146
HAINES AND MUSGRAVE
Recent
results
of
Begemann®
show
that the T/H ratio in the
northern-hemisphere methane has been essentially constant from 1958
to 1963; during this time the tritium content of atmospheric hydrogen
increased by a factor of 2 to 4. This observation makes it seem most
probable that the tritiated methane was of synthetic origin and not due
to the incorporation of HT into methane in the atmosphere.
A final determination of the source of tritium in methane may not
be possible; it will be apparent, however, that there are sufficient
sources in the nuclear industry to account for the increase in the T/H
‘yatio in atmospheric hydrogen prior to 1952 and that these same
sources were releasing tritiated methane during this period, Although
the methane and the HT may be from a common or a Similar source,
there is no particular significance to be given to an apparent exponential T/H increase in methane or hydrogen in the northern hemisphere.
CAUSE OF THE T/H INCREASE
IN ATMOSPHERIC HYDROGEN PRIOR TO 1952
Fairly detailed information is available from the tritium produc-
tion techniques employed at Los Alamos Scientific Laboratory.'* The
system involved a thermal-diffusion column that included seven massspectrometer leaks for controlling the feed and for withdrawing tritium
from the column. The combined leak total was about 10 ml of tritium
per day, mostly as T,. The depleted tritium was reprocessed, with the
depleted fraction from the second cycle being exhausted into the atmosphere. At the minimum estimated rate of operation of the system, the
reprocessing released another 10 mi of tritium per day. It is stated
that the final stripped product was “vented with safety.” It can be as-
sumed that the vacuum systems connected to the mass spectrometers
and those used for final sample storage were vented in a like manner.
The rate of tritium release estimated for this thermal-diffusion
column fits the increase in the T/H ratio reported for hydrogen be-
tween 1949 and 1952. Examining this rate of release from a different
approach, we can estimate the minimum amount of tritium that even-
tually must have been released by the time of the 1954 Operation Castle
test series. For the production system to release the amount of tritium
that was estimated to have been released by the Ivy and Castle tests,
the minimum amount released should have been 9 to 12 g. This corre-
sponds to a T/H ratio of approximately 0.2 to 0.3 x 10° tritium units
(T.U.) as of 1954. The amount released may have been as high as 22 g;
this would give a T/H ratio of 0.5 10° T.U. for the 1954 level. The
values measured® were in the range of 0.4 to 1.2 x 10° T.U. for 1954
and 1955. The highest of these values was from a sample taken before
the Castle test series.