Nuclear Structure Studies of BROMINE-73, Bromine -75 and Investigation of Oblate Shape in SELENIUM-71
Abstract
Three experiments have been performed to establish the band structure for ^{73}Br nucleus. The experiment at the University of Rochester used a Recoil Mass Spectrometer to identify ^ {73}Br transitions, by employing the reaction ^{54}Fe(^ {28}Si,xp,xn) at 128 MeV energy. The transitions which appeared in the mass 73 gate were compared with all other mass gates to ensure no feed through from other reaction channels. The following two experiments were done at the Holifield tandem accelerator. The first was a neutron-gamma, and gamma-gamma experiment to verify ^{73}Br transitions obtained from the RMS data, and the second was a high quality gamma-gamma coincidence experiment with 20 BGO shielded gamma-ray detectors to build the ^{73}Br band structure. The nuclear structure of ^{73 }Br reveals three rotational bands up to high spins. A positive parity, positive signature band was observed up to 29^+/2, and is interpreted as a band built upon an aligned 9^+/2 proton orbital. Strong B(E2) values, potential energy surface calculations as a function of deformation parameters (beta_2,gamma) and the moment of inertia of the band indicate that the ^{73}Br deformation parameters are (beta_2 = 0.38, gamma = -15^circ), which is a triaxial shape with large quadrupole deformation. This is consistent with the neighboring ^{75}Br results. Two negative parity bands were observed with spins up to 27^-/2 and 29 ^-/2. Signature inversion among the bands was traced to a crossing of a three-quasi-particle state with a one-quasi-particle state. Two in-beam gamma-ray experiments were also done for ^{71}Se to look for possible oblate bands. New transitions in ^ {71}Se were established from RMS- gamma, RMS-n-gamma and RMS-p-gamma^ectra. Later gamma-gamma coincidence data revealed a DeltaI = 1 positive parity rotational band. An evaluation of the mixing ratio delta for 894 keV(11^ {+}/2 = 9^+/2) transition strongly supports the existence of an oblate rotational band (beta_2 = -0.24). This deformation is stabilized by the Z = 34 oblate shell gap.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1989
- Bibcode:
- 1989PhDT........50Z
- Keywords:
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- BROMINE;
- SELENIUM-71;
- Physics: Nuclear