High-spin rotational band structure of 177W and 178W

The rotational band structure of 177W and 178W was investigated using the techniques of in-beam gamma ray spectroscopy. Of particular interest in this region of deformed rare-earth nuclei is the anomalous behavior which occurs in yrast sequences at very large values of angular momentum, and the possible involvement of i/sub -13/2/ neutrons in this phenomenon. In the experiments discussed, the 7/2+[633] band in 177W was populated to spin 33/2 and the ground band of neighboring 178W to spin 16. The i/sub -13/2/ band in 177W was compared with similar bands in other odd-A tungsten nuclei, and the results were applied to the systematics of the doubly even tungsten ground band structures. Levels in 177W were populated in the 177Hf(α,4nγ) reaction. The ground state is assigned as 1/2-[521]; other low-lying bands which were seen include the 7/2+[633], 5/2-[512], and 7/2-[514]. The 7/2+[633] band displays a highly perturbed structure which can be theoretically reproduced through Coriolis-induced mixing of higher energy positive parity bands. The 177Hf(α,3nγ) reaction was used to populate states in 178W. The K/sup π/ = 0+ ground band was observed up to spin 16. On a plot of (Dirac constant2/2J)-1 vs. (Dirac constant ω)2 the band shows some deviation from normal rotational behavior at high spin. The K/sup π/ = 2- octupole band was located at 1045 keVand has an alternating energy sequence, with the odd spin members ''favored''. A pair of two-quasiparticle bands was identified and is tentatively assigned as K/sup π/ = 6+ and K/sup π/ = (6,7)-. The β-vibrational band was identified from spin 6 to spin 16. A discussion of backbending and the i/sub -13/2/ neutron orbitals is made in the light of a systematic study of odd-even isotopic pairs