TRENDS IN THE GLOBAL DISTRIBUTION
OF TRITIUM SINCE 1961
L. L, THATCHER, B. R, PAYNE, and J, F. CAMERON
International Atomic Energy Agency, Vienna, Austria
ABSTRACT
A tritium project was organized in 1961 by the International Atomic
Energy Agency and the World Meteorological Organization, The latter
group is responsible for precipitation-sample collection in their worldwide network of 102 stations. Several conclusions from this project
have been reached.
Tritium levels rose from an average base of 80 tritium units
(T.U.) for continental sites in the northern hemisphere to average peaks
of 2000 T.U. in 1962 and 4000 to 5000 T.U. in 1963. Individual peaks
were higher, reaching 10,000 T.U. in northern Canada, Levels in pre-
cipitation were lower in 1964, The peakyear appears to have been 1963.
The rate of decrease from 1963 to 1964 is less than the comparable
period 1959 to 1961, possibly reflecting the higher altitudes involved in
the last testing.
Tritium and Sr deposition values over the globe show interesting
consistencies that may permit the estimation of tritium concentration
for unsampled areas. The HTO/**Sr ratio increases toward the high
mid-latitudes in the northern hemisphere.
The southern-hemisphere precipitation averaged only 15 T.U. in
1963 compared to several thousand tritium units for the northern
hemisphere.
It is estimated that in 1962 and 1963 the deposition of tritium had
been approximately 44 or 96 kg, depending on whether or not oceanic
exchange was included in the calculation. This would leave either 124
or 72 kg in the stratosphere based on the assumption of a 168-kg pro-
duction in 1961 and 1962.
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