arXiv subjects

R. J. deBoer

Publications and source records attributed to R. J. deBoer.

At least 19 recordsLinked to original sources

arXiv2025

Nuclear Physics Mid Term Plan at LNGS

The Istituto Nazionale di Fisica Nucleare-Laboratori Nazionali del Gran Sasso (LNGS) is one of the largest underground physics laboratory, a very peculiar environment suited for experiments in Astroparticle Physics, Nuclear Physics and Fundamental Symmetries. The newly established Bellotti Ion Beam facility represents a major advance in the possibilities of studying nuclear processes in an underground environment. A workshop was organized at LNGS in the framework of the Nuclear Physics Mid Term Plan in Italy, an initiative of the Nuclear Physics Division of the Instituto Nazionale di Fisica Nucleare to discuss the opportunities that will be possible to study in the near future by employing state-of-the-art detection systems. In this report, a detailed discussion of the outcome of the workshop is presented.

nucl-ex↗

arXiv2025

Solar fusion III: New data and theory for hydrogen-burning stars

In stars that lie on the main sequence in the Hertzsprung-Russel diagram, like our sun, hydrogen is fused to helium in a number of nuclear reaction chains and series, such as the proton-proton chain and the carbon-nitrogen-oxygen cycles. Precisely determined thermonuclear rates of these reactions lie at the foundation of the standard solar model. This review, the third decadal evaluation of the nuclear physics of hydrogen-burning stars, is motivated by the great advances made in recent years by solar neutrino observatories, putting experimental knowledge of the proton-proton chain neutrino fluxes in the few-percent precision range. The basis of the review is a one-week community meeting held in July 2022 in Berkeley, California, and many subsequent digital meetings and exchanges. The relevant reactions of solar and stellar hydrogen burning are reviewed here, from both theoretical and experimental perspectives. Recommendations for the state of the art of the astrophysical S-factor and its uncertainty are formulated for each of them. Several other topics of paramount importance for the solar model are reviewed, as well: recent and future neutrino experiments, electron screening, radiative opacities, and current and upcoming experimental facilities. In addition to reaction-specific recommendations, also general recommendations are formed.

astro-ph.SR↗

arXiv2025

Total cross section of $^{14}$N+$n$ from 0.1 to 12~MeV

The reaction $^{14}$N$(n,p)^{14}$C is one of the main neutron poisons during $s$-process nucleosynthesis. In addition, the reaction provides insight into the yields of atmospheric nuclear weapon testing. Because of their high level of sensitivity, total neutron cross sections provide a great deal of constraint on the modeling of reaction cross sections through the $R$-matrix analyses used for nuclear data evaluations. Yet for $^{14}$N+$n$, only one high sensitivity measurement is available and it lacks detailed information about its experimental conditions and uncertainties. With these motivations in mind, a new measurement of the $^{14}$N+$n$ total cross section has been performed at the nELBE facility. The cross sections were found to be in good agreement with previous data over much of the energy range with the key exception of the lowest energy resonance at a neutron energy of 433 keV.

nucl-ex↗

arXiv2024

Asymptotic normalization coefficients for $α+ {}^{12}{\rm C}$ synthesis and the $S$-factor for ${}^{12}{\rm C}(α, \,γ){}^{16}{\rm O}$ radiative capture

The $^{12}{\rm C}(α,γ)^{16}$O reaction, determining the survival of carbon in red giants, is of interest for nuclear reaction theory and nuclear astrophysics. A specific feature of the $^{16}$O nuclear structure is the presence of two subthreshold bound states, (6.92 MeV, 2$^+$) and (7.12 MeV, 1$^-$), that dominate the behavior of the low-energy $S$-factor. The strength of these subthreshold states is determined by their asymptotic normalization coefficients (ANCs), which need to be known with high accuracy. Recently, using a model-independent extrapolation method, Blokhintsev {\it et al.} [Eur. Phys. J. A {\bf 59} (2023) 162] determined the ANCs for the $α$-particle removal taking into account three subthreshold states in $^{16}$O. The goal of this paper is to address four main problems elucidating the impact of the subthreshold ANCs on the low-energy $S$-factor. Firstly, we analyse the connection between variations of the subthreshold ANCs and the low-energy $S$-factor, in particular, at the most effective energy of $300$ keV. Secondly, we calculate contributions to the $S(300\,{\rm keV})$-factor from the subthreshold $1^{-}$ and $2^{+}$ resonances, that are controlled by the subthreshold ANCs. We also evaluate the contribution of the uncertainties of the subthreshold ANCs to the budget of the low-energy $S$-factor uncertainty, especially, the $S(300\,{\rm keV})$-factor. Thirdly, we analyse interference of the subthreshold resonances (SRs) with higher resonances and with the $E1$ and $E2$ direct captures to the ground state. Finally, we investigate a correlated effect of the subthreshold and ground-state ANCs on the low-energy $S$-factor and, in particular, on the $S(300\,{\rm keV})$-factor.

nucl-th↗

arXiv2024

Strength measurement of the $E_α^{lab}$ = 830 keV resonance in $^{22}\rm{Ne}(α,n)^{25}\rm{Mg}$ reaction using a stilbene detector

The interplay between the $^{22}$Ne$(α,γ)^{26}$Mg and the competing $^{22}$Ne$(α,n)^{25}$Mg reactions determines the efficiency of the latter as a neutron source at the temperatures of stellar helium burning. In both cases, the rates are dominated by the $α$-cluster resonance at 830 keV. This resonance plays a particularly important role in determining the strength of the neutron flux for both the weak and main $s$-process as well as the $n$-process. Recent experimental studies based on transfer reactions suggest that the neutron and $γ$-ray strengths for this resonance are approximately equal. In this study, the $^{22}$Ne$(α,n)^{25}$Mg resonance strength has been remeasured and found to be similar to the previous direct studies. This reinforces an 830 keV resonance strength that is approximately a factor of three larger for the $^{22}$Ne$(α,n)^{25}$Mg reaction than for the $^{22}$Ne$(α,γ)^{26}$Mg reaction.

nucl-ex↗

arXiv2024

Energy, strength, and alpha width measurements of $E_{\rm{c.m.}} = 1323$ and $1487$ keV resonances in $^{15}$N($α,γ$)$^{19}$F

The $^{15}$N($α,γ$)$^{19}$F reaction produces $^{19}$F in asymptotic giant branch (AGB) stars, where the low energy tails of two resonances at $E_{\rm{c.m.}} = 1323 \pm 2$ and $1487 \pm 1.7$ keV are estimated to contribute about $30\%$ of the total reaction rate in these environments. However, recent measurements have shown discrepancies in the energies, the strengths, and the corresponding alpha widths of these two resonances, resulting in an increase in the systematic uncertainty of the extrapolated cross section to helium burning energies. With this motivation, we have undertaken new measurements of the $^{15}$N$(α,γ)^{19}$F at the University of Notre Dame Nuclear Science Laboratory. The setup consisted of an alpha particle beam impinged on a solid Ti$^{15}$N target with gamma-ray spectroscopy accomplished using a high purity germanium detector. Using the Doppler corrected gamma-ray energies, we confirmed the lower resonance energy to be $1321.6 \pm 0.6$ keV and found a value for the higher one of $1479.4 \pm 0.6$ keV that is more consistent with those found from previous elastic scattering studies. We found that the resonance strengths for both were consistent with most values found in the literature, but a larger alpha width has been recommended for the $E_{\rm{c.m.}} = 1487$ keV resonance. The larger alpha width suggests a reaction rate increase of about $15\%$ at temperatures $T < 0.1$ GK relevant to low mass AGB stars. The impact of the increased reaction rate requires further investigations.

nucl-ex↗

arXiv2024

Probabilistic neural networks for improved analyses with phenomenological models

Physics models typically contain adjustable parameters to reproduce measured data. While some parameters correspond directly to measured features in the data, others are unobservable. These unobservables can, in some cases, cause ambiguities in the extraction of observables from measured data, or lead to questions on the physical interpretation of fits that require these extra parameters. We propose a method based on deep learning to extract values of observables directly from the data without the need for unobservables. The key to our approach is to label the training data for the deep learning model with only the observables. After training, the deep learning model can determine the values of observables from measured data with no ambiguities arising from unobservables. We demonstrate this method on the phenomenological R-matrix that is widely utilized in nuclear physics to extract resonance parameters from cross section data. Our deep learning model based on Transformers successfully predicts nuclear properties from measurements with no need for the channel radius and background pole parameters required in traditional R-matrix analyses. Details and limitations of this method, which may be useful for studies of a wide range of phenomena, are discussed.

nucl-th↗

arXiv2022

Deep underground laboratory measurement of $^{13}$C($α$,$n$)$^{16}$O in the Gamow windows of the $s$- and $i$-processes

The $^{13}$C($α$,$n$)$^{16}$O reaction is the main neutron source for the slow-neutron-capture (s-) process in Asymptotic Giant Branch stars and for the intermediate (i-) process. Direct measurements at astrophysical energies in above-ground laboratories are hindered by the extremely small cross sections and vast cosmic-ray induced background. We performed the first consistent direct measurement in the range of $E_{\rm c.m.}=$0.24 MeV to 1.9 MeV using the accelerators at the China Jinping Underground Laboratory (CJPL) and Sichuan University. Our measurement covers almost the entire i-process Gamow window in which the large uncertainty of the previous experiments has been reduced from 60\% down to 15\%, eliminates the large systematic uncertainty in the extrapolation arising from the inconsistency of existing data sets, and provides a more reliable reaction rate for the studies of the s- and i-processes along with the first direct determination of the alpha strength for the near-threshold state.

nucl-ex↗

arXiv2022

The role of low-lying resonances for $^{10}$Be(p,$α$) reaction rate and implications for the formation of the Solar System

Evidence for the presence of short-lived radioactive isotopes when the Solar System formed is preserved in meteorites, providing insights into the conditions at the birth of our Sun. A low-mass core-collapse supernova had been postulated as a candidate for the origin of $^{10}$Be, reinforcing the idea that a supernova triggered the formation of the Solar System. We present a detailed study of the production of $^{10}$Be by the $ν$ process in supernovae, which is very sensitive to the reaction rate of the major destruction channel, $^{10}$Be(p,$α$)$^{7}$Li. With data from recent nuclear experiments that show the presence of a resonant state in $^{11}$B at $\approx$~193 keV, we derive new values for the $^{10}$Be(p,$α$)$^{7}$Li reaction rate which are significantly higher than previous estimates. We show that, with the new $^{10}$Be(p,$α$)$^{7}$Li reaction rate, a low mass CCSN is unlikely to produce enough $^{10}$Be to explain the observed $^{10}$Be/ $^{9}$Be ratio in meteorites, even for a wide range of neutrino spectra considered in our models. These findings point towards spallation reactions induced by solar energetic particles in the early Solar System as the origin of $^{10}$Be.

astro-ph.HE↗

arXiv2022

Horizons: Nuclear Astrophysics in the 2020s and Beyond

Nuclear Astrophysics is a field at the intersection of nuclear physics and astrophysics, which seeks to understand the nuclear engines of astronomical objects and the origin of the chemical elements. This white paper summarizes progress and status of the field, the new open questions that have emerged, and the tremendous scientific opportunities that have opened up with major advances in capabilities across an ever growing number of disciplines and subfields that need to be integrated. We take a holistic view of the field discussing the unique challenges and opportunities in nuclear astrophysics in regards to science, diversity, education, and the interdisciplinarity and breadth of the field. Clearly nuclear astrophysics is a dynamic field with a bright future that is entering a new era of discovery opportunities.

nucl-ex↗

arXiv2021

Observing intermediate-mass black holes and the upper--stellar-mass gap with LIGO and Virgo

Using ground-based gravitational-wave detectors, we probe the mass function of intermediate-mass black holes (IMBHs) wherein we also include BHs in the upper mass gap $\sim 60-130~M_\odot$. Employing the projected sensitivity of the upcoming LIGO and Virgo fourth observing (O4) run, we perform Bayesian analysis on quasi-circular non-precessing, spinning IMBH binaries (IMBHBs) with total masses $50\mbox{--} 500\, M_\odot$, mass ratios 1.25, 4, and 10, and dimensionless spins up to 0.95, and estimate the precision with which the source-frame parameters can be measured. We find that, at $2σ$, the mass of the heavier component of IMBHBs can be constrained with an uncertainty of $\sim 10-40\%$ at a signal-to-noise ratio of $20$. Focusing on the stellar-mass gap with new tabulations of the $^{12}\text{C}(α, γ)^{16} \text{O}$ reaction rate and its uncertanties, we evolve massive helium core stars using \MESA\, to establish the lower and upper edge of the mass gap as $\simeq$\,59$^{+34}_{-13}$\,$M_{\odot}$ and $\simeq$\,139$^{+30}_{-14}$\,$M_{\odot}$ respectively, where the error bars give the mass range that follows from the $\pm 3σ$ uncertainty in the $^{12}\text{C}(α, γ) ^{16} \text{O}$ nuclear reaction rate. We find that high resolution of the tabulated reaction rate and fine temporal resolution are necessary to resolve the peak of the BH mass spectrum. We then study IMBHBs with components lying in the mass gap and show that the O4 run will be able to robustly identify most such systems. Finally, we re-analyse GW190521 with a state-of-the-art aligned-spin waveform model, finding that the primary mass lies in the mass gap with 90\% credibility.

gr-qc↗

arXiv2021

The Status and Future of Direct Nuclear Reaction Measurements for Stellar Burning

The study of stellar burning began just over 100 years ago. Nonetheless, we do not yet have a detailed picture of the nucleosynthesis within stars and how nucleosynthesis impacts stellar structure and the remnants of stellar evolution. Achieving this understanding will require precise direct measurements of the nuclear reactions involved. This report summarizes the status of direct measurements for stellar burning, focusing on developments of the last couple of decades, and offering a prospectus of near-future developments.

nucl-ex↗

arXiv2020

Lifetime measurements of excited states in $^{15}$O

The CNO cycle is the main energy source in stars more massive than our sun, it defines the energy production and the cycle time that lead to the lifetime of massive stars, and it is an important tool for the determination of the age of globular clusters. One of the largest uncertainties in the CNO chain of reactions comes from the uncertainty in the $^{14}$N$(p,γ)^{15}$O reaction rate. This uncertainty arises predominantly from the uncertainty in the lifetime of the sub-threshold state in $^{15}$O at $E_{x}$ = 6792 keV. Previous measurements of this state's lifetime are significantly discrepant. Here, we report on a new lifetime measurement of this state, as well as the excited states in $^{15}$O at $E_{x}$ = 5181 keV and $E_{x}$ = 6172 keV, via the $^{14}$N$(p,γ)^{15}$O reaction at proton energies of $E_{p} = 1020$ keV and $E_{p} = 1570$ keV. The lifetimes have been determined with the Doppler-Shift Attenuation Method (DSAM) with three separate, nitrogen-implanted targets with Mo, Ta, and W backing. We obtained lifetimes from the weighted average of the three measurements, allowing us to account for systematic differences between the backing materials. For the 6792 keV state, we obtained a $τ= 0.6 \pm 0.4$ fs. To provide cross-validation of our method, we measured the known lifetimes of the states at 5181 keV and 6172 keV to be $τ= 7.5 \pm 3.0$ and $τ= 0.7 \pm 0.5$ fs, respectively, which are in good agreement with previous measurements.

nucl-ex↗

arXiv2020

New measurement of $^{12}$C+$^{12}$C fusion reaction at astrophysical energies

Carbon and oxygen burning reactions, in particular, $^{12}$C+$^{12}$C fusion, are important for the understanding and interpretation of the late phases of stellar evolution as well as the ignition and nucleosynthesis in cataclysmic binary systems such as type Ia supernovae and x-ray superbursts. A new measurement of this reaction has been performed at the University of Notre Dame using particle-$γ$ coincidence techniques with SAND (a silicon detector array) at the high-intensity 5U Pelletron accelerator. New results for $^{12}$C+$^{12}$C fusion at low energies relevant to nuclear astrophysics are reported. They show strong disagreement with a recent measurement using the indirect Trojan Horse method. The impact on the carbon burning process under astrophysical scenarios will be discussed.

nucl-ex↗

arXiv2017

The 12C(a,g)16O reaction and its implications for stellar helium burning

The creation of carbon and oxygen in our universe is one of the forefront questions in nuclear astrophysics. The determination of the abundance of these elements is key to both our understanding of the formation of life on earth and to the life cycles of stars. While nearly all models of different nucleosynthesis environments are affected by the production of carbon and oxygen, a key ingredient, the precise determination of the reaction rate of 12C(a,g)16O, has long remained elusive. This is owed to the reaction's inaccessibility, both experimentally and theoretically. Nuclear theory has struggled to calculate this reaction rate because the cross section is produced through different underlying nuclear mechanisms. Isospin selection rules suppress the E1 component of the ground state cross section, creating a unique situation where the E1 and E2 contributions are of nearly equal amplitudes. Experimentally there have also been great challenges. Measurements have been pushed to the limits of state of the art techniques, often developed for just these measurements. The data have been plagued by uncharacterized uncertainties, often the result of the novel measurement techniques, that have made the different results challenging to reconcile. However, the situation has markedly improved in recent years, and the desired level of uncertainty, about 10%, may be in sight. In this review the current understanding of this critical reaction is summarized. The emphasis is placed primarily on the experimental work and interpretation of the reaction data, but discussions of the theory and astrophysics are also pursued. The main goal is to summarize and clarify the current understanding of the reaction and then point the way forward to an improved determination of the reaction rate.

nucl-ex↗

arXiv2016

Shell and explosive hydrogen burning

The nucleosynthesis of light elements, from helium up to silicon, mainly occurs in Red Giant and Asymptotic Giant Branch stars and Novae. The relative abundances of the synthesized nuclides critically depend on the rates of the nuclear processes involved, often through non-trivial reaction chains, combined with complex mixing mechanisms. In this review, we summarize the contributions made by LUNA experiments in furthering our understanding of nuclear reaction rates necessary for modeling nucleosynthesis in AGB stars and Novae explosions.

nucl-ex↗

arXiv2015

Probing astrophysically important states in $^{26}$Mg nucleus to study neutron sources for the $s$-Process

The $^{22}$Ne($α$,n)$^{25}$Mg reaction is the dominant neutron source for the slow neutron capture process ($s$-process) in massive stars and contributes, together with the $^{13}$C($α$,n)$^{16}$O, to the production of neutrons for the $s$-process in Asymptotic Giant Branch (AGB) stars. However, the reaction is endothermic and competes directly with the $^{22}$Ne($α,γ)^{26}$Mg radiative capture. The uncertainties for both reactions are large owing to the uncertainty in the level structure of $^{26}$Mg near the alpha and neutron separation energies. These uncertainties are affecting the s-process nucleosynthesis calculations in theoretical stellar models. Indirect studies in the past have been successful in determining the energies, $γ$-ray and neutron widths of the $^{26}$Mg states in the energy region of interest. But, the high Coulomb barrier hinders a direct measurement of the resonance strengths, which are determined by the $α$-widths for these states. The goal of the present experiments is to identify the critical resonance states and to precisely measure the $α$-widths by $α$ transfer techniques . Hence, the $α$-inelastic scattering and $α$-transfer measurements were performed on a solid $^{26}$Mg target and a $^{22}$Ne gas target, respectively, using the Grand Raiden Spectrometer at RCNP, Osaka, Japan. Six levels (E$_x$ = 10717 keV , 10822 keV, 10951 keV, 11085 keV, 11167 keV and 11317 keV) have been observed above the $α$-threshold in the region of interest (10.61 - 11.32 MeV). The rates are dominated in both reaction channels by the resonance contributions of the states at E$_x$ = 10951, 11167 and 11317 keV. The E$_x$ =11167 keV has the most appreciable impact on the ($α,γ$) rate and therefore plays an important role for the prediction of the neutron production in s-process environments.

nucl-ex↗

arXiv2015

The first direct measurement of 12C(12C,n)23Mg at stellar energies

Neutrons produced by the carbon fusion reaction 12C(12C,n)23Mg play an important role in stellar nucleosynthesis. However, past studies have shown large discrepancies between experimental data and theory, leading to an uncertain cross section extrapolation at astrophysical energies. We present the first direct measurement that extends deep into the astrophysical energy range along with a new and improved extrapolation technique based on experimental data from the mirror reaction 12C(12C,p)23Na. The new reaction rate has been determined with a well-defined uncertainty that exceeds the precision required by astrophysics models. Using our constrained rate, we find that 12C(12C,n)23Mg is crucial to the production of Na and Al in Pop-III Pair Instability Supernovae. It also plays a non-negligible role in the production of weak s-process elements as well as in the production of the important galactic gamma-ray emitter 60Fe.

nucl-ex↗