Aerosol Preparation, Generation, and Assessment, Project Hare


                                                  SWRHL-75r
AEROSOL, PREPARATION, GENERATION, AND ASSESSMENT
                      PROJECT HARE
                             by
     R.  H.  James,  D.  N. McNeils,  E.  L. Whittaker and
               N. C. Kennedy, ESSA, ARL-LV
                    Radiological Research
         Southwestern Radiological Health Laboratory

     U. S. Department of Health, Education, and Welfare
                    Public Health Service
                Environmental Health Service
                        February 1970
        This study performed under a Memorandum of
                Understanding (No. SF 54 373)
                           for the
            U. S. ATOMIC ENERGY COMMISSION

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                         LEGAL NOTICE


This report was prepared as an account of  Government sponsored
work.  Neither the United States,  nor the Atomic Energy Commission,
nor any person acting on behalf of the Commission:

A.  makes any warranty or representation,  expressed or implied,
with respect to the accuracy,  completeness,  or usefulness of the in-
formation contained in this  report, or that  the use of any information,
apparatus, method,  or process disclosed in this report may riot in-
fringe  privately owned rights; or

B.  assumes any liabilities with respect to the use of,  or for damages
resulting from the use of any information,  apparatus,  method, or pro-
cess disclosed in this report.

As used in the above,  "person  acting on behalf of the Commission"
includes any employee or contractor of the Commission, or employee
of such contractor, to the extent that such employee or contractor of
the  Commission, or employee  of such contractor prepares, dissemin-
ates,  or provides  access to, any information pursuant to his employ-
ment or contract with the Commission, or  his employment with such
contractor.

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                                                     SWRHL-75r
AEROSOL PREPARATION,  GENERATION, AND ASSESSMENT
                      PROJECT HARE
                             by
     R. H. James, D. N. McNeils, E. L. Whittaker and
               N.  C.  Kennedy, ESSA, ARL-LV
                   Radiological Research
        Southwestern Radiological Health Laboratory

     U. S.  Department of Health, Education, and Welfare
                   Public Health Service
                Environmental Health Service
            Environmental Control Administration
                Bureau of Radiological Health
                       February 1970
        This study performed under a Memorandum of
               Understanding (No. SF 54 373)
                          for the
            U.  S.  ATOMIC ENERGY COMMISSION

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                                ABSTRACT  .-

Project HARE was the sixth in a series of experiments in which a radioactive
contaminant was released under controlled conditions to simulate the passage
of a nuclear event-related radioactive cloud.   The history of the radio-
nuclide from the nuclear event to a constituent of man's diet is studied  as
a function of the interrelated physical, chemical  and biological variables.
This paper reports on the measurement of some  of the physical and chemical
parameters involved in the preparation, generation and assessment of the
aerosol.

A dry aerosol consisting of submicrometer diatomaceous earth particles
tagged with 54.1 mCi of 131I was released over two types of growing forage
(alfalfa and Sudan) at the U. S. Public Health Service Experimental  Farm
at the Nevada Test Site.  The study area was instrumented with fallout
planchets, glass slides, air samplers, cascade impactors, and meteorological
equipment.  The aerosol was air-carried over the study area and deposited
with an average activity concentration of 1.25 yCi/m2 on the Sudan and
1.43 yCi/m2 on the alfalfa.  The count median  diameter of the aerosol was
0.6 pm which varied only slightly from one location to another.  Average
integrated air concentration and average deposition velocity were
87.5 yCi-sec/m3 and 1.59 cm/sec, respectively.

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                            TABLE OF CONTENTS

ABSTRACT                                                                  i
TABLE OF CONTENTS                                  .                      ii
LIST OF FIGURES                                                         ill
LIST OF TABLES                                                          iii
  I.  INTRODUCTION                                                        1
 II.  PROCEDURE                                                           2
III.  RESULTS                                                             9
 IV.  DISCUSSION                                                         17
  V.  CONCLUSIONS                                                        21
REFERENCES                                                               22

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                             LIST OF FIGURES
Figure 1      Sample Grid
Figure 2      Activity Deposition Distribution
Figure 3      Depletion Vector Diagram
 4
10
11
                             LIST OF TABLES
TABLE I       Air Temperature and Humidity Data
TABLE II      Wind Data
TABLE III     Particle Size Distribution
TABLE IV      Cascade Impactor Data
TABLE V       Air Sampler Data
TABLE VI      Filter Pack Data
TABLE VII     Deposition Velocities
 7
 8
13
14
15
16
18
                                   m

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                            I.  INTRODUCTION

Five controlled releases of 131I have been conducted at the U.  S.  Public
Health Service (USPHS) Experimental Farm, Area 15, Nevada Test Site.   These
have included three releases of dry aerosols, one of a hydrosol, and one of
131I gas over various types of forage which were then fed to groups of
lactating dairy cows.  One of the principal parameters of interest has been
the ratio of the peak activity in milk to the peak activity on the forage.

Comparison of the milk to forage ratios for the first two experiments
shows that the ratio for Project Alfalfa was approximately four times the
ratio for Project Hayseed.1"2  The two parameters which most probably
account for the difference are:
1.  Difference in count median diameter (2 ym vs 23 ym) of the aerosols;
    and
2.  Difference in forage species (alfalfa vs Sudan).

The primary objective of Project HARE was to determine whether aerosol
particle size, or forage species, if either, contributed to these  differing
results.  Additional objectives included developing procedures  for aerosol
preparation'and generation; determining the deposition, particle size, and
aerial concentration of the aerosol; and correlating meteorological data
with radiological measurements.  The experimental results, as reported in
reference 3, indicate that the type of contaminated forage ingested exerts
a significant effect upon the resultant 131I activity secreted in  milk.

The USPHS Farm lies on a slope with the gravity wind from the north-
northwest.  Meteorological records were examined to determine the  probability
of favorable conditions for release.  Prior experience at the farm during
earlier releases showed that satisfactory conditions (winds 345° ± 30° and
speed less than 4 meters per second for a two-hour period) can be  expected
during periods of light gradient winds and moderate radiative cooling.

-------
Records for the last three weeks of September for the years 1965 and 1967
were examined.  Satisfactory conditions had occurred about 40% of the hours
between 2300 PDT and 0700 PDT.  A ready time of 0000 PDT with release no
later than 0500 PDT was set.

Dry 131I labeled diatomaceous earth (DE) was generated and air-carried over
the study area at 0100 hours on September 18, 1968.   The study area of Sudan
and alfalfa was instrumented with fallout planchets  for deposition calcula-
tions, glass slides for size measurement, and various types of air samplers
for aerial concentration measurement.  Meteorological equipment was also
placed at various locations around the study area.  It was expected that
the desired peak contamination level on the forage of 105 pCi/kg could be
accomplished with approximately 50 mCi 131I.

                             II.  PROCEDURE

The preparation of the aerosol was accomplished at the Southwestern
Radiological Health Laboratory in Las Vegas, Nevada.  In the previous
exercises the air-dried aerosol, after 131I labeling, was sieved again
to assure particle separation.  For this exercise the aerosol  material (DE),
after mixing in the generator flask with the 131I labeling solution, was
dried under vacuum and kept sealed in the generator flask until generation
time.   To assure that 50 mCi of activity would be released, 100 mCi 131I
activity was supplied to allow for preparation time  and any delays in
execution of the experiment.  The 131I (Na131I in NaOH solution) received
from the supplier was diluted to 17 ml and divided into 32 x 0.5 ml aliquots,
one aliquot for each of 32 generator flasks.  The extra 1 ml was used for
calibration purposes.  Each aliquot was put into a 2 oz polyethylene bottle
containing 1 ml 1M Na2S203, 5 ml 2M Na2C03 and 25 ml distilled water.
           jj
The generators (2000 ml, two neck, round bottom flasks) were prepared in
two groups of 16.   Stoppers were wired to the flasks and included as part
of the flask tare weight.   Each flask was placed in  double plastic bags
taped to close the bags about the flask necks to ensure containment should
the flask break.   The plastic bags remained around the flask throughout  the

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preparation, transportation, and generation of the aerosol.   A screen was
placed in the outlet ports of the flasks to assist in the break-up of any
agglomerates.  Isopropanol (450 ml) and 7 g of glass beads (3mm diameter)
were added to each flask.  The 131I spike aliquots were added to the flasks
under a hood behind a lead shield.  Each flask was stoppered and its contents
mixed thoroughly.  A 150 g portion of presized DE was added  to each flask,
the flasks stoppered, then swirled to mix the contents.   The DE was pre-
sized by sieving using a Tyler sieve shaker with 400 mesh (37 ym pore size)
screen as the final stage.  All 16 flasks, after being prepared in this
manner, were connected to the vacuum manifold.  The first group of 16 flasks
was dried for 40 hours, being warmed by hot tap water for the last 18 hours.
The second group was vacuum dried for 45 hours, being warmed by hot tap
water for the last 17 hours.  The flasks were brought back to atmospheric
pressure, stoppered, individually weighed, and transported to the test site
in lead-lined boxes.  After generation of the aerosol, the flasks were
again individually weighed to determine the weight loss, i.e., the amount
generated.

Before the actual release a sampling grid was set up at the  USPHS Farm, and
is shown in Figure 1.  The Sudan portion of the study area,  located on the
east end of the field, measured 65 m by 16 m.  The alfalfa portion of the
study area, located on the west side, measured 55 m by 16 m.   A 10 m space
separated the two areas.  The samples and samplers were numbered from left
to right across the complete grid and from front to back.

Stainless steel 4%-inch planchets coated with alkyd resin were spread over
the sampling grid on wooden stakes approximately % m off the ground.   The
data from planchets were used to determine the activity level  isopleths
and as input to deposition velocity calculations.   Additional  planchets were
placed in the center rear of the study area for special  forage studies.
Racks containing planchets having both horizontal  and vertical orientations
at ground, T m and 2 m levels were located at three different positions in
the study area to yield a measure of the vertical  profile of the cloud.
Glass slides placed evenly throughout the study area were used to determine
the size distribution of the aerosol.  Fallout trays were evenly spaced to
aid in obtaining a size to activity ratio.

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                              10m
        TD
        10m   .
           Ol
                        Ol
A
• • • • • •
B B B

OB OB BO
*
bbm ""
•

D
A
B

• • • • • i
0 B B
• " ' *
BO DB OB
4 •
' lOnfr 55m


1

1


5m

5m
OOOOOOOOOOOOOOOOOOOOOOOOOO^OOO
                                                                            5.5m
                  •  Cascade Impactor
                  A  Filter Pack
                  A  Planchet Rack
                  B  Glass Slide
                  D  Fallout Tray
 O Tempest
 • Planchet
O Generator
D DAT  Trailer
                                           Figure  1
                                          Sample Grid

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Gelman Tempest air samplers were placed at nine locations  throughout the
study area to measure airborne activity concentrations.   Each  Tempest
filter train consisted of a Whatman 541 prefilter,  MSA charcoal  cartridge
and Microsorban postfilter.

Three additional air samplers which made use of a special  sampling  train
consisting of a Microsorban prefilter, AC-1  charcoal  filter, 727 charcoal
bed, and Microsorban postfilter were also used to aid in  quantitating
aerial activity concentrations.

Unico cascade impactors were placed at five locations in  the study  area to
aid in determining the distribution of the activity with  particle size,
and to correlate this with activity levels.

A line of 32 generators spaced at intervals  of 5.5  m  was  fixed parallel to
and 16 m upwind of the leading edge of the test field.  The generator line
extended four generators beyond each end of the field to  allow for  wind
changes up to 30° from the normal.   One cylinder of dry air was  used as
the generation gas for each group of two generators.   At  0100  hours PDT on
September 18, 1968, the aerosol was generated with  a  dry  air flow rate of
85 liters per minute to each flask.  During the period of generation the
flasks were agitated by hand to insure complete unloading.  The  generation
period lasted for an average of 11  minutes.

Two analog wind systems, with telemetered data to the farm building, were
set at a height of 1 m on each" end of the experimental  plot—one over
alfalfa, the other over Sudan grass.  Two Data Acquisition and Telemetry  (DAT)
trailers each having aspirated temperature sensors  and wind direction and
velocity sensors at 9.4 m and 0.4 m elevations were located 10 m downwind
of the test plot, one centered on the Sudan  plot, the other centered on the
alfalfa plot.  The trailer instrumentation gave printouts  at two-minute
intervals of air temperature and the temperature differences between eleva-
tions.  Hygrothermographs in standard instrument shelters  at a height of
0.25 m were located, one 200 m northeast of the plot, the  other  in  the alfal-
fa at the edge of the experimental  plot.  Analog wind information was also
available from the farm meteorological tower located  110 m north of the
study area with instrumentation at 1 m, 10 m, and 30  m elevations.

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At 0100 PDT, September 18, 1968, the skies were clear, with the wind at
1 m elevation from the northwest at 2 mph (0.9 m/sec).  A pronounced sur-
face inversion had been established.  The temperature difference between
the 9.4 m and 0.4 m levels ranged from 16 to 20 F° (Table I).   This  was a
larger difference than'in any earlier tests.  The wind flow was observed
to occasionally meander with the direction stabilizing from the northwest.
The wind was steady in direction during the release period, and no temporary
breakdown of the extremely stable temperature structure occurred.   Table II
gives wind information during and shortly after the release at three eleva-
tions on the meteorological tower and on either end of the test plot.   No
precipitation was recorded during the period of the test.1*  Some mean  values
(with instrument uncertainty indicated) measured during the release  period
are:
            wind speed - 1 m Sudan -                  1.3 ± 0.2 m/sec
            wind speed - 1 m alfalfa -                1.2 ± 0.2 m/sec
            mean direction of ;wind -                 326° ± 5°
            temperature - 0.25 m alfalfa -             51 ± 1°F
            humidity - 0.25 m alfalfa -                51 ± 5%
            temperature difference (9.4 m - 0.4 m) - 18.7 ± 0.5 F°

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                                    TABLE I
                       AIR TEMPERATURE AND HUMIDITY DATA
Alfalfa Test Plot
Time
(PDT)
0100
0101
0102
0103
0104
0105
0106
0107
0108
0109
0110
0111
0112
0113
0114
0115
0116
0117
0118
0130
Temp.

 51
 51
 51
 51
 51
 51
 51
 51
 51
 51
 51
 51
 51
 51
 50
 50
 50
 50
 50
 50
                Rel. Hum.
                   50
                   50
                   50
                   50
                   50
                   50
                   50
                   50
                   50
                   50
                   51
                   51
                   51
                   51
                   52
                   52
                   53
                   53
                   53
                   54
Alfalfa
0.4m Temp.
46
46
47
46
46
45
47
47
46
46
DAT System
9.4m-0.4m
ATemp. (F°)
18.1
16.5
16.5
17.8
19.2
19.2
18.9
19.6
20.3
20.6
Sudan
0.4m Temp.
49
46
47
48
47
47
47
47
47
48
DAT System
9 . 4m-0 . 4m
ATemp. (F°)
16.7
17.6
17.0
17.0
18.4
18.2
18.5
18.9
18.9
19.1

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                              III. RESULTS

During the aerosol preparation procedure a cold trap was used between the
flasks and vacuum pump.  Approximately 68 yCi (0.1%) of 131I activity was
collected in the cold trap during the drying procedure.5  The loss of
activity to the vacuum pump oi'l was determined to be less than 0.02% of the
total activity.  A Tempest air sampler was operating near the vacuum pump
exhaust.  A total of four prefilters and charcoal cartridges were used
during the drying procedure.  No activity was found on the prefilters, but
there was activity found on the charcoal cartridges.  The maximum air
concentration was found to be 2.69 x lO"4 pCi/cm3, which is well below the
maximum permissible concentration (MPCL of 9 x 10"3 pCi/cm3 based on a
                                       a
40-hour week.6  The same methods of preparation could be used with consid-
erably more activity without exceeding the (MPCL.
                                                a
                             •
The generator flasks were reweighed following the exercise.  Based on the
average weight lost, 98% of the activity was generated.  This represents a
total of 54.1 mCi 131I released during the exercise.

The activity deposited on the field as determined by the planchets along
with the activity isopleths are shown in Figure 2.  By using the average
planchet value of 1.25 yCi/m2, a total of 1.29 mCi or 2.4% of the total
activity released was deposited on the Sudan grass plot.  By using the
average planchet value of 1.43 pCi/m2, a total of 1.26 mCi or 2.3% of the
total activity released was deposited on the alfalfa study plot.  The total
activity deposited on the test grid was 2.55 mCi, or 4.7% of the activity
generated.

The data obtained from the planchet racks together with the respective
"depletion vectors" is shown graphically in Figure 3.  The "depletion vec-
tor" is defined as the resultant deposition vector, using the normal to the
vertical and horizontal orientations of the planchets as vectors and the
corresponding activities as magnitudes.  These data demonstrate that the
cloud was concentrated very close to the ground in a near vertical deposition
direction.  At the higher elevations the horizontal component becomes rela-
tively stronger and the magnitude of the resultant vector decreases.

-------
1-08 1.26 1.01 1.25
. . • •
1-32 1^2 1.46^-v 1.59 1.2
•
1 .39
1. 2
02
80 1.24 ^ l.\l 1.98
1. 20
1.38 0.50 1.29 1.77 0.77 1.68 1.16 0.75 2.09 1.79 2.42 0.97 1-37
Sudan
Act.>2 uCi/m2

l
-------
# 1
# 2
# 3
2 meter
V =
0.1 uCi/m2
0.03
0.08
0.03
1 meter
V =
1.0 pCi/m2
0.21
0.87
0.55
Surface
%" =
1.0 uCi/m2
1.52
1.27
Figure 3
Depletion Vector Diagram
(activities in
1.24
O
Planchet surface
horizontal

Planchet surface
vertical
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The DE particles on 19 glass slides were examined and sized under an optical
microscope. An average of 400 particles per slide were sized using the
Feret diameter measurement.7 The cumulative size distribution data is shown
in Table III. The count median diameter (CMD) of the entire distribution is
0.6 ym.

Portions of five fallout trays were observed under an optical, microscope to
obtain a size distribution. These same portions were autoradiographed and
the spots on the autoradiographs were sized to obtain a relative activity
distribution.

The data collected from the Unico cascade impactors is shown in Table IV.
No data was collected for the No. 4 cascade impactor as it was not operating
during cloud passage. The mass median diameter (MMD) indicated in Table IV
is that calculated for each stage from the cascade impactor flow chart based
on a DE density of 2.3.8 The stage MMD represents that size whereby 50% of
the mass impacted on that stage is associated with particles'less than that
size. A large fraction (83-87%) of the activity was associated with large
particles, i.e., those collected on the first stage.

Table V shows that activity collected on each component of the Gelman
Tempest air sampler heads. It also shows the integrated air concentrations,
the deposition velocities, and the ratios of the prefilter activity to the
charcoal cartridge activity. Integrated air concentration (lAC) is defined
as the ratio of the total activity on the filter elements to the flow rate
through those elements. Deposition velocity is the ratio of the planchet
activity per unit area to the integrated air concentration. An average of
49% of the activity collected on the filter trains remained ori the prefilters
which have a mean pore size of 3.4 to 5 ym. An average of less than 1% of
the activity was collected on the postfilters with a 50% average remaining
on the charcoal cartridges.

The Microsorban prefilter on filter pack air sampler Nos. 1 arid 3 (Table VI)
accounted for 63 and 63.9% respectively of the total activity at their
locations. An additional 36.7 and 35.7% was collected on the Gelman AC-1
filter, thus leaving less than 1% on the combination of the charcoal bed
12
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TABLE III

PARTICLE SIZE DISTRIBUTION
Size Range
(urn)
<.64
.64- .96
.96-1.60
1.60-2.24
2.24-2.88
2.88-3.52
3.52-4.16
4.16-4.80
4.80-5.44
5.44-6.08
6.08-12.5
12.5-18.9
18.9-51.2
>51.2
Number
2547
2827
898
314
116
81
57
69
53
43
236
164
226
196
Percent
32.6
36.2
11.5
4.0
1.5
1.0
0.8
0.8
0.7
0.6
3.0
2.1
2.9
2.3
Cumulative
Number
2547
5374
6272
6586
6702
6783
6840
6909
6962
7005
7241
7405
7631
7827
Cumulative
Percent
32.6
68.8
80.3
84.3
85.8
86.8
87.6
88.4
89.1
89.7
92.7
94.8
97.7
100.0
13
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TABLE IV
CASCADE IMPACTOR DATA
Number 1
Number 2
Number 3
Number 5
Stage
1
2
3
4
Postfilter
TOTAL
Activity
(pCi "ID
3.00x10"
7.06xl02
6.34xl02
2.21xl03
6.22xl02

87.7
2.0
1.8
6.4
1.8
99.7
MMD
(ym)
>5
5.0
2.5
1.3

Acti vi ty
(pCi 131I)
2.06x10"
1.92xl03
1.14xl03
5.91xl02
4.16xl02

83.5
7.7
4.6
2.3
1.6
99.7
MMD
(ym)
>4.8
4.8
2.7
1.2

Activity
(pCi "I!)
1.49x10"
1.06xl03
4.73xl02
3.23xl02
2.46xl02

87.6
6.2
2.7
1.8
1.4
99.7
MMD
(ym)
>5
5.0
2.5
1.3

Acti vi ty
(pCi 131I)
1.31x10"
9.60xl02
3.76xl02
6.27xl02
5.81xl02

83.7
6.1
2.4
4.0
3.7
99.9
MMD
(ym)
>5.8
5.8
3.2
1.4

NOTE: Number 4 cascade impactor was inoperative.
MMD - Mass Median Diameter
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TABLE V

AIR SAMPLER DATA
Sampler Prefilter^ ' Charcoal' '
Number (104 pCi ) (104 pCi)
1
2
3
4
5
6
7
8
9
34.9
16.6
17.8
24.9
20.1
23.7
2.92
29.1
16.9
AVERAGE 20.8
(1)
(2)
(3)
Whatman 541
MSA Cartridge #46727
Delbag Microsorban
36.3
20.8
24.2
20.2
17.1
21.9
7.78
11.7
19.2
19.9

Postfilter^3^
(lO4 pCi)
0.0925
0.291
0.358
0.230
0.281
0.220
0.0949
0.0724
0.329
0.219

Total
(104 pCi)
71.3
37.7
42.4
45.3
37.5
45.8
10.8
40.9
36.4
40.9

Pref liter
Charcoal
0.961
0.798
0.735
1.23
1.18
1.08
0.375
2.49
0.880
1.08

Integrated
Air Cone.
(yCi-sec/m3)
161
82.0
86.9
98.5
76.8
93.8
22.1
92.1
74.6
87.5

Depositionv '
Velocity
(cm/sec)
.859
1.42
2.06
1.39
2.34
1.29
2.08
1.17
1.68
1.59

(4) Calculated relative to planchets
-------
TABLE VI
FILTER PACK DATA
Sample
(1)
Prefliter
Charcoal%
Filter(2)
Charcoal Bed
Postfilter^
(3)
TOTAL
Pref ilter
Charcoal.
Filter^2)
(3)
Charcoal Bed
Postfilter^
TOTAL
Prefilter^
Charcoal.
Filter(2)
Charco
Filter
Charcoal Bed
Postfilter(1J
(3)
TOTAL
Activity
(pCi)
2.74 x 10s
1.88 x 105

1.05 x 105

4.36 x 102
3.36 x 102
4.47 x 102
2.94 x 105
(1)
(2)
(3)
Del bag Microsorban
Gelman AC-1
727 Charcoal Bed
Percent
63.0
1.60 x 105
1.24 x 103
2.72 x 102
4.36 x 105
5.21 x TO1*
8.39 x 104
1.66 x 103
4.42 x 101
1.38 x 105
36.7
0.3
0.1
100.0
37.8
60.8
1.2
0.1
99.9
63.9

35.7

0.1
0.1
0.2
100.0
Integrated
Air Cone.
77.8
Deposition
Velocity
/cm x
(SQC>
2.31
23.8
1.94
52.5
2.06
16
-------
and the Microsorban postfliter. An extra Gelman AC-1 filter was placed in
the third sampler in error; however, less than 0.1% of the total activity
was collected on that sample. No change in flow rate resulted from this
extra filter since flow rate was set to a predetermined value. Filter
pack No. 2 yielded a prefilter to charcoal filter ratio that was about the
inverse of the other two samplers. This same low ratio can also be noted
from Tempest air sampler No. 7 on Table V. These latter two air samplers
were located at the right rear corner of the Sudan plot which received the
lowest level of contamination of the total test grid.

A comparison of two methods of calculating deposition velocity is shown in
Table VII. Lines 2 and 4 show the deposition velocities calculated using
the planchet deposition. In lines 1 and 3 the deposition velocity is
calculated using the deposition on the forage itself. This activity is
calculated from the activity per unit mass on the forage and from the
average density of the forage per unit area of ground surface, given in
columns 1 and 2, respectively. The integrated air concentration is calcu-
lated using Tempest sampler No. 7 for the Sudan, and using the average of
the values from Tempest samplers 5 and 8 for the alfalfa.

IV. DISCUSSION

The distribution of the aerosol was reasonably uniform over the entire
study area. The area of lowest deposition was the southwest corner of the
Sudan study plot with a deposition of about 1/3 of the average deposition
on the Sudan. By comparing the averages of the five lengthwise rows of
planchets (Figure 2), it can be seen that the center row received the highest
deposition with the level falling off both front and rear.

The planchet racks (Figure 3) demonstrated that most of the activity re-
mained very close to the ground, i.e., less than 1 m.

It appears that a large amount of the activity is associated with larger
particles, since such a large portion of the activity was collected on the
first stage of the cascade impactors. The size measurements indicate that
more than half of the particles are quite small (<1 pro). Unfortunately,
17
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TABLE VII

DEPOSITION VELOCITIES
00
Deposition
Surface
Alfalfa
Planchet
(Alfalfa Plot)
Sudan
Forage
Acti vi ty
(pCi/g)
5.23 x 103

1.98 x 103
Forage
Area! Density
(g/m2)
3.90 x 102

2.97 x 102
Area! Activity
(pCi/m2)
2.04 x 106
1.44 x 106
5.88 x 105
Integrated
Air Cone.
(pCi-sec/m3)
8.44 x 107
8.44 x 107
2.22 x 107
Depos i ti on
Velocity
(cm/sec)
2.42
1.75
2.68
Planchet
(Sudan Plot)
4.6 x 105
2.22 x 107
2.08
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accurate measurements of size to activity ratios using the fallout trays
were not possible. Accurate measurements of this value would require
precise positioning of an autoradiograph in back of the fallout tray or
glass slide so that the particle would appear directly over the spot it
created on the X-ray film. In this way the particle could be sized, its
autoradiograph sized, and a direct comparison made of its size to its
activity. In using the fallout trays, great difficulty was encountered
in relocating the autoradiograph in its proper position for the measurements.
In nearly all cases the active particle could not be relocated over its
autoradiograph spot.'

A careful examination of the filter pack activity collection data (Table VI),
the'cascade impactor data (Table IV), and the particle size distribution
(Table III), together with a consideration of the reported efficiency of
the Microsorban filter, suggests that something must have happened to some
of the radioiodine that had been stopped by the Microsorban prefilter to
cause it to be carried off the prefilter and be subsequently collected by
the AC-1 filter (charcoal impregnated paper) in the filter pack system.
The Microsorban filter has a reported efficiency of 99.9% for 0.3 ym size
particles and has a high efficiency for much smaller particles. Table III
shows that 67.4% of the aerosol particles were 0.6 ym or larger. It would
be expected that only a very small fraction of the aerosol would be particles
smaller than 0.3 ym. Then greater than 75% of aerosol particulate should
have been collected by the prefilters.

Microsorban filters which were the last collecting stage of the cascade
impactor system collected only a 2.15% average of the activity of the four
cascade impactor systems. The first stages of the cascade impactor systems
collected an average of 85.6% of the system activity. Therefore, most of
the 131I activity must have been associated with the larger particles.

The question then, is how could so much of the 131I activity have penetrated
the Microsorban prefilters of the filter pack systems (36.7%, 60.8%, 35.7%)
then to be collected by the AC.-1 filters? The 131I activity was put on the
DE aerosol in the form of stabilized Na131I.
19
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Examination of the Tempest sampler data (Table V) suggests that the same
thing may have happened there even though the Whatman 541 filter is known
to be less efficient than the Microsorban filter. The Whatman 541 filter
has a pore size of 3.4-5 ym. The average percent of the activity on Whatman
filters for the nine Tempest samplers was 48.9% and the average activity on
the charcoal cartridge was 50.5%. Again it would seem unlikely that so much
of the activity would penetrate the Whatman filter when such a large frac-
tion of the activity in the cascade impactor systems was collected in the
first stage (85.6%). The Whatman filter ought to have a very high efficiency
for the particles of the size collected by the first stage of the cascade
impactors.

Two explanations are offered as possible mechanisms by which some of the
prefilter 131I activity was carried off the prefilters then was subsequently
collected by the AC-1 filter of the filter pack system and by'the charcoal
cartridge of the Tempest system. Erosion of the DE particles on the pre-
filters to particles small enough to penetrate the prefilters then to be
collected efficiently by the AC-1 filter and the charcoal cartridge is
offered as one plausible mechanism. The oxidation of the I" (solid as Nal)
form of 131I activity to the I2 form by a reaction such as 41" + 02 + 2H20 •*•
40H" + 2I2 caused by the large volume of air being drawn through the pre-
filter is offered as another probable mechanism. The I2 formed by such a
reaction would be collected very efficiently by the Gelman AC-1 charcoal
filter. The latter mechanism is believed to be the more probable.

Extremes of deposition were about an order of magnitude apart and extremes
of integrated air concentration a factor of seven different. Deposition
velocities computed from the air filters and adjacent planchet; activity are
shown in Table V. Values range from 0.86 cm/sec to 2.34 cm/sec with a mean
of 1.6 cm/sec. Grouping the planchet deposition velocities into those
measured over alfalfa and those over Sudan grass gives means of 1.73 cm/sec
for alfalfa plot planchets and 1.4 cm/sec for Sudan plot planchets. A two-
tailed Students "t" test indicates no statistically significant difference
between the two groups at the 0.01 or 0.05 levels.9
20
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The ratio of activity per unit mass (dry weight) of vegetation measured on
the alfalfa to that measured on the Sudan is 2.65 (Table VII). Mean values
were 5.23 x 103 pCi/g for alfalfa and 1.98 x 103 pCi/g for the Sudan. Air
sampler measurements of integrated air concentrations for the samplers
closest to the location of the cutting samples give deposition velocities
of 2.42 cm/sec on the alfalfa and 2.68 cm/sec on the Sudan. Planchet
deposition velocities at these positions were 1.75 cm/sec and 2.08 cm/sec,
respectively.

Quantitative analysis of these differences requires determination of leaf
area to ground surface area ratios as a function of the height of the plant
above the ground and the distribution of radioactivity within the plant
canopy.

V. CONCLUSIONS

The method of preparing the aerosol by the vacuum drying procedure is a
satisfactory one and higher levels of activity could be prepared in the same
manner without exceeding the (MPC) in air for 131I in the preparation room.

An analysis of the experimental results indicates the need for:
1. An accurate method of determining a size to activity ratio. Glass
slides could be used much more effectively than fallout trays as they
allow for more accurate repositioning of the X-ray film with minimum
disturbance to the particles themselves.
2. A thorough knowledge of the efficiencies of the various components of
air sampling trains and other aerosol collection devices as a function
of environmental parameters, e.g., temperature, relative humidity, wind
speed, etc.
3. A further knowledge of meteorological factors and how they affect depo-
sition mechanisms.
4. A further knowledge of the behavior of particulate associated Na131I in
air streams.
21
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REFERENCES

1. Bioerwironmental Research 131I Dairy Cow Uptake Using a Two-Micron
Count Median Diameter Synthetic Dry Aerosol (Project Alfalfa) SWRHL-42r.

2. Black, S. C., Barth, D. S, and Engel, R. E. 131I Dairy Cow Uptake
Studies Using a Synthetic Dry Aerosol, SWRHL-28r.

3. Black, S. C., Stanley, R. E., Barth, D. S. Cow Milk 131I Levels Fol-
lowing Ingestion of Artificially Contaminated Fresh Alfalfa or Sudan
(Project HARE) SWRHL-61r.

4. Meteorological Data, Project HARE, September 18, 1968, ESSA, ARL-
Las Vegas, Nevada.

5. Whittaker, E. L. Report on Project HARE Aerosol Preparation and
Aerosol Generation, Memo to D. N. McNelis, September 20, 1968.

6. Report of Committee II on Permissible Dose for Internal Radiation
(1959), Pergamon Press, Oxford, p. 61.

7. Feret, L. R. Assoc. Int. pour 1'essai des Mat. 2, Group D, Zurich,
1931.

8. Lippmann, M. A Compact Cascade Impactor for Field Survey Sampling,
American Industrial Hygiene Association Journal, Vol. 22, October 1961,
p. 351.

9. Spiegel, M. R. Theory and Problems of Statistics, Schaum Publishing
Company, New York, 1961, Chapter 11, pp. 188-190.
22
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DISTRIBUTION

1 - 20 SWRHL, Las Vegas, Nevada

21 Robert E. Miller, Manager, NVOO/AEC, Las Vegas, Nevada

22 R. H. Thalgott, Test Manager, NVOO/AEC, Las Vegas, Nevada

23 Henry G. Vermillion, NVOO/AEC, Las Vegas, Nevada

24 Chief, NOB/DASA, NVOO/AEC, Las Vegas, Nevada

25 Robert R. Loux, NVOO/AEC, Las Vegas, Nevada

26 D. W. Hendricks, NVOO/AEC, Las Vegas, Nevada

27 Mail & Records, NVOO/AEC, Las Vegas, Nevada

28 Martin B. Biles, DOS, USAEC, Washington, D. C.

29 Director, DMA, USAEC, Washington, D. C.

30 John S. Kelly, DPNE, USAEC, Washington, D. C.

31 Daniel W. Wilson, Div. of Biology & Medicine, USAEC, Washington, D. C.

32 Philip Allen, ARL/ESSA, NVOO/AEC, Las Vegas, Nevada

33 Gilbert Ferber, ARL/ESSA, Silver Springs, Maryland

34 - 35 Charles L. Weaver, BRH, PHS, Rockville, Maryland

36 J. C. Villforth, Director, BRH, PHS, Rockville, Maryland

37 John G. Bailey, BRH, PHS, Rockville, Maryland

38 Regional Representative, BRH, PHS, Region IX, San Francisco, Calif.

39 Bernd Kahn, BRH, RATSEC, Cincinnati, Ohio

40 Northeastern Radiological Health Laboratory, Winchester, Mass.

41 Southeastern Radiological Health Laboratory, Montgomery, Ala.

42 W. C. King, LRL, Mercury, Nevada

43 John W. Gofman, LRL,. Liver more, California

44 Harry L. Reynolds, LRL, Livermore, California

45 Roger Batzel, LRL, Livermore, California

46 Ed Fleming, LRL, Livermore, California
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Distribution (continued)

47 Wm. E. Ogle, LASL, Los Alamos, New Mexico
48 Harry S. Jordan, LASL, Los Alamos, New Mexico
49 Arden E. Bicker, REECo. , Mercury, Nevada
50 Clinton S. Maupin, REECo. , Mercury, Nevada
51 Byron F. Murphey, Sahdia Labs., Albuquerque, New Mexico
52 R. H. Wilson, University of Rochester, New York
53 R. S. Davidson, Battelle Memorial Institute, Columbus, Ohio
54 Steven V. Kaye, Oak Ridge National Lab. , Oak Ridge, Tenn.
55 - 56 DTIE, USAEC, Oak Ridge, Tennessee
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