Shapes of Allowed and Unique First-Forbidden β-Ray Spectra: In114, K42, Rb86, Sr90, and Y90

Abstract

The $\beta$-ray spectra of ${\mathrm{In}}^{114}$, ${\mathrm{K}}^{42}$, ${\mathrm{Rb}}^{86}$, ${\mathrm{Sr}}^{90}$, and ${\mathrm{Y}}^{90}$ (ground-state transitions) have been measured with the Heidelberg double-lens spectrometer. The allowed spectrum of ${\mathrm{In}}^{114}$ was found to have a purely statistical shape; the coefficient $b$ of a possible $\frac{b}{W}$ term turned out to be $b=(0.5\mathrm{}\pm 2.2)\times {10}^{-2\mathrm{}}m{c}^2$. The unique first-forbidden spectra of ${\mathrm{K}}^{42}$, ${\mathrm{Rb}}^{86}$, ${\mathrm{Sr}}^{90}$, and ${\mathrm{Y}}^{90}$ were found to show very small but definite deviations from the simple unique shape.