Decay of Gadolinium-159

Abstract

The decay of ${\mathrm{Gd}}^{159}$ has been studied with the aid of a thin magnetic lens beta-ray spectrometer and coincident scintillation spectrometers. Two principal beta-ray groups, with the end-point energies 580\ifmmode\pm\else\textpm\fi{}10 and 940\ifmmode\pm\else\textpm\fi{}15 kev have been observed to decay with the 18-hour half-life of ${\mathrm{Gd}}^{159}$, revealing energy levels in the residual nucleus, ${\mathrm{Tb}}^{159}$, at 56, 136, and 361 kev. The coincidence measurements gave evidence of a third beta component, with the end-point energy of 880\ifmmode\pm\else\textpm\fi{}20 kev, coincident with the 56-kev gamma ray. The intensities of the three components (580\ifmmode\pm\else\textpm\fi{}10, 880\ifmmode\pm\else\textpm\fi{}20, and 940\ifmmode\pm\else\textpm\fi{}15 kev) have been estimated to be approximately 20, 6, and 74%, respectively. Internal conversion coefficient measurements indicated the 361-kev gamma ray to be a mixed ($M1$ and $E2$) transition.