Abstract
All previous tests of the isotopic-spin selection rule in () reactions were obscured by statistical weight factors because in each case the initial and final nuclear states had spin and parity . The reaction provides a test of the isotopic-spin selection rule free from this restriction. The energy levels of near the lowest level were studied with the and reactions as well as with the reaction. Energy levels in were found at 16.623±0.010 Mev, 16.921±0.010 Mev, and 17.637±0.006 Mev. The widths are 95±20 kev, 85±20 kev, and <15 kev, respectively. The first of these levels is the lowest state, whereas the second is and the third probably . Energy levels at 16.08 Mev and a level at 17.7 Mev, reported by other laboratories, were not observed. The ratio of the differential cross sections for formation of the 16.62- and 16.92-Mev levels was measured over a range of angles and bombarding energies. The ratio is about 1.4 and is roughly constant for both the and reactions. This implies complete violation of the selection rule because the latter reaction should not go to the level. Arguments are given which indicate that the impurities in the 16.62-Mev level are probably quite small. Consequently, the failure of the selection rule probably results from the complete intermixing of and states in the compound nucleus near 28-Mev excitation. Groups from the reaction were seen corresponding to levels in at 5.691±0.008, 5.834±0.008, 6.203±0.008, and 6.440±0.008 Mev.
- Received 28 March 1961
DOI:https://doi.org/10.1103/PhysRev.123.958
©1961 American Physical Society