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Register a new userReevaluation of thermonuclear reaction rate of 50Fe(p,gamma)51Co
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The thermonuclear rate of the 50Fe(p,gamma)51Co reaction in the Type I X-ray bursts (XRBs) temperature range has been reevaluated based on a recent precise mass measurement at CSRe lanzhou, where the proton separation energy Sp=142+/-77 keV has been determined firstly for the 51Co nucleus. Comparing to the previous theoretical predictions, the experimental Sp value has much smaller uncertainty. Based on the nuclear shell model and mirror nuclear structure information, we have calculated two sets of thermonuclear rates for the 50Fe(p,gamma)51Co reaction by utilizing the experimental Sp value. It shows that the statistical-model calculations are not ideally applicable for this reaction primarily because of the low density of low-lying excited states in 51Co. In this work, we recommend that a set of new reaction rate based on the mirror structure of 51Cr should be incorporated in the future astrophysical network calculations.
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Updated stellar rates for the reaction 23Mg(p,gamma)24Al are calculated by using all available experimental information on 24Al excitation energies. Proton and gamma-ray partial widths for astrophysically important resonances are derived from shell model calculations. Correspondences of experimentally observed 24Al levels with shell model states are based on application of the isobaric multiplet mass equation. Our new rates suggest that the 23Mg(p,gamma)24Al reaction influences the nucleosynthesis in the mass A>20 region during thermonuclear runaways on massive white dwarfs.
The $^{23}$Al($p,gamma$)$^{24}$Si reaction is among the most important reactions driving the energy generation in Type-I X-ray bursts. However, the present reaction-rate uncertainty limits constraints on neutron star properties that can be achieved with burst model-observation comparisons. Here, we present a novel technique for constraining this important reaction by combining the GRETINA array with the neutron detector LENDA coupled to the S800 spectrograph at the National Superconducting Cyclotron Laboratory. The $^{23}$Al($d,n$) reaction was used to populate the astrophysically important states in $^{24}$Si. This enables a measurement in complete kinematics for extracting all relevant inputs necessary to calculate the reaction rate. For the first time, a predicted close-lying doublet of a 2$_2^+$ and (4$_1^+$,0$_2^+$) state in $^{24}$Si was disentangled, finally resolving conflicting results from two previous measurements. Moreover, it was possible to extract spectroscopic factors using GRETINA and LENDA simultaneously. This new technique may be used to constrain other important reaction rates for various astrophysical scenarios.
The $^{19}$F($alpha$,p)$^{22}$Ne reaction is considered to be one of the main sources of fluorine depletion in AGB and Wolf-Rayet stars. The reaction rate still retains large uncertainties due to the lack of experimental studies available. In this work the yields for both exit channels to the ground state and first excited state of $^{22}$Ne have been measured and several previously unobserved resonances have been found in the energy range E$_{lab}$=792-1993 keV. The level parameters have been determined through a detailed R-matrix analysis of the reaction data and a new reaction rate is provided on the basis of the available experimental information.
Context. Direct observation of gamma-ray emission from the decay of $^{18}$F ejected in classical nova outbursts remains a major focus of the nuclear astrophysics community. However, modeling the abundance of ejected $^{18}$F, and thus the predicted detectability distance of a gamma-ray signal near 511 keV emitted from these transient thermonuclear episodes, is hampered by significant uncertainties in our knowledge of the key $^{18}$F(p,$alpha$) reaction rate. Aims. We analyze uncertainties in the most recent nuclear physics experimental results employed to calculate the $^{18}$F(p,$alpha$) reaction rate. Our goal is to determine which uncertainties have the most profound influence on the predicted abundance of $^{18}$F ejected from novae, in order to guide future experimental works. Methods. We calculated a wide range of $^{18}$F(p,$alpha$) reaction rates using R-Matrix formalism, allowing us to take into account all interference effects. Using a selection of 16 evenly-spaced rates over the full range, we performed 16 new hydrodynamic nova simulations. Results. We performed one of the most thorough theoretical studies of the impact of the $^{18}$F(p,$alpha$) reaction in classical novae to date. The $^{18}$F(p,$alpha$) rate remains highly uncertain at nova temperatures, resulting in a factor ~10 uncertainty in the predicted abundance of $^{18}$F ejected from nova explosions. We also found that the abundance of $^{18}$F may be strongly correlated with that of $^{19}$F. Conclusions. Despite numerous nuclear physics uncertainties affecting the $^{18}$F(p,$alpha$) reaction rate, which are dominated by unknown interference signs between 1/2$^+$ and 3/2$^+$ resonances, future experimental work should focus on firmly and precisely determining the directly measurable quantum properties of the subthreshold states in the compound nucleus $^{19}$Ne near 6.13 and 6.29 MeV.
Big bang nucleosynthesis (BBN) is the standard model theory for the production of the light nuclides during the early stages of the universe, taking place for a period of about 20 minutes after the big bang. Deuterium production, in particular, is highly sensitive to the primordial baryon density and the number of neutrino species, and its abundance serves as a sensitive test for the conditions in the early universe. The comparison of observed deuterium abundances with predicted ones requires reliable knowledge of the relevant thermonuclear reaction rates, and their corresponding uncertainties. Recent observations reported the primordial deuterium abundance with percent accuracy, but some theoretical predictions based on BBN are at tension with the measured values because of uncertainties in the cross section of the deuterium-burning reactions. In this work, we analyze the S-factor of the D(p,$gamma$)$^3$He reaction using a hierarchical Bayesian model. We take into account the results of eleven experiments, spanning the period of 1955--2021; more than any other study. We also present results for two different fitting functions, a two-parameter function based on microscopic nuclear theory and a four-parameter polynomial. Our recommended reaction rates have a 2.2% uncertainty at $0.8$~GK, which is the temperature most important for deuterium BBN. Differences between our rates and previous results are discussed.
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