Indirect Methods In Nuclear Astrophysics Research Articles

Indirect methods in nuclear astrophysics: Recent results from ANC and THM

Indirect methods in nuclear astrophysics: Recent results from ANC and THM

Transfer reactions as an Indirect Method in Nuclear Astrophysics

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.

Indirect methods in nuclear astrophysics

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.

“Other” indirect methods for nuclear astrophysics

In the house of Trojan Horse Method (THM), I will say a few words about “other” indirect methods we use in Nuclear Physics for Astrophysics. In particular those using Rare Ion Beams that can be used to evaluate radiative proton capture reactions. I add words about work done with the Professore we celebrate today. With a proposal, and some results with TECSA, for a simple method to produce and use isomeric beam of 26m Al.

Indirect methods in nuclear astrophysics

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.

Preface: Eighth European Summer School on Experimental Nuclear Astrophysics

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.

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

The ground state of the proton-rich nucleus 23Al has been studied by one-proton removal on a carbon target at about 50 MeV/nucleon using the EXOGAM + SPEG experimental setup at GANIL. Longitudinal momentum distributions of the 22Mg breakup fragments, inclusive and in coincidence with gamma rays de-exciting the residues, were measured. The ground-state structure of 23Al is found to be a configuration mixing of a d-orbital valence proton coupled to four core states - 0$^{+}_{gs}$, 2$^{+}_{1}$, 4$^{+}_{1}$, 4$^{+}_{2}$. We confirm the ground state spin and parity of 23Al as $J^{\pi} = 5/2^{+}$. The measured exclusive momentum distributions are compared with extended Glauber model calculations to extract spectroscopic factors and asymptotic normalization coefficients (ANCs). The spectroscopic factors are presented in comparison with those obtained from large-scale shell model calculations. We determined the asymptotic normalization coefficient of the nuclear system $^{23}$Al$_{gs}$ $\rightarrow$ $^{22}$Mg(0$^{+}$) + p to be $C^{2}_{d_{5/2}}$($^{23}Al_{gs}$) = (3.90 $\pm$ 0.44) $\times$ 10$^{3}$ fm$^{-1}$, and used it to infer the stellar reaction rate of the direct radiative proton capture $^{22}$Mg(p,$\gamma$)$^{23}$Al. Astrophysical implications related to $^{22}$Na nucleosynthesis in ONe novae and the use of one-nucleon breakup at intermediate energies as an indirect method in nuclear astrophysics are discussed.

Indirect Methods in Nuclear Astrophysics: ANCs

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.

Indirect Methods for Nuclear Astrophysics

Some general features of indirect approaches for determining cross sections of astrophysically relevant reactions at low energies are discussed from a theoretical point of view. The methods of Coulomb dissocation (CD), of the asymptotic normalization coefficient (ANC) and the Trojan-horse method (THM) are considered.

Breakup of loosely bound nuclei as indirect method in nuclear astrophysics: 8B, 9C, 23Al

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.

Elastic scattering of the proton drip-line nucleusF17

Precision data have been obtained for the elastic scattering of $^{17}\mathrm{F}$ on $^{12}\mathrm{C}$ and $^{14}\mathrm{N}$ at 10 MeV/nucleon to clarify the reaction mechanism for loosely bound nuclei at low energies and to assess the validity of a double-folding procedure to predict optical model potentials for use in indirect methods for nuclear astrophysics. The double-folding procedure incorporates density and energy-dependent effective nucleon-nucleon interactions with realistic densities consistent with experimentally determined asymptotic normalization coefficients. The derived potentials provide an excellent description of the data and point to a complete dominance of absorption at the barrier. A semiclassical analysis in terms of multireflection barrier--internal barrier series expansion of the scattering amplitude shows that only the barrier component survives in the scattering process, pointing to the peripheral character of the reactions.

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 breakup reactions of loosely bound nuclei at intermediate energies as an indirect method in nuclear astrophysics. In particular, the breakup of 8B and 9C is described in detail in terms of an extended Glauber model. 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. The predictions of the model are in excellent agreement with independent reaction data (reaction cross sections and parallel momentum distributions for core-like fragments). Final state interaction has been included in the Coulomb dissociation component. Glauber model calculations using different effective interactions give consistent, though slightly different results. The results of this new analysis are compared with the earlier one for the astrophysical factor S17(0) for the key reaction for solar neutrino production 7Be(p,γ)8B. They are consistent with the values from most direct measurements and other indirect methods.