The nuclear structure of 178Hf studied by the 181Ta(p, α)178Hf reaction

The microscopic structures of levels in178Hf have been studied by the 181Ta(p, α) reaction using 17 MeV protons. The reaction products were analyzed with a magnetic spectrograph and detected with photographic emulsions, yielding an overall resolution of ⩽ 20 keV (FWHM). Levels with significant populations must involve a proton in the 72+ [404] Nilsson orbital, which forms the ground state of the 181Ta target nucleus. The admixtures of various two-quasiproton configurations were extracted from the observed cross sections. The ground-state band is populated unusually weakly, while a large 72+ [404] −72+ [404] strength is observed for the Kπ = 0+ band at 1199 keV. This is attributed to the irregular filling of Nilsson proton states in this region, whereby the 72+[404] orbital appears as the ground state for tantalum as well as lutetium nuclei. For the well-known Kπ = 8− bands at 1147 and 1479 keV the present results confirm in a direct manner the 92−[514]π + 72+[404]π admixtures proposed earlier on the basis of gamma-ray mixing ratios and log ft values. An upper limit of ∼ 5% for the 92−[514]π−72+[404]π configuration in the Kπ = 1− band at 1310 keV is consistent with earlier proposals that this is predominantly a 92+[624]v−72−[514]v two-quasineutron band. A new Kπ = 1− band has been assigned at 1513 keV, which has the main 92−[514]π−72+[404]π strength. Levels previously assigned as a Kπ = 2− band at 1566 keV are shown to be rotational excitations based on this new Kπ = 1− band. The Kπ = 3+ band at 1758 keV is found to be predominantly the 72+[404]π−12+[411]π configuration, while the strength for the Kπ = 4+ parallel coupling of the same two protons is spread over more than one band.