648
THATCHER, PAYNE, AND CAMERON
electrolytic enrichment for samples of lower concentration such as
from the southern hemisphere. Occasionally, liquid scintillation counting is used for some very hot samples.
The procedure for the preparation of water samples is vaporization of 5 ml of water through a vacuum furnace containing hot magnesium turnings and reaction of the resultant hydrogen with ethylene
to produce ethane (platinum—palladium catalyst). Ethylene is used to
produce the ethane rather than acetylene, which has a higher tritium
reaction capacity, because acetylene with the necessary low background has not yet been found in Europe. The ethane is then counted
under proportional conditions in a low-background counter (anticoin-
cidence and mass Shielding). Two counting systems are used to provide
intercomparison and cross-checking of results.
Electrolytic enrichment is usually 10-fold. This is achieved by
electrolysis from 250 to 15 ml under the conditions outlined in Ref. 1.
Recently it has been shown’ that both the reproducibility and the per-
cent of tritium recovery can be improved by the use of steel cathodes
treated with phosphoric acid. The phosphoric acid forms a protective
coating on the steel that apparently provides a superior surface for the
tritium—protium fractionation. The treatment produces a gray-brown
surface that becomes covered with a fine, adherent black deposit on
electrolysis. The black deposit (presumably finely divided iron) is
never disturbed. It reaches a maximum thickness after a few electrolyses and then apparently does not change. The enrichment of
tritium becomes constant to within an average of +4% after the black
deposit has stabilized.
Tritium Production
Figure 1, which is an extension of a figure given by Martell,®
reviews the tritium production and its effect on the hydrosphere since
1953, Tritium production history is shown in the upper graph, and the
response of the hydrosphere is illustrated in the lower graph by the
Ottawa tritium precipitation record as given by R. M. Brown of Chalk
River.
The plot represents quarterly averages obtained from the
Ottawa data for individual rains in the Tritium Water Lists.’ Tritium
production has been calculated on the basis of Leipunsky’s estimate of
0.7 kg of tritium per megaton of fusion. World tritium inventory in the
summer of 1961 was estimated to be approximately 40 kg. The 1961
testing is estimated to have increased the levelby approximately 68 kg,
and the 1962 testing, by approximately 100 kg. Thus by the end of 1962
the world tritium inventory is estimated® to have reached approxi-
mately 200 kg.