H. J. Wollersheim

Spontaneous ternary fission of 252Cf: New experiment with GSI super clover detectors

A new multiparameter experiment on ternary fission of 252Cf has recently been successfully performed by using the CODIS2 detector system and two GSI segmented Super Clover Ge γ-ray detectors. The experimental setup and the main subjects of interest are briefly described.

First observation of the decay of a 15{sup -} seniority v=4 isomer in {sup 128}Sn

Isomeric states in the semimagic Sn128-130 isotopes were populated in the fragmentation of a Xe-136 beam on a Be-9 target at an energy of 750 A.MeV. The decay of an isomeric state in Sn-128 at an excitation energy of 4098 keV has been observed. Its half live has been determined to be T-1/2 = 220(30) ns from the time distributions of the delayed gamma rays emitted in its decay. gamma gamma coincidence relations were analyzed in order to establish the decay pattern of the newly established state toward the known (7(-)) and (10(+)) isomers at excitation energies of 2092 and 2492 keV, respectively. Based on a comparison with results of state-of-the-art shell-model calculations the new isomeric state is proposed to have the nu h(11/2)(-3)d(3/2)(-1) configuration with the four neutron holes in Sn-132 maximally aligned to a total spin of I-pi = 15(-).

Isomer spectroscopy of {sup 127}Cd

The spin and configurational structure of excited states of Cd-127, the two-proton and three-neutron hole neighbor of Sn-132, has been studied. An isomeric state with a half-life of 17.5(3) mu s was populated in the fragmentation of a Xe-136 beam on a Be-9 target at a beam energy of 750 MeV/u. Time distributions of the delayed gamma transitions and gamma gamma coincidence relations were exploited to construct a decay scheme. The observed yrast (19/2)(+) isomer is proposed to have dominant configurations of nu(h(11/2)(-3))pi(g(9/2)(-1), p(1/2)(-1)), nu(h(11/2)(-2)d(3/2)(-1))pi(g(9/2)(-2)), and nu(h(11/2)(-2), s(1/2)(-1))pi(g(9/2)(-2)) and to decay by two competing stretched M2 and E3 transitions. Experimental results are compared with the isotone Sn-129. The new information provides input for the proton-neutron interaction and the evolution of neutron hole energies in nuclei around the doubly magic Sn-132 core. (Less)