Doppler Broadening in ${}^{20}$Mg($\beta p\gamma$)${}^{19}$Ne Decay

Abstract

Background: The ${}^{15}$O($\alpha ,\gamma$)${}^{19}$Ne bottleneck reaction in Type I x-ray bursts is the most important thermonuclear reaction rate to constrain experimentally, in order to improve the accuracy of burst light-curve simulations. A proposed technique to determine the thermonuclear rate of this reaction employs the ${}^{20}$Mg($\beta p\alpha$)${}^{15}$O decay sequence. The key ${}^{15}$O($\alpha ,\gamma$)${}^{19}$Ne resonance at an excitation of 4.03 MeV is now known to be fed in ${}^{20}$Mg($\beta p\gamma$)${}^{19}$Ne; however, the energies of the protons feeding the 4.03 MeV state are unknown. Knowledge of the proton energies will facilitate future ${}^{20}$Mg($\beta p\alpha$)${}^{15}$O measurements. Purpose: To determine the energy of the proton transition feeding the 4.03 MeV state in ${}^{19}$Ne. Method: A fast beam of ${}^{20}$Mg was implanted into a plastic scintillator, which was used to detect $\beta$ particles. 16 high purity germanium detectors were used to detect $\gamma$ rays emitted following $\beta p$ decay. A Monte Carlo method was used to simulate the Doppler broadening of ${}^{19}$Ne $\gamma$ rays and compare to the experimental data. Results: The center of mass energy between the proton and ${}^{19}$Ne, feeding the 4.03 MeV state, is measured to be 1.21${}_{-0.22}^{+0.25}$ MeV, corresponding to a ${}^{20}$Na excitation energy of 7.44${}_{-0.22}^{+0.25}$ MeV. Absolute feeding intensities and $\gamma$-decay branching ratios of ${}^{19}$Ne states were determined including the 1615 keV state. A new $\gamma$ decay branch from the 1536 keV state in ${}^{19}$Ne to the ground state is reported. The lifetime of the 1507 keV state in ${}^{19}$Ne is measured to be 4.3${}_{-1.1}^{+1.3}$ ps resolving discrepancies in the literature. Conflicting ${}^{20}$Mg($\beta p$) decay schemes in published literature are clarified.

arXiv comment11 pages, 13 figures

References in corpus (11)

• Dependence of X-Ray Burst Models on Nuclear Reaction Rates
• X-ray binaries
• The ${}^{15}$O($\alpha$,$\gamma$)${}^{19}$Ne Breakout Reaction and Impact on X-Ray Bursts
• The astrophysical rate of 15O(alpha,gamma)19Ne via the (p,t) reaction in inverse kinematics
• Beta-delayed gamma decay of 26P: Possible evidence of a proton halo
• The Influence of Uncertainties in the 15O(alpha,gamma)19Ne Reaction Rate on Models of Type I X-Ray Bursts
• Lifetimes of states in 19Ne above the 15 O + alpha breakup threshold
• Lifetime of 19Ne*(4.03 MeV)
• Beta-decay study of $T_z=-2$ proton-rich nucleus ${}^{20}$Mg
• Revalidation of the isobaric multiplet mass equation for the $A=20$ quintet
• Observation of Doppler broadening in $\beta$-delayed proton-$\gamma$ decay

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