Energies Of Astrophysical Interest Research Articles

Impact of Newly Measured Nuclear Reaction Rates on 26Al Ejected Yields from Massive Stars

Over the last three years, the rates of all the main nuclear reactions involving the destruction and production of 26Al in stars (26Al(n, p)26Mg, 26Al(n, α)23Na, 26Al(p, γ)27Si and 25Mg(p, γ)26Al) have been re-evaluated thanks to new high-precision experimental measurements of their crosssections at energies of astrophysical interest, considerably reducing the uncertainties in the nuclear physics affecting their nucleosynthesis. We computed the nucleosynthetic yields ejected by the explosion of a high-mass star (20 M⊙, Z = 0.0134) using the FRANEC stellar code, considering two explosion energies, 1.2 × 1051 erg and 3 × 1051 erg. We quantify the change in the ejected amount of 26Al and other key species that is predicted when the new rate selection is adopted instead of the reaction rates from the STARLIB nuclear library. Additionally, the ratio of our ejected yields of 26Al to those of 14 other short-lived radionuclides (36Cl, 41Ca, 53Mn, 60Fe, 92Nb, 97Tc, 98Tc, 107Pd, 126Sn, 129I, 36Cs, 146Sm, 182Hf, 205Pb) are compared to early solar system isotopic ratios, inferred from meteorite measurements. The total ejected 26Al yields vary by a factor of ~3 when adopting the new rates or the STARLIB rates. Additionally, the new nuclear reaction rates also impact the predicted abundances of short-lived radionuclides in the early solar system relative to 26Al. However, it is not possible to reproduce all the short-lived radionuclide isotopic ratios with our massive star model alone, unless a second stellar source could be invoked, which must have been active in polluting the pristine solar nebula at a similar time of a core-collapse supernova.

Radiative capture of proton through the 14N(p,γ)15O reaction at low energy

The CNO cycle is the main source of energy in stars more massive than our Sun. This process defines the energy production, the duration of which can be used to determine the lifetime of massive stars. The cycle is an important tool for determining the age of globular clusters. Radiative proton capture via , at energies of astrophysical interest, is an important process in the CNO cycle. In this project, we apply a potential model to describe both non-resonant and resonant reactions in the channels where radiative capture occurs through electric transitions. We employed the R-matrix method to describe the ongoing reactions via resonant transitions, when it was not possible to correctly reproduce the experimental data using the potential model. The partial components of the astrophysical S-factor are calculated for all possible electric and magnetic dipole transitions in 15O. The linear extrapolated S-factor at zero energy (S(0)) agrees well with earlier reported values for all transition types considered in this work. Based on the value of the total astrophysical S-factor, depending on the collision energy, we calculate the nuclear reaction rates for . The computed rates agree well with the results reported in the NACRE II Collaboration and most recent existing measurements.

Study of the energy dependence of the $$^6$$Li(p,$$\alpha $$)$$^3$$He reaction at energies of astrophysical interest

Study of the energy dependence of the $$^6$$Li(p,$$\alpha $$)$$^3$$He reaction at energies of astrophysical interest

CARME — The CRYRING Array for Reaction MEasurements: A new approach to study nuclear reactions using storage rings

The low-energy CRYRING@ESR storage ring, recently commissioned at GSI@FAIR (Germany), is a world-unique facility able to decelerate and store beams produced in-flight to energies E≤10 MeV/u. CRYRING@ESR offers the unique opportunity to exploit high quality, pure, radioactive beams of species difficult to produce via the ISOL method for reaction studies directly at energies of astrophysical interest. The use of thin, pure, windowless in-ring targets combined with the re-circulating beam also presents significant advantages in terms of background and luminosity. This paper describes a new modular nuclear and atomic physics detection array, CARME (CRYRING Array for Reaction MEasurements), specifically designed to allow these investigations to be carried out for the first time in the Extreme High Vacuum (XHV) environment of the CRYRING@ESR. CARME mounts a high granularity silicon strip detector system adapted for XHV conditions, and will be used for high resolution direct and indirect charged particle reaction studies.

The 12C +16 O fusion reaction in carbon burning: Study at energies of astrophysical interest using the Trojan Horse Method

The carbon-burning process in massive stars mainly occurs via the 12C +12 C. However, at temperatures higher than 109K and considering the increased abundance of 16O produced during the later stages of the heliumburning,the 12C+16O fusion can also become relevant. Moreover, 12C+16O also plays a role in the scenario of explosive carbon burning. Thus, the astrophysical energy region of interest ranges from 3 to 7.2 MeV in the center-of-mass frame. However, the various measurements of the cross-section available in the literature stop around 4 MeV, making extrapolation necessary. To solve this uncertainty and corroborate direct measurement we applied the Trojan Horse Method to three-body processes 16O(14N, α24Mg)2H and 16O(14N, p27Al)2H to study the 12C(16O, α)24Mg and 12C(16O, p)27Al reactions in their entire energy region of astrophysical interest. In this contribution, after briefly describing the method used, the experiment and the preliminary phases of the data analysis will be presented and discussed.

Development of irradiation-resistant enriched 12C targets for astrophysical [formula omitted] reaction measurements

The production of irradiation-resistant enriched 12C target is one of the key technologies in the direct measurement of the 12C(α,γ)16O reaction at energies of astrophysical interest. In this work, we produced the enriched Ti12C targets on Ta substrates via the filter cathodic vacuum arc (FCVA) technology. The target stability under the bombardment of a high-intensity 4He beam was investigated by monitoring the γ-ray yields of the 12C(p,γ)13N reaction regularly. A 25% deterioration of 12C in the target was observed after bombardment by a 740 keV, 500 μA 4He2+ beam with a charge of 280 C, which is stronger than the implanted targets developed before. Furthermore, the 13C/12C ratio in the Ti12C target was measured to be (1.1±0.3)×10−4, which can meet the requirement of the 12C(α,γ)16O measurement at the China JinPing underground Laboratory (CJPL).

Astrophysical S-factor for radiative capture of proton by 13C at low energy

Radiative capture p + 13C → 14N + γ at energies of astrophysical interest is one of the important process in the CNO cycle. We focus the reader’s attention on the possibility of describing this reaction within the framework of a single-particle potential model even when the reaction has a resonant characteristic. The partial components of the astrophysical S-factor are calculated for electric dipole transition. The calculated value of S-factor is in good agreement with experimental data both at low and high energy from the resonance position.

Role of the shape deformation in 12C + 12C fusion at sub-Coulomb energies

The fusion cross section of 12C+12C system at the energies of astrophysical interest is calculated in the framework of barrier penetration model taking into account the deformed shape of interacting nuclei. In particular, the quadrupole surface deformation of both projectile and target nuclei has been included during the fusion process. The real and imaginary parts of nucleus-nucleus interactions performed using the Woods-Saxon square and Woods-Saxon functions, respectively have been carefully tested by 12C-12C elastic scattering data analysis before employed to evaluate the astrophysical S factors (the fusion cross sections). The optical model results of elastic angular distributions are consistent with the experimental data. Within the barrier penetration model, the real part of the obtained optical potential gives a good description of the non-resonant astrophysical S factor. It turns out that the taking into account of quadrupole deformation of 12C nuclei increases the astrophysical S factor at energies below Coulomb barrier.

Nuclear Astrophysics deep underground and the LUNA experiment

The cross sections of nuclear reactions relevant for astrophysics are crucial ingredients to understand the energy generation inside stars and the synthesis of the elements. In stars, nuclear reactions take place at energies well below the Coulomb barrier. As a result, their cross sections are often too small to be measured in laboratories on the Earth’s surface, where the signal would be overwhelmed by the cosmic-ray induced background. An effective way to suppress the cosmic-ray induced background is to perform experiments in underground laboratories. LUNA is a unique facility located at Gran Sasso National Laboratories (Italy) and devoted to Nuclear Astrophysics. The extremely low background achieved at LUNA allows to measure nuclear cross sections directly at the energies of astrophysical interest. Over the years, many crucial reactions involved in stellar hydrogen burning as well as Big Bang Nucleosynthesis have been measured at LUNA. This paper provides a short overview on underground Nuclear Astrophysics and discusses the latest results and future perspectives of the LUNA experiment.

Application of the THM to the investigation of reactions induced by unstable nuclei: the 18F(p,α)15O case

The Trojan Horse Method is applied to the investigation of the 18F(p,α)15O reaction, by extracting the quasi free contribution to the 2H(18F,α15O)n process. For the first time the method is applied to a reaction of astrophysical importance involving a radioactive nucleus. After investigating the reaction mechanism populating the a + 15O + n exit channel, we could extract the 18F(p,α)15O cross section and calculate the astrophysical factor over the 0 – 1 MeV energy interval. The possibility of exploring the cross section with no need of extrapolation allowed us to to point out the possible occurrence of a 7/2+ state at 126 keV, which would strongly influence the trend of the astrophysical factor at the energies of astrophysical interest. However, the low energy resolution prevents us to draw definite conclusions. Possible astrophysical consequences are also discussed, motivating further work on this reaction.

Nuclear Astrophysics Deep Underground

Cross sections of nuclear reactions relevant for astrophysics are crucial ingredients to understand the energy generation inside stars and the synthesis of the elements. At astrophysical energies, nuclear cross sections are often too small to be measured in laboratories on the Earth surface, where the signal would be overwhelmed by the cosmic-ray induced background. LUNA is a unique Nuclear Astrophysics experiment located at Gran Sasso National Laboratories. The extremely low background achieved at LUNA allows to measure nuclear cross sections directly at the energies of astrophysical interest. Over the years, many crucial reactions involved in stellar hydrogen burning as well as Big Bang nucleosynthesis have been measured at LUNA. The present contribution provides an overview on underground Nuclear Astrophysics as well as the latest results and future perspectives of the LUNA experiment.

The LUNA experiment: past and future

The essential ingredients of nuclear astrophysics are the thermonuclear reac-tions which shape the life and death of stars and which are responsible for the synthesis of the chemical elements in the Universe. Deep underground in the Gran Sasso Laboratory the cross sections of the key reactions responsible for the hydrogen burning in stars have been measured with two accelerators of 50 and 400 kV voltage right down to the energies of astrophysical interest. In particular, the main results obtained during the 'solar' phase of LUNA are here reviewed and their influence on our understanding of the properties of the neutrino and of the Sun is discussed. Then, the future of LUNA during the next decade is outlined. It will be mainly focused on the study of the nuclear burning stages after hydrogen burning: helium and carbon burning. All this will be accomplished thanks to a new 3.5 MV accelerator able to deliver high current beams of proton, helium and carbon which will start running under Gran Sasso in 2019.

Concurrent Application of ANC and THM to assess the 13C(α, n)16O Absolute Cross Section at Astrophysical Energies and Possible Consequences for Neutron Production in Low-mass AGB Stars

Abstract The reaction is considered to be the main neutron source responsible for the production of heavy nuclides (from to ) through slow n-capture nucleosynthesis (s-process) at low temperatures during the asymptotic giant branch phase of low-mass stars ( , or LMSs). In recent years, several direct and indirect measurements have been carried out to determine the cross section at the energies of astrophysical interest (around ). However, they yield inconsistent results that cause a highly uncertain reaction rate and affect the neutron release in LMSs. In this work we have combined two indirect approaches, the asymptotic normalization coefficient and the Trojan horse method, to unambiguously determine the absolute value of the astrophysical factor. With these, we have determined a very accurate reaction rate to be introduced into astrophysical models of s-process nucleosynthesis in LMSs. Calculations using this recommended rate have shown limited variations in the production of those neutron-rich nuclei (with ) that receive contribution only by slow neutron captures.

The Luna experiment

One of the main ingredients of nuclear astrophysics is the cross section of the thermonuclear reactions which power the stars and synthesize the chemical elements in the Universe. Deep underground in the Gran Sasso Laboratory the cross section of the key reactions of the proton-proton chain and of the Carbon-Nitrogen-Oxygen (CNO) cycle have been measured right down to the energies of astrophysical interest. The main results obtained during the solar phase of LUNA are reviewed before describing the current LUNA program devoted to the study of the nucleosynthesis of the light elements in AGB stars and Classical Novae. Finally, the future of LUNA with the new 3.5 MV accelerator devoted to the study of helium and carbon burning is discussed.

Helium burning and neutron sources in the stars

Helium burning represents an important stage of stellar evolution as it contributes to the synthesis of key elements such as carbon, through the triple- $ \alpha$ process, and oxygen, through the 12C( $ \alpha$ , $ \gamma$ )16O reaction. It is the ratio of carbon to oxygen at the end of the helium burning stage that governs the following phases of stellar evolution leading to different scenarios depending on the initial stellar mass. In addition, helium burning in Asymptotic Giant Branch stars, provides the two main sources of neutrons, namely the 13C( $ \alpha$ , n)16O and the 22Ne( $ \alpha$ , n)25Mg, for the synthesis of about half of all elements heavier than iron through the s-process. Given the importance of these reactions, much experimental work has been devoted to the study of their reaction rates over the last few decades. However, large uncertainties still remain at the energies of astrophysical interest which greatly limit the accuracy of stellar models predictions. Here, we review the current status on the latest experimental efforts and show how measurements of these important reaction cross sections can be significantly improved at next-generation deep underground laboratories.

The nuclear physics of the hydrogen burning in the Sun

Underground nuclear astrophysics focuses its efforts towards a deeper knowledge of the nuclear reactions that rule stellar evolution processes and enable the synthesis of the elements of the periodic table. Deep underground in the Gran Sasso laboratory, the cross-sections of the key reactions of the hydrogen burning have been measured right down to the energies of astrophysical interest. The main results obtained by the LUNA Collaboration are reviewed, and their contributions to the solution of the solar neutrino problem and to the age of the globular cluster are discussed.

Fusion measurements of12C+12C at energies of astrophysical interest

The cross section of the ^12C+^12C fusion reaction at low energies is of paramount importance for models of stellar nucleosynthesis in different astrophysical scenarios, such as Type Ia supernovae and Xray superbursts, where this reaction is a primary route for the production of heavier elements. In a series of experiments performed at Argonne National Laboratory, using Gammasphere and an array of Silicon detectors, measurements of the fusion cross section of ^12C+^12C were successfully carried out with the gamma and charged-particle coincidence technique in the center-of-mass energy range of 3-5 MeV. These were the first background-free fusion cross section measurements for ^12C+^12C at energies of astrophysical interest. Our results are consistent with previous measurements in the high-energy region; however, our lowest energy measurement indicates a fusion cross section slightly lower than those obtained with other techniques.

Test of statistical model cross section calculations forα-induced reactions onAg107at energies of astrophysical interest

Astrophysical reaction rates, which are mostly derived from theoretical cross sections, are necessary input to nuclear reaction network simulations for studying the origin of $p$ nuclei. Past experiments have found a considerable difference between theoretical and experimental cross sections in some cases, especially for ($\alpha$,$\gamma$) reactions at low energy. Therefore, it is important to experimentally test theoretical cross section predictions at low, astrophysically relevant energies. The aim is to measure reaction cross sections of $^{107}$Ag($\alpha$,$\gamma$)$^{111}$In and $^{107}$Ag($\alpha$,n)$^{110}$In at low energies in order to extend the experimental database for astrophysical reactions involving $\alpha$ particles towards lower mass numbers. Reaction rate predictions are very sensitive to the optical model parameters and this introduces a large uncertainty into theoretical rates involving $\alpha$ particles at low energy. We have also used Hauser-Feshbach statistical model calculations to study the origin of possible discrepancies between prediction and data. An activation technique has been used to measure the reaction cross sections at effective center of mass energies between 7.79 MeV and 12.50 MeV. Isomeric and ground state cross sections of the ($\alpha$,n) reaction were determined separately. The measured cross sections were found to be lower than theoretical predictions for the ($\alpha$,$\gamma$) reaction. Varying the calculated averaged widths in the Hauser-Feshbach model, it became evident that the data for the ($\alpha$,$\gamma$) and ($\alpha$,n) reactions can only be simultaneously reproduced when rescaling the ratio of $\gamma$- to neutron width and using an energy-dependent imaginary part in the optical $\alpha$+$^{107}$Ag potential.......

Electroweak structure of light nuclei

We review the most recent studies performed within the chiral effective field theory framework of electroweak processes, among which, in particular, the electromagnetic structure of light nuclei, the weak muon capture on deuteron and 3He, and the weak proton-proton capture reaction at energies of astrophysical interest. The presented results will be compared with the available experimental data and with those obtained within the conventional phenomenological approach.

Origin and status of LUNA at Gran Sasso

The ultimate goal of nuclear astrophysics, the union of nuclear physics and astronomy, is to provide a comprehensive picture of the nuclear reactions which power the stars and, in doing so, synthesize the chemical elements. Deep underground in the Gran Sasso Laboratory the key reactions of the proton–proton chain and of the carbon–nitrogen–oxygen cycle have been studied down to the energies of astrophysical interest. The main results obtained in the past 20 years are reviewed and their influence on our understanding of the properties of the neutrino, the Sun, and the Universe itself is discussed. Finally, future developments of underground nuclear astrophysics beyond the study of hydrogen burning are outlined.