arXiv subjects

Richard Longland

Publications and source records attributed to Richard Longland.

At least 19 recordsLinked to original sources

arXiv2026

The 2025 Evaluation of Experimental Thermonuclear Reaction Rates (ETR25)

This work describes the formalism for estimating thermonuclear reaction rates for astrophysical applications, emphasizing modern statistical approaches such as Monte-Carlo sampling and Bayesian models. We discuss related topics including the calculation of resonance energies from nuclear Q values, indirect estimates of particle partial widths, and matching of reaction rates at elevated temperatures to statistical-model results. We have evaluated available experimental data on cross sections, resonance energies and strengths, partial widths, life-times, spin-parities, and spectroscopic factors. Based on these results, we have estimated numerical values of 78 experimental charged-particle thermonuclear reaction rates for target nuclei in the A = 2 to 40 mass region, for temperatures ranging from 1 MK to 10 GK. For each reaction, three rate values are provided: low, median, and high, corresponding to the 16th, 50th, and 84th percentiles, respectively, of the cumulative reaction rate probability density distribution. Additionally, we present the factor uncertainty of each rate at each temperature grid point. These results enable users to sample the reaction rate probability density in nucleosynthesis calculations, facilitating uncertainty estimates of nuclidic abundances. The rates presented here refer to their laboratory values. For use in stellar model simulations, these values need to be corrected for the effects of thermal excitations of the interacting nuclei. For each reaction, we include graphs that illustrate the fractional contributions to the overall reaction rate along with the associated uncertainty. These visuals are designed to assist both stellar modelers and nuclear experimentalists by identifying the primary sources of rate uncertainty at specific stellar temperatures. A graphical comparison with earlier Monte-Carlo rates is also provided.

astro-ph.SR↗

arXiv2026

Propagating Uncertainties from Nuclear Physics to Gamma-rays in Core Collapse Supernovae

Nuclear yields are powerful probes of supernova explosions, their engines and their progenitors. In addition, as we improve our understanding of these explosions, we can use nuclear yields to probe dense matter and neutrino physics, both of which play a critical role in the central supernova engine. Especially with upcoming gamma-ray detectors that can directly detect radioactive isotopes out to increasing distances from gamma-rays emitted during their decay, nuclear yields have the potential to provide some of the most direct probes of supernova engines and stellar burning. To utilize these probes, we must understand and limit the uncertainties in their production. Uncertainties in the nuclear physics can be minimized by combining both laboratory experiments and nuclear theory. Similarly, astrophysical uncertainties caused by simplified explosion trajectories can be minimized by higher-fidelity stellar-evolution and supernova-engine models. This paper reviews the physics and astrophysics uncertainties in modeling nucleosynthetic yields, identifying the key areas of study needed to maximize the potential of supernova yields as probes of astrophysical transients and dense-matter physics.

astro-ph.HE↗

arXiv2025

Bayesian Analysis of the $^{86}$Sr$(\alpha, \alpha)$ Reaction to Constrain the $^{86}$Sr$(\alpha, n)$ Cross Section at Astrophysical Energies

The Alpha Optical Model Potential (\aomp \!) is a phenomenological approach used to describe elastic scattering where multiple reaction channels are open. It is one of the most critical inputs for the calculation of thermonuclear reaction rates in explosive stellar environments, but uncertainties within the $\alpha$-OMP lead to imprecise predictions hindering comparisons between calculations and observations. In order to improve the precision of the $\alpha$-OMP, additional nuclear physics data are required. In this paper, a measurement of the $^{86}$Sr($\alpha$, $\alpha$) elastic scattering cross section at multiple energies is reported. A local optical potential is constructed via a fully Bayesian analysis of the elastic scattering data. The resulting uncertainties on the low energy cross sections relevant to nuclear astrophysics are then calculated and shown to be on the order of $50 \%$.

nucl-ex↗

arXiv2025

Indirect Measurement of the $^{23}\textbf{Na}(p,\gamma)^{24}$Mg Direct Capture Reaction Rate via ($^3$He,d) Spectroscopy

The cross section of the $^{23}\text{Na}(p,\gamma)^{24}\text{Mg}$ reaction is dominated by direct capture at low energies relevant for stellar burning. Such cross sections can be constrained using spectroscopic factors($C^2S$) or asymptotic normalization coefficients(ANCs) from transfer reactions. In this work, the $^{23}\text{Na}(^3\text{He},d)^{24}\text{Mg}$ reaction was measured at $E_{lab}=21$ MeV to extract spectroscopic factors for $^{24}\text{Mg}$ states with excitation energies in $E_x=7\sim12~$MeV using the Enge split-pole spectrograph at the Triangle Universities Nuclear Laboratory. A new non-resonant astrophysical S factor and the direct capture reaction rate for the $^{23}\text{Na}(p,\gamma)$ reaction are calculated and presented based on this measurement. The new rate at $T<0.04$ GK is 43$\%$ smaller than in previous studies. Rigorous treatments of uncertainties are presented using a Bayesian Markov Chain Monte Carlo (MCMC) method. Sources of uncertainties for computing the direct capture cross section are also discussed in detail.

nucl-ex↗

arXiv2025

Low-metallicity nova explosions: a site for weak rp-process nucleosynthesis

Classical novae are common cataclysmic events involving a binary system of a white dwarf and a main sequence or red giant companion star. In metal-poor environments, these explosions produce ejecta different from their solar counterparts due to the accretion of sub-solar metallicity material onto the white dwarf. In particular, it has been suggested that the nucleosynthesis flow in such low-metallicity nova explosions extends up to the Cu-Zn region, much beyond the expected endpoint, around Ca, predicted for solar-metallicity classical novae. This behavior resembles a weak rp-process, and such nuclear activity has never been observed in accreting white dwarf binaries with typical accretion flows. In this work, we study the characteristics of the weak rp-process for four nova models with metallicities $Z= 2\times 10^{-9}$, $10^{-7}$, $2\times 10^{-6}$, and $2\times 10^{-5}$, and explore the impact of the nuclear physics uncertainties via a Monte Carlo sensitivity study. We identify nuclear reactions whose uncertainties affect the production of intermediate-mass nuclei under these conditions. These reactions and relevant nuclear quantities are targets for measurements at stable or radioactive beam facilities to reduce their rate uncertainties.

astro-ph.HE↗

arXiv2025

Investigation of $^{31}$P levels near the proton threshold by Nuclear Resonance Fluorescence and the impact on the $^{30}$Si(p,$\gamma$)$^{31}$P thermonuclear rate

We investigated the nuclear structure of $^{31}$P near the proton threshold using Nuclear Resonance Fluorescence (NRF) to refine the properties of key resonances in the $^{30}$Si(p,$\gamma$)$^{31}$P reaction, which is critical for nucleosynthesis in stellar environments. Excitation energies and spin-parities were determined for several states, including two unobserved resonances at $E_r$ $=$ $18.7$~keV and $E_r$ $=$ $50.5$~keV. The angular correlation analysis enabled the first unambiguous determination of the orbital angular momentum transfer for these states. These results provide a significant update to the $^{30}$Si(p,$\gamma$)$^{31}$P thermonuclear reaction rate, with direct implications for models of nucleosynthesis in globular clusters and other astrophysical sites. The revised rate is substantially lower than previous estimates at temperatures below $200$~MK, affecting predictions for silicon isotopic abundances in stellar environments. Our work demonstrates the power of NRF in constraining nuclear properties, and provides a framework for future studies of low-energy resonances relevant to astrophysical reaction rates.

nucl-ex↗

arXiv2024

High Resolution Study of $^{40}$Ca to Constrain Potassium Nucleosynthesis in NGC 2419

The globular cluster NGC 2419 was the first to exhibit a Mg-K anticorrelation, linked to hydrogen burning at temperatures between 80-260 MK. However, the key K-destroying reaction, $^{39}\mathrm{K}(p,γ)^{40}\mathrm{Ca}$, has a large rate uncertainty in this range. We significantly constrain this rate with a high resolution $^{39}\mathrm{K}(^{3}\mathrm{He},d)^{40}\mathrm{Ca}$ study. We resolve the E$_{\text{r}}^{\text{c.m.}} = 154$ keV resonance in $^{39}\mathrm{K}+p$ for the first time, increasing the previous rate by up to a factor 13 and reducing its $1σ$ width by up to a factor of 42. Reaction network calculations for NGC 2419 suggest that this could lower temperatures needed to reproduce the Mg-K anticorrelation.

nucl-ex↗

arXiv2022

White Paper on the TUNL Nuclear Astrophysics Program

The White Paper describes the nuclear astrophysics program at the Triangle Universities Nuclear Laboratory (TUNL), with the intent of providing input for the 2023 NSAC Long Range planning process. TUNL is operated jointly by North Carolina Central University, North Carolina State University, The University of North Carolina at Chapel Hill, and Duke University. TUNL houses three world-class facilities for nuclear astrophysics research: the Laboratory for Experimental Nuclear Astrophysics (LENA); the Enge Magnetic Spectrograph; and the High-Intensity gamma-ray Source (HIgS). We discuss past successes, the present status, and future plans.

nucl-ex↗

arXiv2020

Correlated Energy Uncertainties in Reaction Rate Calculations

Context. Monte Carlo methods can be used to evaluate the uncertainty of a reaction rate that arises from many uncertain nuclear inputs. However, until now no attempt has been made to find the effect of correlated energy uncertainties in input resonance parameters. Aims. To investigate the impact of correlated energy uncertainties on reaction rates. Methods. Using a combination of numerical and Monte Carlo variation of resonance energies, the effect of correlations are investigated. Five reactions are considered: two fictional, illustrative cases and three reactions whose rates are of current interest. Results. The effect of correlations in resonance energies depends on the specific reaction cross section and temperatures considered. When several resonances contribute equally to a reaction rate, and are located either side of the Gamow peak, correlations between their energies dilute their effect on reaction rate uncertainties. If they are both located above or below the maximum of the Gamow peak, however, correlations between their resonance energies can increase the reaction rate uncertainties. This effect can be hard to predict for complex reactions with wide and narrow resonances contributing to the reaction rate.

astro-ph.IM↗

arXiv2019

Thermonuclear Reaction Rate of $^{30}$Si(p,$γ$)$^{31}$P

Silicon synthesis in high-temperature hydrogen burning environments presents one possible avenue for the study of abundance anomalies in globular clusters. This was suggested in a previous study, which found that the large uncertainties associated with the $^{30}$Si(p,$γ$)$^{31}$P reaction rate preclude a firm understanding of the stellar conditions that give rise to the Mg-K anti-correlation observed in the globular cluster NGC 2419. In an effort to improve the reaction rate, we present new strength measurements of the $E_r^{lab} = 435$ keV and $E_r^{lab} = 501$ keV resonances in $^{30}$Si(p,$γ$)$^{31}$P. For the former, which was previously unobserved, we obtain a resonance strength of $ωγ= (1.28 \pm 0.25$) $\times 10^{-4}$ eV. For the latter, we obtain a value of $ωγ= (1.88 \pm 0.14)$ $\times 10^{-1}$ eV, which has a smaller uncertainty compared to previously measured strengths. Based on these results, the thermonuclear reaction rate has been re-evaluated. The impact of the new measurements is to lower the reaction rate by a factor of $\approx$10 at temperatures important to the study of NGC 2419. The rate uncertainty at these temperatures has also been reduced significantly.

nucl-ex↗

arXiv2019

A study of $^{35}$Cl excited states via $^{32}$S($α, p$)

Presolar grains originating in oxygen-neon novae may be identified by their sulfur isotopic ratios compared with theoretical estimates. These ratios depend on reliable $^{33}$S($p, γ$)$^{34}$Cl and $^{34}$S($p, γ$)$^{35}$Cl reaction rates. The latter rate has recently been computed based on experimental input, and many new excited states in $^{35}$Cl were discovered above the proton threshold. The experimental $^{34}$S($p, γ$)$^{35}$Cl rate was found to be 2 - 5 times smaller than the theoretical one, and the simulated $^{34}$S/$^{32}$S isotopic ratio for nova presolar grains was thus predicted to be smaller than that of type II supernova grains by up to a factor of 3.7. The present study was performed to confirm the existence of these new resonances, and to improve the remaining uncertainties in the $^{34}$S($p, γ$)$^{35}$Cl reaction rate. Energies and spin-parities of the $^{35}$Cl excited levels were investigated with an Enge split-pole spectrograph using the $^{32}$S($α, p$)$^{35}$Cl reaction. Differential cross sections of the outgoing protons were measured at $E_α$ = 21 MeV. The existence of the newly discovered states are largely confirmed, although a few states were not observed in this study. The spins and parities of several $^{35}$Cl states were assigned tentatively for the first time. The present $^{34}$S($p, γ$)$^{35}$Cl experimental thermonuclear reaction rate is consistent within 1$σ$ with the previous evaluation. However, our rate uncertainty is larger due to a more realistic treatment of the experimental uncertainties. The uncertainty in the present rate is up to a factor of 3.5 at nova temperatures. We recommend future work to focus on the unknown properties of four excited states of $^{35}$Cl at 6643 keV, 6761 keV, 6780 keV, and 6800 keV.

nucl-ex↗

arXiv2018

On the parallelization of stellar evolution codes

Multidimensional nucleosynthesis studies with hundreds of nuclei linked through thousands of nuclear processes are still computationally prohibitive. To date, most nucleosynthesis studies rely either on hydrostatic/hydrodynamic simulations in spherical symmetry, or on post-processing simulations using temperature and density versus time profiles directly linked to huge nuclear reaction networks. Parallel computing has been regarded as the main permitting factor of computationally intensive simulations. This paper explores the different pros and cons in the parallelization of stellar codes, providing recommendations on when and how parallelization may help in improving the performance of a code for astrophysical applications. We report on different parallelization strategies succesfully applied to the spherically symmetric, Lagrangian, implicit hydrodynamic code SHIVA, extensively used in the modeling of classical novae and type I X-ray bursts. Speed-up factors of 26 and 35 have been obtained with a parallelized version of SHIVA, in a 200-shell simulation of a type I X-ray burst carried out with two nuclear reaction networks: a reduced one, consisting of 324 isotopes and 1392 reactions, and a more extended network with 606 nuclides and 3551 nuclear interactions. Maximum speed-ups of 41 (324-isotope network) and 85 (606-isotope network), are also predicted for 200 cores, stressing that the number of shells of the computational domain constitutes an effective upper limit for the maximum number of cores that could be used in a parallel application.

astro-ph.SR↗

arXiv2018

Excited states of $^{39}$Ca and their significance in nova nucleosynthesis

Background: Discrepancies exist between the observed abundances of argon and calcium in oxygen-neon nova ejecta and those predicted by nova models. An improved characterization of the $^{38}$K($p, γ$)$^{39}$Ca reaction rate over the nova temperature regime ($\sim$ 0.1 -- 0.4 GK), and thus the nuclear structure of $^{39}$Ca above the proton threshold (5770.92(63) keV), is necessary to resolve these contradictions. Purpose: The present study was performed to search for low-spin proton resonances in the $^{38}$K $+$ $p$ system, and to improve the uncertainties in energies of the known astrophysically significant proton resonances in $^{39}$Ca. Method: The level structure of $^{39}$Ca was investigated via high-resolution charged-particle spectroscopy with an Enge split-pole spectrograph using the $^{40}$Ca($^{3}$He, $α$)$^{39}$Ca reaction. Differential cross sections were measured over 6 laboratory angles at 21 MeV. Distorted-wave Born approximation calculations were performed to constrain the spin-parity assignments of observed levels with special attention to those significant in determination of the $^{38}$K($p, γ$)$^{39}$Ca reaction rate over the nova temperature regime. Results: The resonance energies corresponding to two out of three astrophysically important states at 6154(5) and 6472.2(24) keV are measured with better precision than previous charged-particle spectroscopy measurements. A tentatively new state is discovered at 5908(3) keV. The spin-parity assignments of a few of the astrophysically important resonances are determined. Conclusions: The present $^{38}$K($p, γ$)$^{39}$Ca upper limit thermonuclear reaction rate at 0.1 -- 0.4 GK is higher than that determined in [Physical Review C 97 (2018) 025802] by at most a factor of 1.4 at 0.1 GK.

nucl-ex↗

arXiv2018

Reaction rates for the $^{39}$K(p,$γ$)$^{40}$Ca reaction

The magnesium-potassium anti-correlation observed in globular cluster NGC2419 can be explained by nuclear burning of hydrogen in hot environments. The exact site of this nuclear burning is, as yet, unknown. In order to constrain the sites responsible for this anti-correlation, the nuclear reactions involved must be well understood. The $^{39}$K+p reactions are one such pair of reactions. Here, we report a new evaluation of the $^{39}$K(p,$γ$)$^{40}$Ca reaction rate by taking into account ambiguities and measurement uncertainties in the nuclear data. The uncertainty in the $^{39}$K(p,$γ$)$^{40}$Ca reaction rate is larger than previously assumed, and its influence on nucleosynthesis models is demonstrated. We find the $^{39}$K(p,$γ$)$^{40}$Ca reaction cross section should be the focus of future experimental study to help constrain models aimed at explaining the magnesium-potassium anti-correlation in globular clusters.

nucl-ex↗

arXiv2018

The Focal plane Detector Package on the TUNL Split-pole Spectrograph

A focal plane detector for the Enge Split-pole Spectrograph at Triangle Universities Nuclear Laboratory has been designed. The detector package consists of two position sensitive gas avalanche counters, a gas proportionality energy loss section, and a residual energy scintillator. This setup allows both particle identification and focal plane reconstruction. In this paper we will detail the construction of each section along with their accompanying electronics and data acquisition. Effects of energy loss throughout the detector, ray tracing procedures, and resolution as a function of fill pressure and bias voltage are also investigated. A measurement of the $^{27}\!$Al$(d,p)$ reaction is used to demonstrate detector performance and to illustrate a Bayesian method of energy calibration.

physics.ins-det↗

arXiv2017

Correlated Uncertainties in Monte Carlo Reaction Rate Calculations

Context. Monte Carlo methods have enabled nuclear reaction rates from uncertain inputs to be presented in a statistically meaningful manner. However, these uncertainties are currently computed assuming no correlations between the physical quantities that enter those calculations. This is not always an appropriate assumption. Astrophysically important reactions are often dominated by resonances, whose properties are usually normalized to a well-known reference resonance. This insight provides a basis from which to develop a flexible framework for including correlations in Monte Carlo reaction rate calculations. Aims. The aim of this work is to develop and test a method for including correlations in Monte Carlo reaction rate calculations when the input has been normalized to a common reference. Methods. A mathematical framework is developed for including correlations between input parameters in Monte Carlo reaction rate calculations. The magnitude of those correlations is calculated from the uncertainties typically reported in experimental papers, where full correlation information is not available. The method is applied to four illustrative examples: a fictional 3-resonance reaction, $^{27}$Al(p,$γ$)$^{28}$Si, $^{23}$Na(p,$α$)$^{20}$Ne, and $^{23}$Na($α$,p)$^{26}$Al. Results. Reaction rates at low temperatures that are dominated by a few isolated resonances are found to minimally impacted by correlation effects. However, reaction rates determined from many overlapping resonances can be significantly affected. Uncertainties in the $^{23}$Na($α$,p)$^{26}$Al reaction, for example, increase by up to a factor of 5. This highlights the need to take correlation effects into account in reaction rate calculations, and provide insight into which cases are expected to be most affected by them. The impact of correlation effects on nucleosynthesis is also investigated.

astro-ph.IM↗

arXiv2015

New reaction rates for improved primordial D/H calculation and the cosmic evolution of deuterium

Primordial or big bang nucleosynthesis (BBN) is one of the three historical strong evidences for the big bang model. Standard BBN is now a parameter free theory, since the baryonic density of the Universe has been deduced with an unprecedented precision from observations of the anisotropies of the cosmic microwave background (CMB) radiation. There is a good agreement between the primordial abundances of 4He, D, 3He and 7Li deduced from observations and from primordial nucleosynthesis calculations. However, the 7Li calculated abundance is significantly higher than the one deduced from spectroscopic observations and remains an open problem. In addition, recent deuterium observations have drastically reduced the uncertainty on D/H, to reach a value of 1.6%. It needs to be matched by BBN predictions whose precision is now limited by thermonuclear reaction rate uncertainties. This is especially important as many attempts to reconcile Li observations with models lead to an increased D prediction. Here, we re-evaluates the D(p,g)3He, D(d,n)3He and D(d,p)3H reaction rates that govern deuterium destruction, incorporating new experimental data and carefully accounting for systematic uncertainties. Contrary to previous evaluations, we use theoretical ab initio models for the energy dependence of the S-factors. As a result, these rates increase at BBN temperatures, leading to a reduced value of D/H = (2.45$\pm0.10)\times10^{-5}$ (2$σ$), in agreement with observations.

astro-ph.CO↗

arXiv2014

Statistical Methods for Thermonuclear Reaction Rates and Nucleosynthesis Simulations

Rigorous statistical methods for estimating thermonuclear reaction rates and nucleosynthesis are becoming increasingly established in nuclear astrophysics. The main challenge being faced is that experimental reaction rates are highly complex quantities derived from a multitude of different measured nuclear parameters (e.g., astrophysical S-factors, resonance energies and strengths, particle and gamma-ray partial widths). We discuss the application of the Monte Carlo method to two distinct, but related, questions. First, given a set of measured nuclear parameters, how can one best estimate the resulting thermonuclear reaction rates and associated uncertainties? Second, given a set of appropriate reaction rates, how can one best estimate the abundances from nucleosynthesis (i.e., reaction network) calculations? The techniques described here provide probability density functions that can be used to derive statistically meaningful reaction rates and final abundances for any desired coverage probability. Examples are given for applications to s-process neutron sources, core-collapse supernovae, classical novae, and big bang nucleosynthesis.

nucl-ex↗