The beta-delayed three-body breakup of neon-17 and its relation to astrophysics

This is a study on the feasibility of using the β-delayed 3-body decay of 17Ne to constrain the astrophysically important 12C(α, γ)16O reaction rate at stellar energies. The relative rate of this reaction to that of 3α → 12C+γγ is believed to strongly affect the evolution of massive stars subsequent to the phase of helium burning. The usefulness of the cascade decay of 17Ne in this study hinges on the existence of α-unbound states of 16O in the decay chain. Detection of all the daughter particles, p + α + 12C in triple coincidence, is necessary to optimize the kinematic information inherent in each event to discriminate against background. The first triple-coincidence measurement was accomplished in 1996, at the TRIUMF-TISOL facility in Vancouver, BC, Canada, in which the isobaric analogue state in 17F at 11.193 MeV (J π = $12$−) was observed to decay into three particles via three channels, viz., the 9.59 MeV (Jπ = 1− ) state in 16O, and the 2.37 (Jπ = $12$+) and 3.50/3.55 MeV (Jπ = $32$−/$52$+) states in 13N. In two subsequent measurements, various techniques were incorporated to improve the efficiency in background discrimination. The connection between experiment and theory is made through extensive Monte Carlo simulations and analytic calculations within the framework of R-matrix theory. Based on a single-channel, 2-level R-matrix calculation, an optimum detection geometry has been defined to constrain the strength of the E1 component of the 12C(α, γ)16O reaction. According to results from another single-channel, single-level R-matrix calculation, the 10.03 MeV state in 17F has been identified as the best candidate to constrain the strength of the E2 component. However, more studies are required before the feasibility of using the decay of 17Ne to constrain the strength of the E2 component can be established.