Radioactive Decay ofPm143,Pm144, andPm146

Abstract

The decay of ${\mathrm{Pm}}^{143}$, ${\mathrm{Pm}}^{144}$, and ${\mathrm{Pm}}^{146}$ has been studied with permanent magnet spectrographs, an intermediate-image beta spectrometer, and scintillation counters. Results on the electron-capture decay of ${\mathrm{Pm}}^{143}$ and ${\mathrm{Pm}}^{144}$ confirm the findings of previous investigators. The results of gamma-gamma directional correlation measurements are consistent with the spin assignments for the ${\mathrm{Nd}}^{144}$ levels made by Ofer. ${\mathrm{Pm}}^{146}$ (${T}_{\frac{1}{2}}\ensuremath{\sim}710$ days) is found to decay both by beta emission to a level of 749 kev in ${\mathrm{Sm}}^{146}$ and by electron capture to levels of 453 and 1198 kev in ${\mathrm{Nd}}^{146}$. The percentage branchings are 35%, 35%, and 30%, respectively. Gamma-ray transitions of 453 and 745 kev in cascade in ${\mathrm{Nd}}^{146}$ and 749 kev in ${\mathrm{Sm}}^{146}$ are observed. The end-point energy for the beta-decay branch is measured to be 779 kev. Directional correlation and internal conversion coefficient measurements are most consistent with a 3+ assignment for the 1198-kev level in ${\mathrm{Nd}}^{146}$, with a 2+ assignment being possible, but less likely, since the cross-over transition is absent or extremely weak.