Abstract
Information about the 90-, 1068-, 2201-, 2417-, 2788-, 2914,- and 3353-keV levels in has been obtained by measuring -ray angular correlations in a collinear geometry. The reaction was used to populate the levels of at an incident triton energy of 2.6 MeV. NaI (Tl) detectors were used for -ray spectroscopy. -ray angular correlations were obtained by measuring the yield of rays at angles between 0° and 90° in coincidence with reaction-produced particles detected near 180° with respect to the incident-beam direction. The coincidence data were collected employing two-parameter analysis. -ray branching data were obtained for all the levels mentioned above, and angular correlations were extracted from these data for rays from the decay of the 1068-, 2201-, 2914-, and 3353-keV levels. Analysis of these data resulted in a definite spin assignment for only one level: for the 2201-keV level. The spin of the 90-keV level was restricted to either , while the 2914- and 3353-keV levels have spin . The angular correlation of the 979-keV ray following the decay of the 1068-keV level was found to be isotropic, supporting the assignment to this level. More information about the -ray branching modes of these levels was obtained using the reaction. A Ge (Li) -ray spectrometer located at 90° to the beam direction was used to measure -ray pulse-height distributions coincident with reaction-produced protons. Two-parameter techniques were used. Intensity ratios of -ray transitions to the ground and the first excited states were extracted from these spectra; was found to be 0.13±0.01, 2.6±0.2,>12, >50, <0.04, 4±1, and 0.23±0.02 for the 1068-, 2201-, 2417-, 2788-, and 2914-keV levels, respectively. We also report some other transitions in . Measured -ray energies are compared with transition energies computed from energy levels quoted by Hinds, Marchant, and Middleton; good agreement was obtained, and as a result, we adopt level energies (in keV) for of 90±1, 1068±2, 2201±2, 2417±3, 2788±3, 2914±4, 3353±3, 3455±7, 3685±4, 3928±7, 3950±4, and 3995±5. An upper limit sec was determined for the lifetime of the levels mentioned above. Several of these low-lying states are tentatively described in terms of the shell model.
- Received 21 August 1969
DOI:https://doi.org/10.1103/PhysRev.188.1783
©1969 American Physical Society