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STUDIES IN THE TECHNIQUE
DF X-RAY PHOTOGRAPHY

THESIS FOR THE DEGREE OF M. S.

Luther Herbert Lyndrup
1932

 

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TECHNIQUE

O F

X-n-RAYPHOTOGR

A

X - R A

P A R T

T E C H Ii I<3 a U E

O F
Y P H O T O G
E S I S S U B m I T T
AS
I A L F U L F I L L M

OF

E h E N T S FOR D

P:

OF

T E R OF S C I E N C

LUTHER HERBERT LYNDRUP

AUGUST 1952.

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17.

18.

T A B L E OF C O N T E h T S
history of X-Rays..........................
Theory of X-hays...........................
Properties of X-hays.......................
Development of X-Ray Tubes.................
Development of high Potential Apparatus....
Development of miscellaneous Equipnent.....
Technique of X-hay Photography.............
Happler machine............................
Special Problem............................
Photography of Pigs........................
Results of Experiment......................
Crystal Structure Equipment................
Crystal Structure Theory...................
X-Ray Pave Diffraction.....................
Experimental Results.......................
Precautions tohbe Observed by X-Ray Operator
Conclusion.................... ............

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INTRODUCTION

Several months ago hr. V. A. Freeman, Assist-
ant Professor and Research Assistant in Animal hus-
bandry at Michigan State College, in cooperation
with Dr. H. R. hunt, Professor of Zoology, re-
quested the assistance of the Department of Physics
in a study, by means of X-ray, of the variation in
the number of vertebrae and ribs among pigs of dif-
ferent breeds. Accordingly the writer, under the
direction of Associate Professor 0. L. Snow of the
Physics Department, was assigned the problem of
repairing, assembling, and adjusting an old dis-
carded equipment to the end that the above men-
tioned study involving the making of at least
two hundred skiographs of pigs might be success-
fully pursued.

This thesis is primarily a report on the prob-
lems encountered and the lessons learned by the
writer in the manipulation of available X-ray
equipnent in connection with this major project
and a few minor projects.

The Animal husbandry and Animal Genetics as-
pect of this study of pigs will be reported in a

separate thesis by hr. Freeman at a later date.

STUDIES Ill TIEE ‘i‘EChI‘EI'4UE OF X-RAY PiOTCGEtAPHY

history of X—Ray

In order to more fully appreciate any contri-
bution made by the scientific world, it is well to
look at its historical background. Often a study
of the history of the discovery and development of
some of our simplest and most widely used conveniences
reveals a story of struggles and hardships which seem
more like fiction than fact. The early history of
the X-ray is very interesting, showing how one man
receives credit for discovering a new phenomenon,
although others had ungnowingly produced the same
effect.

Throughout the nineteenth century extensive
tresearch work was conducted on the phenomena of
electrical discharge through a tube of gas at low
pressures. The first develpment worthy of note was
hichael Faraday's discovery of electromagnetic in-
duction in 1831. This enabled him to produce high
potentials, and in 1858 he began a series of experi-
ments dealing with electrical discharges through
rarified gases. he named the positive and negative
"anode" and "cathode" as we know them todafi. The
next important step was the development of the
vacuum tube by Geissler in 1857. He noticed a pecu-

liar glow when a discharge was passing through the tube.

2
This vacuum tube influenced a famous physicist, Pro-
fessor Hittoff of Munster, to investigate this type
of tube more thoroughly. he succeeded in exhausting
a tube to a much higher degree of vacuum than had
Geissler. This tube offered more resistance to
an electrical discharge than did Geissler's tube.
Sir william Crookes discovered that he could pro-
duce a more perfect vacuum tube, and with it dis-
covered "Cathode Raya" 1878. While conducting his
research on these rays, he noticed that the walls
of his tube would glow with a greenish "fhorescence.
We know that this was due to the production of X-rays
by the impact of the cathode rays against the glass
walls of the tube. Text hertz and his assistant,
Lenard, experimented with cathode rays and unknowingly
discovered more of the phenomena due to the produc-
tion of X-rays. lhen in 1895 Professor Wilhelm Conrad
Roentgen, while duplicating an experiment described
by Lenard, made his remarkable discovery.

Roentgen was experimenting with a Crooke's dis-
charge tube which had carefully been covered with
black paper to make it impossible for visible radia-
tion to paSS from the tube into the darkened room.

To his great amazement he discovered that, while the
discharge was passing through the tube, a flourescent
screen some three meters away glowed brightly. This

screen was made up of a sheet of cardboard covered

with a fresh coating of barium platino-cyanide.

It had been set up against the wall to dry. at-
tracted by this amazing develOpment, Roentgen

walked over to the screen to examine the flnresoence
more closely. As he passed between the tube and

the screen a shadow of his body appeared on the
screen. His hand cast a remarkable shadow on the
screen, for the bones cast a deeper shadow than did
the fleshy portions. Apparently the phenomena which
was producing the fluorescence on the screen pene—
trated flesh more readily than it did bones. Roentgen
traced the emanation back to its source. The rays

had as their origin the point of impact of the cathode

glass walls of the tube.

rays on the g

Prfessor Roentgen completed a great deal of re-
search on his new discovery, and then communicated
his discovery to the Physico-nedical Society of Nurz-
burg. The scientific world was startled at the

announcement of the discovery of the new X-ray which

made it possible to look within Opaque objects.

TILEORY
Before discussing recent deveIOpments in the
science of X-ray, it will be well to discuss the pre-
vailing theory concerning X-ray radiation. Roentgen
gave the new phenomena its present name because its

exact nature was unknown. The pioneer research workers

&
in this field only knew that the rays were pro-
duced when electrons, moving at a high velocity
under the influence of a strong electric field, en-
countered matter and suffered a change of motion.
when the electrons strike an obstacle, a pulsation
is sent out into the ether with the speed of light
in all directions. The theory asserts that the
energy of the ray is contained in a thin spherical
shell. The more sudden the change in Speed of the
moving electron, the thinner is the shell and the
more energetic is the pulse. X-rays are generally
classified in that large range of wave motions which
contains all forms of electromagnetic radiation.
The wave length of X-rays has been found to be of
order 1 x 10-8 centimeters.
PROPERTIES OF X—RaY

The following list contains the most common
properties of X—ra_ radiation. X-ra s are:
l. Produced by impact of cathode rays on patter;
2. Propogated in straig t lines,
3. Invisible and pass through space without any

transference of matter,
4. Unaffected by electric or magnetic fields;
5. Propogated with the same velocity as light;
7. Capable of ionizing gases;
8. Absorbed by matter;
9. Able to stimulate or kill living matter. It is

now widely believed that exposure of living

tissue to X-ray radiation hastens the process

of evolution;

Cl

10. Capable of exciting certain chemicals to
fluorescence;

ll. Capable of darkening photographic plates. This
property makes X-ray invaluable to the medical
profession.

12. Capable of producing X—rays of shorter wave
length when absorbed by matter.

DhVSLOEkENT OF X-hAI TUBES
Roentgen conducted his exper'ments with a tube
of the type shown in figure I. The operation of
this type of tube and in fact any of the common type

of "gas” tubes may be explained as follows:

The evacuation of the tube is intentionally never com-

pleted, but a very small amount of gas is always

left in the tube. The pressure within the tube ranges

from 0.001 to 0.010 mm. of mercur . hormally the

number of ions present in this residual gas is very
small. when a high potential is applied, the effect

is to accelerate the motion of these ions toward the
plates of the tube, causing them to produce many ions
by collision with gas molecules. The electric field
drives the positive ions against the cathodewith con-
siderable force, causing it to emit Cathode rays; also,
the electric fields directs the cathode rays against
the target with considerable velocity. The cathode
rays are suddenly stopped by the target and X-rays are

the direct result.

In Roentgen's tube the cathode rays were directed
against the end of the glass tube. This proved very
unsatisfactory because the greater part of the energy
carried by the cathode rays is converted into heat Wen
the motion is checked. Since glass melts easily, such
a tube was readily susceptible to puncture while in
operation. Early research workers found that metal
targets could be substituted in place of the glass
wall. It was also discovered that the metals of high
atomic numbers gave a larger output of rays. The
metals best suited for use as targets were those of
high atomic numbers, high melting point-—to permit
sharp focusing of the cathode rays without fusing the
target, and those that were good conductors of heat
so that the heat would be conducted away from the pdnt
of impact of cathode rays rapidly. Platinum and tungs-
ten are most widely used metals, with the latter being
considered the more suitable. Aluminum is generally
the metal chosen to serve as cathode in gas tubes.

Figure II shows the general type of gas tube.
There is one bad feature connected with the operation
of all gas tubes. The pressure within the tube may
vary frOn day to day or even from hour to hour dur-
ing operation. The metal parts and the glass walls
of the tube no matter how carefully prepared contain
small amounts of gas within them. When the tube is
heated by continued operation, some of this gas may

be given off. This raises the pressure within the

7
tube and makes it easier for the cathode rays to pass
from cathode to anode and rays are produced which car
tain less energy. This condition is known as "soften-
ing" the tube. The metal parts and glass walls are
also capable of absorbing gases and reducing pressure
within the tube. Then it becomes harder to produce
the necessary electrical discharge through the tube,
and the tube is labelled "hardy There are remedies
for both of these conditions, but they are not very
accurate for one has no means of knowing exactly the
condition existing within the tube. It is almost in-
possible to set up a standard condition of pressure
under vhich to operate the tuhe and always adjust the
tube to this pressure when using.

To reduce the pressure within the tube it is
necessary to cause some of the gas to be absorbed by
some agency. Often letting the tube be idle for some
period of time will produce the desired effect. Con-
tinued heating and cooling of tube sometimes reduces
pressure. Operating tube under very high potential
with cathode and anode interchanged may help.

Raising the pressure within the tube is a somefl1at
sigpler problem. The method most comhonl* employed
is heating some substance which has been build into
an arm on the tube. A spark gap is adjusted so that
when the tube gets too gard, the discharge will pass
across this gap and through the substance. The sub-
stance is therebf heated and gives off small amounts

of gas. as soon as the tube offers less resistance

8
to the discharge than does the gap, then we have

normal production of X-rays once again.

Gas tubes glow with a weird greenish lightwhile

/

producing X-rays. This fluorescence is not caused
by any action of the X-ray on the walls of the tube.
The fluorescence is produced by cathode rays which
miss the target and are sent against the glass of the
tube.

The Coolidge tube was developed to give the
operator practically complete control of the condi-
tions within the tube during any period of operation.
In this type of tube the gas is exhausted to such a
low pressure that it plays little or no part in the
actual production of X-rays. .Coblidge, inventor of
this tube, became interested in applying the phe-
nomena of thermionic emmission of electrons as a source
of cathode rays in an X-ray tube. He is directly re-
sponsible for the production of the modern "hot cathode"
tu”es nkich are rapidly replacing gas tubes. The
cathode consists of a spiral of tungsten wire which
is heated to incandescence by means of an electric
current. Large quantities of thermions are liberated,
tae number liberated dependilg directly upon the
temperature of the wire. After these electrons have
been produced, the operation of the tube is similar
to that of the gas tube.

The Coolidge tube can be Operated on either
alternating or uni-directional potential. Besides

serving as a source of electrons the filament, cath-

ode also serves as one of the terainals of the tube.

X-RAY TU3E8----_- ,., -GAS T,_E Tug?

Fig.1

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l.

2.

10

I‘ZEY ‘I‘O FLEUh’E. I

Anode

Glass wall wnich served as target
Cathode

Glass rod for supporting tube

Sealing tip.

kEY TO FIGURE II
auxiliary anode
Sealing tip
Softening material
Adjustable gap for softening
Copper block
Tungsten or platinum button

aluminum cathode.

11

0001.1 30:3 X-RAY TUBES

 

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Fig. III Lnixc;“sxl Trpe Tube

 

 

 

 

 

 

 

 

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Fig. IV Radiator Type Tube

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4.

12

KEY TO FIGURE III
molybdenum stem
Anode, Tungsten targe
fiathode, Spiral of Tungsten wire

Device for directing cathode rays

K3‘ TO FIGURE IV
Cooling or radiating fins.
Molybdenum stem
Tungsten target
Cathode

Device for directing cathode rays.

15

when alternating potential is applied, it is alter-
nately charged positively and negatively. When posi-
tive, no electrons leave the cathode and we have not
other source of electrons. Thus on this half of the
cycle there is no discharge. however, if the target
bec mes heated to a high temperature. it may emit
electrons. This would produce a cathode ray bom‘ard-
ing the fragile cathode and the vital part of the tue
would soon be destroyed. The target must be kept at
a low temperature if alternating potential is used.

All tubes of the hot cathode type are commonly
-called Coolidge tubes. There are many Special designs
of this type of tube for special lines of work. These
types are built with fine, medium, and large focal
spots, depending upon the use of the tube in question.
To get the sharpest and the clearest pictures, it is
necessary to have almost a point source of X-rays.
This condition is affected by special shaping of the
cathode spiral. a hemispherical spiral placed close
to the targe gives a small focal spot. Such a fine
focus tube has its disadvantages because the cathode
rays bombard only a very small area, and considerable

energy is released at a point. The target becomes
badly pitted and distortion results in pictures if
tube is operated for long periods of time. For work
where less starpnessis desired, broad focus tubes can
be used. The broad focus type of tube does,faster

work than the fine focus tube.

14

The Nestinghouse Electric Company have developed
a tube which differs narkedly from the ordinary X-ray
tube in construction. This new tube has target arranged
perpendicular to the path of the cathode rays. The
X—rays are sent back over the safe path the cathode
rays travel and right on through the cathode. By
suitably arranvinv the focal area on target, the rays
can be made more nearly parallel than in tubes where
the target is inclined forty five degrees to the path
of the cathode rays. Figures III and IV show schematic
diagrams of Coolidge tubes. Figure IV shows a tube
with an external device to aid in radiating heat away

from the target.
DEVELOPnEhT OF hIGh POTENTIAL APPihaTUS

The Induction Coil is a device for transforming
IOWpotential current from a battery into high-potential
current suitable for the operation of an eriy tube.
It consists essentially of a few turns of wire around
an iron core, outside of which thousand of turns of
fine wire are wound. The iron core becones'nagnetised
when the switch is closed and the battery send cur-
rent through the few turns around the core. This
magnet attracts a small metal arm which act breaks up
battery circuit, and the core loses its magnetic pro-
perties, releasing the metal arm which is pulled back

into its original position by a small spring.

15

This the circuit agaii, and the whole process
is repeated. as the circuit is thus alternately"iade"
and "brokenfl an alternating current is induced in the
coil surrounding the primary. It is desirable to em-
ploy a direct potential across the terminals of the
tube. Therefore a condenser is placed in circuit,
as shown by Figure V, so that it is charged when the
primary circuit is closed and discharges rapidly when
the circuit is broken. This domagnitisfis the iron
core rapidly. The induced potentials in the secondary
are much feebler at the "make" than at the "break" of
the primary circuit. The current induced on the "make"
is known as "inverse" current and is very nearly sup-
pressed in a good coil. This method of generating high
potentials for X-ray work is not very widely used in
United States but finds considerable use abroad. It
is often employed in semi-portable outfits.

The Tesla coil is in a way a double induction
coil. Figure VI is a sketch showing the principles
of operation. An alternating current is applied to
the primary of the first coil and is stepped up to a
high voltage by the secondary. This induced current
is then sent to the terminals of a circuit including‘
condenser, coil and spark gap. The current is oscillat-
ing rapidly as it leaves the condenser. a high fre-
quency, high—potential current is delivered at the
terminals of the secondary coil. The use of the Tesla
coil is usually confined to small portable outfits be-

cause an X-ray tube expecially adapted to high fre-

quency potential must be used.

16

The Influence hachine has also had some use in
generatin high potentials. Two sets of conductors
are rotated in opposite directions. One set of con-
ductors becomes charged by friction or sens other
method and this charge induces charges on the other
set of conductors. Brushes are arranged to pick up
these charges which are stored in Leyden jars until
the potential difference across the terminals of the
machine becomes sufficiently high for the desired use.
A properly operating influence machine produces a
beautifully steady potential for X-ray work. however,
it is very difficult to keep such a machine operating
properly. many plates must be rotated at a high
velocity which involves considerable danger to the
attendant.

The method most commonly used for the production
of the high potentials required for X-ray work is step—
ping up a low alternating voltage by means of a closed
iron core transformer. The primary and secondary
windings are both wound about the iron core. The
whole set-up is generally immersed in oil which has
a very low carbon content. The resultant high poten-
tial will bear the same ratio to the impressed voltage
as the number of turns in the secondary winding bears
to the nu ber of turns in primary winding.

Some tubes are built to operate under an alter-
nating potential, but the tube is twice as efficient

when full wave uni-directional potential is applied.

HIGH POTEITTI AL APPARATUS

 

 

 

 

 

 

 

 

 

 

 

Fig. V Induction Coil

 

 

 

 

 

 

Fig. VI Tesla Coil

l.
2.

3.

18

KEY TO FIGURE V

Primary circuit

Secondary circuit

metal arm, pri ary circuit interrupter
Frequency adjuster

Battery

Condenser

KEY TO FIGURE VI

Alternating potential applied to primary
Condenser
Spark gap

Secondary terminals

19

The method for producing high voltages by trans-
former produces an alternating current. maxiwum ef-
ficiency of operation is obtained when the alternating
electromotive force is rectified, converted into direct
e. m. f. The nethods most commonly employed for
rectifying high potential alternating current are:
the kenetron tube circuits and the mechanical rotat-
ing disc.

The kenetron tube is so constructed as to allow
current-to flow through it i; one direction only.
Figure VII pittures a circuit employing one kenetron
tube and giving half wave rectification. Oaly one
half of the voltage cycle is effective in producing
X-rays. Figures VIII and Ix picture circuits using_
two and four kenetron tubes respectively. These
circuits give full wave rectification, that is, the
one half of cycle is reversed in direction and the
resulting potential is u i-directional.

Figure X gives a scneuatic drawing of the
mechanical rotating disc rectifying switch. A large
disc made up of mica or other suitable insulating
naterial is driven by-a synchronous motor. The disc
is driven at 1800 revolutions per Linute, and in
exact synchronisn with alternating potential delivered
to brushes 1 and 2 shown in diagran. metal conductors
A and B are iounted on the periphery of the mica

1

disc. ”hen brush 1 is n65301V9 then 4 is 3130 “333'

tive (from Fig x and 5 and 2 are positive. “hen

20

one half of a cycle is completed, terminal 1 has

Ho

become positive, but the d so has rotated through

ninety dcgrees and conductor B now joins brushes 1
and 2. Therefore 2 is always positive and brush 4 is
always negative and uni-directional potential is
applied to terminals of the tube.

Figures XI and XII show the voltage curce before
and after rectifying. Althoug; the rectified potential
is u idirectional it is of pulsating form as shown in
diagram. The shaded portions represent voltage wasted
in the process of rectifying and in heating the tube.

The nethods are commonly employed for controlling
the kilovoltage applied to the terminals of the X-ray
tube. A variable resistance is often connected in
series with the primary winding of the transformer.
This nethod is not very dependable where accuracy is
desires because the resister becomes heated during
the Operation of tube. Due to atmospheric conditions
the heat may not be radiated from the resister at the
same rate on two successive days for any one setting.
a more accurate method is to place an auto-transformer
in the pri ary circuit so that the voltage applied
to the prirary coil of the transformer can be easily

and accurately adjusted.

DEVELOPMENT OF OThER X—RAY PHOTOGnAPhIC EWUIPMENT
The first X-ray photographs required long expo-
sures to the rays. The films used were not very sensitive

t0 the X-rays, and intefiSifying screens had not yet

Fig. IX

21

HI CH POTEZIE

TI AT.

T1 nrfi

1*. hi I FYI TIC APPAR A ".‘U R
5

 

d_ M
——

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o X-rav tube

1 J
rig. VII Kenetron Tube half wave rectifying circuit.

 

 

 

 

 

fiT I
.4;—
Fig. VIII Two tube rectifying circuit

full wave.

 

 

 

 

 

III:

 

 

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4”}—

Four tube full

 

wave rectifying circuit

 

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Fig. X hechanieal rectifying device

 

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Fig. XI Alternating voltage sine curve

 

‘ V

Fig. XII Rectified voltage curve.

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25

been invented. However, scientists who noticed that
the X-ray was capable of causing Certain chemical
compounds to fluoresce with visible light conceived
the idea of placing such a screen against the film
during the exposure. Since the film was more sensi-
tive to visible light than to X—ray, this snould pro-
duce a good picture. The results were satisfactory
and the idea was developed. The usual type of in-
tensif ing screen is now made up of a fluorescent
haterial consisting large y of calcium tungstate which
fluoresces with a light of wave length about good.
angstroa units. This is the wave length for which the
emulsion is LOSt sensitive.

Only a very small portion of the ray is absorbed
by the film. If the plate is backed up by a lead
s eet pore of the energy is utilized. The Lastman
Kodak Company manufacture a film for Xfray photography
which is heavily coated wita sensitive emulsion on
both sidgs of the film. This cuts the time for
exposure in half. The intensifying screens, one
placed on each side of such a film reduces the time
to about one eighth the tine for ordinary exposure

wit: E'stuan's duplitized film.

TECHNIWUJ OF X—iaY PhOTOGfihPhY
The operator should try to becone thoroughly
familiar with his machine before trying to produce
perfect pictures. He should try to work out a technique

for different sizes, objects, using different settings

25
been invented. LOUGVéT, scientists who noticed that
the X-rav was capable of causing certain chemical

coupounds to Iluour

24

of the switches. a proper procedure in Jandling
tube and machine is indispensable. A method should
be adopted which will save tige and tube, render re-
production of results possible, pply to any machine,
require a minimum bf instrument reading when tube is
operating, and indicate the working range of the ma-
chine. X-ray apparatus is eXpersive, handle Jith Care.
Never close the operating switch while some person is
too close to a high tension wire. lever test your
tube and apparatus with patient in position. lever
close the Lain switch before you know that current is
flowing through the filament of a Coolidge tube. Do
not try to take pictures of thick d nse objects with
low power, not try to use excessive power for thin
objects. Develop a good darkroom technique.

It will soon become apparent to an X-ray
operator that the rays produced by higher potentials
have considerable more penetrating power and tore
energy than the rays excited by loner potentials. The
lower pote tials Sgow more detail in a picture vhile
higher potentials tend to penetrate and obliterate
details. The effect of the ray on a plate is
proportional to the sguare of the voltage exciting file
ray. This stateme.t deals with a constant potential

or with the effective voltage.

25

Variation in the tu,e current also produces a
decided effect on the exposed plates. If the potenthal
is kept constant, the effect on plate varies directly
with the tube current. however, (at least with our
,achine), as you lower the tube current, the applied
potential raises. Thus the effect of lowering tube
current may not produce direct variation in blacken-
ing of plate unless constant potential is raintained.

The blackening of the plate varied indirectly
as the square of the distance from the plate to the
target of the tube. The distance chosen should be
great enough so that distortion of image does not
result.

If tic Operator has plenty of time in which to
make the exposure, he should choose a technique involv-
ing low enough potential to give good detail, a large
enough plate to target distance to give no marked
distortion, and the tube current should be moderate.
Intensifying screens nay be used or omitted as the
operator chooses. If fast work is required, the fol-
lowing conditions should be met: very large current,
high voltag , fast plates and intensifying screens,
and if necessary, Shall target-plate distance. most
machines are equipped with automatic timing devices
but the operator can tine his exposure by a stOp watch

or by counting off seconds. "One thousand one, one

1

thousand two, one thousand three,‘ is a covenient system
with which one can acquire a great deal of accuracy

with a little practice.

26

Darkroom technique is also very important in the
production of good X-ray pictures. Several important
rules follow:

lever handle the films with wet or greasy fingers
before or after exposure;

Learn how to handle the plate without touching
the emulsion;

Do not expose film to any liggt at any time until
the film is almost fully developed;

A weak red light may be used in darkroom to View
developing plate; this is best done by using reflected
light.

Nash all negatives thoroug ly before and after

Leave the films in the fixing bath for a few
ninutes after they seem fully cleared up;

Do not leave films in the developer or hymn too
long as this is harmful to the plate and poor pictures
will surely be the result;

Try to have the darkroom well ventilated;

Arrange the materials in an orderly fashion and
learn the arrangement so that you can find things in
the dark;

Do not leave any boxes open when you leave the room;
X-ray filrs are expensive and a small amount of light
renders them useless;

Do not leave fixed negatives in the water for

long periods of time, for the emulsion will soak off.

27
JAPELER KILG hODdL X-haY aaCHIEE

Figure XIII on following page shows a schematic
wiring diagram of the Jappler hing model K-ray machine
with which the writer's work was carried out. Tris
wacnine is rathe old and not very dependable. The
first pr blem was to hake the machine run for it had

#5";

not been used for some tine andAdecidedly out of ad-

justment. The rotating disc is really driven by tw

O

motors. An induction motor serves as a startin: motor,
but this is left running even after the synchronous
motor reaches full speed. Alternating current is
delivered to the one end of the armature of the syl—
c ronous motor. Direct current is taken from the
other end by neans of a commutator and bruswes. This
direct current is used to excite the field and was
also intended to operate the automatic timing device,
but we used a separate source of direct current. The
synchronous motor offered considerable trouble before
it Was finally made to run at the right speed. after
considerable delay the machine was finallt made to
run and a few good pictures were obtained, Print num-
ber l was made at this time.

Before attacking any proble:, the operator must
first becoxe fariliar with the peculiarities of his
machine and work out a suita le technique which will
cover all phases of his problem. It is very helpful
to know what voltage the transformer is delivering
for each setting of the switches. A calibrated

spark gap was used to record these voltages.

 

88

 

Print Number I

Showing Wrist Structure

29
The terminals of t4e gap were connected to the termi—
nals of the tune, and the readings were taken while
the tube was operating. The potential control Was a
variable resister in the primary circuit. On it were
ninefins to aid in radiating the heat. These fins
were numbered 0, l, 2,-—8. Jith the arm on fin hummer
0, no resistance was in the circuit. All the resist-
ance was in the circuit wnen the arm was set on fin
number 3 etc. There Jere also various settings of the
primary convolution switch for which the voltages were
calib:ated. These settings as indicated on wiring
diagram of the machine, were for various nunber of
turns in the primary of transformer. A table of
values appears on separate sheet. Values of potential
given in each case represent peak voltages and not

the effective value of the potential.

SPnCIAL PROBLEh

Nith the above information and knowledge we
were ready to begin taking X-ray pictures. The
Animal Husbandry Department was interested in the
variation in the nunber of ribs and vertabrae which
existed among pigs. They desired to make X-ray
photographs of all the young pigs born in the michigan
State College experiment station at East Lansing
during the spring farrowing season. The X-ray offered
an easy W1, to make a count of the vertebrae and then
feeding tests were to be conducted to determine if

these variations were of any econoric importance.

SCHEMATIC WIRING DIAGRAM 0F KING MODEL X-RAY MACHINE

 

 

 

110 volts A.C.

 

 

 

 

 

 

   

110 volts D.C.

 

 

 

 

 

 

 

 

 

 

 

l2

 

 

 

 

 

v

 

 

 

 

+9

 

15
16

 

 

 

 

 

 

 

Fig. XIII

51

KEY TO FIGURE XIII

l. Filament transformer

2. Filament current control

5. Coolidge X-ray tube

4. Auto-transformer, supplies 280 volts to

motors and primary of transformer.

5. Automatic timing device

6. Ahmeter

7. Time switch

8. Lain switch

9. Key to aid in setting timing device
10. Polarity reversing switch

ll. Spark gap
12. Variable resistance potential control
15. Primary convolution switch
14. Rotating rectifying disc
15. Primary transformer winding

16. Secondary transformer winding

17. Tube current milliammeter

52
Chi ULIVERSAL TUBE

PEAR VOLTAGfiS

 

 

 

 

 

 

 

Tube current hes. Rheo. Potential Potential
mo no Setting Prim. Con. 4 Prim. Gen. #5

25 O 80 Not determined
2:; 1 vs " "
25 2 74 " "
25 5 es " "
2 J 4 45 " ”
25 5: 234 " "
25 5 in? ” "
2O 0 88 57
2O 1 81 55
2O 2 75 50
2O 5 72 42
2O 4 58 52
2O 5 44 18
23C) 63 ]L() #é=:
15 O 90 6O
15 l 88 6O
15 2 84 56
15 5 85 56
15 4 70 46
15 5 65 4O
1 5 6 .3 I:
lO 0 9» 65
lO 1 91 64
10 2 9c 62
IO 5 9? 62

10 4 84 58
IO 5 76 57
lO 6 57 5O
10 7 28 65*

hadiator Tube (all readings taken on Prim. Con. #4)

lO 0 105

10 l 100
10 2 98

10 5 96

10 4 88

10 5 84

10 6 7O

10 7 52

5 0 7-6

5 l .L U‘:

5 2 102

5 5 98

5 4 96

5 5 so

5 6 86

5 7 76

55

A permanent record was desired, so it was necessary
to invent some system of iumbering the filn and the
individual pig, so that the; could both be accurately
identified in the future. ha‘king the film was an
easy matter because a small thickness of lead stops
X-rays. we used lead wire numbers and letters indicat-
ing the breed, sex, litter, and individual pig nunber.
The pigs were parked by heads of notches i: their ears.
notches in a certain position represented a definite
number, those on one ear representing the litter num-
ber and tnUSG on the other ear representing the indivi-
dual pig nunber. A notation on the film of $8207 would

be interpreted as Yorkshire sow, litter 20, pig #7.

PHOTOGAAPhIKG ThE PIGS

Due to the trouble in repairing the machine, a
late start was made. Several litters of pigs had already
come into existence and were rapidly growing too large
for us to handle. There were about two hundred young
pigs to photograph. This involved much work besides
the actual photography, for the pigs had to be caught,
loaded into a truck, and transported over to the Physics
building, and then returned to the pastures. we wanted
to film as many as possible at the age of one to two
weeks. The technique set up was not one that produced
perfect negatives, but our object was to get readable
pictures of as m ;y of tie pigs as possible. Our ma-
chine would not take good pittures of pigs which were
thicker than five inches through the chest and was

absolutely stopped at eight inches.

54

One of the difficulties encountered in photo-
rraphing pigs was keeping them from moving during
exposure to the rays. anet er due to static electri-
city, noise of the machine, or the effect of X-rays,
the pigs would begin to Sguirm when the main switch
was closed. Several methods for holding the pig were
invented. Only two were successful and one of these
was discarded as being too dangerous to attendants.

In this latter method two men held the legs of the pig,
but this was apt to result in over exposure of their
hands. The nost satisfactory method consisted in roll-
ing the pig tightly in a heavy fabric cloth which did
not absorb an appreciable amount of the rays. huboer
bands were stretched about the bundle over the pigs
legs.

:no or three pigs were rolled up and placed on a
small wooden frare.l Long wooden boards were placed
between the Walls of the frame and the pigs to hold
them fiiml; in position. Between the pigs were—placed
boards with lead strips on bottom to mark division
between pigs on film. The "patients" were laid on
their backs. Numbers and letters to identify each
individual were mounted on a thin strip of wood and placed
beneath the pig to which it referred.

The wooden frame was built to allow the loaded
cassette to be placed beneath it. The cassette was
10 X 12 inches and was equipped with two intensifying

screens 0

56

The time of exposure varied with the size of the
pigs. Due to our many difficulties, we were not able
to take the pictures of all the pigs while they were of
a certain age. Pigs ranging in age from eight days to
ten week were dealt with. Tre time of exposure was
decided by the operator, one picture was taken and
developed, and from the resulting negative, the operator
determined a suitable ti e. Th actual exposures were
from one to eight seconds. The general fault of our
technique was over-exposure. all pictures were taken
at a target-plate distance of 56 inches.

Two tubes were used for this work. The first
employed was a Coolidge tube of the universal type.
This tube was rather old and performed erratically. It
was a finQLfocus tube, and the target was rather badly
pitted. Its perfornance beca e more and more erratic
until it had to be discarded. This tube was operated
at sixty to eighty Kilovolts potential and twenty-five
nilliamperes tube current. The above tube was employed
because the tine necessart for an exposure was less
than with our Coolidge radiator tube which was designed
for only ten nillianperes tube current. The latter
tube was employed in the latter half of the experiment
with LUCh better results. Toward tfle eed of the ex-
peri ent the transformer became erratic, probably due
to a break in tPe insulation of the secondary circuit.

Prints 2, 5, and 4 show some of the variations

found.

$6

“.1

Th’ RESULTS OF IUVESTIGaTION
a complete record of the results of our experi-
ment is not yet compiled, but since this paper is not
concerned with genetic importance of the experinent,
the following table of results will satisfactorily

show the variations found.

 

 

Breed No. of Pins ‘29 Vt. g; Vt. g~ Vt. fig Vt.
Chester white 56 l 25 lO 0
Duroc 27 6 18 5 0
Poland China 25 2 l6 6 l
Berkshire 28 O 9 17 2
Yorkshire 56 O 47 9 O

172 ‘ 9 115 45 5

Prints 2, 5, and 4 shOW'sohe of the variations

found.

 

 

 

 

 

Print II 16 Pr. ribs and 21 vertebrae

v *— .4___ —«

E.
Q.
I

Print Ill: 14 Pr.

 

ribs and 20 vertebrae

§

In.
N
w
”A
a
7
u
_

 

vertebrae

V I"
aim 2d

ribs

Pr.

lb

Print IV

4O

CRYSTAL STRUCTURE ADD X-RAE DIFFRaCTION

After completing the in ediate task of taking
pictures of all the pigs available the writer, desir-
iug to get further experience in the manipulation of
other available X-ray equipment, elected to make a
study of the equipment especially designed by the
General Electric Company for Crystal structure
analysis by the X-ray diffraction method. The

discussion following is a report on this study.

During the seventeen years following Roentgen's
discovery of the X-ra; considerable research work was
carried on to prove or disprove that X-rays and light
were similar in nature. Nearly all experiments failed
to produce any definite proof. Not until 1912 was the
"truth definitely establis ea. Drrir* that year Prof.
Laue of hunich published a paper asserting that the
regularly spaced planes of a crystal should produce
diffraction of X-rays if the latter were a wave phe-
nomena. he calculated mathematically what effects
would be produced on a photographic plate when a mono-

hromatic beam of Xerays was passed through a crystal
of zinc blends. Friedrich and Knipping put his argu-
ment to test experimentally and obtained the results
prophesied by Laue, definitely establishing the fact

that X-ray radiation is wave phenomena similar to light.

41

X-ray diffrac:ion by crystals interested other
scientists and was soon being applied to identifying
crystal structures and determining the wave length of
X-rays. The chief difficulty encountered was in find-
ing perfect large crystals of compounds. Only a few
crystalline substances yielded suitable crystals for
118 type of research. Debye and Scherer, and hull
advanced a new method for producing X-ray diffraction.
The method consisted in sending a fine beam of monochrom-
atic X-rays through a mass of finely powdered crystalline

.
material, the particles of which are arranged at random
so their axes are oriented in all directions.

Special apparatus was developed for this type of
research. Figure XIV shows a schematic diagram of the
X-ray Diffraction Apparatus, Type VHS, form E, manu-
factured by the General Electric Conpany. Item #5 on
diagram, Victor Stabilizer, is designed to control the
filament current and thereby regulate the tube current.
Jhen the desired adjustment is obtained, the stabilizer
will autonatically maintain these conditions. In the
filament circuit of the tube is an automatic water pres-
care .Sumtih wink+a breaws Q)¥uvt .3 vv¢+er Pres-
sure falls below fifteen pounds per square inch. The
tube is a Coolidge type tube with a water cooled
molybdenum targer, permitting the application of un-
rectified potential. This metal produces very nearly
monochromatic X-rays at a potential of 50,000 volts.
Detailed description and instructions for operation are

furnished with the apparatus.

42

X-RAY DI FFRA CTI ON APP ARATU S

(0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

m;

 

 

 

 

 

 

7‘»,
:W

(L [Ml/’12?” "I (7’)

 

 

 

 

 

 

 

 

 

 

 

Fig. XIV General Electric Diffraction Apparatus.

glib
x
L

 

Mk “"1

 

10.

11.

45

KEY TO FIGURE XIV

Voltmeter, line voltage

110 volts alternating e. m. f.
Fuses

lilliamleter, tube current
Victor stabilizer

Cage type resistance

automatic water pressure switch
Switch

Switch

Safety break on door of can

Safety breatiown spark gap

12. Filament transforner

15.
14.
15.
16.
17.

18.

high potential tr nsformer

Slit

Powdered specimen in glass tube
Slit

Film

Hater circulating system of cooling target

44
ThEORY 0F ChISTaL STRUCTURE

Crystallographers had produced the prevailing
theory of crystal structure before X-ray diffraction by
crystals was developed. However the latter did much
to confirm the theory. It is believed that crystals
are made of atoms, arranged in perfectly definite
geometric pattern. Every atom is contained a set of
parallel, equally spaced planes. There are several
such systems of planes, but we will think of three sets
of parallel planes corresponding somewhat in general
directions to the planes making up the rectangular
system of coordinates so commonly used to lbctte
points in space. Each set of planes are equally spaced
but the spacing in one set need not equal that in either
of the other sets. We can refer such a structure to
a coordinate system by taking any point of inter-
section of three planes as the origin and the three
lines formed by intersection of pairs of planes as the
coordinate axes. Parallelopipeds are formed through-
out the crystal by the intersection of the three sets
of planes. Each of these parallelopipeds is a unit
crystal. The length of the edges of the unit cell
beaches the unit of length on the corresponding axis.

All crystals can be classified into six systems:

CUhIC SISThn. Crystals referable to three equal
rectangular axes,

TJTLaGOHAL SISTEL. Crystals referable to three
rectangular axes, two of which are equal, the third

being a tetragonal axis.

45

hEXXGOhAL SISTEn. Crystals referable to three
equal oblique axes making equal angles with each other;

OhThCthhBIC SISTjn. Crystals referable to three
unequal rectangular axes;

MOIOCLIIIC SISTJn. Crystals referable to three
unequal axis one of which is perpendicular to the other
two;

AHORTHIG SISTEM. Crystals referable to three

unequal oblique axes and possessing a center of symnetry.

Figures XV, XVI, and XVII show three types of
crystals belonging to the cubic system. Figure XV
pictures a sinple cubical lattice. Figures XVI and
XVII picture face centered and body centered cubical
lattices respectively.

There exists a method for nuhbering the various
planes which consists in labelling the plane with the
reciprocals of its intercepts on the coordinate axis.
In figure XV the method would be applied thus:

Plane GLaF---100 plane

Plane ChDG--—001 plane

Plane BDGF---010 plane

Plane aCB---- 111 plane

Plane CBFE--- 011 plane

1A

rlane DBaE-~- 110 plane

X-hai nxVh DIFFhACTION
wave Diffraction phenomena may be eXplained by
aid of diagram XVIII. we learned that one of the
properties of X-rays is the power to produce a seconda?y

radiation of rays when absorbed by matter. The diagra m

46

CUSIC LATTICES

 

 

 

 

 

 

 

 

E:
G
\
\
w
’_, H
110. XV

 

Fig. xv:

 

Fig. XVII

47

X-RAY DIFFRACTION

I"
w  I"'

g. W/A\"
\

p
p

 

I

I

Fig. XVIII

 

48
represents a two dimensional figure, but the lines pp'
represent planes in the crystal which are thickly studded

with atoms. Let a-A'-a"

, a1, a2, 35, etc. represent
wave fronts of a train of X-ra* waves striking the
planes pp' at angle 0. Since the secondary radiation
is sent in all directions, we may consider any part
of the secondary ray which is sent out in a direction
naking angle 180- 20 degrees with the incident beam.
Then we can consider this a phenomena of reflection.
The atoms at B, B' and B" all tend to send radiation
out in this direction. If the waves from each of these
separate sources reach point X in phase, constructive
interference is the result and a dark line or spot
would be formed on a photograpiic film. The conditions
necessary for such a result can be worked out readily.
Let X be the wave length of the original X-ray.
Produce A'B' to next plane, calling point of intersection
D. Then B‘D is equal to B'B. The difference in path
for ray AB and n'B' equals B'B-B'N. But by correct
substitution this remainder is equal to ND. ND can
be expressed as a function of the angle 0 and the
distance between parallel planes pp'.

my :2 2d signed: ax
For constructive interference hD must be NX where n
represents integral values. If the waves are not
exactly in phase the resulting radiation from the many
layers approaches zero intensity and the film is not

affected. Other systems of planes will have different

angle of reflection and hence the dark line for this

49

system of planes will appear in different position on
the film. Knowing the distance of the Specimen from
the film the angles of diffraction can be measured from
the spacing between lines on the negative. For another
set of planes the above formula becomes: 3X.: 2d' sine fl.

The powdered specimen is placed in a small glass
tube about one thirty-second of an inch internal diameter.
The ends of the tube are plugged with cotton so that no
chemical change shall take place during the long ex-
posure. The specimen is held in place by the cassetfi.
which holds the film. This cassetE.is in the shape of a
quadrant of a circle of flight inch radius. The bands
resulting on the negative are in reality arcs of circles
though they appear to be straight lines.

The spacing between planes can be read directly
from the negative by means of a scale furnished by the
General Electric Company. They also furnish graphs
containing curves drawn from data about hundreds of
crystal substances. If a paper with Spacing on film
indicated on logarithmic scale is moved up across graph,
always keeping the paper strip parallel with the
abscissa, an exact fit of curves with lines on paper
can be found. This will then identify the crystal struc-
ture of the substance dealt with.

To check results the spacing between the (100)
planes of the crystalline substance can be calculated

mathematically from the following formula.:

(neat page)

"U
H

so
Ni x 1.649 xAio‘24

 

"I

:3
H II

:3
i!

(d x 10'8)Z

density of substance

side of elementary cube, parallelopiped,
equals distance between the (100) planes.

molecular weight of substance

number of points associated with unit cell

1 for simple cubic lattice

2 for body centered cubic lattice

4 for face centered cubic lattice

8 for diamond cubic lattice.

Sinilar formulas have been developed for tetra-

gonal and hexa
rections for a

involves side

gonal crystals but these involve cor—
xial ratios and the hexagonal formula

of triangle rather than edge of cube.

EXPERILEETRL RESULTS

The follo

crystalline st

wing substances were examined and their

ructure identified in our laboratory:

 

 

Substance Structure
Sodium chloride Face entered cube
Potassium chloride Simple cube lattice

Sodium Bromide
Sodium Iodide
A lumi hum
hickle

Antimony

Face centered cube

H ‘1 II

51
Other substances were studied but the results were
of no value due to impure sa ples. Print number V on
following sheet shows a typical film of diffraction

Pattern.

iRSJxUTIOJS TO ”B O“S£i 4D BI OPERATOR

inere is considerable danger connected with the
operation of an X-ray machine if special care is not
taken to avoid undue exposure to the rays. The body
absorbs the rays fron day to day. The effects are
cumulative and may not appear for a week or two after
the operator has been exposed. Severe and painfully
slow healing wounds may result on surface of the body,
and ste-ilization is often produced by too much ex-
posure to the rays.

The danger can be greatly reduced if the
Operator will observe the following rules:

1. Use lead glass shield about the tube;

2. If possible, stand behind a lead barrier wh n
operating machine;

3. Iever use your bod: for fluorOSCOpic of photo-
graphic demonstrations if you are constantly operating
an X—ray nachine;

4. From time to time test the position in which
you stand at controls for intensit; of exposure; This
can be done with a fluoroscope.

5. If doubtful about the amount of exposure your
body undergoes, carry a dental film in pocket; Develop
it after a week. If the film is blackened appreciably,

use more care in shielding the body.

52
6. It is a good plan to “eep an accurate record
showing when and how long your body was directly
exposed to K-rays;

7. Take good care of the high potential apparatus

and wires. Be sure that all high tension leads are well

away from control switches and from the patient.

 

Print V Diffraction Pattern

CONCLUSION

The writer has gained invaluable experience
from his contacts with X—ray photography. He has
learned to apply the principles of X-rays to practical
problems tdobtain desired results. A proper technique
of handling costly apparatus has been dateloped. He
has been taught that each problem should be carefully
analyzed and the method of attack planned carefully
before one tries to obtain a solution. Above all, this
work has taught him to appreciate the importance of
setting up a suitable technique for reaching a desired
goal whether the probl m deals with the phenomena of

X—rays or other branche.3.o5 science.

55

BIBLIOGLaPHY

Crowther "Ions, Electrons, and Ionizing nadiationsl
Clark "applied X-hays"

Kaye "X-hays"

thoy "Dental and Oral Radiography"

Terril &
Ulrey "X-Ray Technology"
W. L1 0 and
J. L. Bragg "K-Rays and Crystal Structure"
Starling "Electricity and hagnetism"
"United States Army X-Ray manual"
General Electric Bulletin G. E. I. -— 2082
Compton "X-Rays and Electrons"
Kegerreis "neat Energy of X-hays"

Robertson 'K-Rays and X-Ray apparatus"

Rollins "Notes on x-Light"
Thompson '"hoentgen Rays and Phenomena of Anode

and Cathode"

Worsnop "X-hays"

Rutherford " Science ms 69:259-63 er. 8, '29
Tyler Hygeia 7:1218—21 Dec. '29
Compton Sci. American 140:254-6 1r. '29
Clark Sci. ronthly 28:172-8 F. '29
Schwartz hygeia 7:461-3 my. '29

Sci. American 143:454-5 D. '50

hichtmeyer Sci. lonthly 52:454-7 my. '51

Popular mechanics 54:540 0. '50

Rev. of Rev. 82:116 Aug. '50

hickey Science ns 73:627-52 Je. '51

hull Physical

Review 1026614+ '1"

' 1929

1927
1926

1916

1930

1925

1929

1918

1926
1927
1924

1904

1896

.eW ' '

 

 

HICHIGQN STATE UNIV.

LIBRQRIES

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