Reinvestigation of the Decays ofEu146andPm146and the Existence of Two Close-Lying States at ≈1381 keV inSm146

Abstract

The decays of ${\mathrm{Pm}}^{146}$ and ${\mathrm{Eu}}^{146}$ have been reinvestigated with the primary purpose of establishing the character of the second excited state previously reported at 1384 keV in ${\mathrm{Sm}}^{146}$. Gamma-gamma directional correlation data obtained from studies of both the beta decay of ${\mathrm{Pm}}^{146}$ and the electron capture and positron decay of ${\mathrm{Eu}}^{146}$, along with the $K$-shell internal-conversion-coefficient data, establish the existence of two close-lying states in ${\mathrm{Sm}}^{146}$ at 1380.7 and 1382.0 keV with spins and parties 3- and 4+, respectively. The gamma-ray spectra were studied with a lithium-drifted germanium detector. In the beta decay of ${\mathrm{Pm}}^{146}$ the feeding of the 3- state is at least 9.7 times that to the 4+ state, while in the decay of ${\mathrm{Eu}}^{146}$ the total feeding to the 3- state is ≈1.2 times that to the 4+ state. In addition, gamma-ray energies and intensities are presented for the transitions observed in the decay of ${\mathrm{Pm}}^{144}$ to ${\mathrm{Nd}}^{144}$ and ${\mathrm{Pm}}^{146}$ to ${\mathrm{Nd}}^{146}$ and ${\mathrm{Sm}}^{146}$, and for some of the more intense transitions observed in the decay of ${\mathrm{Eu}}^{146}$. Energy systematics of 3- and 4+ states for even-even nuclei in the transition region $A=142\mathrm{} \mathrm{to} 152$ are presented.