High-spin states in the continuum. I. Ne20

Abstract

We describe a new angular-correlation method for assigning spins to states that are selectively populated in reactions of the type C12(C12,α)Ne20 and which decay by the emission of an α particle to a state of nonzero spin, which decays in turn to a spin-zero state by the emission of a γ ray. Such states are not accessible to conventional particle-particle angular-correlation techniques. The new method consists of measuring the triple-angular correlation of the two α particles and the γ ray from the reaction C12(C12,α1α2γ)O16 with the first emitted α particle observed at zero degrees, the γ ray observed at a fixed angle, and the second emitted α particle observed over a range of angles. Applications of this method to the determination of the spins of two states in Ne20, at 15.18 ± 0.02 MeV (6+) and 17.40 ± 0.02 MeV (9-), are discussed. The 17.40-MeV state has been identified as the 9- member of the lowest negative-parity band in Ne20; the 6+ assignment to the level at 15.18 MeV is in disagreement with an earlier assignment of spin and parity 9- to this level. [NUCLEAR REACTIONS C12(C12,α1)Ne*20(α2)O*16(γ)O16 (g.s.), E=36.3,37.2 MeV; measured σ(Eα1,Eα2,Eγ,θα1,θα2, θγ,γ). Ne20 deduced levels J, π, branching ratios.] Show more