Investigation of ThuliumαEmitters; New Isotopes,Tm155andTm156

Abstract

In the present investigation the $\ensuremath{\alpha}$ decay of the previously unknown isotopes $^{155}\mathrm{Tm}$ and $^{156}\mathrm{Tm}$ was observed. These thulium nuclides were produced by bombarding targets of $^{144}\mathrm{Sm}$ and $^{147}\mathrm{Sm}$ with 103-MeV $^{14}\mathrm{N}$ ions accelerated in the Oak Ridge isochronous cyclotron. Supplementary data were also obtained by irradiating $^{162}\mathrm{Er}$ with 110-MeV $^{3}\mathrm{He}$ particles. The experimental apparatus used in this study is based on the idea of stopping recoil products in helium gas. The stopped recoils are then swept out through a small orifice and deposited on a wheel which, after bombardment, conveys the collected radioactivity to a position in front of a Si(Au) detector for the assay of $\ensuremath{\alpha}$ activity. Three new $\ensuremath{\alpha}$ emitters were observed. Their decay characteristics and mass assignments (made on the basis of yield-curve measurements and parent-daughter relationships) are as follows: (1) $^{155}\mathrm{Tm}$, ${E}_{\ensuremath{\alpha}}=4.45\ifmmode\pm\else\textpm\fi{}0.01$ MeV, ${T}_{\frac{1}{2}}=39\ifmmode\pm\else\textpm\fi{}3$ sec; (2) $^{156}\mathrm{Tm}$ (low-spin isomer), ${E}_{\ensuremath{\alpha}}=4.23\ifmmode\pm\else\textpm\fi{}0.01$ MeV, ${T}_{\frac{1}{2}}=80\ifmmode\pm\else\textpm\fi{}3$ sec; and (3) $^{156}\mathrm{Tm}$ (high-spin isomer), ${E}_{\ensuremath{\alpha}}=4.46\ifmmode\pm\else\textpm\fi{}0.01$ MeV, ${T}_{\frac{1}{2}}=19\ifmmode\pm\else\textpm\fi{}3$ sec.