Natural Radioactivity of V50 and Ta180

The methods of proportional counter and scintillation spectroscopy have been used to examine the possible radioactivity of the naturally occurring nuclides V50 and Ta180. Some positive evidence is obtained that V50 decays by K capture to the 1.58-Mev excited state of Ti50 with a half-life of (4.8±1.2)×1014 yr. A search for titanium K x-rays gave negative results. For Ta180 a lower limit of (2.3±0.7)×1013 years was found for the half-life against decay by K capture and a lower limit of (1.7±0.6)×1013 years against beta decay.