We examine the relationship between the asymptotic normalization coefficient (ANC) of 6Li and other low-energy observables in the alpha-deuteron system. Our analysis uses a set of calculations carried out within the ab initio no core shell model with continuum (NCSMC) using a variety of inter-nucleon interactions and basis sizes, and yielding 6Li deuteron separation energies between 1.3 and 1.8 MeV (Hebborn et al 2022 Phys. Rev. Lett. 129 042503). These NCSMC calculations show that the square of the ANC is strongly correlated with the separation energy over this range. In this work, we investigate the origin of this correlation using the phenomenological R-matrix, a single-channel potential and a perturbative approach. We show that this correlation occurs because the depth of the alpha-deuteron central potential changes by only a small relative amount as the separation energy varies. We then investigate if the ANC can be accurately extracted from alpha-deuteron phase shifts in an ideal case in which low-energy data are available and there are no experimental errors. We find that both R-matrix and Coulomb-modified effective-range theory (CM-ERE) yield extracted ANCs close to, although not exactly equal to, the NCSMC value, provided the extrapolation is constrained by the known position of the bound-state pole and at least three terms are included in the fit function. The R-matrix approach converges faster than the CM-ERE as the number of parameters increases and is also more robust against the inclusion of low-energy and high-energy phase shift data. Finally, our study also shows that a naive quantification of uncertainties by comparing different truncations used in both theories is not accurate, and suggests the accuracy of ANCs extracted from phase shift data needs further investigation.

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.

Measurements of the elastic scattering cross section of $^{3}\mathrm{He}$ and $^{4}\mathrm{He}$ are important in order to improve constraints on theoretical models of $^{4}\mathrm{He}(^{3}\mathrm{He},\ensuremath{\gamma})^{7}\mathrm{Be}$, a key reaction in Big Bang nucleosynthesis and solar neutrino production. The astrophysical $S$ factor for this reaction is a significant source of uncertainty in the standard-solar-model prediction of the $^{7}\mathrm{Be}$ and $^{8}\mathrm{B}$ solar neutrino fluxes. The elastic scattering measurements reported in the literature do not extend to low energies and lack proper uncertainty quantification. A new measurement of the $^{4}\mathrm{He}(^{3}\mathrm{He},^{3}\mathrm{He})^{4}\mathrm{He}$ reaction has been made at center-of-mass energies ${E}_{\text{c.m.}}=0.38\ensuremath{-}3.13$ MeV using the Scattering of Nuclei in Inverse Kinematics (SONIK) scattering chamber: a windowless, extended gas target surrounded by an array of 30 collimated silicon charged particle detectors situated at TRIUMF. This is the first elastic scattering measurement of $^{3}\mathrm{He}+^{4}\mathrm{He}$ made below 500 keV and it has greater angular range and better precision than previous measurements. The elastic scattering data were analyzed using both $R$-matrix and halo effective field theory frameworks, and values of the $s$-wave scattering length and effective range were extracted. The resulting improvement in knowledge of the $s$-wave effective-range function at low energies reduces the overall uncertainty in ${S}_{34}$ at solar energies.

We report on the first experimental measurements made at a magnetic confinement fusion device of the tritium(T)-tritium(T) reaction T + T 4 He + 2 n indicating the presence of the intermediate two -body resonant reaction T + T 5 He + n . During the second deuterium -tritium campaign (DTE2) at the Joint European Torus, measurements of fusion plasmas with high tritium concentrations, n T / ( n T + n D ) approximate to 0 . 99, heated with tritium neutral beam injection, were performed using the neutron time -of -flight (TOF) spectrometer TOFOR. We detect a peak in the neutron emission TOF spectrum consistent with the two -body resonant reaction. The TT neutron emission energy spectrum is modeled using an R -matrix framework where the distributions of the most likely model parameters given our experimental TOF data are determined utilizing a Markov chain Monte Carlo approach. We compare our best estimate of the T + T neutron emission energy spectrum with results obtained at inertial confinement fusion experiments at the OMEGA facility and find a spectral shape that is consistent with the energy dependency in the neutron spectrum observed at OMEGA.

The cross section of the C13(α,n)O16 reaction is needed for nuclear astrophysics and applications to a precision of 10% or better, yet inconsistencies among 50 years of experimental studies currently lead to an uncertainty of ≈15%. Using a state-of-the-art neutron detection array, we have performed a high resolution differential cross section study covering a broad energy range. These measurements result in a dramatic improvement in the extrapolation of the cross section to stellar energies potentially reducing the uncertainty to ≈5% and resolving long standing discrepancies in higher energy data.Received 18 March 2023Revised 5 September 2023Accepted 17 January 2024DOI:https://doi.org/10.1103/PhysRevLett.132.062702© 2024 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasH & He burningH & He induced nuclear reactionsHydrostatic stellar nucleosynthesisNeutron physicsResonance reactionsS-factors processProperties6 ≤ A ≤ 19TechniquesNuclear data analysis & compilationNuclear Physics

Proton spectra and double differential cross sections were measured from 7Li-induced reactions on 63,65Cu with a 15.5 MeV lithium beam. Protons were measured at four angles: 37, 52, 97, and 142 degrees in the laboratory frame. The spectra measured at 97 and 142 degrees were used to test level density models for 69,71Ga nuclei populated by protons. Also, the level density excitation energy functions were extracted and compared directly with model calculations and with previous results on level densities for near mass nuclei 74,76Ge. It was found that the level density for 69Ga is consistent with the prediction of the back-shifted Fermi-gas model, while the level density for 71Ga is consistent with the ones for 74,76Ge, which all are systematically lower than this model predicts. The models based on the Gilbert and Cameron approach and microscopic model are not supported by experimental data.

Two of the astrophysically important reactions for X-ray burst models are 24Mg(α, γ)28Si and 59Cu(p, γ)60Zn. However, since these models are sensitive to nuclear reaction rates, it is important to constrain them to reduce possible model uncertainties. Constraining these reaction rates will help to improve the precision of model calculations and our understanding of the behavior of matter in astrophysical environments. We performed 27Al(d, n)28Si neutron evaporation spectrum measurements to constrain the nuclear level density of 28Si and benchmark this method against known levels from the level scheme. We also briefly discuss ongoing work to upgrade our lab with the charged-particle-neutron spectrometer which will enable the simultaneous measurements of neutrons and charged particles.

We report on the first experimental measurements made at a magnetic confinement fusion device of the tritium(T)-tritium(T) reaction T+T→He4+2n indicating the presence of the intermediate two-body resonant reaction T+T→He5+n. During the second deuterium-tritium campaign (DTE2) at the Joint European Torus, measurements of fusion plasmas with high tritium concentrations, nT/(nT+nD)≈0.99, heated with tritium neutral beam injection, were performed using the neutron time-of-flight (TOF) spectrometer TOFOR. We detect a peak in the neutron emission TOF spectrum consistent with the two-body resonant reaction. The TT neutron emission energy spectrum is modeled using an R-matrix framework where the distributions of the most likely model parameters given our experimental TOF data are determined utilizing a Markov chain Monte Carlo approach. We compare our best estimate of the T+T neutron emission energy spectrum with results obtained at inertial confinement fusion experiments at the OMEGA facility and find a spectral shape that is consistent with the energy dependency in the neutron spectrum observed at OMEGA. Published by the American Physical Society 2024

We present a method for measurement analyses based on probabilistic deep neural networks that provide several advantages over conventional analyses with phenomenological models. These include predicting physical quantities directly from data, the rapid generation of statistically robust uncertainties, and the ability to bypass some parameters that may induce ambiguities and complications in data analysis. As deep learning methods make predictions through "black boxes," the uncertainty quantification is typically challenging. We use a probabilistic framework that provides thorough uncertainty quantification and is straightforward to follow in practice. With the network architecture based on the Transformer, we demonstrate the current method for predicting nuclear resonance parameters from scattering data using the phenomenological R-matrix model.

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.

Measurements of the elastic scattering cross section of 3He and 4He are important in order to improve constraints on theoretical models of 4He(3He, gamma)7Be, a key reaction in Big Bang nucleosynthesis and solar neutrino production. The astrophysical S factor for this reaction is a significant source of uncertainty in the standard -solar -model prediction of the 7Be and 8B solar neutrino fluxes. The elastic scattering measurements reported in the literature do not extend to low energies and lack proper uncertainty quantification. A new measurement of the 4He(3He, 3He) 4He reaction has been made at center-of-mass energies Ec.m. = 0.38-3.13 MeV using the Scattering of Nuclei in Inverse Kinematics (SONIK) scattering chamber: a windowless, extended gas target surrounded by an array of 30 collimated silicon charged particle detectors situated at TRIUMF. This is the first elastic scattering measurement of 3He + 4He made below 500 keV and it has greater angular range and better precision than previous measurements. The elastic scattering data were analyzed using both R-matrix and halo effective field theory frameworks, and values of the s-wave scattering length and effective range were extracted. The resulting improvement in knowledge of the s-wave effective-range function at low energies reduces the overall uncertainty in S34 at solar energies.

40K is one of the main isotopes responsible for the radiogenic heating of the mantle in Earth-like exoplanets [1] and hence, plays a very important role in the internal geophysical dynamics of a planet. The abundance of 40K in the mantle and the core of such planets is not always possible to be determined by astrophysical observations, although constraining the nuclear reaction rates of 40K during stellar evolution can also lead to constraining the present amount of 40K in these planets, which will improve our understanding on the habitability potential of Earth-like exoplanets. This study aims to constrain the 40K(n,α)37Cl reaction rate, one of the two major destruction paths of 40K in stellar nucleosynthesis,by measuring the reverse reaction 37Cl(α,n)40K and applying the principle of detailed balance as we have done before for the 40K (40K(n,p)40Ar reaction rate) [2]. During the first set of measurements we performed differential cross-section measurements of the 37Cl(α,n1γ)40K, 37Cl(α,n2γ)40K and 37Cl(α,n3γ)40K reaction channels, for six different center of mass energies in the range between 5.1 and 5.4 MeV. The experiment took place at the Edwards Accelerator Laboratory of Ohio University. The gamma rays from the reaction channels mentioned above were detected by two LaBr3 scintillators. Using the swinger facility to change the angle of the beam-target system with respect to the detection system, we were able to take measurements for the differential cross-section at six different angles between 20° and 120° in the lab system.

Solar neutrino measurements have recently reached a level of sensitivity such that CNO fluxes can now be experimentally determined. While these first measurements are still only sensitive to the higher energy neutrinos resulting from the & beta;+ decays of 15O produced by the 14N(p, & gamma; ) 15O reaction, future measurements will work towards detection of neutrinos from the & beta;+ decay of 13N from the 12C(p, & gamma; )13N reaction. This paper reports on a recent measurement of the 12C(p, & gamma; ) 13N reaction covering a broad laboratory energy range between 1.0 and 2.5 MeV. The measurement was made to better determine the overall normalization of the absolute cross section and to explore the interference effects between the two broad, overlapping resonances at proton energies of 0.460 and 1.689 MeV and the direct capture to the ground state of 13N in the framework of a multichannel R-matrix analysis. This work takes into account previous radiative capture as well as elastic 12C(p, p) 12C scattering data, making uncertainty estimations using a Bayesian framework, to determine a reliable extrapolation of the low energy S factor towards the stellar energy range of CNO hydrogen burning. These new experimental results, and a detailed investigation of the past literature data, suggest that the resonant component of the cross section should be 30% lower than previously accepted.

Solar neutrino measurements have recently reached a level of sensitivity such that CNO fluxes can now be experimentally determined. While these first measurements are still only sensitive to the higher energy neutrinos resulting from the ${\ensuremath{\beta}}^{+}$ decays of $^{15}\mathrm{O}$ produced by the $^{14}\mathrm{N}(p,\ensuremath{\gamma})^{15}\mathrm{O}$ reaction, future measurements will work towards detection of neutrinos from the ${\ensuremath{\beta}}^{+}$ decay of $^{13}\mathrm{N}$ from the $^{12}\mathrm{C}(p,\ensuremath{\gamma})^{13}\mathrm{N}$ reaction. This paper reports on a recent measurement of the $^{12}\mathrm{C}(p,\ensuremath{\gamma})^{13}\mathrm{N}$ reaction covering a broad laboratory energy range between 1.0 and 2.5 MeV. The measurement was made to better determine the overall normalization of the absolute cross section and to explore the interference effects between the two broad, overlapping resonances at proton energies of 0.460 and 1.689 MeV and the direct capture to the ground state of $^{13}\mathrm{N}$ in the framework of a multichannel $R$-matrix analysis. This work takes into account previous radiative capture as well as elastic $^{12}\mathrm{C}(p,p)^{12}\mathrm{C}$ scattering data, making uncertainty estimations using a Bayesian framework, to determine a reliable extrapolation of the low energy $S$ factor towards the stellar energy range of CNO hydrogen burning. These new experimental results, and a detailed investigation of the past literature data, suggest that the resonant component of the cross section should be 30% lower than previously accepted.

We present results from direct measurements of the total C-13(alpha, n) O-16 cross section over laboratory energies E-alpha = 2.9-8.0 MeV, performed with the (HeBF3)-He-3 giant barrel neutron detector at the Edwards Accelerator Laboratory. The cross sections reported in this work are considerably lower than prior direct measurements for E-alpha > 5 MeV, in agreement with prior corrections based on Hauser-Feshbach estimates. However, applying branching ratios based on Hauser-Feshbach estimates to our data would not reproduce existing direct measurements for partial decay channels. This indicates both the promise and limitations of Hauser-Feshbach for branching ratio estimates of (alpha, n) reactions on light nuclides. The C-13(alpha, n) thick-target yields inferred from this work for E-alpha > 6 MeV are significantly larger than those currently employed in estimates of dark matter and neutrino detector backgrounds.

We present results from direct measurements of the Al-27(alpha, n) thick-target yield from laboratory incident energies E-a approximate to 3 to 5 MeV, performed with the (HeBF3)-He-3 Giant Barrel (HeBGB) neutron detector at the Edwards Accelerator Laboratory. Our measurements have a small energy cadence in order to address discrepancies and sparseness of thick-target-yield data sets existing for this energy region. We find general agreement with existing data sets, including yields derived from cross-section data, while resolving a discrepancy between existing thick-target-yield data sets for E-a approximate to 4to5 MeV. However, for E-a < 3.5 MeV, our results are substantially lower than previous thick-target-yield data and somewhat larger than yields calculated from existing cross-section data. Our data complete the energy range needed for estimates of the Al-27(alpha, n) contribution to neutrino and dark matter detector backgrounds and result in increased viability of Al-27(alpha, n) as a plasma diagnostic tool at fusion facilities such as the National Ignition Facility.

The spin cutoff parameter for 59Ni has been studied from different types of experimental data including neutron angular distributions from the 56Fe(alpha, n) 59Ni reaction, spin of discrete levels, the level density from the proton evaporation spectrum of the 54Fe(6Li, p) 59Ni reaction and neutron resonance spacing. Experimental data points were compared with calculations using models widely used in literature. It was found that the available empirical models overestimate data points in the energy region below the neutron separation energy, while microscopic calculations which take into account pairing correlations within Hartree-Fock + Bardeen-Cooper-Schrieffer approach are consistent with data. It confirmed earlier findings that pairing correlations play an important role and need to be taken into account when the spin cutoff parameter is calculated below the neutron separation energy.

Measurements of ( γ ,p ) and ( γ ,α ) photonuclear reaction cross sections are relevant for several nucleosynthesis scenarios, from the primordial Big Bang, to stellar burning, and the p-process. Studies of photonuclear reaction cross sections marked a steady development in the last 20 years with the advent of mono-energetic γ -ray beam facilities and improved detection methods. Charged-particle detection from photon-induced reactions in solid targets is mainly achieved with silicon-strip detectors, while time projection chambers were developed for measurements with active gas targets. This review tracks the evolution of charged-particle detection methods and highlights recent ^7 Li( γ ,t ) ^4 He and ^16 O( γ ,α ) ^12 C cross section measurements using mono-energetic γ -ray beams.

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.

We present results from direct measurements of the total $^{13}\mathrm{C}(\ensuremath{\alpha},n)^{16}\mathrm{O}$ cross section over laboratory energies ${E}_{\ensuremath{\alpha}}=2.9$--8.0 MeV, performed with the ${}^{3}{\mathrm{HeBF}}_{3}$ giant barrel neutron detector at the Edwards Accelerator Laboratory. The cross sections reported in this work are considerably lower than prior direct measurements for ${E}_{\ensuremath{\alpha}}>5$ MeV, in agreement with prior corrections based on Hauser-Feshbach estimates. However, applying branching ratios based on Hauser-Feshbach estimates to our data would not reproduce existing direct measurements for partial decay channels. This indicates both the promise and limitations of Hauser-Feshbach for branching ratio estimates of $(\ensuremath{\alpha},n)$ reactions on light nuclides. The $^{13}\mathrm{C}(\ensuremath{\alpha},n)$ thick-target yields inferred from this work for ${E}_{\ensuremath{\alpha}}>6$ MeV are significantly larger than those currently employed in estimates of dark matter and neutrino detector backgrounds.