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 ${\mathrm{V}}^{50}$ and ${\mathrm{Ta}}^{180}$. Some positive evidence is obtained that ${\mathrm{V}}^{50}$ decays by $K$ capture to the 1.58-Mev excited state of ${\mathrm{Ti}}^{50}$ with a half-life of (4.8\ifmmode\pm\else\textpm\fi{}1.2)\ifmmode\times\else\texttimes\fi{}${10}^{14}$ yr. A search for titanium $K$ x-rays gave negative results. For ${\mathrm{Ta}}^{180}$ a lower limit of (2.3\ifmmode\pm\else\textpm\fi{}0.7)\ifmmode\times\else\texttimes\fi{}${10}^{13}$ years was found for the half-life against decay by $K$ capture and a lower limit of (1.7\ifmmode\pm\else\textpm\fi{}0.6)\ifmmode\times\else\texttimes\fi{}${10}^{13}$ years against beta decay.