(He-3, d) and (alpha, t) reaction studies of Gd-154: nature of K-pi=4(+) bands in heavy deformed nuclei

Levels in Gd-154 have been studied with (He-3, d) and (alpha, t) reactions using beams of 24 MeV He-3 and 27 MeV alpha particles. Particle spectra wer e measured with a magnetic spectrograph at theta = 30 degrees and 60 degree s for the (He-3, d) and at theta = 45 degrees and 60 degrees for the (alpha , t) reaction. Cross sections were compared with predictions based on Disto rted Wave Born Approximation and Nilsson model calculations. The gamma -vib rational band has an admixture of similar to 15% of the 5/2(+)[413] - 1/2()[411] two-quasiproton state, in good agreement with predictions of the Qua siparticle-Phonon Model. The K-pi = 4(+) band at 1646 keV is very strongly populated, with a pattern of cross sections indicating its dominant compone nt is an similar to 80% admixture of the 5/2(+)[413] + 3/2(+)[411] two-quas iproton state. Bands with similar structures have previously been found at 1510 keV in Gd-156 and 1380 keV in Gd-158. Although there were earlier doub le-gamma -phonon claims for the bands in Gd-154 and Gd-156, quantitative an alyses show that all the data (including the E2 strengths) agree better wit h a predominantly g boson, or single hexadecapole phonon, character. Some i nsights are provided which assist in understanding how microscopic structur es of the K-pi = 4(+) and gamma bands help produce the relatively large E2 strengths coupling these bands. Two closely-spaced K-pi = 1(+) bands based at 2175 keV and 2186 keV share the single-proton stripping strengths for th e 5/2(+)[413] - 3/2(+)[411] configuration, and a level at 2569 keV is propo sed as the 7(-) member of a Coriolis-mixed band formed by transfer of a pro ton to h(11/2) orbitals. (C) 2001 Elsevier Science B.V. All rights reserved .