The 3.06 and 3.85 MeV states in O 17

Abstract

The 3.06 and 3.85 MeV states in O 17 have been excited by the reaction C 14( α, n)O 17, the gamma-ray de-excitation of these states being observed in coincidence with neutrons. The attenuated Doppler shifts of the gamma rays were measured and lead to lifetime estimates of 1.2 −0.6 +0.8 and ≦ 0.25 × 10 −13 sec respectively. The n-γ angular correlations from the two states were also measured. These correlations alone do not lead to unique spin assignments but in conjunction with the lifetime measurements, they confirm the 1 2 − assignment to the 3.06 MeV state but favour 5 2 − over 7 2 for the 3.85 MeV state. Upper limits have been put on two unobserved decay modes of these levels. They are 2% for the decay of the 3.06 MeV state directly to the ground state, and 5% for the cascade of the 3.85 MeV state through the first excited state.