fell than could be contained in the
tanks and much waslost through overflow. The results are based on the
water remaining in the tanks at the end
of the collection period.
Floccing procedure. The rainwater
in the tanks was stirred with a jet of
compressed air and a solution of alumi-
num sulfate was added to make the
final
concentration
about
0.2
gm
Al.(SO4)3:18 HO per gallon of water.
The pH was adjusted to 7.0 + 0.1
with a sodium carbonate solution using
LaMotte standards with bromthymol
blue indicator. Stirring was continued for 45-60 min and the treated
water allowed to settle undisturbed
overnight. After settling, the clear
supernate was removed by syphoning
and the Al(OH); floc transferred to
glass bottles for further settling and
concentrating. The floc from 1,000
gal of water could generally be concentrated to a volume of 2-5 gal.
This procedure has been checked by
adding 50-100 mg of soluble lead and
bismuth salts to 100 gal of water and
then collecting them with aluminum
hydroxide floc as described above. At
the concentrations used (0.6-1.1 * 10-8
mole/liter}, recoveries were about
70-90%, including all losses due to
separation of the floc and chemical
separation of the material.
Chemical procedure. The floc samples were boiled with hydrochloric acid
(1:4) and filtered from anyinsoluble
residue. In some cases this residue
was further treated with nitric, sulfuric,
and hydrofluoric acids and analyzed
separately. This treatment was discontinued wheninsignificant quantities
of RaD, RaE, and Po activities were
found to be associated with this
material.
Carriers equivalent to about 75 mg
each of BizO; and PbSO, were added
to the solutions and equilibrated with
the radioisotopes. Standard procedures for separating bismuth and lead
were used. The separated materials
were redissolved and reprecipitated to
improve the radiochemical purity.*
The time of separation was noted and
the samples ignited, weighed, and
from the analysis of a few rainwater
samples collected at Washington, D.C.,
are shown in Table 1. The identity of
the RaD (22-yr Pb?!") was established
by following the rate of buildup of Rak
(5-day Bi*!°) in the lead fraction. The
RaE contained in the bismuth fraction
deeayed with a 5-day half-life. Some
a-activity due to Po#!® was invariably
found in the bismuth fractions. The
separation of Po?! in earrier-free condition gave activities as high as 5,000
dpm from several collections; however,
this procedure was not employed
routinelysince it gave only qualitative
results.
A number of studies were made on
the distribution of the RaD in different
Vol-
Location,
date collected
(1960)
Glenview,Ill.
Jan.
Jun, 2-3
Jun, 24-30
Jul. 6-19
Panama
Mar, 7-14
Mar, 16—Apr. 24
May 18-27
Rainfall (in.)
1.6 (squall)
Flash showers
1,23 (showers)
0.48
15.96 (continuous)
Jun. 28-Jul. 20
10.78
Jul. 20-Aug. 14
16.17
Nov. 24-Dec. 15 20.27
Jan. 5-Feb. 6 (51) 1.75
Hawaii
Mar. 8—Apr. 7
May 2-Jun. 12
Aug. 13-Sep. 18
Sep. 18-Dec. 11
Philippine Islands
May 4-25
Jul. 4-Aug. 2
Aug. 2-30
Oct. 3-25
Oct. 30-Nov. 30
Samoa
Apr. 1-30
May 1-31
Jun, 1-30
Jul. 1-31
Aug. 1-31
(continuous)
(continuous)
(continuous)
(showers)
insoluble material and the highest concentration of activity.
Collections of RaD activity made at
a numberofdifferent sites are compared
in Table 3. Some variations are to be
noted at each site though they are not
as great as the differences between col-
lections at different locations.
Rain-
water collections from inlandsites such
as Glenview, Ill., and Washington,
D.C., exhibit the highest concentration
265
Insol-
uble
residue
(gm)
*
Car-
rier
recovery
(%)
89
B-activity of Bi20,
fraction}
dpm dpm/gal
6,600
25
564
563
38.9
95
76
13,100
413,700
23
24
563
6.6
22
5,640
10
170
0.1
102
500
0.3
87
250
500
500
500
500
0.8
470
dpm/gal
(avg)
21
2.8
96
2,270
*
0.5
4.5
*
101
96
79
83
1,920
1,210
1,070
1,130
3.8
2.4
2.1
2.3
3
600
9
1.2
107
100
89
90
1,310
7200
4,890
5,340
3.3
«2.1
12
18
)
shuwers
continuous
cont. for 2 wk
showers
showers
270
270
270
270
270
*
*
*
*
3.4
152
108
143
94
94
2,090
2,070
2,280
3,060
3,000
8
8
8
11
11
9
daily
400
96.5
204
2,960
daily
daily
daily
daily
400
400
400
400
verted to decomposition rates by applying appropriate geometry corrections,
Oct, 23-Nov. 6
Dec. 5-27
0.4 (scattered)
2.1 (scattered)
Kodiak, Alaska
ume
collected
(gal)
*
0.2
5,0
3=16.7
2.3
3.3
1.9
7.6
* At times when fission-product activity
is present in the sample, further radiochemical purification of these fractions is
required.
eral, however, the first portion of the
rain contains the greatest amount of
400
350
400
300
Jun. 6-19
Jun, 19-Jul. 5
Jul. 7-17
Sep. 11-25
Some of the data resulting
concentration of activity in the sample
and quantity of dirt, character of the
rain, or time between rains. In gen-
showers
showers
showers
continuous
Sep. 1-30
Results.
There
TABLE 3—Distribution of RaE in Rainwater at Various Locations
mounted on plastic planchets for count-
ing. The counting rates obtained by
use of standard techniques were con-
portions of the rain (Table 2).
seems to be no correlation between the
daily
(scattered)
(scattered)
(scattered)
(continuous)
7.4
0.7
0.4
106
90
92
97
95
1,010
400
500
500
500
4.8
1.7
6.8
1.0
90
107
100
89
2,620
2,300
1,550
3,450
6.5
4.6
3.1
6.9
500
500
5.5
4.0
89
101
6,350
2,590
12.7
5.2
400
*
4.5
* Residues dissolved completely by wet ashings and fusions.
Tt Corrected to time of Pb-Bi separation.
330
290
460
170
6=6—0..8
0.7
1.1
(0.4
2.5
2
6.5