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 <sup>72g,72m,74m,75,76,77<sup>Br, Spectroscopic information on <sup>72-77</sup>Se and also identified the ground state spin of <sup>73</sup>Br 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 <sup>75-81</sup>Br characterizes the transformation of the prolate ground state configuration from largely π[301]3/2 in <sup>79,81</sup>Br to almost pure π[312]3/2 in <sup>75,77</sup>Br. 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 <sup>73</sup>Br 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 <sup>74</sup>Br<sup>m</sup>, 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 <sup>192</sup>Pt of sin η = ±11(12) x 10<sup>-3</sup>.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:253021 |
| Date | January 1989 |
| Creators | Griffiths, Austyn Glyn |
| Contributors | Stone, N. J. |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://ora.ox.ac.uk/objects/uuid:d8bdd79d-9621-46c3-be82-3a13d1d629cb |
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