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Background: Resonance scattering has been extensively used to study the structure of exotic, neutron-deficient nuclei. Extension of the resonance scattering technique to neutron-rich nuclei was suggested more than 20 years ago. This development is based on the isospin conservation law. In spite of broad field of the application, it has never gained a wide-spread acceptance.Purpose: To benchmark the experimental approach to study the structure of exotic neutron-rich nuclei through resonance scattering on a proton target.Method: The excitation function for $p+^{8}\mathrm{Li}$ resonance scattering is measured using a thick target by recording coincidence between light and heavy recoils, populating $T=3/2$ isobaric analog states (IAS) in $^{9}\mathrm{Be}$.Results: A good fit of the $^{8}\mathrm{Li}(p,p)^{8}\mathrm{Li}$ resonance elastic scattering excitation function was obtained using previously tentatively known $5/{2}^{\ensuremath{-}}\phantom{\rule{4pt}{0ex}}T=3/2$ state at 18.65 MeV in $^{9}\mathrm{Be}$ and a new broad $T=3/2\phantom{\rule{4pt}{0ex}}s$-wave state---the $5/{2}^{+}$ at 18.5 MeV. These results fit the expected isomirror properties for the $T=3/2\phantom{\rule{4pt}{0ex}}A=9$ isoquartet.Conclusions: Our analysis confirmed isospin as a good quantum number for the investigated highly excited $T=3/2$ states and demonstrated that studying the structure of neutron-rich exotic nuclei through IAS is a promising approach.

Low-lying negative-parity states in $^{11}\mathrm{Be}$ having dominant $p$-wave neutron configurations were studied using the $^{12}\mathrm{B}(d,^{3}\mathrm{He})\phantom{\rule{0.16em}{0ex}}^{11}\mathrm{Be}$ proton-removal reaction in inverse kinematics. The $1/{2}_{1}^{\ensuremath{-}}$ state at 0.32 MeV, the $3/{2}_{1}^{\ensuremath{-}}$ state at 2.56 MeV, and one or both of the states including the $5/{2}_{1}^{\ensuremath{-}}$ level at 3.89 MeV and the $3/{2}_{2}^{\ensuremath{-}}$ level at 3.96 MeV were populated in the present reaction. Spectroscopic factors were determined from the differential cross sections using a distorted wave Born approximation method. The $p$-wave proton removal strengths were well described by the shell model calculations while the Nilsson model calculation underestimates the spectroscopic factors for the higher excited states. Results from both variational Monte Carlo and no-core shell-model calculations were also compared with the experimental observations.

This paper describes the production and characterization of a 26Al beam comprised of both, its 5 + ground state, and its 0 + isomeric state. The 26Al beam was produced in-flight via the p (26Mg, 26Al)n reaction. The isomer fraction of the 26Al beam was maximized by choosing a bombarding energy of 158.5 MeV for the 26Mg primary beam. The resulting beam had an energy of 120 MeV, a total intensity of 2 × 10 5 particles/sec, a purity of 98% and an isomer content of 70%. This high-quality 26Al isomeric beam was used to study the 26Al m (d, p)27Al reaction relevant for understanding the nucleosynthesis of 26Al in the Galaxy.

A high-count-rate ionization chamber design with position-sensitivity has been developed and deployed at several accelerator facilities. Counting rates of ≥ 500 kHz with good Z -separation (up to 5% energy resolution) for particle identification have been demonstrated in a series of commissioning experiments. A position-sensitive capability, with a resolution of 3 mm, has been implemented for the first time to record position information and suppress pileup. The design and performance of the detectors are described.

A large number of (α,p)(α,p) and (α,n)(α,n) reactions are known to play a fundamental role in nuclear astrophysics. This work presents a novel technique to study these reactions with the active target system MUSIC whose segmented anode allows the investigation of a large energy range of the excitation function with a single beam energy. In order to verify the method, we performed direct measurements of the previously measured reactions 17O (α,n)(α,n)20Ne, 23Na (α,p)(α,p)26Mg, and 23Na (α,n)(α,n)26Al. These reactions were investigated in inverse kinematics using 4He gas in the detector to study the excitation functions in the energy range of about 2–6 MeV in the center of mass. We found good agreement between the cross sections of the 17O (α,n)(α,n)20Ne reaction measured in this work and previous measurements. Furthermore we have successfully performed a simultaneous measurement of the 23Na (α,p)(α,p)26Mg and 23Na (α,n)(α,n)26Al reactions.

New experimental data for the $^{38}$Ar($\alpha$,n)$^{41}$Ca and $^{38}$Ar($\alpha$,p)$^{41}$K reactions were used to find a best-fit set of parameters for statistical model calculations. The very good agreement between the experimental data and the best-fit calculation confirms the applicability of the statistical model for nuclei in the vicinity of the doubly-magic $^{40}$Ca despite of their relatively low level densities. The present study investigates the sensitivities and finds that the $\alpha$-nucleus and the nucleon-nucleus potentials are the most important ingredients for the calculation of ($\alpha$,n) and ($\alpha$,p) reactions in the statistical model. Furthermore, the width fluctuation correction plays an essential role in the peculiar case of $^{38}$Ar. The best-fit parameters from $^{38}$Ar are applied to the mirror nucleus $^{38}$Ca and the neighboring $^{36}$Ar and $^{40}$Ar nuclei. For $^{38}$Ca this results in an astrophysical reaction rate of the $^{38}$Ca($\alpha$,p)$^{41}$Sc reaction which has a flatter temperature dependence compared to all previous calculations. For $^{40}$Ar a better reproduction of $^{40}$Ar($\alpha$,p)$^{43}$K data from literature is obtained. The disagreement between calculation and an early experimental data point for the $^{36}$Ar($\alpha$,p)$^{39}$K reaction persists.

The ^{36}Ar(n,γ)^{37}Ar (t_{1/2}=35 d) and ^{38}Ar(n,γ)^{39}Ar (269 yr) reactions were studied for the first time with a quasi-Maxwellian (kT∼47 keV) neutron flux for Maxwellian average cross section (MACS) measurements at stellar energies. Gas samples were irradiated at the high-intensity Soreq applied research accelerator facility-liquid-lithium target neutron source and the ^{37}Ar/^{36}Ar and ^{39}Ar/^{38}Ar ratios in the activated samples were determined by accelerator mass spectrometry at the ATLAS facility (Argonne National Laboratory). The ^{37}Ar activity was also measured by low-level counting at the University of Bern. Experimental MACS of ^{36}Ar and ^{38}Ar, corrected to the standard 30 keV thermal energy, are 1.9(3) and 1.3(2) mb, respectively, differing from the theoretical and evaluated values published to date by up to an order of magnitude. The neutron-capture cross sections of ^{36,38}Ar are relevant to the stellar nucleosynthesis of light neutron-rich nuclides; the two experimental values are shown to affect the calculated mass fraction of nuclides in the region A=36-48 during the weak s process. The new production cross sections have implications also for the use of ^{37}Ar and ^{39}Ar as environmental tracers in the atmosphere and hydrosphere.

The single-neutron configurations of several low-lying states in $^{22}\mathrm{F}$ have been determined from neutron-adding cross sections of a ($d,p$) reaction using a $^{21}\mathrm{F}$ radioactive beam in inverse kinematics. Final states in $^{22}\mathrm{F}$ consisting of a proton in the $\ensuremath{\pi}0{d}_{5/2}$ orbital coupled to a neutron in either the $\ensuremath{\nu}0{d}_{5/2}$, $\ensuremath{\nu}1{s}_{1/2}$, or $\ensuremath{\nu}0{d}_{3/2}$ orbitals were observed up to an excitation energy of $\ensuremath{\sim}5$ MeV. Spectroscopic factors and strengths were determined from the angular distribution of the cross sections using a distorted wave Born approximation method. The distribution of the $\ensuremath{\nu}0{d}_{5/2}$ and $\ensuremath{\nu}1{s}_{1/2}$ strength was well described by all USD effective shell model interactions, while only the more recent USDA/USDB interactions showed a marked improvement in describing the observed $\ensuremath{\nu}0{d}_{3/2}$ strength. Diagonal two-body matrix elements of the ${(0{d}_{5/2})}_{J=0--5}^{2}$ effective nucleon-nucleon interaction were extracted from the data and compared with previous determinations of the same matrix elements from particle-particle and hole-hole spectra, as well as the calculated results of the USDA interactions. No significant discrepancies were observed. Inspection of the monopole energies showed that an improved agreement between the different empirical matrix elements is found if a mass dependence is included.

In massive stars, the $^{41}\mathrm{Ca}(n,\ensuremath{\alpha})^{38}\mathrm{Ar}$ and $^{41}\mathrm{K}(p,\ensuremath{\alpha})^{38}\mathrm{Ar}$ reactions have been identified as the key reactions governing the abundance of $^{41}\mathrm{Ca}$, which is considered as a potential chronometer for solar system formation. So far, due to experimental limitations, the $^{41}\mathrm{Ca}(n,\ensuremath{\alpha})^{38}\mathrm{Ar}$ reaction rate is solely based on statistical model calculations. In the present study, we have measured the time-inverse $^{38}\mathrm{Ar}(\ensuremath{\alpha},n)^{41}\mathrm{Ca}$ and $^{38}\mathrm{Ar}(\ensuremath{\alpha},p)^{41}\mathrm{K}$ reactions using an active target detector. The reactions were studied in inverse kinematics using a 133-MeV $^{38}\mathrm{Ar}$ beam and $^{4}\mathrm{He}$ as the active-gas target. Both excitation functions were measured simultaneously in the energy range of $6.8\ensuremath{\le}{E}_{\mathrm{c}.\mathrm{m}.}\ensuremath{\le}9.3$ MeV. Using detailed balance the $^{41}\mathrm{Ca}(n,\ensuremath{\alpha})^{38}\mathrm{Ar}$ and $^{41}\mathrm{K}(p,\ensuremath{\alpha})^{38}\mathrm{Ar}$ reaction rates were determined, which suggested a 20% increase in the $^{41}\mathrm{Ca}$ yield from massive stars.

A beam containing a substantial component of both the J^{π}=5^{+}, T_{1/2}=162 ns isomeric state of ^{18}F and its 1^{+}, 109.77-min ground state is utilized to study members of the ground-state rotational band in ^{19}F through the neutron transfer reaction (d,p) in inverse kinematics. The resulting spectroscopic strengths confirm the single-particle nature of the 13/2^{+} band-terminating state. The agreement between shell-model calculations using an interaction constructed within the sd shell, and our experimental results reinforces the idea of a single-particle-collective duality in the descriptions of the structure of atomic nuclei.

Data for the $^{13}\mathrm{C}(^{6}\mathrm{Li},t)^{16}\mathrm{O}$ reaction, obtained in inverse kinematics at a $^{13}\mathrm{C}$ incident energy of 7.72 MeV, are presented. A distorted wave Born approximation (DWBA) analysis was used to extract spectroscopic factors and asymptotic normalization coefficients (ANCs) for the $\ensuremath{\langle}^{16}\mathrm{O}\ensuremath{\mid}^{13}\mathrm{C}+^{3}\mathrm{He}\ensuremath{\rangle}$ overlaps, subject to the assumption of a fixed $\ensuremath{\langle}^{6}\mathrm{Li}\ensuremath{\mid}^{3}\mathrm{He}+^{3}\mathrm{H}\ensuremath{\rangle}$ overlap. The variation of the extracted spectroscopic factors and ANCs as a function of various inputs to the DWBA calculations was explored. The extracted ANCs were found to vary as a cubic function of the radius of the potential well binding the transferred $^{3}\mathrm{He}$ to the $^{13}\mathrm{C}$ core while the spectroscopic factors varied as a quartic function of the radius. The ANC values could be determined to within a factor of two for this system.

International audience; Carbon burning is a critical phase for nucleosynthesis in massive stars. The conditions for igniting this burning stage, and the subsequent isotope composition of the resulting ashes, depend strongly on the reaction rate for C12+C12 fusion at very low energies. Results for the cross sections for this reaction are influenced by various backgrounds encountered in measurements at such energies. In this paper, we report on a new measurement of C12+C12 fusion cross sections where these backgrounds have been minimized. It is found that the astrophysical S factor exhibits a maximum around Ecm=3.5–4.0 MeV, which leads to a reduction of the previously predicted astrophysical reaction rate.

Reaction rates involving α-particles are known to be important in different astrophysical scenarios. Direct measurements of these reactions at relevant astrophysical energies are experimentally challenging. This is due to the typically small cross sections of these reactions and the experimental difficulties associated with low intensity radioactive beams needed to study them. As a consequence, most of these reaction rates are still unknown. The MUlti-Sampling Ionization Chamber (MUSIC) detector, a simple and highly efficient active target system, has been developed for measurements of (α, n) and (α, p) reactions. Recent results on the direct measurement of (α, p) and (α, n) reactions in the MUSIC detector and future possibilities are presented in this work.

Here, the rate of the T=1, 2+ to T=1, 0 + transition in 10B ( T=1, T z=0) is compared to the analog transitions in 10Be ( T=1, T z=–1) and 10C ( T=1, T z=+1) to provide constraints on ab initio calculations using realistic nuclear forces. The relevant state in 10B, at E x=5.164 MeV, is particle unbound. Therefore, a determination of the B( E2) electromagnetic transition rate requires a precise and accurate determination of the width of the state, as well as the α-particle and γ-ray branching ratios. Previous measurements of the α-particle branching ratio are just barely in agreement. We report on a new study of the α-particle branch by studying the 10B(p,p') 10B* reaction in inverse kinematics with the HELIOS spectrometer. The α-particle branching ratio that we observe, 0.144±0.027, is in good agreement with the evaluated value and improves the associated uncertainty. The resulting experimental B( E2) value is 7.0±2.2 e 2fm 4 and is more consistent with a flat trend across the A=10 triplet than previously reported. This is inconsistent with Green's function Monte Carlo predictions using realistic three-nucleon Hamiltonians, which overpredict the B(E2) value in 10C and 10B.

The existence of $^{26}\mathrm{Al}$ (${t}_{1/2}=7.17\ifmmode\times\else\texttimes\fi{}{10}^{5}\text{ }\text{ }\mathrm{yr}$) in the interstellar medium provides a direct confirmation of ongoing nucleosynthesis in the Galaxy. The presence of a low-lying ${0}^{+}$ isomer (${^{26}\mathrm{Al}}^{m}$), however, severely complicates the astrophysical calculations. We present for the first time a study of the ${^{26}\mathrm{Al}}^{m}(d,p)^{27}\mathrm{Al}$ reaction using an isomeric $^{26}\mathrm{Al}$ beam. The selectivity of this reaction allowed the study of $\ensuremath{\ell}=0$ transfers to $T=1/2$, and $T=3/2$ states in $^{27}\mathrm{Al}$. Mirror symmetry arguments were then used to constrain the ${^{26}\mathrm{Al}}^{m}(p,\ensuremath{\gamma})^{27}\mathrm{Si}$ reaction rate and provide an experimentally determined upper limit of the rate for the destruction of isomeric $^{26}\mathrm{Al}$ via radiative proton capture reactions, which is expected to dominate the destruction path of ${^{26}\mathrm{Al}}^{m}$ in asymptotic giant branch stars, classical novae, and core collapse supernovae.

International audience; The 12C+12C fusion reaction is one of the most important for nuclear astrophysics since it determines the carbon ignition in stellar environments. Two experiments which make use of the gamma-particle coincidence technique to measure the 12C+12C S-factors at deep sub barrier energies are discussed. Results are presented showing a decrease of the S-factor below Ec.m. = 3 MeV.

Carbon burning plays a crucial role in stellar evolution, where this reaction is an important route for the production of heavier elements. A particle-γ coincidence technique that minimizes the backgrounds to which this reaction is subject and provides reliable cross sections has been used at the Argonne National Laboratory to measure fusion cross-sections at deep sub-barrier energies in the 12 C+12 C system. The corresponding excitation function has been extracted down to a cross section of about 6 nb. This indicates the existence of a broad S-factor maximum for this system. Experimental results are presented and discussed.

The $^{23}\mathrm{Na}(\ensuremath{\alpha},p)^{26}\mathrm{Mg}$ and $^{23}\mathrm{Na}(\ensuremath{\alpha},n)^{26}\mathrm{Al}$ reactions are important for our understanding of the $^{26}\mathrm{Al}$ abundance in massive stars. The aim of this work is to report on a direct and simultaneous measurement of these astrophysically important reactions using an active target system. The reactions were investigated in inverse kinematics using $^{4}\mathrm{He}$ as the active target gas in the detector. We measured the excitation functions in the energy range of about 2 to 6 MeV in the center of mass. We have found that the cross sections of the $^{23}\mathrm{Na}(\ensuremath{\alpha},p)^{26}\mathrm{Mg}$ and the $^{23}\mathrm{Na}(\ensuremath{\alpha},n)^{26}\mathrm{Al}$ reactions are in good agreement with previous experiments and with statistical-model calculations. The astrophysical reaction rate of the $^{23}\mathrm{Na}(\ensuremath{\alpha},n)^{26}\mathrm{Al}$ reaction has been reevaluated and it was found to be larger than the recommended rate.

The s-process is responsible of the synthesis of most of the nuclei in the mass range 90 ≤ A ≤ 208. It consists in a series of neutron capture reactions on seed nuclei followed by β-decays, since the neutron accretion rate is slower than the β-decay rate. Such small neutron flux is supplied by the 13C(α,n)16O reaction. It is active inside the helium-burning shell of asymptotic giant branch stars, at temperatures < 108 K, corresponding to an energy interval of 140–230 keV. In this region, the astrophysical S (E)-factor is dominated by the −3 keV sub-threshold resonance due to the 6.356 MeV level in 17O. In this work, we have applied the Trojan Horse Method (THM) to the 13C(6Li,n16O)d quasi-free reaction to extract the 6.356 MeV level resonance parameters, in particular the asymptotic normalization coefficient . A preliminary analysis of a partial data set has lead to , slightly larger than the values in the literature. However, the deduced 13C(α, n)16O reaction rate is in agreement with most results in the literature at ~ 108 K, with enhanced accuracy thanks to our innovative approach merging together ANC and THM.

International audience; 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.

Measurements of fusion excitation functions of Ni58+Sn124 and Ni64+Sn124 are extended towards lower energy to cross sections of 1 μb and are compared to detailed coupled-channels calculations. The calculations clearly show the importance of including transfer reactions in a coupled-channels treatment for such heavy systems. This result is different from the conclusion made in a previous article which claimed that the influence of transfer on fusion is not important for fusion reactions of Ni+Sn. In the energy region studied in this experiment no indication of fusion hindrance has been observed, which is consistent with a systematic study of this behavior.

Background: Accurate knowledge of the $^{13}\mathrm{C}(\ensuremath{\alpha},n)^{16}\mathrm{O}$ reaction cross section is important for the understanding of the $s$ process in asymptotic giant branch stars, since it is considered to be the main source of neutrons. The subthreshold $1/{2}^{+}$ state at excitation energy of 6.356 MeV in $^{17}\mathrm{O}$ has a strong influence on the reaction cross section at energies relevant for astrophysics. Several experiments have been performed to determine the contribution of this state to the $^{13}\mathrm{C}(\ensuremath{\alpha},n)^{16}\mathrm{O}$ reaction rate. Nevertheless, significant discrepancies between different measurements remain.Purpose: The aim of this work is to investigate these discrepancies.Method: An 8 MeV $^{13}\mathrm{C}$ beam (below the Coulomb barrier) was used to study the $\ensuremath{\alpha}$-transfer reaction $^{6}\mathrm{Li}(^{13}\mathrm{C},d)^{17}\mathrm{O}$.Results: The squared Coulomb-modified asymptotic normalization coefficient of the $1/{2}^{+}$ state in $^{17}\mathrm{O}$ measured in this work is ${({\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{C}}_{\ensuremath{\alpha}{\ensuremath{-}}^{13}\text{C}}^{^{17}\mathrm{O}(1/2+)})}^{2}=3.6\ifmmode\pm\else\textpm\fi{}0.7\phantom{\rule{4pt}{0ex}}{\text{fm}}^{\ensuremath{-}1}$.Conclusions: Discrepancy between the results of $\ensuremath{\alpha}$-transfer experiments have been resolved. However, some discrepancy with the most recent measurement using the Trojan Horse method remains.

Measurements of fusion excitation functions of Ni-58 + Sn-124 and Ni-64 + Sn-124 are extended towards lower energy to cross sections of 1 mu b and are compared to detailed coupled-channels calculations. The calculations clearly show the importance of including transfer reactions in a coupled-channels treatment for such heavy systems. This result is different from the conclusion made in a previous article which claimed that the influence of transfer on fusion is not important for fusion reactions of Ni + Sn. In the energy region studied in this experiment no indication of fusion hindrance has been observed, which is consistent with a systematic study of this behavior.

The 12C(α,γ)^16O reaction plays a fundamental role in astrophysics and needs to be known with accuracy better than 10%. Cascade γ transitions through the excited states of 16 O are contributing to the uncertainty. We constrained the contribution of the 0+ (6.05 MeV) and 3- (6.13 MeV) cascade transitions by measuring the asymptotic normalization coefficients for these states using the α-transfer reaction 6 Li(12C,d)^16O at sub-Coulomb energy. The contribution of the 0+ and 3- cascade transitions at 300 keV is found to be 1.96 ± 0.3 and 0.12 ± 0.04 keV b for destructive interference of the direct and resonance capture and 4.36 ± 0.45 and 1.44 ± 0.12 keV b for constructive interference, respectively. The combined contribution of the 0+ and 3- cascade transitions to the 12C(α,γ)16O reaction cross section at 300 keV does not exceed 4%. Significant uncertainties have been dramatically reduced.

Background: Many important $\ensuremath{\alpha}$-particle induced reactions for nuclear astrophysics may only be measured using indirect techniques due to the small cross sections at the energy of interest. One such indirect technique is to determine the asymptotic normalization coefficients (ANCs) for near-threshold resonances extracted from sub-Coulomb $\ensuremath{\alpha}$-transfer reactions. This approach provides a very valuable tool for studies of astrophysically important reaction rates since the results are practically model independent. However, the validity of the method has not been directly verified.Purpose: The aim of this Rapid Communication is to verify the technique using the $^{16}\mathrm{O}(^{6}\mathrm{Li},d)^{20}\mathrm{Ne}$ reaction as a benchmark. The $^{20}\mathrm{Ne}$ nucleus has a well-known ${1}^{\ensuremath{-}}$ state at an excitation energy of 5.79 MeV with a width of 28 eV. Reproducing the known value with this technique is an ideal opportunity to verify the method.Method: The ${1}^{\ensuremath{-}}$ state at 5.79 MeV is studied using the $\ensuremath{\alpha}$-transfer reaction $^{16}\mathrm{O}(^{6}\mathrm{Li},d)^{20}\mathrm{Ne}$ at sub-Coulomb energies.Results: The partial $\ensuremath{\alpha}$ width for the ${1}^{\ensuremath{-}}$ state at excitation energy of 5.79 MeV is extracted and compared with the known value, allowing the accuracy of the method to be evaluated.Conclusions: This study demonstrates that extracting the ANCs using sub-Coulomb $\ensuremath{\alpha}$-transfer reactions is a powerful tool that can be used to determine the partial $\ensuremath{\alpha}$ width of near-threshold states that may dominate astrophysically important nuclear reaction rates.

Background: Clustering phenomena in $N\ensuremath{\ne}Z$ nuclei provide an opportunity to understand the interplay between cluster and nucleon degrees of freedom.Purpose: To study resonances in the ${}^{18}\mathrm{O}$ spectrum, populated in ${}^{14}\mathrm{C}+\ensuremath{\alpha}$ elastic scattering.Method: The thick target inverse kinematics technique was used to measure the excitation function for the ${}^{14}\mathrm{C}+\ensuremath{\alpha}$ elastic scattering. A 42-MeV ${}^{14}\mathrm{C}$ beam was used to populate states of excitation energy up to 14.9 MeV in ${}^{18}\mathrm{O}$. The analysis was performed using a multilevel, multichannel $R$-matrix approach.Results: Detailed spectroscopic information, including spin parities, partial $\ensuremath{\alpha}$- and neutron-decay widths and dimensionless reduced widths, was obtained for excited states in ${}^{18}\mathrm{O}$ between 8 and 14.9 MeV in excitation energy. Cluster-nucleon configuration interaction model calculations of the same quantities are performed and compared to the experimental results.Conclusions: Strong fragmentation of large $\ensuremath{\alpha}$-cluster strengths is observed in the spectrum of ${}^{18}\mathrm{O}$, making the $\ensuremath{\alpha}$-cluster structure of ${}^{18}\mathrm{O}$ quite different from the pattern of known quasirotational bands of alternating parity that are characteristic of $N=Z$, even-even nuclei like ${}^{16}\mathrm{O}$ and ${}^{20}\mathrm{Ne}$.

Most of the nuclei in the mass range 90 ≲ A ≲ 208 are produced through the so-called s-process, namely through a series of neutron capture reactions on seed nuclei followed by β-decays. The 13C(α, n)16O reaction is the neutron source for the main component of the s-process. It is active inside the helium-burning shell of asymptotic giant branch stars, at temperatures ≲ 108 K, corresponding to an energy interval of 140 − 230 keV. In this region, the astrophysical S(E)-factor is dominated by the −3 keV sub-threshold resonance due to the 6.356 MeV level in 17O. Direct measurements could not soundly establish its contribution owing to the cross section suppression at astrophysical energies determined by the Coulomb barrier between interacting nuclei. Indirect measurements and extrapolations yielded inconsistent results, calling for further investigations. The Trojan Horse Method turns out to be very suited for the study of the 13C(α, n)16O reaction as it allows us to access the low as well as the negative energy re- gion, in particular in the case of resonance reactions. We have applied the Trojan HorseMethod to the 13C(6Li, n16O)d quasi-free reaction. By using the modified R-matrix approach, the asymptotic normalization coefficient (C˜α13 C17O(1/2+))2${\left( {\tilde C_{{\alpha ^{13}}{\rm{C}}}^{17{\rm{O(1/}}{{\rm{2}}^{\rm{ + }}}{\rm{)}}}} \right)^2}$ of the 6.356 MeV level has been deduced as well as the n-partial width, allowing to attain an unprecedented accuracy for the 13C(α, n)16O astrophysical factor. A preliminary analysis of a partial data set has lead to (C˜α13C17O(1/2+))2 = 6.7−0.6+0.9 fm−1,${\left( {\tilde C_{{\alpha ^{13}}{\rm{C}}}^{17{\rm{O(1/}}{{\rm{2}}^{\rm{ + }}}{\rm{)}}}} \right)^2}\, = \,6.7_{ - 0.6}^{ + 0.9}\,{\rm{f}}{{\rm{m}}^{ - 1}},$ slightly larger than the values in the literature, determining a 13C(α, n)16O reaction rate in agreement with the most results in the literature at ∼ 108 K, with enhanced accuracy thanks to this innovative approach.

The 13C(α,n)16O reaction is considered to be the most important neutron source for producing the main component of the s-process in low mass stars. In this paper we focus our attention on two of the main open problems concerning its operation as a driver for the slow neutron captures. Recently, a new measurement of the 13C(α,n)16O reaction rate was performed via the Trojan Horse Method greatly increasing the accuracy. Contemporarily, on the modelling side, magnetic mechanisms were suggested to justify the production of the 13C pocket, thus putting the s-process in stars on safe physical ground. These inputs allow us to reproduce satisfactorily the solar distribution of elements.

The 13C(α,n)16O reaction is the neutron source of the main component of the s-process. The astrophysical S(E)-factor is dominated by the −3 keV sub-threshold resonance due to the 6.356 MeV level in 17O. Its contribution is still controversial as extrapolations, e.g., through R-matrix calculations, and indirect techniques, such as the asymptotic normalization coefficient (ANC), yield inconsistent results. Therefore, we have applied the Trojan Horse Method (THM) to the 13C(6Li,n16O)d reaction to measure its contribution. For the first time, the ANC for the 6.356 MeV level has been deduced through the THM, allowing to attain an unprecedented accuracy. Though a larger ANC for the 6.356 MeV level is measured, our experimental S(E) factor agrees with the most recent extrapolation in the literature in the 140-230 keV energy interval, the accuracy being greatly enhanced thanks to this innovative approach, merging together two well establish indirect techniques, namely, the THM and the ANC.

Resonance scattering with rare isotope beams provides direct access to continuum properties of exotic nuclei and can serve as a stringent test for modern theoretical approaches. Properties of neutron deficient isotope 8B, that were studied using resonance scattering of protons of 7Be, are discussed and compared to the predictions of the ab initio theories. New experimental data on clustering in 10Be studied using 6He+α resonance elastic scattering is presented.

The 13C(?, n)16O reaction is the neutron source for the main component of the s-process, responsible for the production of most of the nuclei in the mass range 90 A 208. This reaction takes place inside the helium-burning shell of asymptotic giant branch stars, at temperatures 108?K, corresponding to an energy interval where the 13C(?, n)16O reaction is effective in the range of 140-230?keV. In this regime, the astrophysical S(E)-factor is dominated by the ?3?keV sub-threshold resonance due to the 6.356?MeV level in 17O, giving rise to a steep increase in the S-factor. Its contribution is still controversial as extrapolations, e.g., through the R-matrix and indirect techniques such as the asymptotic normalization coefficient (ANC), yield inconsistent results. The discrepancy amounts to a factor of three or more precisely at astrophysical energies. To provide a more accurate S-factor at these energies, we have applied the Trojan horse method (THM) to the 13C(6Li, n 16O)d quasi-free reaction. The ANC for the 6.356?MeV level has been deduced through the THM as well as the n-partial width, allowing us to attain unprecedented accuracy for the 13C(?, n)16O astrophysical factor. A larger ANC for the 6.356?MeV level is measured with respect to the ones in the literature, ?fm?1, yet in agreement with the preliminary result given in our preceding letter, indicating an increase of the 13C(?, n)16O reaction rate below about 8 ? 107?K if compared with the recommended values. At ~108?K, our reaction rate agrees with most of the results in the literature and the accuracy is greatly enhanced thanks to this innovative approach.

The $^{13}\mathrm{C}(\ensuremath{\alpha},n)^{16}\mathrm{O}$ reaction is the neutron source for the main component of the $s$-process, responsible for the production of most nuclei in the mass range $90\ensuremath{\lesssim}A\ensuremath{\lesssim}204$. It is active inside the helium-burning shell in asymptotic giant branch stars, at temperatures $\ensuremath{\lesssim}{10}^{8}\text{ }\text{ }\mathrm{K}$, corresponding to an energy interval where the $^{13}\mathrm{C}(\ensuremath{\alpha},n)^{16}\mathrm{O}$ is effective from 140 to 230 keV. In this region, the astrophysical $S(E)$-factor is dominated by the $\ensuremath{-}3\text{ }\text{ }\mathrm{keV}$ subthreshold resonance due to the 6.356 MeV level in $^{17}\mathrm{O}$, giving rise to a steep increase of the $S(E)$-factor. Notwithstanding that it plays a crucial role in astrophysics, no direct measurements exist inside the $s$-process energy window. The magnitude of its contribution is still controversial as extrapolations, e.g., through the $R$ matrix and indirect techniques, such as the asymptotic normalization coefficient (ANC), yield inconsistent results. The discrepancy amounts to a factor of 3 or more right at astrophysical energies. Therefore, we have applied the Trojan horse method to the $^{13}\mathrm{C}(^{6}\mathrm{Li},n^{16}\mathrm{O})d$ quasifree reaction to achieve an experimental estimate of such contribution. For the first time, the ANC for the 6.356 MeV level has been deduced through the Trojan horse method as well as the $n$-partial width, allowing to attain an unprecedented accuracy in the $^{13}\mathrm{C}(\ensuremath{\alpha},n)^{16}\mathrm{O}$ study. Though a larger ANC for the 6.356 MeV level is measured, our experimental $S(E)$-factor agrees with the most recent extrapolation in the literature in the 140--230 keV energy interval, the accuracy being greatly enhanced thanks to this innovative approach.

A highly efficient MUlti-Sampling Ionization Chamber (MUSIC) detector has been developed for measurements of fusion reactions. A study of fusion cross sections in the 10,12,13,14,15 C+ 12 C and 20,22 Ne+ 20,22 Ne systems has been performed at ATLAS. Experimental results and comparison with theoretical predictions are presented. Furthermore, results of direct measurements of the 17 O( α, n ) 20 Ne, 23 Ne( α, p ) 26 Mg and 23 Ne( α, n ) 26 Al reactions will be discussed.

The {sup 13}C({alpha},n){sup 16}O reaction is the neutron source for the main component of the s-process, responsible of the production of most nuclei in the mass range 90 < A < 204. It is active inside the helium-burning shell in asymptotic giant branch stars, at temperatures < 10{sup 8} K, corresponding to an energy interval where the {sup 13}C({alpha},n){sup 16}O is effective of 140 - 230 keV. In this region, the astrophysical S(E)-factor is dominated by the -3 keV sub-threshold resonance due to the 6.356 MeV level in {sup 17}O, giving rise to a steep increase of the S-factor. Notwithstanding that it plays a crucial role in astrophysics, no direct measurements exist. Therefore, we have applied the Trojan Horse Method (THM) to the {sup 13}C({sup 6}Li,n{sup 16}O)d quasi-free reaction to achieve an experimental estimate of such contribution. For the first time, the ANC for the 6.356 MeV level has been deduced through the THM as well as the n-partial width, allowing to attain an unprecedented accuracy in the {sup 13}C({alpha},n){sup 16}O study. Though a larger ANC for the 6.356 MeV level is measured, our experimental S(E) factor agrees with the most recent extrapolation in the literature in the 140 -more » 230 keV energy interval, the accuracy being greatly enhanced thanks to this innovative approach.« less

The neutron-rich $N=28$ nucleus $^{44}\mathrm{S}$ was studied using the two-proton knockout reaction from $^{46}\mathrm{Ar}$ at intermediate beam energy. We report the observation of four new excited states, one of which is a strongly prolate deformed 4${}^{+}$ state, as indicated by a shell-model calculation. Its deformation originates in a neutron configuration which is fundamentally different from the ``intruder'' configuration responsible for the ground-state deformation. Consequently, we do not have three coexisting shapes in $^{44}\mathrm{S}$, but three coexisting configurations, corresponding to zero-, one-, and two-neutron particle-hole excitations.

Clustering phenomena in 10Be and 18O were studied by means of resonance elastic scattering of α-particles on 6He and 14C. Excitation functions for α+6He and α+14C were measured and detailed R-matrix analyses of the excitation functions was performed. We compare the experimental results with the predictions of modern theoretical approaches and discuss properties of cluster rotational bands.

We report on the study of a new nuclide, 14F, and on the idea of an experiment to solve the structure mystery of nuclei in the region around 9He.

We measured the excitation function for 13 O + p elastic scattering to obtain data on the unknown 14 F nucleus. The ground state and several low-lying excited states in 14 F were observed and spin/parity assignments were made. 14 F appears to be much less unstable than was predicted. We compare theoretical predictions for the 14 F level scheme with the experimental results.

International audience; We present a status report of recent neutron capture experiments performed with the mA-proton beam (1.92 MeV, 3 kW) of the Soreq Applied Research Accelerator Facility (SARAF) and the Liquid-Lithium Target (LiLiT). Experiments and preliminary results for (n) reactions on 36,38Ar, studied for the first time with 30-keV neutrons, on natKr, natCe and on radioactive targets 147Pm and 171Tm are described.