Structure of23Al from the one-proton breakup reaction and astrophysical implications

We discuss the use of one-nucleon breakup reactions of loosely bound nuclei at intermediate energies as an indirect method in nuclear astrophysics. These are peripheral processes, therefore we can extract asymptotic normalization coefficients (ANC) from which reaction rates of astrophysical interest can be inferred. To show the usefulness of the method, three different cases are discussed. In the first, existing experimental data for the breakup of 8B at energies from 30 to 1000 MeV/u and of 9C at 285 MeV/u on light through heavy targets are analyzed. Glauber model calculations in the eikonal approximation and in the optical limit using different effective interactions give consistent, though slightly different results, showing the limits of the precision of the method. The results lead to the astrophysical factor S_17(0)=18.7+/-1.9 eVb for the key reaction for solar neutrino production 7Be(p,\gamma)8B. It is consistent with the values from other indirect methods and most direct measurements, but one. Breakup reactions can be measured with radioactive beams as weak as a few particles per second, and therefore can be used for cases where no direct measurements or other indirect methods for nuclear astrophysics can be applied. We discuss a proposed use of the breakup of the proton drip line nucleus 23Al to obtain spectroscopic information and the stellar reaction rate for 22Mg(p,\gamma)23Al.

Breakup of loosely bound nuclei at intermediate energies as indirect method in nuclear astrophysics: 8B, 9C and the S17, S18 astrophysical factors

We discuss the use of one‐nucleon removal reactions of loosely bound nuclei at intermediate energies as an indirect method in nuclear astrophysics. The breakup reactions are proved to be good spectroscopic tools and can be used to study a large number of loosely bound proton‐ or neutron‐rich nuclei over a wide range of beam energies. As peripheral processes, they can be used to extract asymptotic normalization coefficients (ANCs) from which non‐resonant capture reaction rates of astrophysical interest can be calculated parameter free. In this talk, we present results of a proton‐breakup experiment carried out at GANIL (France) with a cocktail beam centered around 23Al at 50 MeV/nucleon. Momentum distributions of the breakup fragments, inclusive and in coincidence with gamma rays detected by EXOGAM Germanium clover array, were measured in the focal plan of SPEG energy‐loss spectrometer. We present in particular the investigations of reaction rates for 22Mg(p,γ)23Al and 23Al(p,γ)24Si important for novae and X‐ray bursts, respectively.

Our understanding of stellar evolution depends on knowing beta-decay rates and reaction cross sections for a wide range of nuclear capture reactions. Direct laboratory measurements of important stellar reaction rates are hindered by low cross sections and, in some cases, the need for radioactive targets. Indirect techniques have been developed to determine reaction rates for systems that are particularly difficult to measure in a direct experiment. One of the indirect techniques involves measurements of Asymptotic Normalization Coefficients (ANCs) which determine the direct-capture contribution to a capture reaction. Also ANCs can be used to understand the role of subthreshold states in stellar capture. This essay gives an introduction to ANCs and describes how they are used in nuclear astrophysics. Examples are given of measurements which have been carried out with both stable and radioactive beams.

We discuss the use of one‐nucleon removal reactions of loosely bound nuclei at intermediate energies as an indirect method in nuclear astrophysics. These breakup reactions are good spectroscopic tools and can be used to study a large number of loosely bound proton‐ or neutron‐rich nuclei over a wide range of beam energies. They are peripheral processes that can be used to extract asymptotic normalization coefficients (ANC) from which direct capture proton reaction rates of astrophysical interest can be calculated parameter free. We emphasize the importance of reaction model calculations and of exclusive measurements to check them. We review several cases: the breakup of 8B, 9C, 15C and 23Al. Firrst we review how we have used the data for the breakup of 8B at energies from 30 to 1000 MeV/nucleon on light and heavy targets to extract the astrophysical factor S17(0) = 18.7±1.9 eV⋅b for the key reaction for solar neutrino production. Glauber model calculations in the eikonal approximation and in the optical l...

In my presentation, I will discuss the use of transfer reactions as an indirect method of determining information important for nuclear astrophysics. Specifically, I will focus on peripheral reactions and their analysis with the Asymptotic Normalization Coefficients (ANC) method. I will present results from related experiments that have been conducted at the Cyclotron Institute, Texas A&M University with focus on the 0ptical Model Parameters obtained and the need for reliable calculations. Additionally, I will describe the im- provements in the measured data that we obtained after upgrading the detection system used.

In this book a collection of the lecture notes given during the Eighth European Summer School on Experimental Nuclear Astrophysics is given. The school, whose first edition was first held in 2003, took place from 13 to 20 of September 2015 in Santa Tecla, a small village about 15 km north of Catania, characterized by its position on the volcanic shores of the Ionian Sea, surrounded by the spectacular "Timpa" area, a green protected park specific for its mediterranean vegetation. 80 young students and researchers from more than 20 countries attended the lectures and were also encouraged to present their work and results.

Reactions induced by Rare Isotope Beams (RIB) at low or intermediate energies represent a major tool to enrich our knowledge about exotic nuclei (along with decay studies and mass measurements). They allowed us, in the last decade or more, to go beyond the beta‐stability line with our structure or reaction mechanism studies, and are considered to be the way low energy nuclear physics will go. I will present here a few of the types of reactions currently used: elastic scattering, single‐nucleon transfer, breakup at intermediate energies. I will focus on the experimental aspects but, while remaining general, due to my own experience, I will concentrate on reactions that are indirect methods in nuclear astrophysics. The material will, hopefully, prepare you for some of next week’s subjects.

We discuss indirect methods that make use of transfer reactions to determine cross sections of reactions in stellar burning processes. We focus on two of them that have been extensively used in the past decades: the asymptotic normalization coefficients method and the Trojan horse method. We provide a comprehensive description of their theoretical as well as basic experimental features.

We discuss recent developments in indirect methods used in nuclear astrophysics to determine the capture cross sections and subsequent rates of various stellar burning processes, when it is difficult to perform the corresponding direct measurements. We discuss in brief, the basic concepts of Asymptotic Normalization Coefficients, the Trojan Horse Method, the Coulomb Dissociation Method, (d,p), and charge-exchange reactions.

It is well known that measuring cross-sections of thermonuclear reactions at the low energies typical of astrophysical sites is very difficult. This is due to the presence of the Coulomb barrier between the interacting nuclei. For non-explosive scenarios at astrophysical sites, the relevant energies typically span from few tens to few hundreds of keV while the Coulomb barrier is in the order of MeV. The fusion processes then proceed via tunnel effect and their cross-sections are strongly depending on the probability of penetration through the barrier. In a first approximation, this probability is given by the Gamow factor. Owing to the exponential decrease in this factor with energy, the cross-section values of thermonuclear fusion processes in stellar systems often reach values as small as micro- and nanobarn and even lower ones. Neutron-induced reactions, in spite of the absence of Coulomb barrier, are also difficult to measure. Indeed, it is the possible presence of a centrifugal barrier that can hinder the measurement of the values of the cross-sections of these processes. In either cases the cross-sections of astrophysical nuclear processes result in experimental difficulties, due to the low signal-to-noise ratio, that have been a challenge for scientists since the setting of this scientific field: Nuclear Astrophysics. In the last two to three decades, experimental improvements, including the construction of underground laboratories, allowed for the first time the measurement of cross-sections of astrophysical nuclear processes in the relevant energy region for astrophysics. Also, indirect methods were developed. As a general and common feature, using these methods it is possible to relate the features --typically the cross-section-- of a process that is experimentally simpler to measure, although not directly linked to astrophysics, to those of another process that is of interest for this latter field. This didactic paper will briefly describe some of these indirect methods with a special emphasis on Trojan Horse and on its application also to reactions that involve the use of radioactive ion beams and to neutron-induced reactions.

Indirect methods in nuclear astrophysics with relativistic radioactive beams

Indirect Methods in Nuclear Astrophysics with Transfer Reactions

Nuclear reactions within stars typically occur at energies significantly below 1 MeV. Consequently, the Coulomb barrier exponentially suppresses the cross section, reducing it to values as small as a few nanobarns for charged particles. This challenge in obtaining accurate input data for astrophysics has led to the introduction of indirect methods. Specifically, techniques such as ANC and THM have been employed to derive cross sections for reactions involving photons and charged particles in the exit channel, respectively, eliminating the need for extrapolation. The discussion delves into recent results from the application of these methods. For instance, the 6Li(3He,d)7Be measurement is utilized to deduce the ANC’s of the 3He+4He→ 7Be and p+6Li→ 7Be channels, along with their corresponding radiative-capture cross sections. Additionally, the THM measurement of the 27Al(p, α)24Mg cross section via the 2H(27Al,α 24Mg)n reaction is highlighted. In both cases, the cross section at astrophysical energies has been established with unprecedented accuracy.

Context. An accurate 28P(p, γ)29S reaction rate is crucial to defining the nucleosynthesis products of explosive hydrogen burning in ONe novae. Using the recently released nuclear mass of 29S, together with a shell model and a direct capture calculation, we reanalyzed the 28P(p, γ)29S thermonuclear reaction rate and its astrophysical implication. Aims. We focus on improving the astrophysical rate for 28P(p, γ)29S based on the newest nuclear mass data. Our goal is to explore the impact of the new rate and associated uncertainties on the nova nucleosynthesis. Methods. We evaluated this reaction rate via the sum of the isolated resonance contribution instead of the previously used Hauser-Feshbach statistical model. The corresponding rate uncertainty at different energies was derived using a Monte Carlo method. Nova nucleosynthesis is computed with the 1D hydrodynamic code SHIVA. Results. The contribution from the capture on the first excited state at 105.64 keV in 28P is taken into account for the first time. We find that the capture rate on the first excited state in28 P is up to more than 12 times larger than the ground-state capture rate in the temperature region of 2.5 × 107 K to 4 × 108 K, resulting in the total 28P(p, γ)29S reaction rate being enhanced by a factor of up to 1.4 at ~1 × 109 K. In addition, the rate uncertainty has been quantified for the first time. It is found that the new rate is smaller than the previous statistical model rates, but it still agrees with them within uncertainties for nova temperatures. The statistical model appears to be roughly valid for the rate estimation of this reaction in the nova nucleosynthesis scenario. Using the 1D hydrodynamic code SHIVA, we performed the nucleosynthesis calculations in a nova explosion to investigate the impact of the new rates of 28P(p, γ)29S. Our calculations show that the nova abundance pattern is only marginally affected if we use our new rates with respect to the same simulations but statistical model rates. Finally, the isotopes whose abundance is most influenced by the present 28P(p, γ)29S uncertainty are 28Si, 33,34S, 35,37Cl, and 36Ar, with relative abundance changes at the level of only 3% to 4%.