Quasirotational Levels inGd152and Excited Levels ofTb152from the Decay of 4.2-minTb152m

Abstract
In the decay of the 4.2-min isomeric state in Tb152, 8γ rays are found to be associated with the deexcitation of levels in Tb152 and 25γ rays with that in Gd152. Experimental studies were made chiefly with Ge(Li)γ-ray detectors in singles and coincidence modes. Conversion-electron spectra were obtained with a Si(Li) spectrometer. The isomeric state, believed to be an 8+ state, is at 501.8 keV, and the isomeric transition is a 159.59-keV E3 transition to a level at 342.2 keV. Other levels in Tb152 are proposed at 58.9, 65.1, and 106.7 keV. An alternative but less likely level scheme is also possible. The ground state (2) and levels at 58.9, 342.2, and 501.8 keV appear to be best described in terms of Nilsson states. The electron-capture decay of the 501.8-keV isomeric state is by an allowed unhindered transition (logft 4.7) which leads almost entirely to a level at 2394.5 keV in Gd152. The deexcitation of the latter level populates 6+ and 8+ members of the quasiground-state and quasi-β-vibrational bands. The quasirotational character of levels in Gd152 which has been proposed by Sakai and coworkers appears to be amply confirmed. A previously unreported level in Gd152 at 1861.7 keV (5+) is proposed. In contrast to previous work, no α-decay branch was observed.