Study ofHf173Levels Populated in the Decay ofTa173

Abstract

The decay of $^{173}\mathrm{Ta}$ was studied using high resolution Ge(Li), Si(Li), and Si surface-barrier detectors in singles and coincidence modes. The $^{173}\mathrm{Ta}$ activity was produced via the reaction $^{165}\mathrm{Ho}(^{12}\mathrm{C}, 4n)^{173}\mathrm{Ta}$, at a carbon beam energy of 6.3-6.9 MeV per nucleon. All spectra were obtained from chemically separated Ta sources. Besides the previously known energy levels of $^{173}\mathrm{Hf}$, the following levels in keV were determined: 255.5, 451.9, 508.9, 635.8, 775.5, 785.3, 811.7, 927.5, 942.5, 1020.3, 1111.4, 1127.0, 1192.8, 1248.3, 1450.0, 1574.2, 1655.6, 1667.1, 1694.3, and 2263.3. Rotational bands based on the ${(\frac{1}{2})}^{\ensuremath{-}}[521]$ (g.s.), ${(\frac{5}{2})}^{\ensuremath{-}}[512]$ (107.2 keV), and ${(\frac{7}{2})}^{+}[633]$ (197.5 keV) Nilsson states were observed. The half-lives of the ${(\frac{5}{2})}^{\ensuremath{-}}[512]$ and the ${(\frac{1}{2})}^{+}[633]$ band heads were determined to be (182\ifmmode\pm\else\textpm\fi{}20) nsec and (160\ifmmode\pm\else\textpm\fi{}40) nsec, respectively. The probability of the radiative $E1$ transition between the [633] and [512] band heads was calculated within the framework of Nilsson model including the pairing and Coriolis interactions. From measurement of the ${\ensuremath{\beta}}^{+}$ end-point energy, the mass difference between $^{173}\mathrm{Ta}$ and $^{173}\mathrm{Hf}$ was determined to be 3670\ifmmode\pm\else\textpm\fi{}200 keV.