Stellar Energies Research Articles

First direct measurement of theC11(α,p)N14stellar reaction by an extended thick-target method

The $^{11}$C($\alpha$, p) reaction is an important $\alpha$-induced reaction competing with $\beta$-limited hydrogen-burning processes in high-temperature explosive stars. We directly measured its reaction cross sections both for the ground-state transition ($\alpha$, $p_{0}$) and the excited-state transitions ($\alpha$, $p_{1}$) and ($\alpha$, $p_{2}$) at relevant stellar energies 1.3 - 4.5 MeV by an extended thick-target method featuring time of flight for the first time. We revised the reaction rate by numerical integration including the ($\alpha$, $p_{1}$) and ($\alpha$, $p_{2}$) contributions and also low-lying resonances of ($\alpha$, $p_{0}$) using both the present and the previous experimental data which were totally neglected in the previous compilation works. The present total reaction rate lies between the previous ($\alpha$, $p_{0}$) rate and the total rate of the Hauser-Feshbach statistical model calculation, which is consistent with the relevant explosive hydrogen-burning scenarios such as the $\nu p$-process.

Underground nuclear astrophysics: Why and how

The goal of nuclear astrophysics is to measure cross sections of nuclear physics reactions of interest in astrophysics. At stars temperatures, these cross sections are very low due to the suppression of the Coulomb barrier. Cosmic ray induced background can seriously limit the determination of reaction cross sections at energies relevant to astrophysical processes and experimental setups should be arranged in order to improve the signal-to-noise ratio. Placing experiments in underground sites, however, reduces this background opening the way towards ultra low cross section determination. LUNA (Laboratory for Underground Nuclear Astrophysics) was pioneer in this sense. Two accelerators were mounted at the INFN National Laboratories of Gran Sasso (LNGS) allowing to study nuclear reactions close to stellar energies. A summary of the relevant technology used, including accelerators, target production and characterisation, and background treatment is given.

Progress of Jinping Underground laboratory for Nuclear Astrophysics (JUNA)

Jinping Underground laboratory for Nuclear Astrophysics (JUNA) will take the advantage of the ultra-low background of CJPL lab and high current accelerator based on an ECR source and a highly sensitive detector to directly study for the first time a number of crucial reactions occurring at their relevant stellar energies during the evolution of hydrostatic stars. In its first phase, JUNA aims at the direct measurements of 25Mg(p,γ)26Al, 19F(p,α)16O, 13C(α,n)16O and 12C(α,γ)16O reactions. The experimental setup, which includes an accelerator system with high stability and high intensity, a detector system, and a shielding material with low background, will be established during the above research. The current progress of JUNA will be given.

Indirect study of 12C(α,γ)16O reaction

The radiative capture reaction 12C(α,γ)16O plays an important role in helium burning in massive stars and their subsequent evolution [1]. However, despite various experimental studies, the cross section of this reaction at stellar energies remains highly uncertain. The extrapolation down to stellar energy (Ecm∼300 keV) of the measured cross sections at higher energies is made difficult by the overlap of various contributions of which some are badly known such as that of the 2+ (Ex=6.92 MeV) and 1− (Ex=7.12 MeV) sub-threshold states of 16O. Hence, to further investigate the contribution of these two-subthreshold resonances to the 12C(α,γ)16O cross section, a new determination of their a-reduced widths and so their a- spectroscopic-factors was performed using 12C(7Li,t)16O transfer reaction measurements at two incident energies and a detailed DWBA analysis of the data [2]. The measured and calculated differential cross sections are presented as well as the obtained spectroscopic factors and the a- reduced widths as well as the assymptotic normalization constants (ANC) for the 2+ and 1− subthreshold states. Finally, the results obtained from the R-matrix calculations of the 12C(α,γ)16O cross section using our obtained a-reduced widths for the two sub-threshold resonances are presented and discussed.

T(T,2n)4He and3He(3He,2p)4He: The Reaction Mechanism from Solar Energies to 10 MeV

We have studied the energy dependence of the reaction mechanism of the T(t,2n)4 He reaction at stellar energies and of its charge symmetric analog reaction 3 He(3 He,2p)4 He at energies up 10 MeV. We find that the reaction mechanism changes dramatically over this energy range in part due to the interference of the two identical fermions in the three-body final state.

Neutron Energy Spectra and Yields from the 7Li(p,n) Reaction for Nuclear Astrophysics

Neutrons produced by the 7Li(p, n)7Be reaction close to threshold are widely used to measure the cross section of s-process nucleosynthesis reactions. While experiments have been performed so far with Van de Graaff accelerators, the use of RF accelerators with higher intensities is planned to enable investigations on radioactive isotopes. In parallel, high-power Li targets for the production of high-intensity neutrons at stellar energies are developed at Goethe University (Frankfurt, Germany) and SARAF (Soreq NRC, Israel). However, such setups pose severe challenges for the measurement of the proton beam intensity or the neutron fluence. In order to develop appropriate methods, we studied in detail the neutron energy distribution and intensity produced by the thick-target 7Li(p,n)7Be reaction and compared them to state-of- the-art simulation codes. Measurements were performed with the bunched and chopped proton beam at the Van de Graaff facility of the Institute for Reference Materials and Measurements (IRMM) using the time-of-flight (TOF) technique with thin (1/8") and thick (1") detectors. The importance of detailed simulations of the detector structure and geometry for the conversion of TOF to a neutron energy is stressed. The measured neutron spectra are consistent with those previously reported and agree well with Monte Carlo simulations that include experimentally determined 7Li(p,n) cross sections, two-body kinematics and proton energy loss in the Li-target.

Indirect Study of the16O+16O Fusion Reaction Toward Stellar Energies by the Trojan Horse Method

The 16 O+ 16 O fusion reaction is important in terms of the explosive oxygen burning process during late evolution stage of massive stars as well as understanding of the mechanism of low-energy heavy-ion fusion reactions. We aim to determine the excitation function for the most major exit channels, α + 28 Si and p + 31 P, toward stellar energies indirectly by the Trojan Horse Method via the 16 O( 20 Ne , α 28 Si) α and 16 O( 20 Ne , p 31 P) α three-body reactions. We report preliminary results involving reaction identification, and determination of the momentum distribution of α - 16 O intercluster motion in the projectile 20 Ne nucleus.

Four-body calculation of 12C(α, γ)16O radiative capture reaction at stellar energies

On the basis of the four-alphamodel, the 12C(α, γ)16Oradiative capture process is investigated by using the four-body Faddeev–Yakubovsky equations as well as the two- and three-body electromagnetic currents. The present calculation is an application of our current conservation realistic potentials method for the 12C(α, γ)16Oradiative capture process. This work clears the way formore refinedmodels of radiative capture based on two- and three-body realistic potentials and current conservation. The calculation is carried out by considering the 4He + 12C (1 + 3) and the 8Be + 8Be (2 + 2) subamplitudes, respectively. Radiative capture 12C(α, γ)16Oreaction is one of the most important reactions in nuclear astrophysics. For this reaction, the electric dipole transitions between states with the same isospin are forbidden in the first order. Because the state 1+ and 0+ ground state nuclei 16O have zero isospin, thus the electric dipole radiations are not at the first order between two levels and electric dipole radiation will be the second order and electric dipole radiation is the same order as the electric quadrupole radiation. Therefore, we must consider the effects of both radiations. In comparison with other theoretical methods and available experimental data, good agreement is achieved for the E 1 and E 2 contribution to the cross section and the astrophysical S factor for this process.

Progress of Jinping Underground laboratory for Nuclear Astrophysics (JUNA)

Jinping Underground lab for Nuclear Astrophysics (JUNA) will take the advantage of the ultralow background in Jinping underground lab, high current accelerator based on an ECR source and highly sensitive detector to study directly a number of crucial reactions to the hydrostatic stellar evolution for the first time at their relevant stellar energies. In its first phase, JUNA aims at the direct measurements of 25 Mg(p,γ)26 Al, 19 F(p,α)16 O, 13 C(α,n)16 O and 12 C(α,γ)16 O. The experimental setup, which include the accelerator system with high stability and high intensity, the detector system, and the shielding material with low background, will be established during the above research. The current progress of JUNA will be given.

Underground Nuclear Astrophysics in China

AbstractUnderground Nuclear Astrophysics in China (JUNA) will take the advantage of the ultra-low background in Jinping underground lab. High current accelerator with an ECR source and detectors will be set up. We plan to study directly a number of nuclear reactions important to hydrostatic stellar evolution at their relevant stellar energies, such as 25Mg(p,γ)26Al, 19F(p,α)16O, 13C(α,n)16O and 12C(α,γ)16O.

Three-Body Calculation of 4He(αα,γ)12C Reaction at Stellar Energies**Supported by the University of Birjand.

The triple-alpha reaction is the key to our understanding about the nucleosynthesis and the observed abundance of 12C in stars. On the basis of our model, the triple-alpha radiative capture process is studied by using the three-body Faddeev approach as well as two- and three-body electromagnetic currents. The bound and resonance states of 12C are calculated via an inverse process: three-α photodisintegration of a 12C nucleus.

First Direct Measurement of (12)C((12)C,n)(23)Mg at Stellar Energies.

Neutrons produced by the carbon fusion reaction (12)C((12)C,n)(23)Mg 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 (12)C((12)C,p)(23)Na. 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 (12)C((12)C,n)(23)Mg is crucial to the production of Na and Al in pop-III pair instability supernovae. It also plays a nonnegligible role in the production of weak s-process elements, as well as in the production of the important galactic γ-ray emitter (60)Fe.

First Direct Measurement of C 12 (C 12,n) Mg 23 at Stellar Energies

B. Bucher, 2, ∗ X. D. Tang, † X. Fang, A. Heger, ‡ S. Almaraz-Calderon, § A. Alongi, A. D. Ayangeakaa, ¶ M. Beard, A. Best, ∗∗ J. Browne, C. Cahillane, M. Couder, R. J. deBoer, A. Kontos, L. Lamm, †† Y. J. Li, A. Long, W. Lu, S. Lyons, M. Notani, D. Patel, N. Paul, M. Pignatari, 7, ‡ A. Roberts, D. Robertson, K. Smith, E. Stech, R. Talwar, W. P. Tan, M. Wiescher, and S. E. Woosley Institute for Structure and Nuclear Astrophysics, Joint Institute for Nuclear Astrophysics, University of Notre Dame, Notre Dame, Indiana 46556, USA Lawrence Livermore National Laboratory, Livermore, California 94550, USA Institute of Modern Physics, Chinese Academy of Science, Lanzhou, Gansu 730000, P.R. China Monash Center for Astrophysics, School of Mathematical Sciences, Monash University, Victoria 3800, Australia China Institute of Atomic Energy, Beijing 102413, P.R. China Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Konkoly Thege Miklos ut 15-17, H-1121 Budapest, Hungary Department of Physics, University of Basel, Basel, CH-4056, Switzerland Department of Astronomy and Astrophysics, University of California, Santa Cruz, California 95064, USA (Dated: July 15, 2015)

Relating molecular structure and low-energy fusion through time-dependent wave-packet dynamics: the12C+12C collision

Recent progress in a quantitative study of the 12 C+ 12 C sub-Coulomb fusion is reported. It is carried out using full-dimensional, time-dependent wave-packet dynamics, a quantum reaction model that has not been much exploited in nuclear physics, unlike in chemical physics. The low-energy collision is described in the rotating center-of-mass frame within a nuclear molecular picture. A collective Hamiltonian drives the time propagation of the wave-packet through the collective potential-energy landscape that is calculated with a real- istic two-center shell model. Among other preliminary results, the theoretical sub-Coulomb fusion resonances for 12 C+ 12 C seem to correspond well with observations. The method appears to be useful for expanding the cross-section predictions towards stellar energies.

Peripheral elastic and inelastic scattering ofO17,18on light targets at 12 MeV/nucleon

A study of interaction of neutron-rich oxygen isotopes $^{17,18}\mathrm{O}$ with light targets has been undertaken in order to determine the optical potentials needed for the transfer reaction $^{13}\mathrm{C}(^{17}\mathrm{O},^{18}\mathrm{O})^{12}\mathrm{C}$. Optical potentials in both incoming and outgoing channels have been determined in a single experiment. This transfer reaction was used to infer the direct capture rate to the $^{17}\mathrm{F}(p,\ensuremath{\gamma})^{18}\mathrm{Ne}$ which is essential to estimate the production of $^{18}\mathrm{F}$ at stellar energies in ONe novae. The success of the asymptotic normalization coefficient (ANC) as indirect method for astrophysics is guaranteed if the reaction mechanism is peripheral and the distorted wave Born approximation cross-section calculations are warranted and stable against the optical model potential (OMP) used. We demonstrate the stability of the ANC method and the OMP results by using good-quality elastic and inelastic-scattering data with stable beams before extending the procedures to rare-ion beams. The peripherality of our reaction is inferred from a semiclassical decomposition of the total-scattering amplitude into barrier and internal barrier components. Comparison between elastic scattering of $^{17}\mathrm{O}$, $^{18}\mathrm{O}$, and $^{16}\mathrm{O}$ projectiles is made.

Combiningab initiocalculations and low-energy effective field theory for halo nuclear systems: The case ofBe7+p→B8+γ

We report a leading-order (LO) calculation of $^7\mathrm{Be}(p,\gamma)^8\mathrm{B}$ in a low-energy effective field theory. $^8\mathrm{B}$ is treated as a shallow proton$+^7\mathrm{Be}$ core and proton$+^7\mathrm{Be}^{*}$ (core excitation) $p$-wave bound state. The couplings are fixed using measured binding energies and proton-$^7\mathrm{Be}$ $s$-wave scattering lengths, together with $^8\mathrm{B}$ asymptotic normalization coefficients from ab initio calculations. We obtain a zero-energy $S$-factor of $18.2 \pm 1.2~({\rm ANC~only})$ eV b. Given that this is a LO result it is consistent with the recommended value $S(0)=20.8\pm1.6$ eV b. Our computed $S(E)$ compares favorably with experimental data on $^7\mathrm{Be}(p,\gamma)^8\mathrm{B}$ for $E <0.4$ MeV. We emphasize the important role of proton-$^7\mathrm{Be}$ scattering parameters in determining the energy dependence of $S(E)$, and demonstrate that their present uncertainties significantly limit attempts to extrapolate these data to stellar energies.

Note: Proton irradiation at kilowatt-power and neutron production from a free-surface liquid-lithium target.

The free-surface Liquid-Lithium Target, recently developed at Soreq Applied Research Accelerator Facility (SARAF), was successfully used with a 1.9 MeV, 1.2 mA (2.3 kW) continuous-wave proton beam. Neutrons (~2 × 10(10) n/s having a peak energy of ~27 keV) from the (7)Li(p,n)(7)Be reaction were detected with a fission-chamber detector and by gold activation targets positioned in the forward direction. The setup is being used for nuclear astrophysics experiments to study neutron-induced reactions at stellar energies and to demonstrate the feasibility of accelerator-based boron neutron capture therapy.

Astrophysical reaction rate forF17(p,γ)Ne18from the transfer reactionC13(O17,O18)C12

The asymptotic normalization coefficients of the bound states ${J}^{\ensuremath{\pi}}=({0}_{1}^{+},{2}_{1}^{+},{4}_{1}^{+},{2}_{2}^{+})$ in $^{18}\text{O}$ are extracted from the peripheral neutron transfer reaction $^{13}\text{C}$$(^{17}\text{O}$$,^{18}\text{O}$$)^{12}\text{C}$. They are then converted to their mirror states in $^{18}\text{Ne}$, which are further used to evaluate the astrophysical $S$ factor for the proton capture reaction $^{17}\text{F}$($p$,$\ensuremath{\gamma}$)$^{18}\text{Ne}$. The elastic-scattering cross sections have been measured in both incoming and outgoing channels in order to extract the optical potentials needed for distorted-wave-Born-approximation calculations. The $S$ factor is found to be ${S}_{1\ensuremath{-}17}(0)=2.17\ifmmode\pm\else\textpm\fi{}0.37$ keV b. The contribution of the direct capture rate to this reaction is estimated, and its consequences on the production of $^{18}\text{F}$ at stellar energies in ONe novae are discussed.

Nucleosynthesis in Stars and the Chemical Enrichment of Galaxies

After the Big Bang, production of heavy elements in the early Universe takes place starting from the formation of the first stars, their evolution, and explosion. The first supernova explosions have strong dynamical, thermal, and chemical feedback on the formation of subsequent stars and evolution of galaxies. However, the nature of the Universe's first stars and supernova explosions has not been well clarified. The signature of the nucleosynthesis yields of the first stars can be seen in the elemental abundance patterns observed in extremely metal-poor stars. Interestingly, those patterns show some peculiarities relative to the solar abundance pattern, which should provide important clues to understanding the nature of early generations of stars. We thus review the recent results of the nucleosynthesis yields of mainly massive stars for a wide range of stellar masses, metallicities, and explosion energies. We also provide yields tables and examine how those yields are affected by some hydrodynamical effects during supernova explosions, namely, explosion energies from those of hypernovae to faint supernovae, mixing and fallback of processed materials, asphericity, etc. Those parameters in the supernova nucleosynthesis models are constrained from observational data of supernovae and metal-poor stars. Nucleosynthesis yields are then applied to the chemical evolution model of our Galaxy and other types of galaxies to discuss how the chemical enrichment process occurred during evolution.

A drop in the [formula omitted] reaction at low energies

The low-energy astrophysical S factors of the Li6(p,γ)Be7 reaction have been investigated on a 320 kV platform at the Institute of Modern Physics in Lanzhou. The experimental S factor of this reaction shows an interesting sizable drop contrary to any existing theoretical expectations at energies below 200 keV. Such drop has not been fully understood yet and may reflect a novel reaction mechanism. The appearance of an interesting new positive-parity 1/2+ or 3/2+ resonance at Ec.m.≈195 keV is discussed. This study shows the danger of extrapolating experimental data over too large an energy range and demonstrates the need for careful direct experimental studies of reaction cross sections at or near stellar energies. In addition, our new results are discussed in the framework of a SUSY assisted Big-Bang Nucleosynthesis (BBN) model.