Isospin-Forbidden particle decays of T=32 levels in mirror nuclei

Absolute branching ratios for the isospin-forbidden particle decays of the lowest T=32 levels of C13, N13, O17, and F17 have been measured by populating the levels in (He3, p), (He3, α), or (He3, n) reactions and observing the resulting decay products in coincidence. Branching ratios of 0.070 ± 0.018, 0.261 ± 0.030, and 0.026 ± 0.018 (0.236 ± 0.012, 0.150 ± 0.010, 0.053 ± 0.015) were determined for the neutron (proton) decays of the 15.1-MeV, T=32 level of C13(N13) to the ground state and first two excited states of C12, respectively. Branching ratios of 0.91 ± 0.15 and 0.05 ± 0.02 (0.088 ± 0.016, 0.23 ± 0.05) were determined for the neutron (proton) decays of the 11.08-(11.20-) MeV, T=32 level of O17(F17) to the ground state and unresolved 6.05- and 6.13- MeV excited states of O16, respectively. The α-decay branching ratios of the 15.1-MeV, T=32 level of N13 to the ground state and first two excited states of B9 were determined to be 0.049 ± 0.027, 0.039 ± 0.039, and 0.072 ± 0.045, respectively. Possible origins of the large asymmetries observed in the nucleon decays of these analog levels are discussed. The value obtained for Γp0Γ for the lowest T=32 level of N13 may be combined with C13(e,e′) and C12(p,γ)N13 measurements to determine the ratio ΓγM1(C13)ΓγM1(N13)=1.0±0.2 for γ decay to the ground state. This places an upper limit on the isotensor transition matrix element at 7% of the isovector matrix element.