Table t. Activity levels measured in New York City during 1959 (sotopic activines are reported as
of the end of the sampling month. Totai beta activity estimates are reported as of the counting dale
(in parentheses).
Activity leveis (me /mi2)
Sampling
month
Seve
Cs
Jan.
Feb.
1,00
1.81
1.60
3.36
Mar.
Apr.
May
June
- 4.45
4.16
~ 1.52
2.43
6.58
6.93
190
3.46
July
0.52
0.88
Sept.
Oct.
Nov.
Dec.
~ Olt
0.39
0.54
- 0.§2
0.20
0.6!
0.51
0.43
Aug
Total deposition
= 0.65
0.88
Ruiee
48
56
13
Cette
Zr*s
30.9
49.0
-8L.7
- 88.6
19.4
-thg
36.0
83.1
31.3
5.69
1,24
19
2.70
(64
2.53
17.9
27.3
320
36.1
48.5
275
790.0
“79.4
15.7
Sr
36.3
31.3
6.
3197
8.03
8.01
256
<0.78
[of
$0.33
$0.24
$0.1?
$0.2
$0.36
$0.17
S0.16
419
221
223
$0.49
From estimated radiotungsten yields
Wiss
22.4
16.9
18.4
9.84
4.69
3.05
0.94
<0.50
$0.20
$0.4
<0.42
<0,068
83.8
for the Hardtack series (6, 8) and
Gross activity
24t
229
356
413
(6 Feb. 59)
(23 Mar. 59)
(29 Apr. 59)
(5 May $9)
78.7 (9 June 59)
97B
(t3 July
59)
210 (10 Aug. 59)
23.3 (8 Sept. 59)
406
8 30
5.96
7.54
(12
(24
(15
(13
Oct.
Nov
Bec.
Jan.
59)
59)
59}
60)
1480
Activity
level on
J) Dee.
1959
it possible to identify coneributions to
total fallout from these sources with
some degree of accuracy.
measured fission-product yields (atoms
per fission) for thermonuclear weapons
in general (/9), the Sr*/W™ and Sr*/
W" ratios at an assumed mean production date of 1 June 1958 are estimated
to be 0.00380 and 0.436, respectively.
Monthly depositions of Sr in New
York City from Hardtack aré calculated
directly from measured W™ levels by
extrapolation of the Sr*/W™ produc-
tion ratio to the reporting dates for the
fallout measurements. Levels of Sr®
from
28.1
5.63
9.8
542
nuclides. Emission energies, decay constants, and other pertinent decay-scheme
characteristics were taken from the listings of Strominger, Hollander, and Seaborg (/6). The radiation sources are
assumed to be evenly distributed over
an infinite plane, and no corrections are
made for weathering, shielding, Compton scattering, or the effects of the
ground-to-air interface.
The beta-radiation counters used
were standard end-window GeigerMiiller tubes surrounded by anti-coincidence rings and shielded with mercury. The gama-radiation instrument
was a 3- by 2-inch sodium iodide
scintillator equipped with a transistorized single-channel analyzer (/7).
Monthly fallout activity levels measured during 1959 are listed in Table 1.
Each value is the mean of at least two
determinations. The Zr”, Sr*, and W™
concentrations were considered undetectable after August, June, and July,
respectively, when the counting error,
expressed as one standard deviation,
exceeded the apparent counting rate.
In other cases, the relative percentage
of uncertainty due to counting factors
averaged 3 percent and ranged from
2.1 to 12 percent of the activities reported. The total depositions were ob-
and 1.5 curies, respectively, of beta
activity per square mile were deposited
in New York City during 1958 and
1989 The predominance of shorterlived nuclides noted in 1958 continued
through the first half of 1959, with the
result that the effects of radioactive decay reduced the two years’ total deposition by a factor of 10 by the end of
1959,
and correcting for decay during the
sampling period (9).
The activity
levels shown to exist at the end of 1959
Kingdom, and United States test series
tained by summing the monthly levels
include totals previously reported for
the end of 1958, corrected for decay
through the end of 1959. The cumulative gross activity estimate for 1958
was obtained by assuming 2 mean production date of 30 June 1958 and
correcting for decay by the T'? law
(/8). The decay corrections for the
1959 monthly increments are the results
of actual measurements described in
the ruthenium analyses.
Since the counters used were not
sensitive enough to detect the less energetic beta emitters, the gross activity
estimates are probably low, and more
representative of activities with energies
in excess of 0.3 Mev. However, these
levels do show that at least 5.1 (9)
other
sources
It is generally conceded that delayed
fallout is primarily of stratospheric
origin and that the mean atmospheric
residence time of weapon-test debris
is from one to three years, depending
on testing conditions (5, 6). It follows
veowucrion gare (s2°*/sa" crag re
’
J
0.
‘
‘A
%
s
x
e
<
3
t
‘.3
L
®
z
';
=
z
\
\
+e
Yo wssseree
|e coreetgree
New York City fallout reported in
Table 1! are limited to Soviet, United
54
by
before June 1958. The increases in the
Tatio observed during the summer
months of 1958 are attributed to the
arriva] in New York City of mixed
debris. The compositions of these mixtures are determined by extrapolating
the ratio curve for the earlier measurements through the middle of 1959 and
that the possible major sources of the
conducted during 1957 and 1958.
Although the sensitivity of debris dating methods is lessened by consideration of monthly collections rather than
individual rainfalls, the production of
W'S in the United States Hardtack
series and the cessation of testing after
the Soviet series of October 1958 make
obtained
éarly 1958 testing in samples taken
\
Age and Origin of Debris
are
subtracting the Hardtack Sr™ and similarly determined Sr” fractions from the
total isotopic concentrations and analyzing the Sr*/Sr™ ratios calculated for
the non-Hardtack debris.
The interpretation of these ratios is
illustrated in Fig. 1. The clearest indication of debris age occurs in the 1959
ratios, which uniformly show the Soviet
series of October 1958 to be the predominant source. A second trend indicates contributions from Jate 1957 and
'
eae
t
+9o8
TamPlLin®
Fig.
1.
Fallout’
2039
‘e
oare
from
non-Hardtack
sources in New York City during 1958
and 1959; Sr®/Sr* ratios, corrected for
calculated
Hardtack
concentrations,
are
used. Most of the 1958 data are taken
from the report of Welford and Collins
(9). Strontium-89 values for the first
three months of 1958 are taken from the
datu summuries of Hurdy ef a/. (2).