Small-Order Effects in Beta Spectra

An intermediate-image spectrometer and a thin-lens spectrometer were used to examine carefully the beta spectra of ${\mathrm{P}}^{32}$, ${\mathrm{K}}^{42}$, and ${\mathrm{As}}^{76}$. The ${\mathrm{P}}^{32}$ beta spectrum was examined for a Fierz-type deviation, and within the experimental error none was found. The value of the parameter $r$, describing the magnitude of the Fierz deviation as defined by Davidson and Peaslee, was found to be 0.00±0.03. The first forbidden transitions with $\Delta I=0\mathrm{}$, "yes" of ${\mathrm{K}}^{42}$ and ${\mathrm{As}}^{76}$ were examined for deviations from a linear Kurie plot. Within experimental error no deviations were found. From the shape factors calculated by Mahmoud and Konopinski on the basis of an STP combination, one would expect deviations for these first-forbidden transitions if the best previous estimate of certain parameters are correct. A deviation of the ${\mathrm{K}}^{42}$ Kurie plot below 500 kev was attributed to an additional beta group.