Measurement ofα-Decay Branching Ratios forDy150,151andTbm149

Abstract

With the use of the helium-gas-jet technique and a high-resolution Ge(Li) detector $\alpha$-decay branching ratios were measured for ${}_{}{}^{150}{}_{}{}^{}\mathrm{Dy}$, ${}_{}{}^{151}{}_{}{}^{}\mathrm{Dy}$, and ${}_{}{}^{149}{}_{}{}^{}\mathrm{Tb}_{}^m{}_{}{}^{}$. Sources containing these activities were produced by bombarding ${}_{}{}^{141}{}_{}{}^{}\mathrm{Pr}$ with ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ ions. They were then assayed for both $\alpha$-particle and x-ray radioactivity. The branching ratios deduced are as follows: 0.32 ± 0.05 for ${}_{}{}^{150}{}_{}{}^{}\mathrm{Dy}$, 0.055 ± 0.008 for ${}_{}{}^{151}{}_{}{}^{}\mathrm{Dy}$, and (2.0 ± 0.4) × ${10}^{-4\mathrm{}}$ for ${}_{}{}^{149}{}_{}{}^{}\mathrm{Tb}_{}^m{}_{}{}^{}$. The ${}_{}{}^{151}{}_{}{}^{}\mathrm{Dy}$ and ${}_{}{}^{149}{}_{}{}^{}\mathrm{Tb}_{}^m{}_{}{}^{}$ ratios were found to be in good agreement with previous measurements. While the ratio deduced for ${}_{}{}^{150}{}_{}{}^{}\mathrm{Dy}$ is almost midway in value between two earlier determinations, it appears to be in real disagreement with the more precise of the two previous measurements. Consequences of this discrepancy are discussed with respect to published cross-section data and $\alpha$-decay reduced widths for 84-neutron even-even nuclei. In the course of the investigation the half-life of ${}_{}{}^{149}{}_{}{}^{}\mathrm{Dy}$ was determined to be 4.6 ± 0.4 min from x-ray decay-curve analyses and 5.1 ± 0.9 min from the initial growth period observed in the decay of the 4.1-h, ${}_{}{}^{149}{}_{}{}^{}\mathrm{Tb}$ 3.967-MeV $\alpha$ group.