u r e •

To

of

envelope

their port of entry the total ionization

I

ionization

n

visualize

t i n . ,

f

i

r

t

k

s

t

only

la t i o n

i n the d i r e c t i o n o f

s

^

m

.

e

t

z

g

electrons).

of

in

til,, s y s t e m

In th,

should

situation,

size b u t

wltn i n c r e a s i n g

increase

p e n e t r a t i o n of

as n o t

of

shrinking

e

the

should have decreased.

al so

one
t l i e

can

t h i n k of

i n c i d e nt elc ctrons
a tra ns-

suffering

the e l e c t r o n w un - l o n j
(the l i n e o h

absence

of

the

['] i g i t

any m o c s u r e a b l e

tlie a x i s

of
c

t

.

m

h

n

incident

e

g

e

I"

the

80
value

o f Iv os

cludes

then

a function of

that few

C-'ptured b y

tne

increasing pressure,

if a n y o f

the

incident

ioniz-ation c h a m b e r w a l l

near

on e

con­

electrons

are

t h e i r port of

entry•

bith
was not

diffusion

and

th e l a r y e

volume used

surprising

diffusion

and/or

to

Recombination Effects

encounter

i n the p r e s e n t
exponential

r e c o m b i n a t i o n of

the

oiui.ll e f f e c t s

were observed h a v i n 0 a

two iiiliiUUs.

A careful

stuuy of

w o r k it

decays

due

to

ionisation prouucts.
time

this h a s

c o n s t a n t of

34

about

no t b e e n uncle.

81

Kj-iSULTS
First
^iven

a re

accuracy

it

slioula b e

not

to b e

o ex's tion.
U ;e nor t

all*.
rerhays

section,

.'u c o n v e n i e n c e
_ i-o s e n t
1 1

...l . :

re s o r t

l *^

alon^
w i ll

of
is

e a e i ' . L i i . e

obtninln_

which

the

ccn-at,

u .. 1•.r

.1
.

i.u:riziy

v •riou s
V. l u c

of

tin

the

su

- e s t i o n s L l v c n in

a c c u r a c y of

the.m.

the

results

y.i..lte .arbitrarily

ter d.

t Ion of

; Linn of b h a s

i*i c )asl.. a raid e uc-t-v.il,

di. r f u c toi'S

of

its

the

the p r e -

u .

ibLti.ou^ii the
c >'
•s : Cu

Increase

totally

tlie e -uip mcnt and

tlie li n e

conr!u.erce
n

even over

f i e l d o f 1000 e v e l e c t r o n s

Xiaprovements i n

to be

the ultim*. te

\,ith the p r o son t e q u i p m e n t

restricted

absorbed, i n

tlie r e s u l t s

t a k e n as i n d i c a t i v e o f

obtainable

tne h i g h l y

era.>hasized t ha t

it

1; ..mass •
'f1el

mtrtienl* rly

nrerr an t s a re
h,

the

sire.'-'ey beer: uis-

'V

to con si:, er

the i x l b o u s

la

cor.ibi nei i to \ 1e 1e an
".r^y

f->y tin

format*on

o r‘ an i o :i- p .1r •
ihe
elc c t r o n s

c 1'i•re; a t essoci: teu. . tub

by

tl:■- F a r so.ay

)'• ■
. 1 ■_c t x-Oiis , •.v 1 •y_. a n e n a y y
n aa.i' the

c.m r

^ oi'tlo.a.l

to

Ic.s.

7

the

of 1 O 0

■ uei'w y .is si; stem

in u i s c s i a i y

■-.reci

c:ye

d'l s trlbut Lon c - r v c

th.'.n 0.1 nei- cent.

at '•i no ;v•i

s tre.'i:! o f

c n te ri'i,, the i o r i ^ u tion c h a m b e r

enva-e.•t c o l l e c t e d

i'lvolvcu

the

ely

is
m

m:o lo;;-eni)yj
.fill'

f o r 800

ev

-was, tak* -n ••••s ti e

minus
ev

initial

the

snail n u m b e r

or l e s s .
a

tn.

r o x i m a t e l y pro ^ys,

, 1 cti'ons

tin. •-ra r^y

a re a

the

mi,

error

.■ r, c. r e.,t j.1^

.Istributioa

to 1 0 r'0 ev o l c c t r o n s ,

it

is
is

82
believea,

with

the

support of meager

elections

with

total

energies betwe en

Into

the

ionization chamber.

v,1 tn

the-

accuracy

in

the

of

one half

the

initial

,vas c o m p a r e d
electrons
Ini tial

with

were

the

current

the b a t t e r i e s

electron

muring

results

c u r r e n t of

in the v a r i a t i o n

the p e r i o d w h i l e

obtained

when

the

This variation
m a l :ly f r o m

the g u n f i l a m e n t

supplying

combined

y i e l d a n uncertainty

involved

absorbed.

electron current

errors

pass

ce n t.

ion current

totally

of

above

initial

error was

electron

Ion b o m b a r d m e n t
of

the
per

Considerably more
of

The

that few

these limits

the j a l v a n o m e t e r

a e t e r m i n a t i o n of

plus or minus

evidence,

ana

the h e a t e r

the

it

initial

in the

the

positive

slow discharge

voltage

for

the g u n

fIlameat•
T he
of

value

of K w as

measurements.

ursmu.nt o f

the

A

Initial

ana

then once

To

a systematic

tire b o a m c u r r e n t
set w e r e
varied
of

thirty

tile i n t e r v a l

sensitivity
of

the

with

election
a^ala

of

noise

source

of

the

average

was

the

time,

current

chiefly

the
time

to f i v e

resdtiig

from

difficulty.

reading

The

a ineas-

in

each

Intervals

T h i s variation,

the rnierophonlc

Tlie s c s l e

change

sets

ion

for

These

changed between
the

the

of

steady decrease

m'uutos.

caused by

twenty

e l e c t r o n current.

intcrv- Is.

the JDC a m p l i f i e r .
to be

then

I ritial
the

of

consisted

current,

to

seconds

amplifier haa

switch

the

error due

t a k e n at c o n s t a n t

from

as

set o f m e a s u r e m e n t s

current,
avoid

taken

of

data usea

ox
each

s c al e
in

amplification
reaaingj
was

the

the

tire aeter. :i n a t i o n

83
of I-, is
b^

shown

4.

in T a b l e

a horizontal

left of

the

the

two

Initial

ana

f ollov/lng

jwach set of d a t a

line of numbers#

column headed
electron

the

Xn parentheses

"Initial
current

ion current

Electron

readings

At the

right of

the p a r e n t h e s e s

tlie two

Initial

electron

currents.

Included

negatively
to

the

charged

initial

electron

air u r a w n f r o m

were

values

consistent.
of A plus

is

the
Ion

average of
current

as w e l l

as

the l a b o r a t o r y

^.ach of

taken on a fresh

through

i n the

their

of the i o n c u r r e n t

Is K p l u s one.

sets o f d a t a w e r e

o f Iv p l u s

T he p r o b a b l e

one has b e e n

cent of A plus

one.

i n d i c a t i v e of
was

tne h i r h l v
current.

in the n e x t

a vapor

ionization

sa m p l e

ti’ap.

There

chamber

and co ll ec t i o n p ot en ti al s used.

T he

to b e

the r a t i o

are

taken preceding

the

electrons

current

in t e n t i o n ; 1 d i f f e r e n c e s

pressure

u?t&

initial

products,

of f o u r

tlie g r o u p s
of

the

As

at the

Current"

reading given

cohjin.

measured

is r e p r e s e n t e d

reated

numerical

Tlie a u t h o r
the
in

in T a b l e

accuracy of

the

work has

uoes

4 are

err o r of

c a l c u l a t e d to b e

linear nature
This

on e

the a v e r a g e

0 . 0 5 o r 0.2 p e r

not b e l i e v e

t hi s e r r o r

the d e t e r m i n a t i o n .

m a n n e r of T a b l e
of

surprisingly

the d e c r e a s e

The

4 to e m p h a s i z e
of

the I n i t i a l

determined

K - 27.5 i 3g
ion-pairs
The

per

Initial

average

as

the

potential

i^

to o n e - h a l f

lOOCev

energy
re

the

of

uirea
initial

election.
tne

i :iciuent

to reuucu
current.

electrons

tlie F a r a d a y
“ ecuuse

of

was

cage
the

t«wcen

current
sha rp

84
TA B LA

IV

jeXPmRILANT/.L V A L b i -8 I N TilA DAl'AUAII'ATTIOK O P K
Initial Electron
Current

Ion Current
(Llectron)

K

1

Deviation from
Grand. A v e r a g e

i o n i z a t i o n c h a m b e r p r e s s u r e - 50 m i c r o n s
lositive collection potential - 4 v
( I D . 7, 1 3 . 3 )
13.5
376
27.9
( I D .0, 1 2 . 4 )
12.7
354
27 . 8
11.2
(11.3, 11.1 )
309
27.5
9.4)
9.7
10 0
271
28.0
Av
27 . 80

0.0
0.1

0.4

( .,

0.1

I o n i z a t i o n cham b e r p r e s s u r e - bO m i c r o n s
Positivecollection
notontisl - IQ v
(11.1, 1 0 . 9 )
11.0 ‘
3 11
28.25
27.55
(10.6,
9.8)
10.2
281
8.75
244
( 0.3,
8.4)
27.9
7.6
211
( 7 .8 5 , 7 . 35 )
27.8
Av
27.87

0.4
0.4
0.0

0.1

I o n i z a t i o n c h a m b e r p r e s s u r e - 65 m i c r o n s
Positive c o l l e c t i o n p otential - 40 v
13.6
380
27.9
13.3)
27.8
12.5
348
11.9)
27.4
307
10.75)
11.2
230
S .3
9.9
(1 0 .
9.5 )
Av
27 .85

0.0
0.1
0.5
0.5

I o n i z a t i o n c h a m b e r p r e s s u r e - 50 m i c r o n s
P o s i t i v e c o l l e c t i o n p o t e n t i a l - 25 v
27 .7
270
9.75
(11.0, 8.5)
27.75
8 15
7.75
(8.2,
7.3)
27.5
140
5.1
( 5.5, 4.7)
27 .3
260
9.53
(10. 05, 9.0)
Av
27161

0.2
0.2

0.4
0.6

•jlo ni zn t i o n c ija m o o r p r e s s u r e — 50 m i c r o n s
Fo j’
-’ ;,ivt, c o l l e c t i o n pot>. n tinl - 40 v
23.7
420
14.65*
1 4.3)
(15.0
29 •2
420
14.4
1a . 3 )
27 .8
3
8
7
1
5
.
9
15.1 )
20.0
35
6
18.7
18. e )
18 •4
Av
li-a d
Iiu

aval*

1 correcteu

.^V

o
n
<s i

onL
m ■ -

0.2
1.3
0.1
0.1
To tal

5.7

l e c t m n s = 20 •e
r>
for
op i n i t i a l e l e d r;
-jo n- p a x r s
l l o v j

'■

iv = ;e t .o a. j,.
•ob.ollo Iiumcrical e r r o r - 0 . 8 4 5 3Ed ~"n 7 n - T

cut-off* o f
is

the v e l o c i t y d i s t r i b u t i o n

introduced by

...ere m e a s u r e d
ui Ui r e s p e c t
a,n. also

to b e

to a v o l t a g e - d i v i d e r ,

energy

of

1 0 5 2 v * !/<?•

actual

the

T he v a l u e
formula

of

of

path.

37.6 ev

i n air.

The

5 7 . 0 ev p e r
The, v a l u e
possible

4 .5,0 p e r

,V f o r 1 0 0 0 e v
of 3 6 . S ev

»« f o r

electrons

this value

ev *

limits

p r o p o s e d by

i.man f r e e
become

38.5

value

lie b e t w e e n

calibrated.

p o t e n t i o m e t e r netv;orkf

tlie i n c i d e n t

With

network.

was

measured,

a n d K,
i o n — pair.

electrons
and 40.2

in

ai r

should

e v pier i o n - p a i r

e l e c t r o n s i n a ir f r o m tlie
.~it y
L e h m a n n ane. 0 s ^ o o u ° ' is 4 5 . 2 ev p e r

This

1000 ev

result

is

c o r r e c t e d by

T h o m s o n 40 to

p e r i o n - p a i r f o r 1000 ev e l e c t r o n s

relation

advanced by

i o n - p a i r for lOOO ev

GerbesiD
electrons

a d v a n c e d b y Leinnann arid O s g o o d
limits

error

retarding potential

the v o l t u ~ e - d i v i d e r , p o t e n t i o m e t e r

W becomes
The

The

little

with a voltmeter wnich hau been

with

I'he av^rajje

this assu m p t i o n .

curve,

for W

o f ^.isl14 d o

not

apply

w i t h 9000 ev

to 6 0 , 0 0 0

s et b y

the

for his
ev

present

absorbed

sets W eoual
absorbed

lies
work.

i n air

outside
The

to

the

result

d e t e m n i n a t i o n of W was made

electrons.

86

SUG G LSTbh

A major weakness
variability
small

of

orifice

the

i n the

s t r e a m of

into

the

were

that
the
by

quite

they

were

r e g u l a t i o n of
the

"au"

supplying
caused
as

went

on.

was a l s o
of
the

the se

in

the

the

to

of

would be
of

e m i s s i o n of

the

of

initial

The

electron cur­
as

the f i l a m e n t
positive

is u s e d
current

tlie gun.
of

the 0 u n

i ons.

borne

f l o w o f {gas f r o m

r e m a i n d e r f r o m the

oi l

anu m e r ­

and the LieLeo d {gaugje •
still be o u t - g a s i n g s fi’O m

ef ^ usive f l o w f r o m

the i o n i z a t i o n c h a m b e r
filament becomes

time

can be virtua n y

tne i o n i z a t i o n

the U u n c h a m b e r is l i n e a r l y d e p e n d e n t

the

improved

the b a t t e r i e s

storage b a t t e r y

tlie e f f u s i v e

the v a p o r m a y

the

quite d i r e c t l y

the h e a t e r f o r

the d i f f u s i o n p u m p

fraction

in to

the y u n

in n e a t e r c u r r e n t

i o n s o r i g i n o tea f r o m

pjL-fcc sure o f

bardment

for

for

Unquestionably

uischarge

i t s b o m b a r d m e n t by

the v a c u u m w a l l s •
chamber

The

the

the p r o b a b i l i t y

c h a r g e r d e l i v e r i n g an appropriate

caused by

of

variation.

quality lead

ionizationchamber,

A smell

the

to e x c l u d e

the

apt.ears tha t

current noticeably diminished

the u i s c h a r g e d u e

cury v a p o r s

through

accelerating voltage

the v a r i a t i o n i n the

if a h i g h

Variation

It

accelerating voltage

This va r i a t i o n

a trickle

passing

chamber.

regulated

regulation.

the h e a t e r

to o f f s e t

the

of

d e t e r m i n a t i o n is

electrons

tlie h e a t e r v o l t a g e

eliminated
with

cause
the

ty pe

some o f

rent

ana

adequately
the

present

ionization

the d e f l e c t i o n v o l t a g e
Uu n

IL iF h O V - h ^ ATS

ana hes.ee

upon

tlie b o m ­

serio-i s ot .-iyh i o n i z a t i o n

87
chamber pressures.
any of

The

tlie s e v e r a l

alternative,

magnetic

ions may be

ejection

removed by

systems.

As an

tlie o x i d e — c o a t e d f i l a m e n t m a y b e

a tungsten filament

which

bombardment*

The h i g h

ment used

not

uitions

positive

was

is c o n s i d e r a b l y

e m i s s i o n of

in

less

sensitive

the o x i d e - c o a t e d

exploited because

which developed

replaced by

of

the

fila­

sp a ce c h a r g e

tlie c o l l e c t i o n of

to

con-

the i o n i z a t i o n

p r o d u ct s •
The
vapors

following

which

bombardment
probably

are

suggestions

responsible

anu. w h e n

will

the

to

An

between

the h i g h v a c u u m v o l u m e

which

adequate

is n o w

considerable
i ts

in

sma l l

system.

aru

traps.

To

too

is

the

might

well be u s e d

uni t •

coils

of

line

coulu

th is p u r p o s e ,

the

as

the

be

s.

but

of

too
to

s e r v e d bp

the

the

the a d d i t i o n a l

in the g u n c h a m b e r p u m p i n g

A trap f o r

tr ap

a

the gun,

w a t e r a de -uately c o l a

expansion

There

The

stem has made

l i n e s w h i c h w e r e u s e d ar e

trap

inserted

l a c k of an adequate

the e f f e c t i v e n e s s
the

s h o u l d be

tlie o p e r a t i o n of

limited by

r e f r i g e r a t i o n unit.

pumain£

in

chamber

the d i f f u s i o n p u m

chamber pumping

ion

o n the u i s t r i b u t i o n

vapors

traps f o r

l o n 0 to u c l i v e r

increase

anu

the

the p o s i t i v e

ionization

"pip"

for oil

Tlie w a t e r

trap,

hold

gun

i- i p r o v o m e n t

effectiveness

cooling

tr ap

types of

the

the

peculiar

curve.

are m a n y

additional

reduce or remove

for m u c h of

applied

remove

will

c o i l s of

line

a small h o u s e ­

the i o n i z a t i o n c h a m b e r
same

refrigeration

88
Tlie m e r c u r y
ducing
lines

a ury

ice

and

acetone,

connecting

the

McLeod gauge

In a u d i t i o n
of

v a p o r can of course be

It

woulu be

reasonable

rapidly

surface

remove

w el l

or

to

a liquid
a n d the

the j u n

evolved

intro­

a i r t r ap
rest of

introduce

a r e a i nt o

the v a p o r s

removed by

into
the

the

system.

o refrigerated

chamber Itself

f r o m the w a l l s o f

trap

to

the

chamber•
iJue to
been

so m e

tlie l o n ^ e x p o s u r e

a m a l g a m a t i o n of

_.un c h a m b e r

one

the

the m e r c u r y

surfaces,

they

the m a n n e r

inuicated

earlier.

shoulu be

a vapor

s h o u l d be

the lira-':I g a u g e

p r e s tiurc
should

much

be

ssed

jl/uspite s o m e o b v i o u s
used

to c x t e n u

the

Tlie a tp.lif i e r

is

construction,

ane. w i t h

x-e s u it s .

The

u m s l i f i e r la b„

is i*a tixer

t e m p e r aim. n t n l •

amplifier

is

be

simple

reliable •

a f a c t ox* o f

aiif'.ca.l L-. in

level
can be

dor i r e d .

tube

and r i n s e d in

above measures
a final

safeguard,
than

to m o n i t o r

the: v a p o r

situation,

the j C

current

_ a 1v :no me. t o i* h a s
forward

in

t h e o r y and

iminlin^ yields

;o me.-ms e a s y

accurate

to o p e r a t e b u t

dome o p t i m u m d e s i g n
the d e s i g n

Cci-talvil^

a propel- Jo s ig n is

more

ased.

caused by

One
the

but. l o w o p e r a t i n g

hue op-ej*-. tion o f

io w o v a r , it may be
.1m >a 'VCd : re

owe

conditions

actustip

o h n r s c t e r i e tics at

amplifier

th e se m e r i t s :

n o w e v e r , >"ith ex. ■<,r 1e ace

at

the

sen: si tive

straight

competent

to n f r o m

arriving

lack of pub l i s h e d

one

the

this f r o m

more

failings,

ra n^c of

remove

scrubbed

As

t h er e h a s

the w a l l s of the
To

./itb the

a d e -u-.tely cl e an .

sensitive

end

ioniza ti on chamber.

the v a c u u m

vacuum

to m e r c u r y v a p o r ,

bru

•- v

e;elif.\er
frcoo;

to

89
use

one

of

aescribed
of

the m o r e
in

a current

electrometer*
strbiJ i ty o f
of

the

complex but

literature*

amplifier
This

As

an

amplifiers frequently

alternative,

c a n b e bj'-passed b y

will

place

the w u n b e c a u s e

tlie e l e c t r o m e t e r *

stable

of

a greater
the

the

need

the u s e o f

p r e m i u m on

an

the

I n t e g r a tin^j p r i n c i p l e

90

CONCLUSION
A new
the

Instrument

avernye

electron!:
has b e e n

energy

totally
set f o r

a n i o n - p a i r b^

AIlw ACKNOA'LiJd(Jh_NTS

wa s c o n s t r u c t e d

f o r the f o r m a t i o n o f
a b s o r b e d i n ya s e s .

tlie a v e r a g e

1000 ev

electrons

electron volts.

of

ueturui'Vir.io:-: is 4 . 5 p e r

it sp. e a r s
mime

lively

with an

accuracy

ti.it. f re r;uent h e l p f u l

tion is d e c
school

of

A

of one

preliminary value

ap

tlie f o r m a t i o n of

totally

Cent •

At

may

per cent or

to e x p r e s s h i s

s.;'w U ct:t1 o n e

the physic;

hr • T h o m a s H.

e n d f o r m e r iisae' o f

: ■;at

ay

d e p a r t .ms t .
Osyod,

a uv c

Appreciation
do 1.1i*e-l 1 F und,
whose

financial

i n air

accuracy

the prose; t time
ultiu- te-ly be

less.
i*eci a tio n for

discussion s offered
Particular

dean of

t>'<o clepnrtmf rt,

launched, till;", r e s e a r c h p r o g r a m a :u_, w h o s e
iudrment have

absorbed

ar«.nt a b s o l u t e

t h a t d e t e r ..in; t i o n ?

The. a u t h o r w i s h e s

by m e m b e r s

The

to d e t e r m i n e

an ion- p a i r by

energy for

at 0 8 . 5
this

with which

a.A p r c c i a -

the g r a d u a t e
w h o se

initiative

1 oterest

s.;id

ce<; its n c v e l o p m e n t •
is

also

.lue to

a d m i n i s t r a t e d by
support made

the
the

Frederick
Ac- s e a r c h

th is w o r k

Tnrduer

Corporation,

possible.

M

91
b 113L 1 0 G A AP ifY
1*

juachman, C. A* T e c h n i u e s i n .experimental e l e c t r o n i c s , ,
od. 1, J o h n .,iley an.., dons, I nc . , h e w ’rork, 1°48, 2 59 pp

2.

jschiiisn,

G. L.

reference

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5•

La d r u m n,

C.

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4.

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5.

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5.

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8.

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S.

a

P r o c , o' ..Trri..w e

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^ - n p ;

p'PO C . .VO y • wO C . -X, 1 0 4

ail. on, e. T.
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nns j? - 3 !!VS b y
the
.
do c . -x, 1 • ~

by