α-decay branching ratios forTb151,Dy150−153, andEr152−155

Abstract

The isotopes $^{152\ensuremath{-}155}\mathrm{Er}$ and $^{151}\mathrm{Tb}$, $^{150\ensuremath{-}153}\mathrm{Dy}$ were produced by bombarding $^{147}\mathrm{Sm}$ and $^{144}\mathrm{Nd}$, respectively, with $^{12}\mathrm{C}$ ions accelerated in the Oak Ridge isochronous cyclotron. With the use of a gas-jet-capillary transport system $\ensuremath{\alpha}$-particle, x-ray, and $\ensuremath{\gamma}$-ray spectra were measured simultaneously and $\ensuremath{\alpha}$-decay branching ratios deduced for the above mentioned nuclides. The ratios were determined primarily by measuring the number of $K{\ensuremath{\alpha}}_{1}$ x rays emitted and then applying appropriate correction factors to obtain the total number of electron capture and positron decays. In addition, for $^{150,152,153}\mathrm{Dy}$ it was possible to deduce alternate, and thus independent, $\ensuremath{\alpha}$-decay branching ratios from $\ensuremath{\gamma}$-ray spectral measurements. Within error limits the two sets of values were found to be in agreement. Because of the essentially equal half-lives of $^{151}\mathrm{Tb}$ and $^{152}\mathrm{Tb}$ the \ensuremath{\alpha} branch for $^{151}\mathrm{Tb}$ could not be determined from the $K{\ensuremath{\alpha}}_{1}$ ray intensity; instead it was deduced solely on the basis of its known decay to levels in $^{151}\mathrm{Gd}$. Branches for $^{149}\mathrm{Tb}$, $^{149}\mathrm{Tb}^{m}$, and $^{150}\mathrm{Tb}$, as well as for the fine structure $\ensuremath{\alpha}$ decays observed in the case of $^{153}\mathrm{Dy}$ and $^{149,151}\mathrm{Tb}$, were taken from a survey of published values. These data were combined with our own results and $\ensuremath{\alpha}$-decay reduced widths were calculated using the formalism developed by Rasmussen. As is customary, reduced widths for ground-state transitions between even-even nuclei were assumed to represent unhindered decay and then compared with values for the remaining $\ensuremath{\alpha}$ decays. As we had found earlier for the neighboring odd-$Z$ holmium nuclides these latter reduced widths ranged from values close to those of even-even nuclei down to much smaller ones. This result is examined from the standpoint of what is known about spin assignments for states connected by specific $\ensuremath{\alpha}$-decay transitions.RADIOACTIVITY $^{151}\mathrm{Tb}$, $^{150,151,152,153}\mathrm{Dy}$, $^{152,153,154,155}\mathrm{Er}$; ${I}_{\ensuremath{\alpha}}$, $I$ ($K{\ensuremath{\alpha}}_{1}$ x ray), ${I}_{\ensuremath{\gamma}}$, ${E}_{\ensuremath{\gamma}}$; measured $\ensuremath{\alpha}$-decay branching ratios; deduced $\ensuremath{\alpha}$-decay rates. $^{150,152}\mathrm{Tb}$ deduced levels, $J$, $\ensuremath{\pi}$.