Electromagnetic transition strengths in 14C and 14N

Abstract

The lifetimes of the 5.10-MeV and 5.83-MeV levels in 14N and the 6.72-MeV level in 14C have been measured using a recoil distance method and the T(12C, nγ)14N and T(12C, pγ)14C reactions respectively. The lifetimes are 12.4 ± 1.4 and 18 ± 2 ps for the 5.10-MeV and 5.83-MeV levels in 14N respectively and 97 ± 15 ps for the 6.72-MeV level in 14C. These measurements are combined with previous determinations of gamma-ray branching and multipole mixing ratios to obtain the strengths of the transitions involved. Comparison of the strengths with recent calculations shows agreement in general. The ground-state E3 transitions from the 5.10-MeV level in 14N and the 6.72-MeV level in 14C are enhanced by 2.2 ± 0.7 and 3.3 ± 0.8 Weisskopf units respectively. The isotopic spin selection rule for E1 and M2 transitions in the self-conjugate nucleus 14N is observed and discussed for some transitions. For example, the allowed M2 transition from the 5.10-MeV to the 2.31-MeV level has [Formula: see text] whereas the isotopic spin forbidden M2 part of the 5.10-MeV to ground-state transition has [Formula: see text]