Table of contents

The conference poster can be viewed in the PDF

Prof. Claudio Spitaleri, director of the school

It is my pleasure, as co-director of the school, to welcome students and lecturers of the "Eigth European Summer School on Experimental Nuclear Astrophysics". The school is at its seventh edition and we have students coming from several European countries and from all the world, like Lebanon, India, USA, Russia, Canada, Japan, China, Brazil, Kazakhstan. This is a clear sign that the school is considered as an important meeting for the international Nuclear Astrophysics Community worldwide. We are very proud to offer, for the eigth time, our school program, which aims at widening the students' perspectives and sets, hopefully, a milestone in the education of a new generation of scientists. I remind you that among the goals of the school there are two particular points that deserve attention. The first is allowed by the special venue of the school: the program takes place inside a unique building and this allows all the students to continue their scientific activity and the discussions on the lectures beyond the normal lecture hours. The second peculiar feature is that of favouring cultural exchanges between lectures and students with different traditions, customs and religions. Indeed, Sicily has been historically considered as a meeting place for different cultures, a land that offer chances for peaceful and constructive encounters among different peoples.

I wish to thank all the supporting institutions and sponsors, such as INFN - LNS and the University of Catania. To you all I wish a pleasant and fruitful time in our wonderful city.

Dr. Giacomo Cuttone, Director of INFN-LNS

As a nuclear physicist and as the Director of the LNS it is a pleasure to welcome the students and lecturers of the school in our laboratory. For the eigth time Catania assumes the role of an attraction point in the field of Nuclear Astrophysics, since the whole scientific world is represented here. As a scientist I wish you a fruitful attendance and especially to the youngest ones I wish for them to maintain for all their lifetimes the same enthusiasm they show in this moment. The human understanding of the Universe needs also your efforts as Nuclear Astrophysicists to proceed. LNS has an important and active group of Nuclear Astrophysics research and constitutes a leading facility worldwide in this field. I wish you a fruitful and pleasant week in Santa Tecla and Catania.

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.

The school, has tried once more to present to the young students the global picture of nuclear astrophysics research in the last years. Thus the scientific program of the school covered a wide range of topics dealing with various aspects of nuclear astrophysics, such as stellar evolution and nucleosynthesis, neutrino physics, the Big Bang, direct and indirect methods and radioactive ion beams. Nuclear astrophysics plays a key role in understanding energy production in stars, stellar evolution and the concurrent synthesis of the chemical elements and their isotopes. It is also a fundamental tool to explain the ashes of the early universe, to determine the age of the universe through the study of pristine stellar objects and to predict the evolution of the Sun or Stars. The "bone structure" for the above aspects is based on nuclear reactions, whose rates need to be determined in laboratories. Although impressive progress has been made over the past decades, which was rewarded by Nobel prizes, several open questions are still unsolved, which challenge the basis of the present understanding.

A list of the lecture topics is given below:

—Big Bang Nucleosynthesis

—Stellar evolution and Nucleosynthesis

—radioactive ion beams

—detector and facilities for nuclear astrophysics

—indirect methods in nuclear astrophysics

—plasma physics

An often quoted statement of Carl Sagan, "We are all star stuff," is exhaustively describing one of the great discoveries of the 20th century as well as the main aim of nuclear astrophysics. The present theory of stellar nucleosynthesis (based on the famous paper B²FH) predicts chemical evolution of the Universe, which is testable by looking at stellar spectral lines, meteorites, pre-solar grains or other means of investigation. Quantum mechanics explains why different atoms emit light at characteristic wavelengths, and so by studying the light emitted from different stars, one may infer the atmospheric composition of individual stars. However, upon undertaking such a task, observations indicate a strong correlation between a star's heavy element content (metallicity) and its age (red shift).

Big bang nucleosynthesis tells us that the early universe consisted of only the light elements, and so one expects the first stars to be composed of hydrogen, helium, and lithium, the three lightest elements. The recent achievements of WMAP and Planck missions, with the precise measurement of many cosmological parameters, have re-ignited the interest on the primordial nucleosynthesis, especially for the still unclear Lithium primordial abundance.

Stellar structure and the H-R diagram indicate that the lifetime of a star depends greatly on its initial mass and chemical composition, so that massive stars are very short-lived, and less massive stars are longer-lived. As a star dies, nuclear astrophysics argues that it will enrich the interstellar medium with "heavy elements" (in this case all elements heavier than lithium, the third element), from which new stars are formed. This account is consistent with the observed correlation between stellar metallicity and red shift.

The theory of stellar nucleosynthesis would not be very convincing if reliable nuclear physics inputs are adopted. By carefully scrutinizing the table of nuclides, nuclear astrophysicists were able to predict the existence of different stellar environments which could produce the observed isotopic abundances, and the nuclear processes which must occur in these stars. This is also valid for elements heavier than iron production, when fusion reactions are of negligible importance and the main nucleosynthetic path goes through p-process, r-process, and s-process.

Many of the nuclides generated in the huge explosion triggered by the last burnings in the life of a massive star are unstable. Then in order to understand what is going on in Supernovae explosions, Gamma-ray bursts, Novae it was pointed out that the physics of radioactive beams should be explored. Many group of physicists have then taken the opportunities offered by the world-wide developments of radioactive ion beams facilities to start to investigate such environments. In this field also the weak interaction processes are important and in some cases, like type II Supernovae, dominant. Additional nucleosynthetic paths, such as the i-processes were also introduced in one specific lecture.

In order to better understand our Universe, a precise knowledge of nuclear inputs for nuclear astrophysics is therefore needed. They influence sensitively the nucleosynthesis of the elements in the early stages of the universe and in all the objects formed thereafter and control the associate energy generation, neutrino luminosity and stellar evolution. Thus a good knowledge of reaction rates is essential to understand this broad picture. Studies at the energies typical of nuclear astrophysics for charged particle induced reactions (few keV - 1 MeV) are severely hampered by the low signal-to-noise ratio, essentially due to the tiny cross sections that have to be measured (as low as picobarn in some cases). The best experimental solutions to this main problem will be discussed in this book and presented in their details. The pilot project, LUNA, i.e. a 50 keV accelerator installed in the Laboratori Nazionali del Gran Sasso has already given several important results in the last decade. Other experimental methods such as the recoil separator, spectrometers will be reviewed together with the wide field of nuclear astrophysics research opened by the development of radioactive ion beams in several laboratories of the world.

Detectors and facilities useful for the next decade of nuclear astrophysics studies were reviewed in the lectures and attention was devoted to future research possibilities for studies. This knowledge and the facilities will be of groundbreaking importance for solving the future quests for this field.

Although all these efforts in some cases (such as the ¹²C + ¹²C interaction and the ¹²C(α, γ)¹⁶O and many others) the goal is far from being achieved by means of direct measurements. Moreover the presence of the electron screening effect makes very hard and sometimes impossible the measurement of the bare nucleus astrophysical factor, that is the quantity needed for astrophysics. Thus extrapolations (usually supported by R-matrix theory) are adopted. An alternative way to by-pass these problems and measure the bare nucleus astrophysical factor or cross section is given by the indirect methods. Among them the Coulomb Dissociations, the ANC, decay spectroscopy and the Trojan Horse Method will be reviewed.

In recent years, new possibilities of exploring the universe have opened. Not only electromagnetic spectra, luminosities are available for stars, galaxies and compact objects but new windows are opened in particle detection. Cosmic ray detectors will play, in the near future, an important role for a better understanding of what is going on in the universe and therefore they will trigger the opening of a new sector of nuclear astrophysics research. Physics experiments can be performed in laser-induced plasmas available worldwide, opening new possibilities for future research.

Crucial problems related to various issues of nuclear as well as astrophysics are still open, triggering new researches in this field and the enthusiasm to organize events such us our European Summer school on experimental nuclear astrophysics. Once more students, young researchers and lecturers have gathered in Santa Tecla from more than twenty countries of the world. The school, though a European one, keeps playing the role of a meeting point of students of different nationalities from the whole world. These students, we are sure, have left our school not only with an improved knowledge of nuclear astrophysics but also with new friends (as well as future collaborators) all around the world.

We gratefully acknowledge all the participants the lecturers and the members of the Scientific committee. The school could not have taken place without their efforts and help. The Organizing Committee also acknowledges the financial support of the Laboratori Nazionali del Sud - Istituto Nazionale di Fisica Nucleare - Italy under the grant "LNS Astrofisica Nucleare (fondi premiali)", Dipartimento di Fisica e Astronomia of the University of Catania - Italy. All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

The school has been honoured by the welcome addresses of Dr. Giacomo Cuttone, Director of Laboratori Nazionali del Sud and by the school director prof. Claudio Spitaleri. We wish to the reader that the reading of this book can be as fruitful as the participation to our school.

The conference photograph can be viewed in the PDF

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered bythe proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

The measurement of gamma rays from cosmic sources at ~MeV energies is one of the key tools for nuclear astrophysics, in its study of nuclear reactions and their impacts on objects and phenomena throughout the universe. Gamma rays trace nuclear processes most directly, as they originate from nuclear transitions following radioactive decays or high-energy collisions with excitation of nuclei. Additionally, the unique gamma-ray signature from the annihilation of positrons falls into this astronomical window and is discussed here: Cosmic positrons are often produced from β-decays, thus also of nuclear physics origins. The nuclear reactions leading to radioactive isotopes occur inside stars and stellar explosions, which therefore constitute the main objects of such studies. In recent years, both thermonuclear and core-collapse supernova radioactivities have been measured though ⁵⁶Ni, ⁵⁶Co, and ⁴⁴Ti lines, and a beginning has thus been made to complement conventional supernova observations with such measurements of the prime energy sources of supernova light created in their deep interiors. The diffuse radioactive afterglow of massive-star nucleosynthesis in gamma rays is now being exploited towards astrophysical studies on how massive stars feed back their energy and ejecta into interstellar gas, as part of the cosmic cycle of matter through generations of stars enriching the interstellar gas and stars with metals. Large interstellar cavities and superbubbles have been recognised to be the dominating structures where new massive-star ejecta are injected, from ²⁶Al gamma-ray spectroscopy. Also, constraints on the complex interiors of stars derive from the ratio of ⁶⁰Fe/²⁶Al gamma rays. Finally, the puzzling bulge-dominated intensity distribution of positron annihilation gamma rays is measured in greater detail, but still not understood; a recent microquasar flare provided evidence that such objects may be prime sources for positrons in interstellar space, rather than distributed nucleosynthesis. We also briefly discuss the status and prospects for astronomy with telescopes for the nuclear-radiation energy window.

This contribution is meant as a first brief introduction to stellar physics. First I shortly describe the main physical processes active in stellar structures then I summarize the most important features during the stellar life-cycle.

Roughly half of the abundances of the elements heavier than iron in the cosmos are produced by slow neutron captures (the s process) in hydrostatic conditions when the neutron density is below roughly 10¹³ n/cm^-3. While it is observationally well confirmed that asymptotic giant branch (AGB) stars are the main site of the s process, we are still facing many problems in the theoretical models and nuclear inputs. Major current issues are the effect of stellar rotation and magnetic fields and the determination of the rate of the neutron source reactions. I will present these problems and discuss the observational constraints that can help us to solve them, including spectroscopically derived abundances, meteoritic stardust, and stellar seismology. Further, I will present evidence that the s process is not the only neutron-capture process to occur in AGB stars: an intermediate process is also required to explain recent observations of post-AGB stars.

In this lecture I will introduce the concept of galactic chemical evolution, namely the study of how and where the chemical elements formed and how they were distributed in the stars and gas in galaxies. The main ingredients to build models of galactic chemical evolution will be described. They include: initial conditions, star formation history, stellar nucleosynthesis and gas flows in and out of galaxies. Then some simple analytical models and their solutions will be discussed together with the main criticisms associated to them. The yield per stellar generation will be defined and the hypothesis of instantaneous recycling approximation will be critically discussed. Detailed numerical models of chemical evolution of galaxies of different morphological type, able to follow the time evolution of the abundances of single elements, will be discussed and their predictions will be compared to observational data. The comparisons will include stellar abundances as well as interstellar medium ones, measured in galaxies. I will show how, from these comparisons, one can derive important constraints on stellar nucleosynthesis and galaxy formation mechanisms. Most of the concepts described in this lecture can be found in the monograph by Matteucci (2012).

A brief introduction on the main characteristics of the asymptotic giant branch stars (briefly: AGB) is presented. We describe a link to observations and outline basic features of theoretical modeling of these important evolutionary phases of stars. The most important aspects of the AGB stars is not only because they are the progenitors of white dwarfs, but also they represent the site of almost half of the heavy element formation beyond iron in the galaxy. These elements and their isotopes are produced by the s-process nucleosynthesis, which is a neutron capture process competing with the β^- radioactive decay. The neutron source is mainly due to the reaction ¹³C(α,n)¹⁶O reaction. It is still a challenging problem to obtain the right amount of ¹³C that can lead to s-process abundances compatible with observation. Some ideas are presented in this context.

One of the main ingredients of nuclear astrophysics is the knowledge of the thermonuclear reactions which power the stars and synthesize the chemical elements. 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 and their influence on our understanding of the properties of the neutrino and of the Sun is discussed. We then describe the current LUNA program mainly devoted to the study of the nucleosynthesis of the light elements in AGB stars and Classical Novae. Finally, the future of LUNA towards the study of helium and carbon burning with a new 3.5 MV accelerator is outlined.

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.

Neutrino reactions on nuclei play important roles for the dynamics of supernovae and their associated nucleosynthesis. This manuscript summarizes the current status in deriving the relevant cross sections for supernova neutrinos and briefly discusses a few recent advances where

The vp-process is a new nucleosynthetic scenario, proposed 2006, which supposed to take place at the very early epoch of type II supernova, involving nuclear reactions of proton-rich nuclei not only with protons and alphas, but also with neutrons due to the neutrino processes. The vp-process is one of the key processes for investigating the mechanism of type II supernovae, and the process could be possibly responsible for the anomalously abundant p-nuclei around mass 90-100. Specifically, the nuclear physics problems in the vp-process were discussed in this talk including our recent experimental results with low-energy RI beams and a simulation study. Alpha cluster resonances have been identified experimentally which play a crucial role for the stellar (α,p) and (α,γ) reactions just above the alpha threshold. Neutron induced reactions in the proton-rich nuclear regions in the vp-process are also suggested to play an important role, which will discard the waiting points, and accelerate the flow to heavier nuclei. This process involves nuclear structures of very high level density at high excitation energies in neutron deficient nuclei, and both of the projectile and the target are unstable, which is a quite difficult experimental challenge in nuclear astrophysics in the coming years. Some experimental challenges are discussed.

Owing the presence of the Coulomb barrier at astrophysically relevant kinetic energies, it is very difficult, or sometimes impossible to measure astrophysical reaction rates in laboratory. This is why different indirect techniques are being used along with direct measurements. The THM is unique indirect technique allowing one measure astrophysical rearrangement reactions down to astrophysical relevant energies. The basic principle and a review of the main application of the Trojan Horse Method are presented. A step-by-step approach will be adopted in order to describe the features usually unknown to non-experts.

I will present the possibilities and some results of doing nuclear astrophysics research in IFIN-HH Bucharest-Magurele. There are basically two lines of experimental activities: (1) direct measurements with beams from the local accelerators, in particular with the new 3 MV Tandetron accelerator. This facility turns out to be competitive for reactions induced by a-particles and light ions. Extra capabilities are given by the ultra-low background laboratory we have in a salt mine about 2.5 hrs. driving north of Bucharest; (2) indirect measurements done with beams at international facilities, in particular at those providing Rare Ion Beams. Completely new and unique opportunities will be provided by ELI-NP, under construction in our institute.

Nuclear reactions involving radioactive isotopes are extremely relevant in several astrophysical scenarios, from the Big-Bang Nucleosynthesis to Supernovae explosions. In this contribution the production of Radioactive Ion Beams (RIBs) by means of the in-flight technique is reviewed. In particular, the use of direct reactions in inverse kinematics for the production of light weakly-bound RIBs by means of the facility EXOTIC at INFN-LNL (Italy) will be described in detail.

In this contribution a brief overview of the status and recent developments of ab-initio studies of nuclear reactions of astrophysical interest is presented.

¹⁸O(p, γ)¹⁹F and ²³Na(p,γ)²⁴Mg are reactions of astrophysical interest for example in AGB star scenarios. The rates of both reactions are potentially influenced by low-energy resonances for whose strengths either exist only values with large uncertainties, upper limits or even contradictory claims. Measurements at the Laboratory for Underground Nuclear Astrophysics (LUNA) aim at a direct observation of these low-energy resonances, and additional cross section measurements to aid a more precise determination of the reaction rates in astrophysical scenarios. We report the experimental setup and the status of the ongoing measurements of the two reactions at LUNA.

The study of the ¹⁹F(p,α)¹⁶O reaction at low energy is important both for Nuclear Structure and Astrophysics. Despite of its importance, the S-factor of this reaction is poorly known, especially at astrophysical energies. We present an overview of the ¹⁹F(p,α₀)¹⁶O reaction cross section, as obtained from recent direct measurements and from published works in the literature. We include in the systematic also data from an unpublished work, where several excitation functions and angular distributions for α₀ and α_π channels are reported.

¹⁹F experimental abundances is overestimated in respect to the theoretical one: it is therefore clear that further investigations are needed. We focused on the ¹⁹F(α, p)²² Ne reaction, representing the main destruction channel in He-rich environments. The lowest energy at which this reaction has been studied with direct methods is E_C.M. ≈ 0.91 MeV, while the Gamow region is between 0.39 ÷ 0.8 MeV, far below the Coulomb barrier (3.8 MeV). For this reason, an experiment at Rudjer Boskovic Institute (Zagreb) was performed, applying the Trojan Horse Method. Following this method we selected the quasi-free contribution coming from ⁶Li(¹⁹F,p²²Ne)² H at E_beam=6 MeV at kinematically favourable angles, and the cross section at energies 0 < E_C.M. < 1.4 MeV was extracted in arbitrary units, covering the astrophysical region of interest.

The neon-sodium cycle of hydrogen burning influences the synthesis of the elements between ²⁰Ne and ²⁷Al in AGB stars and classical novae explosions.

The ²²Ne(p,γ)²³Na reaction rate is very uncertain because of a large number of unobserved resonances lying in the Gamow window.

A new direct study of the ²²Ne(p,γ)²³Na reaction has been performed at the Laboratory for Underground Nuclear Astrophysics (LUNA) using a windowless gas target and two HPGe detectors. Several resonances have been observed for the first time in a direct experiment.

With the aim to test the present capability of the stellar surface lithium abundance in providing an estimation for the age of PMS stars, we analyze the case of the detached, double-lined, eclipsing binary system PAR 1802. For this system, the lithium age has been compared with the theoretical one, as estimated by applying a Bayesian analysis method on a large grid of stellar evolutionary models. The models have been computed for several values of chemical composition and mixing length, by means of the code FRANEC updated with the Trojan Horse reaction rates involving lithium burning.

Stars in the mass range 1.2-7M_⊙, with solar-like initial composition are evolved from the zero age main sequence till the early AGB phase. Their predicted oxygen isotopic ratios are compared to observationally inferred values in red giants to investigate how well standard evolutionary calculation reproduces available observations and to illustrate the role of convective mixing. We find that extra mixing beyond the convective boundary determined by the Schwarzschild criterion is needed to explain the observational oxygen isotopic ratios, particularly in low mass stars. The effect of recent determinations of proton capture reactions and their uncertainties on ¹⁶O/¹⁷O is also shown.

The unexplored area of heavy neutron rich nuclei is extremely important for nuclear astrophysics investigations and, in particular, for the understanding of the r-process of astrophysical nucleogenesis. For the production of heavy neutron rich nuclei located along the neutron closed shell N=126 (probably the last "waiting point" in the r-process of nucleosynthesis) the low-energy multi-nucleon transfer reaction ¹³⁶Xe+²⁰⁸Pb at E_lab=870MeV was explored. Due to the stabilizing effect of the closed neutron shells in both nuclei, N=82 and N=126, and the rather favorable proton transfer from lead to xenon, the light fragments formed in this process are well bound and the Q-value of the reaction is nearly zero.

Measurements were performed with the PRISMA spectrometer in coincidence with an additional time-of-flight (ToF) arm on the +20 beam line of the PIAVE-ALPI accelerator in Legnaro, Italy. The PRISMA spectrometer allows identification of the A, Z and velocity of the projectile-like fragments (PLF), while the second arm gives access to the target-like fragments (TLF). Details on the experimental setup and preliminary results are reported.

In order to study reactions with unstable nuclei, radioactive-ion beams must be used. One method for producing radioactive beams is the TwinSol experimental setup at the University of Notre Dame. At TwinSol, stable and unstable isotope beams bombard a gas target, where one atmosphere of gas must be confined from the surrounding vacuum. Thin foil windows are used to contain the gas in the cell. In order to optimize the quality of secondary beams from TwinSol, it is necessary to understand and minimize the effects of energy loss and straggling in the windows. This work is the beginning of a process to improve the TwinSol design so that secondary beams produced with heavier ions such as Oxygen, Fluorine, and Neon can be pursued.

The scattering process on 1p-shell nuclei, having the cluster structure, can be seen in the anomaly increasing of cross sections for large angles. Most often, this increasing of cross sections is connected with mechanism of transfer of clusters or nucleons. The study of the α-cluster transfer mechanism in the elastic scattering of ²⁰Ne ions on ¹⁶O nuclei is important for investigation burning process in evolution of the Universe immediately after the Big-Bang. Therefore new experiment on the heavy ion accelerator (Warsaw University) was carried out with a significant expansion of the range of angles up to 170⁰ in center mass system at E_Lab=50.0 MeV. Data analysis of angular distribution was performed in framework of the optical model and coupled channel method. The optimal parameters of the optical potential were obtained and the spectroscopic factor was obtained 1 for ²⁰Ne as α +¹⁶O.

The Big Bang Nucleosynthesis began a few minutes after the Big Bang, when the Universe was sufficiently cold to allow deuterium nuclei to survive photo-disintegration. The total amount of deuterium produced in the Universe during the first minutes depends on the cosmological parameters (like the energy density in baryons, Ω_bh², and the effective neutrino number, N_eff) and on the nuclear cross sections of the relevant reactions. The main source of uncertainty in the deuterium estimation comes from the ²H(p, γ)³He cross section.

Measurements of Cosmic Microwave Background (CMB) anisotropies obtained by the Planck satellite are in very good agreement with the theoretical predictions of the minimal ΛCDM cosmological model, significantly reducing the uncertainty on its parameters. The Planck data allows to indirectly deduce with very high precision the abundances of primodial nuclides, such as the primodial deuterium fraction ²H/H = (2.65 ± 0.07) .10^-5 (68% C.L.).

The astrophysical observations in damped Lyman-a systems at high redshifts provide a second high accuracy measurement of the primodial abundance of deuterium ²H/H = (2.53 ± 0.04) · 10^-5 (68% C.L.).

The present experimental status on the astrophysical S-factor of the ²H(p, γ)³He reaction in the BBN energy range, gives a systematic uncertainties of 9%. Also the difference between ab-initio calculations and experimental values of S12 is at the level of 10%.

In order to clarify the actual scenario, a measurement of ²H(p, γ)³He cross section with a precision of a few percent in the 70-400 keV energy range is planned at LUNA in 2016. A feasibility test of the measurement has been performed in October 2014, giving the preliminary results on the cross section. The experimental setup for the test and final measurement campaign will be presented.

Carbon-carbon fusion reaction represents a nuclear process of great interest in astrophysics, since the carbon burning is connected with the third phase of massive stars (M > 8 M_☉) evolution. In spite of several experimental works, carbon-carbon cross section has been measured at energy still above the Gamow window moreover data at low energy present big uncertainty. In this paper we report the results about the study of the ¹⁶O(¹²C,α²⁰Ne)α reaction as a possible three-body process to investigate ¹²C(¹²C,α)²⁰Ne at astrophysical energy via Trojan Horse Method (THM). This study represents the first step of a program of experiments aimed to measure the ¹²C+¹²C cross section at astrophysical energy using the THM.

The study of pre-compound emission in α-induced reactions, particularly at the low incident energies, is of considerable interest as the pre-compound emission is more likely to occur at higher energies. With a view to study the competition between the compound and the pre-compound emission processes in α-induced reactions at different energies and with different targets, a systematics for neutron emission channels in targets ⁵¹V, ⁵⁵Mn, ⁹³Nb, ^{121, 123}Sb and ¹⁴¹Pr at energy ranging from astrophysical interest to well above it, has been developed.

The off-line γ-ray-spectrometry based activation technique has been adopted to measure the excitation functions. The experimental excitation functions have been analysed within the framework of the compound nucleus mechanism based on the Weisskopf-Ewing model and the pre-compound emission calculations based on the geometry dependent hybrid model. The analysis of the data shows that experimental excitation functions could be reproduced only when the pre-compound emission, simulated theoretically, is taken into account.

The strength of pre-compound emission process for each system has been obtained by deducing the pre-compound fraction. Analysis of data indicates that in α-induced reactions, the pre-compound emission process plays an important role, particularly at the low incident energies, where the pure compound nucleus process is likely to dominate.

B(n,α) Li reaction cross section has been measured using the Trojan Horse method, with the specific aim to separate the α₁ contribution (coming from the first Li excited level) by the α_o (related to the Li ground state), using a very thin target. Preliminary results are shown of the three-body B(d,α⁷ Li)H cross section.

In the present paper we investigate the possible connection between s-process nucleosynthesis occurring during the asymptotic giant branch (AGB) phase of low-mass stars (LMS) and the isotopic anomalies of the "Fe-group" elements observed in several macroscopic samples of meteorites or in grains formed as circumstellar condensates (hereafter CIRCONs). The available measurements of chromium, iron, and nickel are well reproduced by stellar models, which account for the largest shifts in the heaviest isotopes of each element: in particular ⁵⁴Cr, ⁵⁸Fe, and ⁶⁴Ni. Moreover, many circumstellar condensates reflect ⁵⁰Ti excesses and some production of ^46,47,49Ti, as predicted by slow-neutron captures in AGB stars. Nevertheless, some difficulties are found in comparing theoretical calculations of s-process nucleosynthesis with calcium, silicon, and zinc isotopic anomalies.

Heavy-ion fusion reactions between light nuclei such as carbon and oxygen isotopes have been studied because of their significance for a wide variety of stellar burning scenarios. One important stellar reaction is ¹²C+¹²C, but it is difficult to measure it in the Gamow window because of very low cross sections and several resonances occurring. Hints can be obtained from the study of ¹³C+¹²C reaction. We have measured this process by an activation method for energies down to E_cm=2.5 MeV using ¹³C beams from the Bucharest 3 MV tandetron and gamma-ray deactivation measurements in our low and ultralow background laboratories, the latter located in a salt mine about 100 km north of Bucharest. Results obtained so far are shown and discussed in connection with the possibility to go even further down in energy and with the interpretation of the reaction mechanism at such deep sub-barrier energies.

The ²²Ne(p, γ)²³Na reaction takes part in the NeNa cycle of hydrogen burning, influencing the production of the elements between ²⁰Ne and ²⁷Al in red giant stars, asymptotic giant stars and classical novae. The ²²Ne(p,γ)²⁷Na reaction rate is very uncertain because of a large number of tentative resonances in the Gamow window, where only upper limits were quoted in literature. A direct measurement of the ²²Ne(p, γ)²³Na reaction cross section has been carried out at LUNA using a windowless differential-pumping gas target with two high- purity germanium (HPGe) detectors. A new measurement with a 4π bismuth germanate (BGO) summing detector is ongoing. During the HPGe phase of the experiment the strengths of the resonances at 156.2 keV, 189.5 keV and 259.7 keV have been directly measured for the first time and their contribution to the reaction rate has been calculated. The decay scheme of the newly discovered resonances has been established as well and some improved upper limits on the unobserved resonances have been put. The BGO detector with its 70% γ-detection efficiency allows to measure the cross section at lower energy. In order to further investigate the resonances at 71 keV and 105 keV and the direct-capture component, the data taking is ongoing.