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β-Delayed Charged Particle Measurements for Studies of Novae and X-ray Bursts

Moshe Friedman, Michigan State University
Monday, April 1, 2019 - 2:30pm
NPL 178

Classical novae and type I X-ray bursts are energetic and common thermonuclear astrophysical explosions. However, our ability to understand these events is limited by the lack of comprehensive nuclear data on proton-rich nuclei. Specifically, constraining the 30 P(p,γ) 31 S and 15 O(α,γ) 19 Ne reaction rates has been found to be crucial to the understanding of nucleosynthesis and energy generation in these events. As direct measurements of these reactions are not technically feasible at the present time, indirect measurements of dominant resonance strengths by β-delayed protons and α particles are used.

A previous measurement at NSCL identified a new 31 S state at E x = 6390 keV to be a key resonance for 30 P proton capture at peak nova temperatures. A significant feeding of 3.38% from 31 Cl β + decay was observed, which enables the determination of the resonance strength by measuring the corresponding 259 keV β + -delayed protons. Similarly, a previous measurement at NSCL observed a 0.0156% feeding of the 19 Ne state at 4034 keV, a key resonance for the 15 O(α,γ) 19 Ne reaction, by the 20 Mg(β+p) sequence. This feeding is sufficient to determine the resonance strength by measurement of the proton-α pairs.

A gas-filled detector of β-delayed charged particles has been designed and built to measure the aforementioned decays at NSCL. The detector is coupled with the Segmented Germanium Array (SeGA) to enable coincidence γ-ray detection as an additional probe of the decay scheme and for normalization purposes. The first phase of the detector functions as a proton calorimeter, was successfully commissioned with 25 Si(β + p) 24 Mg, and used to measure several decays of interest including 31 Cl. We will report on the performance of the detector and present preliminary results. We will also discuss the upgrade of the detector into a TPC for the measurements of the 20 Mg(β + pα) sequence.

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