The half-lives of three argon isotopes have been carefully determined, with the following results: Ar(37), 35.1 +/- 0.1 days; Ar(39) 269 +/- 3 years; Ar(42), 32.9 +/- 1.1 years. By combining the Ar(42) value with earlier data, a cross section of 0.5 +/- 0.1 barn is calculated for the reaction, with thermal neutrons, Ar(41)(n,gamma)Ar(42).

The principles and methods of mass-spectrometric detection of tiff-decay products and the theoretical purposes for such studies are discussed in detail. We report also the results of our new measurements on two tellurides, one native tellurium sample and one selenide. Concerning the decay Te13~Xe 13~ we have found that Xe 13~ in a native tellurium sample amounts to 67% of the total xenon with an absence of any other anomaly, which is an important improvement over previous measurements. --For the first time the decay SeS2P-P~KrS2 was studied by massspectrometry. A KrS2-excess was positively found in an copper selenide. A detailed discussion of all processes other than double ]/-decay which might contribute to the Xe 13~ and KrS2-anomalies is undertaken. It can be shown that these effects are small compared to the pfl-decay process. It can be said now positively that tiff-decay occurs in nature. Discussing all available data we obtained the effective half-life of Te 13~ to be 6 x 102~177176 y and that of Se s2 equals to 6 x 1019+0"3 y. The results are in agreement with the theoretical predictions for the 2v-tiff-decay. Nevertheless, no-neutrino pfl-decay is still possible. However, from the data we calculated that the leptonnonconservation is at most 0.7%. Diese Arbeit verfolgt zwei Ziele: Erstens soll ein Uberblick fiber die Methode und den gegenw/irtigen Stand des massenspektrometrischen Nachweises yon flfl-Zerfallsprodukten gegeben werden.Zweitens soll fiber unsere neuen MeBergebnisse berichtet werden.Dabei wird auBer dem Zerfall Te13~176 erstmals auch der Zerfall SeS2-p-P-~Kr s2 behandelt.

Cosmic rays and nuclear explosions are adding radioactivity to the atmosphere from which it is then removed by rainfall. The investigation of these activities furnishes a means of obtaining new information of significance in geological problems as well as in the understanding of the hazards of nuclear fallout. Chlorine‐36 is an interesting isotope for such a study as it has a relatively long half‐life, 308,000 years, and at the same time is very soluble in water. Relatively high levels of Cl36 activity have been found in rain. The levels are several orders of magnitude above the level to be expected from cosmic‐ray production. The Cl36 is almost surely the result of neutron irradiation of sea water by nuclear explosions.

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