High-Spin States in the Continuum. I. ²⁰Ne

We describe a new angular-correlation method for assigning spins to states that are selectively populated in reactions of the type ¹²C(¹²C,α)²⁰Ne 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 ¹²C(¹²C,α₁α₂γ)¹⁶O 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 ²⁰Ne, 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 ²⁰Ne; 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 ¹²C(¹²C,α₁)²⁰Ne^*(α₂)¹⁶O^*(γ)¹⁶O (g.s.), E=36.3,37.2 MeV; measured σ(E_α1,E_α2,E_γ,θ_α1,θ_α2,θ_γ,ϕ_γ). ²⁰Ne deduced levels J, π, branching ratios.]