Search for 1-Mev Gamma from N16 Decay

Abstract

In the beta-decay of N16 to the 1- (7.1-Mev) and 3- (6.1-Mev) excited states of O16, respectively, a discrepancy exists between the branching ratio of about 1:1 determined from absorption measurements on the beta-spectrum, and the ratio of about 1:12 from measurement of the associated gamma-ray intensities. If both measurements are to be reconciled, the most likely possibility is a strong E2 gamma-ray transition from the 7.1-Mev to the 6.1-Mev level. The likelihood that this E2could give serious competition to the normal 7.1-Mev E1 ground state transition is enhanced by the isotopic spin selection rule forbidding E1 transitions with [delta]T = N - Z = 0. In order to explain the quantitative discrepancy in this way, however, this selection rule would have to be much stronger than suggested by simple estimates.