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THESIS

This is to certify that the

thesis entitled

"AN INVESTIGATION OF RELATIONSHIPS
BETWEEN METEOROLOGY AND RADIO-
ACTIVITY LEVELS IN RAIN"

presented by
William E. Norris

has been accepted towards fulfillment
of the requirements for

_M__S_._ degree in Maineering

 

 

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Michigan State
University

 

ABSTRACT

AN INVESTIGATION OF RELATIONSHIPS BETWEEN
METEOROLOGY AND RADIOACTIVITY LEVELS IN RAIN

by William Evan Norris

This thesis proposes a laboratory procedure for the
continuous fission product monitoring of air and rain, and
presents the results of a brief sampling period.

Low volume air samples were taken through Millipore
filters in contrast to the usual procedure of high volume
sampling through fiber filters, and the specific activity
of each 0.15 inch increment of rain was measured. Air
activity at the time of the rain and rain activity were
compared in terms of the meteorology describing the rain.

A strong relationship between air and rain activities
was observed. It was also observed that rain activity may
be related to wind speed and overhead pressure systems, and
an equation is pr0posed incorporating the former. In addi-
tion, it is pr0posed that summer rains, which are areally

small, need not decrease in specific activity with time.

AN INVESTIGATION OF RELATIONSHIPS BETWEEN
METEOROLOGY AND RADIOACTIVITY LEVELS IN RAIN

By

William Evan Norris

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Civil and Sanitary Engineering

1963

ACKNOWLEDGEMENTS

The author is sincerely thankful for the guidance of
his major professor, Dr. Shosei Serata, Assistant Professor
of Civil Engineering, Michigan State University. Thanks are
also extended to the U. S. Department of Health, Education,
and Welfare for the award of a Public Health Traineeship, to
Hr. A. H. Eickmeier, Climatologist for the State of Michigan,
for his discussion and the loan of a recording rain gage, and
to Mr. D. E. VanFarowe, Head of the Division of Radiological
Health, Michigan Department of Health, for the availability
of data.

ii

TABLE OF CONTENTS

ACKNOWLEDGEMENTS. . . . . . . .
LIST OF FIGURES . . . . . . . .
Chapter
I. INTRODUCTION . . . . .
II. LITERATURE REVIEW. . .

III. LABORATORY INSTRUMENTATION AND

IV. ANALYSIS OF DATA . . .
V. CONCLUSIONS. . . . . .
VI. FUTURE RESEARCH. . . .
APPENDIX I - LABORATORY . . . .
APPENDIX II - ANALYSIS OF DATA.
TABULATION OF DATA. . . . . . .
BIBLIOGRAPHY. . . . . . . . . .

iii

ii
iv

15
21
22
23
so
40
41

LIST OF FIGURES

.APPENDIX I - LABORATORY

Figure

1.
2.
3.
4.

Laboratory apparatus. . . . . . . . . . . . .
Sample volume graph . . . . . . . . . . . . .
Air activity graph. . . . . . . . . . . . . .
Variation of atmospheric activity with time-—
laboratory and Michigan Department of Health
data. Periods of rains . . . . . . . . . . .

Hourly variation in atmospheric activity. . .

Comparison of atmospheric activity values--

MSU laboratory data versus Michigan.Department

Of Health data. 0 O O O O O O O O O O O O O 0

.APPENDIX II - ANALYSIS OF DATA

Figure

1.

2.

Atmospheric activity (CA) versus rain activity

(03) for each 0.15 inch increment of rain . .

Atmospheric activity (CA) versus average rain
act iVity (CR) 0 o c e o o o o o o o o I o o o

Atmospheric activity (CA) versus rain activity

) for each 0.15 inch increment of rain,
wi h wind speed intervals as parameters . . .

'Logarithms of K values versus logarithms of
v values 0 O O O O O O O 0 O O 0 O O O O O I 0

Predicted versus measured rain activities for
each 0.15 inch increment, comparing CR==2230A

with CR=6O.3V'534CA. . . . . . . . . . . . .

Predicted versus measured average rain activ-
ities, comparing CR==2230A with

— .534
CR— 60o3v CA 0 o o o o o o o o c o o o o 0
U. S. Department of Commerce Weather Maps
related to rain 6, showing the develOpment of
a high pressure system. . . . . . . . . . . .

iv

24
25
26

27
28

29

31

32

33

34

35

36

37

U. S. Department of Commerce Weather Maps
related to rain 11, showing the passage of
a cold front. . . . . . . . . . . . . . . . 38

Variation of specific activity within each
rain according to (a) laboratory measurement,
(b) equation 1, and (c) equation 3. . . . . 39

I. INTRODUCTION

This is one of a series of theses investigating the
fundamental processes of radioactive pollution in surface
and subsurface waters. The pollutional sources are fallout
fission products, radioisotOpe wastes, and naturally occur-
ring adpha emitters.

This thesis is primarily concerned with the development
of a laboratory procedure for the measurement, by gross beta
counting, of fission product radioactivity concentrations in
the atmosphere and rain. Such measurements, correlated with
the work of other researchers, should lead to relationships
yielding the amount of fallout deposited by rain in terms of
the concentration of radioactivity in the atmosphere and the
meteorology describing the rains.

.Although correlation between atmospheric radioactivity
and radioactivity in rainwater exists (1), and some excel-
lent research has been presented in recent months, no rela-
tionship is known which combines all the variables in one
model. ‘

The fallout studied is defined by the U. S. Department
of Defense as ”delayed fallout,” that is; the very fine
particles resulting from nuclear detonations, with radii of
a few microns or less, which fall extremely slowly under the
influence of gravity. These particles remain suspended in
the atmosphere for a considerable time and are carried over

great distances as the result of the movements of air. They

are removed primarily by the scavenging effect of rain and
snow, producing the delayed fallout (2).

The presence of fission product radioactivity has been
reported in streams and waterways (3), foodstuffs (4,5), and
sewage treatment plants (6). This world-wide problem does
not represent an immediate health hazard, but it may result
in long-term injury from internal deposition and possible
genetic effects from low-level irradiation (7). For these
reasons, and because dangerous levels of atmospheric radio-
activity could be attained in all-out nuclear conflict,
studies such as this are justified.

This thesis embodies (a) a literature study which ab-
stracts some of the most recent publications on atmospheric
fission product radioactivity, (b) the laboratory setup,
and (c) the results of a brief sampling period.

The atmospheric radioactivity levels measured in the
laboratory were compared with the same measurements provided
by The Division of Occupational Health of the Michigan
Department of Health. Weather data were obtained from the
United States Weather Bureau at Lansing, Michigan.

II. LITERATURE REVIEW

The purpose of this chapter is to outline some of the
current thought on the migration of fission product debris
from the stratosphere to the earth's surface, insofar as it
is deposited by rain.

.Except for a continual leakage from the stratosphere,
the introduction of fission product debris into the trcpo-
sphere is apparently the result of the violent mixing of the
trcpospheric and stratospheric interface. Miyake, et a1 (8,9)
have correlated remarkable increases in the specific activ—
ities of air and rain with the simultaneous occurrence of
troughs at the 500mb isobaric surface and jet streams.

Sotobayashi and Koyama (10) have investigated the move- ‘
ment of debris from the upper trcposphere to rain producing
layers. They observed that troughs in the 300 and 500mb
isobaric surfaces were accompanied by cold front type rains
which were characterized by generally higher levels of spe—
cific radioactivity. The air currents associated with these
troughs have a sinking motion and serve as a conveyor which
transports the debris into the rain producing layer. By
assuming that this moving air mass neither receives nor
loses debris in its descent, the content of debris per unit
volume in the lower trcposphere increases in proportion to
the magnitude of the downward component of the upper air

current.

4

Greenfield (11) made a theoretical analysis of the rain
scavenging of radioactive particulate matter from the atmos-
phere. The following four mechanisms were considered:

(1) direct collision of falling raindrOps with particles,

(2) sweeping up of particles by water-cloud draplets which
would subsequently reach the ground in rain, (3) rain-induced
downdrafts, and (4) interaction of electrostatic forces be-
tween particles and raindrops. The fourth possibility was
rejected in consideration of a previous paper of Greenfield's
(12), and the third was considered an unlikely contributor

of significant amounts of deposition. Mechanisms (1) and (2)
were analyzed in detail.

Greenfield assumed that any interaction between rain and
a radioactive cloud would involve a rain extensive in compar-
ison with the cloud. In the first analysis it was further
assumed that the percentage of particles of a particular size
removed from a vertical cylinder (with the diameter of the
largest raindrOp) through the cloud, would be equal to the
percentage of the same size particles removed from the entire
cloud. It was concluded that, as the result of the collision
of falling raindrOps with particles, particles with diameters
less than 2p would be removed in only minute amounts, depend—
ing on the amount of rainfall.

A two-step process was involved in the analysis for the
collection of particles by water-cloud dr0p1ets and subse—
quent deposition by rainfall. It was considered that (l) a
certain percentage of particles would be captured by water-

cloud draplets, and (2) a certain percentage of the droplets
would be subsequently captured by falling raindrops. The con-
clusions were that the probability was very small that a water
droplet would pick up significant quantities of particles with
diameters greater than 0.08p, and that the mechanism of drOp-
let capture by raindr0ps would occur in a manner similar to
the direct capture of radioactive particles.

Assuming the parameters which would produce the maximum
realistic contamination, including a mean particle diameter
of 2p, Greenfield showed that over 97 percent of the radio-
activity is scavenged by direct interaction with raindrOps.
For all practical purposes then, the removal is by direct
impingment of falling raindr0ps. Reviewing his equations for
the direct interaction of raindrops with particulate matter,
Greenfield says "the fraction scavenged can be considered to
be independent of rainfall intensity and very dependent on
the actual depth of rainfall experienced.”

Greenfield's analysis was interpreted by Itagaki and
Koenuma (15) to mean that in the process of descent a rain-
drOp or snowflake would collide with a radioactive particle
and carry it to earth, and that this was the predominant trans-
fer mechanism. They measured the radioactivity of seven rains
and nine snows at five different elevations and found that the
specific activity decreased with altitude. In the case of
snow the extrapolated altitudes of zero activity coincided
almost exactly with the measured altitudes of the cloud t0ps.

Salter, et al (14) measured the concentration of Sr-90

in precipitation resulting from large—scale uplift. They in-
terpreted Greenfield's analysis as meaning that the predom-
inant deposition mechanism was by cloud-droplet capture and
subsequent rainout, in apparent contradiction to the above.
By examining three rains they found evidence of correlation
between the cloud ceiling and the concentration of Sr—90 in
the rainwater. The cloud ceiling was interpreted to be a
measure of the concentration of radioactivity resulting from
raindrOp evaporation while falling through the unsaturated
layer of air near the ground.

Miyake, et al (8,15) have preposed an equation for the
deposition of radioactivity in terms of the concentration in
the air and the amount of precipitation, in accordance with
Greenfield's analysis. Their data are accurately represented
by the equation when atmospheric activity is taken as constant
over an extended period of time. It is pointed out that fluc-
tuations of rain activity may be mainly due to fluctuations
in the concentration of radioactive dust in the air.

The author preposes that there will be significant
fluctuations in rain activity as the result of the meteorology
surrounding and defining the rains. With this in mind, the

following laboratory setup was devised.

III. LABORATORY INSTRUMENTATION AND PROCEDURE

The primary goal of this thesis was to provide a labora-
tory setup and procedure for the continuous fission product
monitoring of atmospheric radioactivity and rainfall radio-
activity. The criteria were that the system must be simple
in design and readily adaptable to any laboratory, yet com-
plete in its scepe and capable of statistically reliable data.
It should produce data which would lead not only to straight—
forward correlation analyses, but also to an explanation of
the transfer process. The system should be such that all
rains would be sampled without requiring the presence of a
laboratory technician at other than normal working hours.

Following are descriptions of the air sampling, rain
sampling, and radioactivity counting setups and procedures.
The apparatus is shown in figure 1, Appendix I. Unless
otherwise indicated, all references to figures are to Ap-

pendix I.

Air Sam lin

This technique differed significantly from what may be
regarded as "standard" for measuring fission product radio-
activity. Commonly, as high as 1500 cubic meters of air are
sampled in twenty-four hours through a fibrous filter media,
as has been the procedure at the Taft Sanitary Engineering
Center (16). This large volume has the distinct advantage
that counting statistics are highly reliable. However,

8

error is introduced as the result of particulate matter which
penetrates and is stored within the filter matrix. The result
of deeply imbedded particulate matter is that its emitted
radioactivity is absorbed in the filter matrix and is never
counted. According to Cotton (17) this effect "cannot be
accurately compensated by calculations."

In the following procedure approximately thirty cubic
meters of air were sampled every twenty—four hours through
Millipore filters. The smaller sample volume results in
slightly reduced reliability due to counting statistics.
However, Millipore filters-awhich are cellulose plastic,
uniformly porous membranes-- have the particularly useful
characteristic that they retain on the surface all particles
which exceed in dimension the specified pore size. Moreover,
the electrostatic charge generated at the filter surface
inhibits the penetration of colloidal size particles into
the pore structure. This means that there is negligible
absorption of radioactivity by the filter matrix. Finally,
Millipore filters are available with precisely the diameter
necessary to fit the counting apparatus.

The following procedure was used:

1. Air samples were routinely taken on a twenty-four
hour basis, at a flow reading of 25 liters per minute. The
flowmeter was calibrated at 70° Fahrenheit and no correction
was made for temperature differentials. Pressure drOp was
corrected for and the flow rate was considered to be the

average of the flows at the start and finish of the sampling

period. The sample volume was reported at sea level pressure.
Calculations were facilitated by the use of the graph shown
in figure 2.

2. The amount of dust collected was determined by
weighing the filters before and after sampling. Before
weighing, the filters were dried in an incubator at approx-
imately 100o Fahrenheit for at least eight hours.

3. The filters were mounted on sample mounts and stored
in a dessicator for counting.

The following equipment was used:

1. Type AA, 47mm diameter Millipore filters and holder

2. Rotometer, 30 liters per minute capacity

3. Manometer

4. Building vacuum system

5. Precise balance

Excellent control of the flow rate was attained with the
building vacuum system. It can be stated with a high degree
of certainty that the variation in flow rate did not exceed

10.7 liters per minute.
Rain Sampling

It was assumed that knowledge of the distribution of
radioactivity in rain would be revealing. A collection basin
was situated on the roof of the engineering building and was
connected to a series of five sampling cans in the laboratory
by i—inch cepper tubing. The basin was designed with an area

such that 1080 milliliters of rain were collected with a rain—

10

fall of 0.15 inches. The rain was transferred to the labora-
tory through the copper tubing and collected in the cans,
each successive 1080 milliliters being collected in a dif-
ferent can. An overflow was provided so that all rain in
excess of the five cans, or in excess of 0.75 inches, would
be collected in one container.

A.recording rain gage was also placed on the roof,
approximately 30 feet from the collection basin.

The rain from each can was processed so that suspended
and dissolved radioactivity could be counted separately.

This method did not differ significantly from accepted pro-
cedures, with the exception that one liter samples were pro-
cessed instead of 250 or 500 milliliters. The procedure used
was in all essentials the same as that described by Setter,
Hagee, and Straub (18). Techniques for preparing radioactive
samples on planchets and filters are described by the Nuclear-
Chicago Corporation (19), and by Vaughn, et a1 (20).

The following procedure was used:

1. The rain gage was maintained every four or five days,
and after each rain.

2. Rain samples were acidified, in the collection cans,
by the addition of approximately 5 milliliters of 1N HCl, in
order to reduce activity adsorption on the container surfaces,
and to prevent precipitation of the dissolved solids.

3. One liter of each sample was siphoned off into a
marked one-liter beaker immediately after being vigorously

stirred.

ll

4. The suspended solids were deposited on a preweighed
Millipore filter and the filter was dried, weighed, mounted
on a sample mount and stored in a dessicator for counting.

5. The filtrate was returned to the one-liter beaker
and evaporated under an infrapred lamp to a volume of approx-
imately 20 milliliters. The beaker was then tilted so that
the remainder of the filtrate covered a minimal area and the
sample was transferred to a copper planchet with a clean
medicine dr0pper and evaporated to dryness under an infra—red
lamp. The side of the beaker was washed down with.a.minimum
of 0.1M'HCl and this also was transferred to the cepper plan-
chet. Care was taken in the transfer process to insure that
the dissolved solids were contained within the outer annular
ring impressed in the bottom of the planchet. The planchet
was then flame-dried with a Bunsen burner, placed in a sample
mount and stored in a dessicator for counting.

The following apparatus was used:

1. Rain collection basin and standard

2. Collection cans with valve assembly

3. Belfort rain gage, weighing type

4. 250-watt infra-red lamps

5. Chimney funnel and suction apparatus

The cans were calibrated by pouring water through the
system and observing the filling process. As a can filled,
the rising water lifted a float which, by leverage, pressed
3 rubber tee against the orifice. The flow was substantially

and quickly reduced as the design volume was approached, and

12

the final volume ordinarily fell between 1070 and 1150 milli-
liters.

Counting

All counting was performed with a gas-flow proportional
counter at a sensitivity of 2.5 millivolts and a preamplifier
gain of l. The procedure followed was fundamentally the same
as that described by Better and Coats (16), with the exception
that a blanket counting efficiency of 50 percent was assumed
for all samples.

50 percent closely approximates the efficiency of gas-
flow counters of this type, and was assumed so that the re-
sults could be compared, at the same order of magnitude,
with other data. In the interest of obtaining ”absolute
disintegration rates" separate efficiencies would have to be
determined for the samples on filters and the samples in
planchets.

The following procedure was used:

1. Asbackgrcund count of 500 counts was taken before
and after each counting session, with a sample mount in place.
The background count was considered to be the average of
these counts and was subtracted from the total counting rate
for each sample.

2. 1000 counts were taken on each sample 4-5 days after
sampling. The time lag allowed for the decay of natural
radioactivity. Two or three additional counts were taken at

4-5 day intervals.

13

3. The sample counting rates were plotted against time
on semi-log paper and extrapolated back to the time of sample
collection. The extrapolated counting rates were converted
to micromicrocuries per cubic meter of air and micromicro-

curies per liter of water according to

3 __ counts per minute nd
nuc/m, "T§}22)(counting efficiency)(volume of air)’ a

c/l ._ counts per minutet
up — (2:§§)(counting efficiency)(relative counting rate?

where 2.22 disintegrations per minute is one micromicrocurie.
The conversion of air activity counts to mic/m3 was facilitated
by the use of the graph in figure 3.

4. Throughout the sampling period the counter and scalar
were tested at regular intervals, according to the manufac~
turer's directions, for plateau constancy and sporadic coun-
ting.

The following apparatus was used:

1. Gas—flow preportional counter with preamplifier and
micromil window, and scalar (Nuclear—Chicago Models D—47.
D47P, and 186)

2. Automatic sample changer and printing timer (nuclear-
Chicago Models C-llOB and C~111B)

3. Sample mounts and copper sample pans (planchets)

Setter, et a1 (18) show a self-absorption curve for
mixed fission products. This is a plot of relative counting
rate versus sample thickness in milligrams per square centi-
meter. It shows that for a sample thickness up to 0.8mg/cm2

the relative counting rate is unity. With this procedure the

14

maximum thickness for air samples was 0.3mg/cm2, indicating
that self-absorption could be neglected. The maximum sample
thickness from rainwater was 2.5mg/cm2 and corresponded to a

relative counting rate of 0.8.
Support for the Air Monitoring Technique

Support for the air monitoring technique is derived from
a comparison of data obtained in the laboratory with data from
the Michigan State Department of Health. These sets of data
are plotted against time on figure 4. In spite of the dif-
ferences in sampling techniques, and the 5.5 miles separating
the sampling stations, there is a one—to-one correspondence
between all major peaks and troughs. For the above reasons,
and because the air activity is continuously changing, even
on an hourly basis as shown in figure 5, complete agreement
was not expected. The F-test shows, however, that one can be
99 percent confident that these values are related. This is
summarized in figure 6, where the two sets of data are plotted
against each other. The line, representing the linear re-
gression equation (21), very nearly passes through the origin,
as would be expected. This agreement shows that measurements
are reasonably reliable within a 5.5 mile radius of the
sampling station.

The usefulness of the rain sampling cans is demonstrated
in figure 93, Appendix II. Here, the 0.15 inch increments of
rain are plotted against their respective activities for four
rains. Considerable variation in activity is demonstrated in

three rains.

IV. ANALYSIS OF DATA

It was anticipated that when rain activity is compared
with the air activity at the time of the rain, the effects
of meteorology would be evident.

Two empirical equations for the specific radioactivity
of rain were generated from eleven summer rains. The first
equation assumed a direct relationship between rain activity
and air activity alone, and the analysis for the second equa-
tion considered the influences of rain intensity, cloud
height, and wind speed.

The equations were then compared, and the possible sig-
nificance of wind speed was discussed from which a more
comprehensive equation was proposed. In addition, an expla-
nation of increasing specific activity of rain with time was
proposed.

The data is tabulated on page 40. Unless otherwise

indicated, all references to figures are to Appendix II.
Analysis I

Figure 1 is a plot of the air activity versus the rain
activity of each 0.15 inch increment. Figure 2 is the same
plot for the average activity of each rain. The latter cor-
responds to one type of analysis made by Colpetzer (l), in
which air activity in mic/m3 was plotted against rain activ-

ity in uc/ml. This examination was based on weekly averages,

15

l6

and significant correlation was shown to exist, especially at
higher levels of activity.

Such levels of activity are of the magnitude obtained in
this experiment, and figures 1 and 2 indicate a definite rela-
tionship between air and rain activities. If this relation-
ship is assumed to be given by the straight line in figures 1
and 2, the rain activity (CR) is related to the air activ-
ity (CA) by the equation

0 2230A. (l)

R :

The ability of this equation to predict rain activity is
shown by figures 5a and 6a for the activity of each 0.15 inch
increment of rain and the average rain activity, respectively.

Here, values from equation (1) are plotted against laboratory

values.
Analysis I;

It was originally assumed, by the author, that the con-
centration of rain activity would be some function of rain
intensity, wind speed, cloud height, and atmospheric activ-
ity.

It was observed in figure 1 that higher rain activities
were associated with greater wind speeds. This is demon-
strated in figures 3a, 3b, 3c, and 3d--the same points
plotted in figure 1--where wind speed intervals are param-
eters. Ho relationships involving rain intensity or cloud
height were observed.

For each of the above figures the geometric mean wind

1.7

speed, V, was determined, and an equation of the form

CRZKCA (2)
was written. Assuming x : kt”, logarithms of K values were
plotted against logarithms of V values, figure 4, from which
the constants k and n were resolved. The resulting prediction

equation is

CR 2 60.3v0°534cA. (3)

The ability of this equation to predict rain activity is
shown by figures 5b and 6b for the activity of each 0.15 inch
increment of rain and the average rain activity, respectively.
The activity of each rain is the average of the activities of

all 0.15 inch increments.
Comparison of Prediction Equations

Throughout these analyses rains 6 and 11 were not ac-
counted for. Figures 1 and 5 show that rain 6a (the first
0.15 inches of rain 6) aligns preperly, but 6b never aligns.
Rain 6 lasted approximately two days. An investigation of
weather maps showed that the second portion of the rain oc-
curred nearly under the center of a high pressure system,
and that this occurrence was unique with respect to all
other rains. Figure 7 shows the weather maps related to
this rain. The movement of air was downward, and the rain-
bearing cloud was presumably intensely seeded with radio-
active particles from the upper atmosphere.

Rain 11 occurred at a critical time as far as air activ-

ity is concerned. Examination of figure 4, Appendix I, shows

18

that the air activity underwent a rapid rate of increase at
that time, and could have been as high as six or sevenppc/m3
when the rain occurred. This rain was associated with the
passage of a cold front, and the high activity is undoubtedly
associated with that mass of air. Figure 8 shows the passage
of the cold front.

This behavior of rains 6 and 11, with respect to fronts
and pressure systems, agrees with observations made by
Sotobayashi and Koyama (10).

Figures 5 and 6 show a definite improvement in the align-
ment of points according to equation 3. Excluding rains 6
and 11, equation 3 accounts for all of the points whereas
equation 1 does not.

The variation of activity within the same rain is shown
in figure 9a by the laboratory values for each 0.15 inch
increment. Figures 9b and 9c show the predicted values
according to equations 1 and 3, respectively. variations
in specific activity are apparently explained by variations
in wind speed.

Interpretation of the Wind Speed Effect

The literature review describes theoretical and empirical
evidence that the principal mechanism of particle capture is
by direct collision with raindrops or snowflakes.

If this is true, the amount of particulate matter cap-
tured must then depend on the amount presented to the rain-

drop in the descent. If, as in the case of this data, rain

l9

intensity and cloud height have no significant effect, the
average time of descent is constant and the particulate
matter swept out is proportional to the atmospheric con-
centration. Additionally, particulate matter impinges on
the raindrop with the horizontal speed of the wind. The
amount presented in this manner is pr0portional to the at—
mospheric concentration and the wind speed. This inter-
pretation suggests that, for summer precipitation, an equation
of the form

CR =iKCA-+-kVnCA, (4)
for each increment of rain, might be more descriptive. In
this equation KCA is a constant for a specific atmospheric

activity, and V is the wind speed.
Interpretation of Increasing Specific Activity of Rain

Colpetzer (1) observed increasing specific activity with
increasing depth of rainfall when weekly averages were con—
sidered. This effect is displayed in figure 9a, and might be
explained by the deviation from Greenfield's model and the
horizontal impingment of radioactive particulate matter as
the result of wind speed.

Under the Greenfield model (a rain extensive in compar-~
ison with the radioactive cloud) a decrease in the specific
radioactivity of rain as the result of rainout would be
noticeable. However, the inverse of this model describes
summer rains; that is, radioactive clouds are extensive in

comparison with summer rains. This being the case, the air

20

within the volume occupied by a summer rain may be replenished
with radioactive particulate matter at the rate of rainout,
and a resultant decrease in the specific activity of rain with
time need not occur.

The variation of atmospheric radioactivity with time is
shown in figure 4, Appendix I. An examination of weather maps
and U. S. Weather Bureau data at Iansing, Michigan disclosed
that positive slopes are invariably associated with clear
weather conditions, and negative lepes are associated with
generally cloudy or precipitous conditions. The effect of a .
particular rain on the activity level is, therefore, con—

sidered to be negligible.

V. CONCLUSIONS

The following general conclusions are drawn from this
study:

1. The laboratory setup meets the criteria of simplicity
and adaptability. It produces data which are quantitatively
useful, statistically reliable, and which lend insight into
the transfer mechanism.

2. Atmospheric radioactivity measurements are reliable
within a radius of at least 5.5 miles of the sampling station.
3. The relationship between the specific activity of
rain and the specific activity of air at the time of the rain

is reasonably well described by the equation, CR Z-ZZSQA.

4. Some relationship between the specific activity of
rain and wind speed at the time of the rain appears evident,

and an equation of the form CR1: KC -+ kVnQA, for each incre-

.A
ment of rain, might be more descriptive.

5. In the case of summer rains Greenfield's model does
not apply. No rain observed was extensive to the degree that
the percentage of particles removed from a vertical cylinder
was equal to the percentage of particles removed from the
entire radioactive cloud. It may, therefore, be possible to
predict increasing specific activity with time for summer
rains.

6. The Specific activity of rain did not appear to be
related to either cloud height or rain intensity. The latter
tends to support Greenfield's prOposition that the fraction

scavenged may be considered to be independent of rainfall

intensity.

VI. FUTURE RESEARCH

There are many avenues of exploration to be considered
in addition to those suggested in this thesis.

From this data it is evident that some parameter is
needed to account for the effect of overhead pressure sys—
tems.

It is anticipated that there will be differences between
the behaviors of air and rain activities with different sea-
sons, and that different equations will apply.

An examination of Greenfield‘s analysis with respect to
the mechanics of rainout of different size particles is
needed. The type of capture, by cloud drOplets or raindrOps,
may be selective of radioactive isotopes.

The immediate history of an air mass may yield param-
eters relating to particulate matter rainout, and a study
of thermal gradient effects could explain the rapid build-up
of atmospheric radioactivity.

22

APPENDIX I -- LABORATORY

23

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40 35

Sample Volume, cubic meters
20

 

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‘Rotometer Reading, liters per minute

Figure 2. Sample volume graph

25

Air Activity, ppc/m3

26

 

 

Sample volume,m‘ 9

I I I l I 1 I I

 

 

 

20 40 60 so 100 ' 12b
Counts per Minute

Figure 3. Air activity graph

1
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140

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160

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Figure 5. Hourly variation in
atmospheric activity

28

13“ Sum of Mean

12-- Between 107.24 9 11.91

11“ F 2111.91/3.92 2:3.04

10" Linear Regression Equation

29

 

Analysis of Variance Table

Category Squares df Square 0

 

 

 

 

Within 137.2 35 3.92

 

19.99 = 2.97

9 y = 0.28 + 0.569x 0

 

 

 

O L l 1 L l l 1 J 1 l
O 1 2 3 4 5 6 7 8 9 10
Atmospheric ActivityéDepartment of Health, uuc/m3

Figure 6. Comparison of atmospheric activity values--
MSU laboratory data versus Michigan
Department of Health data.

APPEND
IX I
I - ANALYSIS OF
DATA

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38

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(a) Laboratory measurement

 

 

 

 

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41
BIBLIOGRAPHY

Colpetzer, Thomas R. "A Correlation Study of Environmental
Radioactivity.” Unpublished Master's thesis, Michigan
State University, East Lansing, 1962.

“Residual Nuclear Radiation and Fallout." The Effects 9;
Nuclear Wea ons. Department of the Army Pamphlet No. 39-3.
Washington: Government Printing Office, 1962.

Setter, Lloyd R., John E. Regnier, and Edward AJIDiephaus.
"Radioactivity of Surface Waters in the United States,"
Journal American Water Works Association, 51:1377-92, 1959.

Campbell, J. E., et al. ”The Occurrence of Strontium-90,
Iodine-131, and Other Radionuclides in Milk - May, 1957,
Through April, 1958." American Journal 3; Public Health,
49:2, February, 1959.

Langham, Wright, and E. C. Anderson. "Biospheric Contam-
ination from Nuclear Weapons Tests Through 1958.” Hearings
0onm1""""ttee .92. Atomic Energy, conga. s"""_o_; "t"h"e'"'Uh‘i't'e'd"$t""'a' "too,
May 5, 6, 7, and 8, 1959, Vol. 2. Washington: Government
PrintingQCIffice, 1959. .

Folsom, T. R., and G. J. Mohanrao. TthStudy gf_the
Behavior and Significance 9: Certain Radioactive IEBtopes
Found in the Sewag§_Treatment Plants 2: Selected Cities.

A Research and Development Report Prepared for the United
States Atomic Energy Commission. San Francisco Operations
Office, 1961.

Conard, Robert.A. ”The Effects of Fallout Radiation on
the Skin." Th2 Shorter-Term Biological Hazards gfflg Fall-
92; Field. A Symposium Sponsored by the Atomic Energy
Commission. Washington: Government Printing Office, 1956.

Miyake, Y., K. Saruhashi, Y. Katsuragi, and T. Kanazawa.
"Radioactive Fallout in Japan and Its Bearings on Meteor-
ological Conditions," Papers in Meteorologyggd Geophysics,
XI:1, 1960.

Miyake, Y., K. Saruhashi, Y. Katsuragi, and T. Kanazawa.
"Seasonal Variation of Radioactive Fallout,” Journal g;
GeOphysical Research, 67:1, 1962.

Sotobayashi, Takeshi, and Seitaro Koyama. "Deposition of
Nuclear Debris and Atmospheric Conditions,” Journal 9: the
Faculty 2; Science, Niigata University, Japan, 3:2, 1962.

42

11. Greenfield, S. M. "Rain Scavenging of Radioactive
Particulate Matter from the Atmosphere," Journal 9;
Meteorology, 14:1957.

12. Greenfield, S. M. "Ionization of Radioactive Particles
in the Free Air," Journal 93 GeOphysical Research, 61:1956.

13. Itagaki, K., and S. Koenuma. "Altitude Distribution of
Fallout Contained in Rain and Snow," Journal 2; Gethysical
Research, 67:10, 1962.

14. Salter, L. P., P. Kruger, and C. L. Hosler. 'Srgo Con-
centration in Precipitation Resulting from Large-Scale
Uplift,” Journal 2;.Applied Meteorolo , 1:1962.

15. Miyake, Y., Y. Sugiura, Miss K. Saruhashi, and
Mrs. T. Kanazawa. "The Estimation of the Amount of
Sr-90 Deposition and the External Infinite Dose in Japan
Due to Man-made Radioactivity," UN Scientific Committee
on the Effects of Atomic Radiation Document, A/AC,
82/G/R, No.172. Pap. Met. GeOphys., Tokyo.

16. Setter, L. R., and G. I. Coats. ”The Determination of
Airborne Radioactivity,” (paper presented at the Twenty-
first Annual Meeting of the American Industrial Hygiene
Association, Rochester, New York, April 28, 1960).

17. Cotton, Richard.A., Research.Director, Millipore Filter
Corporation, in a letter to the author, October 15, 1962.

18. Setter, L. R., G. R. Hagee, and C. P. Straub. “Analysis
of Radioactivity in Surface Waters — Practical Laboratory
Methods." American Society for Testing Materials
Bulletin No. 227, January 1958.

19. Nuclear-Chicago Corporation. "How to Prepare Radioactive
Samples for Counting on Planchets,” Technical Bulletin
No. 7 and 7B, 1960.

20. vaughn, James 0., Robert W. Schmidt, Alfred Tenny, and
Arthur Shor. ”Studies of Radioactivity in the Chicago
Water Supply,” Journal American Water Works Association,
50:581, 1958.

 

21. Dixon, Wilfrid J., and Frank J. Massey, Jr. Introduction
32 Statistical Analysis. New York: McGraw-Hill Book
Company, Inc., 1957. 488pp.

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