An interesting observation was made independently by a British
group during the summer of 1954 in flying aircraft over England at
various altitudes.
It is not known exactly how the samples were col-
lected, but the assumption is made that they were obtained in a manner
similar to those obtained by our jet aircraft as mentioned above.
Their
data are:
TABLE }
(fect)
3
1,600
11,000
18,500
27,000
35,000
40,000
4,000
48,000
Fissions/Kg Air
(x10°)
Fissions/Cu. M. Air
(x10°)
58
70
41h
475
1,632
2,388
1,400
1,600
9,320
3,460
2,808
1, 400
33,714
9,900
85,145
131,814
20,650
26,400
This group by some method of extrapolation has estimated that
fission products from 20 M? fission yield, with several Mf in the
troposphere, are present in the total atmosphere.
There are therefore
at least some qualitative data available which tend to show the presence of low levels of radioactivity due to fission products in both the
stratosphere and the troposphere.
The New York Operations office of the Atomic Energy Coumission has
been sampling fall-out at the earth's surface for the past five years.
The method has been to place gummed paper, one foot square, at many
points in the United States and at several locations throughout the
world.
The sample points in the United States are at Weather Bureau
Stations and Atomic Energy Commission installations, while our foreign
samples are taken lergely at embassies and legation buildings.
There are 41 sampling stations in the United States where about
250,000 samples have been collected since 1951.
The number of samples
from foreign stations is much lower than this and many of the stations
aT