GAMMA RADIATION FROM DEPOSITED FISSION PRODUCTS
241
worthy that during the 1962 and 1963 surveys the fallout-gamma levels
were a Significant fraction of the total. Dose rates of 3 to 4 ur/hr
seemed to be typical of the eastern United States during this period.
The highest fallout levels were observed during the spring and sum-
mer of 1963, with dose rates of 4 to 6ur/hr at a number of locations
scattered throughout the eastern states. The 1964 measurements, limited to the northeastern states, all indicate greatly reduced fallout
levels, averaging 1 ur/hr, with '*’Cs replacing 57 r—Nb as the main
contributor,
These apparently rather significant changes in typical fallout-
gamma-radiation fields during the past two years have been followed
closely at three locations in Westchester County, N. Y., separated by
distances of approximately 5 miles from one another. The measurements at these locations all show comparable variations with time, the
fallout-gamma dose rates remaining roughly constant at 5 ur/hr from
May to September 1963 and then declining with an apparent half-life
slightly longer than that for the previously dominant *Zr—**Nb. By the
end of 1963, the levels were down to 1yur/hr and have remained close
to that value throughout 1964, It is interesting to note that these Westchester County measurements are in very close agreement with the
dose-rate values calculated from detailed deposition data for the various fallout gamma emitters obtained at Westwood, N. J., approximately
15 miles to the west.’”
The complete data for the Pelham, N. Y., location are given in
Table 3. The agreement between the two fallout estimates is generally
Table 3— MEASUREMENTS AT PELHAM,N,Y.
Gamma dose rates, ur/hr
U
Th
Total
natural
Fallout i
Fallout 2
Total
2.8
3.0
2.9
2.5
1.5
1.0
1.2
1.2
3.6
3.3
3.4
3.4
7.9
7.3
7.5
7.1
7.2
4,9
5.7
4.8
4.6
5.1
5.8
5.1
2.5
2.3
1.6
1.7
2.9
3.6
7.0
7.6
6.5
5.3
5.1
4.1
2.39
2.4
1.2
1.2
3.4
3.0
6.9
6.6
2.3
2.3
2,4
2.6
12.5
12,4
13.3
12.2
11.6
12.1
11.7
11.3
10.3
9.3
9.2
Jan, 22
Apr. 17
2.1
1.3
2.6
6.0
1.3
1.8
7.8
7,8
May 8
duly 21
2.4
2.1
$1.7
1.4
3.1
2.6
3.2
3.4
7.2
6.1
7.1
8.2
1.2
1,4
1.1
1.1
1.1
1.6
8.3
7.7
Oct, 21
2.1
1.4
2.8
6.3
0.9
0.8
0.4
1.2
7.5
Nov. 27
2.1
1.4
2.8
6.3
1.0
1.0
7.3
K
1963
May 3
May 13
May 27
June 24
July 26
Aug. 6
Aug, 26
Sept. 12
Sept. 27
Oct, 29
Nov, 20
1964
Aug. 12
Sept, 25
Nov, 2
2.7
3.1
2.3
1.2
1.7
1.7
3.0
7.0
ll
0.7
8,2
8.9
7.4