Abstract
Electromagnetic transitions in and have been investigated through the reactions induced (a) by bombardment of targets and (b) by deuteron bombardment of targets employing bombarding energies ranging from 2.0 to 3.5 MeV. Branching ratios for the decay of the bound levels of populated in (a) and (b) by the and reactions were determined through measurements of proton-gamma coincidence spectra. The ratios of radiative width to total width for the unbound 9.19- and 8.92-MeV levels of were obtained as and . Additional measurements of the direct gamma spectra employing a three-crystal Nal(Tl) pair spectrometer, and of the internal pair transitions using an intermediate-image magnetic spectrometer, complement the above results and provide information on the decay of those bound levels of populated by the and reactions. The angular distributions of gamma rays from the four listed reactions were measured with the three-crystal pair spectrometer, and indicate significant anisotropies for those gamma rays arising from decay of the 8.92- and 7.99-MeV levels of and the 7.50-MeV level of formed in the + bombardment. From the Doppler shifts apparent in the angular-distribution data an upper limit of sec was extracted for the mean lifetime of all bound levels of and except the 6.81-MeV level of , which could not be studied in this manner. The intermediate-image spectrometer was used to determine the multipolarity of those internal pair transitions in and having transition energies greater than 4 MeV. These results show that the 7.99- and 7.30-MeV levels of and the 7.50-, 6.90-, and 6.35-MeV levels of decay by ground-state transitions and hence have even parity, while the 8.92- and 6.76-MeV levels of and 6.49-MeV level of decay by and/or ground-state transitions, and hence have odd parity. Combining these results with previously available information leads to spin-parity assignments of and for the 8.92- and 7.99-MeV levels of , respectively, and strongly suggests the assignment for the 7.50-MeV level of . The odd-parity assignment to the 2.14-MeV level of is confirmed while the parity of the 2.00-MeV level is fixed as odd. For the remaining levels the measurements serve to further restrict the range of possible spin-parity assignments. In addition the parities of the ground state and 6.81-MeV level are determined to be even since the beta decay of to the 7.99-MeV level and the 6.81-MeV level are known to be allowed. The level schemes of and as deduced from the present results are discussed in terms of the predictions of the intermediate-coupling shell model and the weak-coupling scheme.
- Received 16 March 1965
DOI:https://doi.org/10.1103/PhysRev.139.B512
©1965 American Physical Society