Radioactivity ofSm153andEu155

The radiations from ${\mathrm{Sm}}^{153}$ and ${\mathrm{Eu}}^{155}$ have been studied by means of a 180-degree, magnetic-focusing, variable-field beta-ray spectrometer-spectrograph using enriched materials. In the disintegration of 47.0-hr ${\mathrm{Sm}}^{153}$, conversion electrons of three gamma rays of energy, 0.0691, 0.1027, 0.548 Mev, and three beta-ray spectra whose end-point energy and relative intensity were 0.255 Mev, 9 percent; 0.685 Mev, 70 percent; 0.795 Mev, 21 percent, respectively, were observed. A fourth beta-ray spectrum of end-point energy 0.62 Mev and intensity less than 6 percent is postulated. A decay scheme in good agreement with these data and with nuclear shell theory is proposed in which spin and parity have been assigned to all levels. The discrepancy between the magnetic moment measurement and the requirements of shell theory as to the parity of the ground state of ${\mathrm{Eu}}^{153}$ has been resolved in favor of shell theory. In the disintegration of ${\mathrm{Eu}}^{155}$ two beta-ray spectra of end-point energy 0.152 and 0.252 Mev and relative intensity 84 percent and 16 percent, respectively, and conversion electrons of four gamma rays of energy 0.0593, 0.0858, 0.1045, 0.1309 Mev were observed, in agreement with earlier work. Weak conversion-electron lines attributed to gamma rays of energy 0.0187 and 0.1368 Mev were also observed.