Decay Constants ofK40
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Abstract
New measurements have been made of the decay constants of ${\mathrm{K}}^{40}$ for beta-ray emission and for electron capture, and a decay scheme is proposed on the basis of these measurements and the previous data. Special counters adapted to the measurement of low levels of activity were developed for making the measurements. The results obtained were 28.3\ifmmode\pm\else\textpm\fi{}1.0 beta-rays per gram of K per sec. and 13.5\ifmmode\pm\else\textpm\fi{}4.0 electron captures per 100 beta-rays, corresponding to a total half-life of 12.7\ifmmode\pm\else\textpm\fi{}0.5\ifmmode\times\else\texttimes\fi{}${10}^{8}$ yr., with 88 percent of the decays by beta-ray emission and 12 percent by electron capture. A previous measurement of the gamma-ray intensity in ${\mathrm{K}}^{40}$, by the present authors, gave 3.6\ifmmode\pm\else\textpm\fi{}0.3 gamma-rays per gram of K per sec., or about 12.7 gamma-rays per 100 beta-rays. Since the numbers of gamma-rays and of electron captures in the decay of ${\mathrm{K}}^{40}$ are essentially the same, and since previous measurements indicate that the gamma-energy is greater than the beta-energy, it is proposed that the gamma-ray be associated with the electron-capture decay, a gamma-ray following each electron capture.