Abstract
Background: Classical novae result from thermonuclear explosions producing several -ray emitters which are prime targets for satellites observing in the MeV range. The early -ray emission depends critically on the reaction rate which, despite many experimental and theoretical efforts, still remains uncertain.
Purpose: One of the main uncertainties in the reaction rate is the contribution in the Gamow window of interference between sub-threshold states and known broad states at higher energies. Therefore the goal of this work is to clarify the existence and the nature of these sub-threshold states.
Methods: States in the compound nucleus were studied at the Tandem-ALTO facility using the charge-exchange reaction. Tritons were detected with an Enge Split-pole spectrometer while decaying protons or particles from unbound states were collected, in coincidence, with a double-sided silicon strip detector array. Angular correlations were extracted and constraints on the spin and parity of decaying states established.
Results: The coincidence yield at was observed to be high spin, supporting the conclusion that it is indeed a doublet consisting of high-spin and low-spin components. Evidence for a broad, low-spin state was observed around 6 MeV. Branching ratios were extracted for several states above the proton threshold and were found to be consistent with the literature. -matrix calculations show the relative contribution of sub-threshold states to the astrophysically important energy region above the proton threshold.
Conclusions: The levels schemes of and are still not sufficiently well known and further studies of the analog assignments are needed. The tentative broad state at 6 MeV may only play a role if the reduced proton width is large.
2 More- Received 28 July 2020
- Accepted 27 October 2020
DOI:https://doi.org/10.1103/PhysRevC.103.015807
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