Measurements of g-factors of excited states in Ba and Ce nuclei using gamma rays from secondary fission fragments

Measurements of g-factors of excited states in barium and cerium fission fr agments have been performed using time-integral perturbed angular correlati ons between secondary-fragment gamma rays. Larmor precession angles have be en obtained for the first I-pi = 2(+) states in Ba-144,Ba-146 and Ce-146,Ce -148 as well as for the 9/2(-) state at 117 keV in Ba-143, the 7/2(-) state at 114 keV in Ba-145 and the first 4(+) state in Ce-150. The deduced g-fac tor fur the 2(+) state in Ba-146 provides substantiating evidence for a dow nward trend in 2(+) g-factors with increasing neutron number, in line with Interacting Boson Model predictions for the neutron-rich barium isotopes, a ssuming the quenching of the Z = 64 shell gap for N>88. The static hyperfin e fields for implanted barium and cerium isotopes are found to be opposite in sign. These results constitute the first use of secondary-fragment gamma -ray emission in the determination of g-factors of excited states in fissio n fragments. (C) 1999 Elsevier Science B.V. All rights reserved.