Evaluation of the K35(p,γ)Ca36 reaction rate using the Ca37(p,d)Ca36 transfer reaction

Abstract

Background: A recent sensitivity study has shown that the K35(p,γ)Ca36 reaction is one of the ten (p,γ) reaction rates that could significantly impact the shape of the calculated x-ray burst light curve. Its reaction rate used up to now in type I x-ray burst calculations was estimated using an old measurement for the mass of Ca36 and theoretical predictions for the partial decay widths of the first 2+ resonance with arbitrary uncertainties. Purpose: In this work, we propose to reinvestigate the K35(p,γ)Ca36 reaction rate, as well as related uncertainties, by determining the energies and decay branching ratios of Ca36 levels, within the Gamow window of x-ray bursts, in the 0.5 to 2 GK temperature range. Method: These properties were studied by means of the one-neutron pickup transfer reaction Ca37(p,d)Ca36 in inverse kinematics using a radioactive beam of Ca37 at 48 MeV nucleon−1. The experiment was performed at the GANIL facility using the liquid hydrogen target CRYPTA, the MUST2 charged particle detector array for the detection of the light charged particles, and a zero degree detection system for the outgoing heavy recoil nuclei. Results: The atomic mass of Ca36 is confirmed and new resonances have been proposed together with their proton decay branching ratios. This spectroscopic information, used in combination with very recent theoretical predictions for the γ-decay width, were used to calculate the K35(p,γ)Ca36 reaction rate. The recommended rate of the present work was obtained within a uncertainty factor of 2 at 1σ. This is consistent with the previous estimate in the x-ray burst temperature range. A large increase of the reaction rate was found at higher temperatures due to two newly discovered resonances. Conclusions: The K35(p,γ)Ca36 thermonuclear reaction rate is now well constrained by the present work in a broad range of temperatures covering those relevant to type I x-ray bursts. Our results show that the K35(p,γ)Ca36 reaction does not affect the shape of the x-ray burst light curve, and that it can be removed from the list of the few influential proton radiative captures reactions having a strong impact on the light curve.Received 18 January 2021Accepted 12 April 2021DOI:https://doi.org/10.1103/PhysRevC.103.055809©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDirect reactionsExplosive burningNuclear astrophysicsNuclear physics of explosive environmentsNucleon induced nuclear reactionsProton emissionRadiative captureTransfer reactionsProperties20 ≤ A ≤ 38Nuclear PhysicsGravitation, Cosmology & Astrophysics