Properties of the rotational bands in the transitional nucleus 189Pt

High-spin states in 189Pt have been studied experimentally using the 176Yb(18O,5n) reaction at beam energies of 88 and 95 MeV. The level scheme of189Pt has been revised significantly and extended to high-spin states.Rotational bands have been analyzed in the framework of triaxial particle-rotor model, and a γ ≈−30◦triaxial shape and a near-prolate shape have been proposed to the νi−113/2 and νf5/2(p3/2) bands, respectively. Two ΔI = 2 transition sequences with similar energies have been observed, and they have been proposed to be associated with the νi−213/2νf5/2(p3/2) configuration. The structure built on the νi−213/2νf5/2(p3/2) configuration could be interpreted theoretical calculations of the triaxial particle-rotor model if a near-oblate shape is assumed.

Experimental study of the beta-delayed neutron decay of N-21

The first spectroscopic study for the beta decay of N-21 is carried out based on beta-n, beta-gamma, and beta-n-gamma coincidence measurements. The neutron-rich N-21 nuclei are produced by the fragmentation of the E/A=68.8 MeV Mg-26 primary beam on a thick Be-9 target and are implanted into a thin plastic scintillator that also plays the role of beta detector. The time of flight of the emitted neutrons following the beta decay are measured by the surrounding neutron sphere and neutron wall arrays. In addition, four clover germanium detectors are used to detect the beta-delayed gamma rays. Thirteen new beta-delayed neutron groups are observed with a total branching ratio of 90.5 +/- 4.2%. The half-life for the beta decay of N-21 is determined to be 82.9 +/- 7.5 ms. The level scheme of O-21 is deduced up to about 9 MeV excitation energy. The experimental results for the beta decay of N-21 are compared to the shell-model calculations.

Prolate and oblate shape coexistence in Pt-188

A standard in-beam gamma-spectroscopy experiment for Pt-188 is performed via the Yb-176(O-18, 6n) reaction at beam energies of 88 and 95 MeV, and the level scheme for (188) Pt is established. Prolate and oblate shape coexistence has been demonstrated to occur in Pt-188 by applying the projected shell model. The rotation alignment of i(13/2) neutrons drives the yrast sequence changing suddenly from prolate to oblate shape at angular momentum 10th, indicating likely a new type of shape phase transition along the yrast line in Pt-188.

High-spin states in Pt-190

The level structure of Pt-190 has been studied experimentally using the Yb-176 (O-18, 4n) reaction at beam energies of 88 and 95 MeV. gamma-gamma-t coincidence measurements were carried out. Based on the analysis of gamma-gamma coincidence relationships, the level scheme of Pt-190 is extended to high-spin states. A new structure built on the 3413.6 keV 14(+) state has been observed, and the vi(13/2)(-2) vh(9/2)(-1) vj (j = p(3/2) or f(5/2)) configuration is tentatively assigned to it.

Observation of negative-parity high spin states of Cs-126

The nucleus Cs-126 was investigated by means of in-beam gamma-ray spectroscopy techniques using the Nordball detector system at the Niels Bohr Institute. Excited states of Cs-126 were populated via the Cd-116(N-14, 4n)Cs-126 reaction at a beam energy of 65 MeV. The Cs-126 level scheme was considerably extended, especially at negative parity and about 40 new levels and 70 new transitions were added into the level scheme. The previously reported negative-parity rotational bands, built on pi g(7/2)circle times nu h(11/2),pi d(5/2)circle times nu h(11/2),pi h(11/2)circle times nu g(7/2), and pi h(11/2)circle times nu d(5/2) configurations, have been extended and evolve into bands involving rotationally aligned (pi h(11/2))(2) and (nu h(11/2))(2) quasiparticles. Two new rotational bands have been tentatively assigned the pi h(11/2)circle times nu s(1/2) and pi g(9/2)circle times nu h(11/2) configurations, respectively