CHEMICAL STATE OF TRITIUM IN THE ATMOSPHERE
147
If one assumes that sources other than those in the United States
were releasing tritium during the period 1950 to 1955, the release
curve_should turn upward. When similar release rates are assumed for
such other tritium-producing laboratories, a value of 0.4 to 1.5 x 10°
T.U. is obtained for a total of two or three of these laboratories. The
tritium released in the early tests then is superimposed on a level
that already has been made fairly high by 1953.
Unknown factors in the estimation of the amount of tritium re-
leased from all sources are the starting dates for the releases and the
period of time over which they occurred. Also unknownis the relative
rate of release from the laboratories outside the United States. The
Significance of accidental releases of large amounts of tritium cannot
be determined. Robinsonet al.'® refer to “accidents releasing appreciable quantities of gaseous tritium.” However, a given size release
would have a greater significance for the T/H levels observed in hydrogen prior to
1953 than would the same amount if released at the
present time. These uncertainties are probably no greater than the
rather large errors in the present estimation.
The quoted value of 15 kg of tritium released during the Ivy and
Castle tests is based on an estimated value for a rate of release per
megaton of nuclear energy.’ These release-rate values must depend,
in a manner not well defined, on the composition of the nuclear devices exploded. It is entirely possible that the tritium level in 1953 and
1954 was due to releases by the production systems only.
At this point at least three different conclusions are possible: (1)
the Ivy and Castle tests did not release significant amounts of “un-
burnt” tritium as HT, (2) the total tritium released in these series was
actually much less than the estimated 15 kg (operating at maximum
capacity, the thermal-diffusion column at Los Alamoscould have pro-
duced 15 kg in the 5.5 years considered between 1949 and 1954); and
(3) perhaps the production systems and the bombtest each might have
released approximately equal amounts of HT.
SOURCES OF ATMOSPHERIC TRITIATED METHANE
In their description of the tritium-production system, Robinson
et al.!° show a mass-spectrum curve for the impurities observed in
tritium handled in a system containing stopcocks and vacuum grease.
These impurities include OH*t, H,O*+, OT*, T,O+, and CTf. The state-
ment “at somewhat lower isotopic purity a CHT, ion of mass 22 appears, etc.” is made. An all-metal system that employed Kel-F seals
was constructed to avoid these impurities. Although this did eliminate
the problem of labeled hydrocarbons appearing in the tritiumproduction system, it did not eliminate the release of tritium-labeled
molecules, particularly methane, into the atmosphere.