Nuclear orientation studies of isotopes far from stability

Thesis



Low Temperature Nuclear Orientation (LTNO) is an important technique in the study of nuclei far from stability. The theory of LTNO and its applications to the measurement of static nuclear moments and other quantities of spectroscopic interest are reviewed.

Among the nuclei off the line of stability those in the A ~ 75 region are of considerable interest, exhibiting large quadrupole deformations, triaxiality and shape coexistence. LTNO measurements performed on neutron deficient bromine isotopes have yielded the static magnetic dipole moments of the nuclei ^{72g,72m,74m,75,76,77Br, Spectroscopic information on 72-77Se and also identified the ground state spin of 73Br as l/2‾}

Existing odd A and odd-odd particle-rotor computer codes have been extended in order to include a Variable Moment of Inertia (VMI) asymmetric rotational core. The formalism necessary for this modification is developed.

The measured magnetic moments are interpreted within the framework of this particle - VMI rotor model. It is shown that the systematic reduction in the moments of the odd A nuclei ^75-81Br characterizes the transformation of the prolate ground state configuration from largely π[301]3/2 in ^79,81Br to almost pure π[312]3/2 in ^75,77Br. This trend is fully consistent with the increase in deformation towards the lower masses suggested by the known electric quadrupole moments. In contrast, the ground state spin of ⁷³Br can only be interpreted in terms of an oblate nuclear shape. This is the first evidence for the predicted prolate-oblate shape transition in the bromine nuclei. In addition the magnetic moment of ⁷⁴Br^m, by identifying a π[431]3/2ν[422]5/2 configuration, strongly suggests a positive parity assignment for the isomeric state.

Finally, an experiment to search for possible T-violation effects in nuclear gamma decay is described. Using coincidence techniques, a measurement of the T-odd P-even quantity (I ‧ k x e)(I ‧ k)(I ‧ e) has lead to a limit on the T-violating phase angle between the E2 and Ml matrix elements associated with the 604 keV gamma transition in ¹⁹²Pt of sin η = ±11(12) x 10^-3.

Authors: Griffiths, A; Griffiths, Austyn Glyn

• Publication date: 1989
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Subjects: Nuclear structure; Nuclear physics; Isotopes; Nuclear orientation; Low temperatures