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New experimental data of the 15N + 13C elastic and inelastic scattering were obtained at the energy Elab(15N) = 84 MeV. The data were analyzed within the coupled-reaction-channels method. The elastic and inelastic scattering of nuclei 15N + 13С as well as the more important nucleon and cluster transfer reactions were included in the channels-coupling scheme. The WS potential parameters for the 15N + 13С nuclei interactions in ground and excited states as well as deformation parameters of these nuclei were deduced. The contributions of one- and two-step transfers in the 15N + 13C elastic and inelastic scattering were estimated. The results of the 15N + 13С elastic scattering at the energy Elab(15N) = 84 MeV, obtained in this work, were compared with that of the 15N + 12С elastic scattering at the energy Elab(15N) = 81 MeV.

The new experimental data of the 12С(15N,14N)13С reaction cross-sections at the energy Еlab(15N) = 81 MeV were measured for the ground and excited states of 14N and 13C nuclei. The experimental data were analyzed within the coupled-reaction-channels method (CRC) using channels-coupling scheme with the 15N + 12С elastic scattering and one- as well as two-step transfers of nucleons and clusters performing CRC-calculations with the Woods - Saxon potentials (WS) for the entrance and exit reaction channels. The WS potential parameters for the 12С + 15N nuclear interaction were taken from the previously studied elastic and inelastic scattering of 15N ions by 12С nuclei at the energy 81 MeV, and the WS potential parameters for the 14N + 13С reaction exit channel were deduced from fitting of the 12С(15N,14N)13C reaction data. The spectroscopic factors (amplitudes) of transferred in the reaction nucleons and clusters, used in the CRC-calculations, were computed within translational invariant shell model of 1p-shell. It was found that transfers of neutrons (n) and deuterons (d) dominate in this reaction. Multi-step transfers of nucleons and clusters give small contributions to the reaction data.

The 12С(15N, 14С)13N reaction at the energy Еlab(15N) = 81 MeV for ground and excited states of 14С and 13N nuclei was investigated. New experimental data of the reaction cross-sections were obtained. The data were analyzed within the coupled reaction channels method (CRC). The 15N + 12С elastic scattering as well as the more important reactions of nucleon and cluster transfers were included in the channels-coupling scheme. In the CRC-calculations, the Woods - Saxon potentials (WS) were used for the interactions of 15N + 12С and 14С + 13N nuclei in the entrance and exit reaction channels. WS potential parameters for the reaction entrance channel were deduced previously from CRC-analysis of the 15N + 12С elastic and inelastic scattering data, then the WS potential parameters for the reaction exit channel were deduced from the fitting of 12С(15N, 14С)13N reaction data. The spectroscopic amplitudes of nucleons and clusters, used in the CRC-calculations, were computed within translational invariant shell model. As the results of the reaction CRC-analysis, the information about WS potential of 14С + 13N nuclei interaction as well as about mechanisms of nucleons and clusters transfer was deduced. It was found, that transfers of protons and 2n-clusters dominate in this reaction. It was also studied the differences of the reaction CRC cross-sections calculated using the 14С + 13N і 14С + 14N potentials in the reaction exit channel (isotopic effects).

Background: The Efimov effect is a universal phenomenon in physics whereby three-body systems are stabilized via the interaction of an unbound two-body subsystems. A hypothetical state in $^{12}\mathrm{C}$ at 7.458-MeV excitation energy, comprising a loose structure of three $\ensuremath{\alpha}$ particles in mutual two-body resonance, has been suggested in the literature to correspond to an Efimov state in nuclear physics. The existence of such a state has not been demonstrated experimentally.Purpose: Using a combination of $\ensuremath{\gamma}$ spectroscopy, charged-particle spectroscopy, and astrophysical rate calculations allowing for strict limits on the existence of such a state to been established here.Method: Using the combined data sets from two recent experiments, one with the TexAT (Texas Active Target) TPC (Time Projection Chamber) to measure $\ensuremath{\alpha}$ decay and the other with Gammasphere to measure $\ensuremath{\gamma}$ decay of states in $^{12}\mathrm{C}$ populated by $^{12}\mathrm{N}$ and $^{12}\mathrm{B}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$ decay, respectively, we achieve high sensitivity to states in close proximity to the $\ensuremath{\alpha}$ threshold in $^{12}\mathrm{C}$.Results: No evidence of a state at 7.458 MeV is seen in either data set. Using a likelihood method, the 95% confidence limit $\ensuremath{\gamma}$-decay branching ratio is determined as a function of the $\ensuremath{\beta}$-decay feeding strength relative to the Hoyle state. In parallel, calculations of the $3\ensuremath{\alpha}$ reaction rate show the inclusion of the Efimov corresponds to a large increase in the reaction rate around $5\ifmmode\times\else\texttimes\fi{}{10}^{7}$ K.Conclusion: From decay spectroscopy---at the 95% confidence limit, the Efimov state cannot exist at 7.458 MeV with any $\ensuremath{\gamma}$-decay branching ratio unless the $\ensuremath{\beta}$ strength is less than 0.7% of the Hoyle state. This limit is evaluated for a range of different excitation energies and the results are not favorable for existence of the hypothetical Efimov state in $^{12}\mathrm{C}$. Furthermore, the $3\ensuremath{\alpha}$ reaction rate with the inclusion of a state between 7.43 and 7.53 MeV exceeds the rate required for stars to undergo the red giant phase.

\textbf{Background:} The influence of halo structure of $^6$He, $^8$B, $^{11}$Be and $^{11}$Li nuclei in several mechanisms such as direct reactions and fusion is already established, although not completely understood. The influence of the $^{10}$C Brunnian structure is less known. \textbf{Purpose:} To investigate the influence of the cluster configuration of $^{10}$C on the elastic scattering at an energy close to the Coulomb barrier. \textbf{Methods:} We present experimental data for the elastic scattering of the $^{10}$C+$^{208}$Pb system at $E_{\rm lab}$ = 66~MeV. The data are compared to the three- and the four-body continuum-discretized coupled-channels calculations assuming $^9$B+$p$, $^6$Be+$\alpha$ and $^8$Be+$p$+$p$ configurations. \textbf{Results:} The experimental angular distribution of the cross sections shows the suppression of the Fresnel peak that is reasonably well reproduced by the continuum-discretized coupled-channels calculations. However, the calculations underestimate the cross sections at backward angles. Couplings to continuum states represent a small effect. \textbf{Conclusions:} The cluster configurations of $^{10}$C assumed in the present work are able to describe some of the features of the data. In order to explain the data at backward angles, experimental data for the breakup and an extension of theoretical formalism towards a four-body cluster seem to be in need to reproduce the measured angular distribution.

We present the development of a neutron detector array module made with $\textit{para}$-terphenyl, a bright, fast, n/$\gamma$ discriminating crystalline organic scintillator. The module is comprised of 2 cm $\times$ 2 cm $\times$ 2 cm $\textit{p}$-terphenyl crystals that have been optically coupled together to create a $\textit{pseudo-bar}$ module. While only relying on two photo detectors, the module is capable of distinguishing interactions between up to eight crystals. Furthermore, the module retains the $\textit{p}$-terphenyl's pulse shape discrimination (PSD) capability. Together this makes the pseudo-bar module a promising position-sensitive neutron detector. Here we present characteristics of the pseudo-bar module - its timing resolution as well as its pulse shape and position discrimination capabilities, and briefly discuss future plans for utilizing an array of pseudo-bar modules in a useful neutron detector system., Comment: 13 pages, 12 figures, published in Nuclear Instruments and Methods in Physics Research Section A

Background: The structure of the Hoyle state, a highly $\ensuremath{\alpha}$-clustered state at 7.65 MeV in $^{12}\mathrm{C}$, has long been the subject of debate. Understanding if the system comprises of three weakly interacting $\ensuremath{\alpha}$ particles in the $0s$ orbital, known as an $\ensuremath{\alpha}$-condensate state, is possible by studying the decay branches of the Hoyle state.Purpose: The direct decay of the Hoyle state into three $\ensuremath{\alpha}$ particles, rather than through the $^{8}\mathrm{Be}$ ground state, can be identified by studying the energy partition of the three $\ensuremath{\alpha}$ particles arising from the decay. This paper provides details on the breakup mechanism of the Hoyle stating using a new experimental technique.Method: By using $\ensuremath{\beta}$-delayed charged-particle spectroscopy of $^{12}\mathrm{N}$ using the Texas active target time-projection chamber, a high-sensitivity measurement of the direct $3\ensuremath{\alpha}$ decay ratio can be performed without contributions from pileup events.Results: A Bayesian approach to understanding the contribution of the direct components via a likelihood function shows that the direct component is $l0.043%$ at the 95% confidence level. This value is in agreement with several other studies, and, here, we can demonstrate that a small nonsequential component with a decay fraction of about ${10}^{\ensuremath{-}4}$ is most likely.Conclusion: The measurement of the nonsequential component of the Hoyle state decay is performed in an almost medium-free reaction for the first time. The derived upper limit is in agreement with previous studies and demonstrates sensitivity to the absolute branching ratio. Further experimental studies would need to be combined with robust microscopic theoretical understanding of the decay dynamics to provide additional insight into the idea of the Hoyle state as an $\ensuremath{\alpha}$ condensate.

Background: Clustering plays an important role in the structure of $^{10}\mathrm{Be}$. Exotic molecular-like configurations, such as $\ensuremath{\alpha}$:$2n$:$\ensuremath{\alpha}$, have been suggested at relatively low excitation energies.Purpose: To search for the high-spin states that may belong to the molecular-like $\ensuremath{\alpha}$:$2n$:$\ensuremath{\alpha}$ configuration in $^{10}\mathrm{Be}$.Method: Measuring excitation functions for $^{6}\mathrm{He}+\phantom{\rule{0.16em}{0ex}}\ensuremath{\alpha}$ scattering, populating states in the excitation energy range from 4.5 MeV to 8 MeV in $^{10}\mathrm{Be}$ using a $^{6}\mathrm{He}$ rare-isotope beam and a thick helium gas target.Results: No new excited states in $^{10}\mathrm{Be}$ have been observed. Stringent limits on the possible degree of $\ensuremath{\alpha}$-clustering of the hypothetical yrast ${6}^{+}$ state have been obtained.Conclusions: The high-spin members of the $\ensuremath{\alpha}$:$2n$:$\ensuremath{\alpha}$ molecular-like rotational band configuration, that is considered to have a ${0}^{+}$ band head at 6.18 MeV, either do not exist or have small overlap with the $^{6}\mathrm{He}$(g.s.)$+\ensuremath{\alpha}$ channel.

β -delayed charged-particle emission is a sensitive probe of three-body decays in light nuclei. Time Projection Chambers (TPCs) offer a significant advantage over traditional charged-particle spectroscopy techniques due to a low-energy threshold and a high-geometric efficiency ( ≈ 4 π ) which are essential for use with radioactive ion beams where the beam intensities are limited. The technique for high-sensitivity spectroscopy of β -delayed charged-particle emission is shown to be possible using the Texas Active Target (TexAT) TPC in conjunction with the General Electronics for TPCs (GET) system. The benchmark case studied was that of 12 N β -decay to the first α -unbound state in 12 C , the Hoyle state. Half-life and branching ratio measurements are presented and are in good agreement with previous studies. The efficacy of using TPCs to study such a near-threshold state and disentangle the three-body dynamics of the decay products is demonstrated.

The TexAT (Texas Active Target) detector is a new active-target time projection chamber (TPC) that was built at the Cyclotron Institute Texas A$\&$M University. The detector is designed to be of general use for nuclear structure and nuclear astrophysics experiments with rare isotope beams. TexAT combines a highly segmented Time Projection Chamber (TPC) with two layers of solid state detectors. It provides high efficiency and flexibility for experiments with low intensity exotic beams, allowing for the 3D track reconstruction of the incoming and outgoing particles involved in nuclear reactions and decays., 18 pages, 36 figures

ew angular distributions of the 15N + 12C elastic and inelastic scattering were measured at the energy Elab (15N) = 81 MeV. The data were analyzed within the coupled-reaction-channels method (CRC). The elastic and inelastic scattering as well as the more important one- and two-step transfer reactions were included in the channels-coupling scheme. The 15N + 12C double folding-potential (DF) and that of Woods - Saxon form (WS) were used in the CRC-calculations. The WS potential parameters as well as deformation parameters of 12C and 15N were deduced. The contributions of one- and two-step transfers in the 15N + 12C elastic and inelastic scattering channels were obtained. The 15N +12C elastic scatterings data, published previously at energies Elab(15N) = 22 – 31 MeV for the large angles, were also analyzed and energy dependence of the WS potential parameters were deduced. Comparing the data of elastic scattering data of the 15N + 12С and 14N + 12С nuclei and CRC calculations of the 15N + 12С scattering with WS potentials of these two nuclear pares, considerable differences were observed as in the experimental data so in the CRC calculations, especially at the large angles where the transfer reactions contribute to the elastic scattering. By other words, the scattering isotopic effects were observed in scattering of nuclei 15N + 12С and 14N + 12С.

An active target detector array, ANASEN, has been developed for nuclear reaction studies with rare isotope beams at low energies. It aims at measurements of the excitation functions for proton and α - particle elastic and inelastic scattering and direct measurements of ( α , p) reactions with exotic nuclei in inverse kinematics. ANASEN is composed of three types of charged particle detectors. The length of the active area is 340 mm and the total covered area is 1300 cm 2 (almost 3 π steradian solid angle coverage) providing high efficiency for experiments with low intensity radioactive beams. A mix of 78 conventional electronics channels (for Proportional Counter and CsI-detectors) and 480 dedicated high-density ASICs electronics channels for the silicon detector are used for readout.

Background: Level structure of the most neutron-deficient nucleon-bound carbon isotope, $^{9}\mathrm{C}$, is not well known. Definitive spin-parity assignments are only available for two excited states. No positive-parity states have been conclusively identified so far and the location of the $sd$ shell in the $A=9, T=3/2$ isospin quadruplet is not known.Purpose: We have studied the level structure of exotic nucleus $^{9}\mathrm{C}$ at excitation energies below 6.4 MeV.Methods: Excited states in $^{9}\mathrm{C}$ were populated in $^{8}\mathrm{B}+p$ resonance elastic scattering and excitation functions were measured using the active target approach.Results: Two excited states in $^{9}\mathrm{C}$ were conclusively observed, and $R$-matrix analysis of the excitation functions was performed to make the spin-parity assignments. The first positive-parity state in the $A=9, T=3/2$ nuclear system, the $5/{2}^{+}$ resonance at 4.3 MeV, has been identified.Conclusions: The new $5/{2}^{+}$ state at 4.3 MeV in $^{9}\mathrm{C}$ is a single-particle $\ensuremath{\ell}=0$ broad resonance and it determines the energy of the $2s$ shell. The $2s$ shell in this exotic nucleus appears well within the region dominated by the $p$-shell states.

The cross sections of nuclear reactions between the radioisotope $^{7}\mathrm{Be}$ and deuterium, a possible mechanism of reducing the production of mass-7 nuclides in big-bang nucleosynthesis, were measured at center-of-mass energies between 0.2 and 1.5 MeV. The measured cross sections are dominated by the $(d,\ensuremath{\alpha})$ reaction channel, towards which prior experiments were mostly insensitive. A new resonance at 0.36(5) MeV with a strength of $\ensuremath{\omega}\ensuremath{\gamma}=1.7(5)\text{ }\text{ }\mathrm{keV}$ was observed inside the relevant Gamow window. Calculations of nucleosynthesis outcomes based on the experimental cross section show that the resonance reduces the predicted abundance of primordial $^{7}\mathrm{Li}$, but not sufficiently to solve the primordial lithium problem.

The cross sections of nuclear reactions between the radioisotope ^{7}Be and deuterium, a possible mechanism of reducing the production of mass-7 nuclides in big-bang nucleosynthesis, were measured at center-of-mass energies between 0.2 and 1.5 MeV. The measured cross sections are dominated by the (d,α) reaction channel, towards which prior experiments were mostly insensitive. A new resonance at 0.36(5) MeV with a strength of ωγ=1.7(5) keV was observed inside the relevant Gamow window. Calculations of nucleosynthesis outcomes based on the experimental cross section show that the resonance reduces the predicted abundance of primordial ^{7}Li, but not sufficiently to solve the primordial lithium problem.

Direct measurements of the total fusion cross section for B 8 + 40 Ar were achieved with the active target technique. The fusion excitation function was extracted at energies near the Coulomb barrier. The cross section is well described by a coupled reaction channels calculation. The data were compared with previous B 8 fusion experiments on Si 28 and Ni 58 targets. No evidence of striking enhancement of the total fusion cross section at near the Coulomb barrier, that was previously reported for the B 8 + 58 Ni system, was observed in these direct measurements. The present data are systematically consistent with the results for B 8 + 28 Si at higher energies and with other weakly-bound systems at near-barrier energies.

The 22Ne(α,γ)26Mg and 22Ne(α,n)25Mg reactions play an important role in astrophysics because they have significant influence on the neutron flux during the weak branch of the s-process. We constrain the astrophysical rates for these reactions by measuring partial α-widths of resonances in 26Mg located in the Gamow window for the Ne22+α capture. These resonances were populated using 22Ne(6Li,d)26Mg and 22Ne(7Li,t)26Mg reactions at energies near the Coulomb barrier. At these low energies α-transfer reactions favor population of low spin states and the extracted partial α-widths for the observed resonances exhibit only minor dependence on the model parameters. The astrophysical rates for both the 22Ne(α,γ)26Mg and the 22Ne(α,n)25Mg reactions are shown to be significantly different than the previously suggested values. Keywords: s-Process, Reaction rate, 22Ne(α,γ)26Mg, 22Ne(α,n)25Mg, Sub-Coulomb α-transfer reaction

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.

The structure of exotic nucleus 10N was studied using 9C+p resonance scattering. Two L=0 resonances were found to be the lowest states in 10N. The ground state of 10N is unbound with respect to proton decay by 2.2(2) or 1.9(2) MeV depending on the 2- or 1- spin-parity assignment, and the first excited state is unbound by 2.8(2) MeV., 6 pages, 4 figures, 1 table, submitted to Phys. Lett. B

In the past several years, there has been a large interest of Time Projection Chambers (TPCs) for use in experimental nuclear physics. This has continued in tandem with the requirement for high efficiency detectors with low intensity radioactive ion beams. TexAT is a Active Target TPC (AT-TPC) built at Texas A&M University utilizing MICRO MEsh GASeous (MicroMegas) pads and GET electronics developed specifically for TPCs. This design combines good TPC pixelation with a surrounding shell of Si/CsI telescopes to make an extremely versatile detector capable of a wide range of different experimental techniques with only minor modifications to the electronics setup. Two recent experiments performed at the Cyclotron Institute, Texas A&M University, are detailed here demonstrating versatility beyond the usual Thick Target Inverse Kinematics (TTIK) or transfer reactions that these TPCs are more typically used for. The first, a measurement of the 12N → 12C* → 3α decay demonstrates the capabilities of TexAT as a low-energy detector operating at low pressure (20 Torr) to measure β-delayed particle decay. The second, a direct measurement of the 8B+40Ar fusion cross section shows the advantages of operating in active target mode where the target also functions as the detector gas.

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.

The basic ion-optical characteristics of the COMBAS fragment separator are analyzed. The momentum distributions of radioactive 6He, 8He, and 9Li nuclei obtained in the reaction 11B (33 A MeV, where A is the mass number of a particle) + 9Be (332.6 mg/cm2) have been investigated in forward-angle measurements on the COMBAS fragment separator. The momentum and angular (horizontal) acceptances of the COMBAS separator have been measured using the 6He, 8He, and 9Li beams. It has been ascertained that the images of the 6He, 8He, and 9Li nuclear beams in final achromatic focus of the separator Fa approximately twofold exceed the size of the beam on a producing target (input focus F0), at which the primary beam has a diameter of 6 mm. The intensities of 6He, 8He, and 9Li beams obtained at a 5-μA intensity of the primary 11B beam are 6.9 × 105, 2 × 104, and 4.7 × 105 particles/s, respectively. These values are sufficient for use in spectroscopic measurements. It is proposed that time-of-flight analysis of nuclear reaction products at the exit from the COMBAS separator will be used not only to measure the energy of transported particles over the whole operating range of the momentum acceptance, but also to identify them by mass A and charge Z without loss of these particles. The problem of reducing the count rates of detectors and further improvement of their energy resolution for detected particles can be solved by placing a high-resolution magnetic spectrometer past the second target accepting the secondary radioactive nuclear beams.

Background: Near-barrier fusion can be strongly affected by the coupling between relative motion and internal degrees of freedom of the collision partners. The coupled channels (CC) method is a usual way of describing the reaction dynamics in this energy region. In the standard approach in the CC method only strong reaction channels (collective excitations) are taken into account. However, in some cases this approach fails to describe experimentally obtained barrier height distributions.Purpose: The influence of weak (noncollective) reaction channels on barrier height distributions was studied.Method: The barrier height distributions were determined from quasielastic scattering of $^{20}\mathrm{Ne}$ on $^{58,60,61}\mathrm{Ni}$ targets. The scattered ions were registered at backward angles (130--150 degrees).Results: In the $^{58}\mathrm{Ni}$ and $^{60}\mathrm{Ni}$ cases one observes a ``structure'' (two peaks) in the barrier height distribution which is completely smoothed out for $^{61}\mathrm{Ni}$.Conclusions: The results support the hypothesis that noncollective excitations of the target nuclei, much more numerous in $^{61}\mathrm{Ni}$ than in $^{58}\mathrm{Ni}$ and $^{60}\mathrm{Ni}$, influence the barrier height distribution and are responsible for smoothing out the structure.

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.

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.

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.

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.

The (13)C(α,n)(16)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/~A/~204. It is active inside the helium-burning shell in asymptotic giant branch stars, at temperatures/~10(8) K, corresponding to an energy interval where the (13)C(α,n)(16)O is effective from 140 to 230 keV. In this region, the astrophysical S(E)-factor is dominated by the -3 keV subthreshold resonance due to the 6.356 MeV level in (17)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)C((6)Li,n(16)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)C(α,n)(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 140-230 keV energy interval, the accuracy being greatly enhanced thanks to this innovative approach.

To further our understanding of the influence of weakly coupled channels on the distribution of Coulomb barrier heights, we have measured transfer cross sections for ${}^{20}$Ne ions backscattered from ${}^{\mathrm{nat}}$Ni, ${}^{118}$Sn, and ${}^{208}$Pb targets at near-barrier energies. The $Q$ value spectrum in the case of ${}^{208}$Pb target has been determined too. The transfer channels appear to be especially important for ${}^{208}$Pb, whose double-closed-shell nature leads to a relatively low level density for noncollective inelastic excitations.