Neubestimmung der natürlichen irdischen Tritiumzerfallsrate und die Frage der Herkunft des „natürlichen“ Tritium

Abstract

The terrestrial decay rate of “natural” tritium has been re-determined from measurements of the tritium content of old snow samples from Greenland. The finding by CRAIG and BEGEMANN and LIBBY has been confirmed that the tritium decay rate is about 10 times higher than was anticipated previously. Two mechanisms to explain the discrepancy are discussed, a) production by the low energy component of the cosmic radiation and b) the accretion of solar tritium by the earth, as suggested by FELD and ARNOLD. It is shown that in case all the tritium is produced by cosmic radiation the tropospheric production rate may be expected to vary in antiphase with the sunspot cycle, whereas in case of accretion of solar tritium by the earth the variation should be in phase with the sunspot cycle. In both cases a phase shift between the stratospheric production rate and the amount of tropospheric tritium is to be expected because of the residence time of tritium in the stratosphere. A measurement of the phase shift should allow to determine this residence time. The data obtained on the Greenland samples appear to show such a variation of the production rate. The results can be explained best by assuming that all the tritium is produced by cosmic radiation. This result, however, is only preliminary. More systematic measurements are required to decide between the two possibilities.