Beta-Spectra of Forbidden Transitions

The beta-spectra of the forbidden transitions of ${\mathrm{Y}}^{91}$, ${\mathrm{Sr}}^{89}$, ${\mathrm{Y}}^{90}$, ${\mathrm{Cs}}^{137}$, RaE, ${\mathrm{Au}}^{198}$, ${\mathrm{Re}}^{186}$, and ${\mathrm{P}}^{32}$ have been measured with thin sources and high resolution. Forbidden type spectra are found for the first five. ${\mathrm{Au}}^{198}$, ${\mathrm{Re}}^{186}$, and ${\mathrm{P}}^{32}$ yield spectra with the allowed shape. Evidence is advanced for the reliability of the nuclear shell structure model and for the validity of G.-T. selection rules. End points found are: ${\mathrm{Y}}^{91}$, 1.537±0.007 Mev; ${\mathrm{Sr}}^{89}$, 1.463±0.005 Mev; ${\mathrm{Y}}^{90}$, 2.180±0.007 Mev; ${\mathrm{Cs}}^{137}$, 0.51±0.01 Mev; ${\mathrm{Au}}^{198}$, 0.956±0.005 Mev; ${\mathrm{Re}}^{186}$, 1.063±0.006; and ${\mathrm{P}}^{32}$, 1.689±0.01 Mev.