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Spatially-correlated overabundances of $^{15}$N and $^{18}$O observed in some low-density graphite meteoritic grains have been connected to nucleosynthesis taking place in the helium-burning shell during core-collapse supernovae. Two of the reactions which have been identified as important to the final abundances of $^{15}$N and $^{18}$O are $^{18}$F($n,\alpha$)$^{15}$N and $^{18}$F($n,p$)$^{18}$O. The relative strengths of the $^{18}$F($n,\alpha$)$^{15}$N and $^{18}$F($n,p$)$^{18}$O reactions depend on the relative $\alpha_0$ and $p_0$ decays from states above the neutron threshold in $^{19}$F in addition to other properties. Experimental data on the charged-particle decays from these highly excited states are lacking or inconsistent. Two experiments were performed using proton inelastic scattering from LiF targets and magnetic spectrographs. The first experiment used the high-resolution Q3D spectrograph at Munich to constrain properties of levels in $^{19}$F. A second experiment using the Orsay Split-Pole spectrograph and an array of silicon detectors was performed in order to measure the charged-particle decays of neutron-unbound levels in $^{19}$F. A number of levels in $^{19}$F have been identified along with their corresponding charged-particle decays. The first state above the neutron threshold which has an observed proton-decay branch to the ground state of $^{18}$O lies 68 keV above the neutron threshold while the $\alpha$-particle decays from the neutron-unbound levels are generally observed to be much stronger than the proton decays. Neutron-unbound levels in $^{19}$F are observed to decay predominantly by $\alpha$-particle emission, supporting the role of $^{18}$F($n,\alpha$)$^{15}$N in the production of $^{15}$N in the helium-burning shell of supernovae. Improved resonant-scattering reaction data are required in order to be able to determine the reaction rates accurately.

Classical novae result from thermonuclear explosions producing several $\gamma$-ray emitters which are prime targets for satellites observing in the MeV range. The early 511 keV gamma-ray emission depends critically on the $^{18}$F(p,$\alpha$)$^{15}$O reaction rate which, despite many experimental and theoretical efforts, still remains uncertain. One of the main uncertainties in the $^{18}$F(p,$\alpha$)$^{15}$O reaction rate is the contribution in the Gamow window of interference between sub-threshold $^{19}$Ne states and known broad states at higher energies. Therefore the goal of this work is to clarify the existence and the nature of these sub-threshold states. States in the $^{19}$Ne compound nucleus were studied at the Tandem-ALTO facility using the $^{19}$F($^3$He,t)$^{19}$Ne charge exchange reaction. Tritons were detected with an Enge Split-pole spectrometer while decaying protons or $\alpha$-particles from unbound $^{19}$Ne states were collected, in coincidence, with a double-sided silicon strip detector array. Angular correlations were extracted and constraints on the spin and parity of decaying states established. The coincidence yield at $E_x$ = 6.29 MeV was observed to be high spin, supporting the conclusion that it is indeed a doublet consisting of high spin and low spin components. Evidence for a broad, low spin state was observed around 6 MeV. Branching ratios were extracted for several states above the proton threshold and were found to be consistent with the literature. R-matrix calculations show the relative contribution of sub-threshold states to the astrophysically important energy region above the proton threshold. The levels schemes of $^{19}$Ne and $^{19}$F are still not sufficiently well known and further studies of the analogue assignments are needed. The tentative broad state at 6 MeV may only play a role if the reduced proton width is large.

Background: It has been recently suggested that hydrogen ingestion into the helium shell of massive stars could lead to high C13 and N15 excesses when the shock of a core-collapse supernova passes through its helium shell. This prediction questions the origin of extremely high C13 and N15 abundances observed in rare presolar SiC grains which is usually attributed to classical novae. In this context the N13(α,p)O16 reaction plays an important role since it is in competition with N13β+ decay to C13. Purpose: The N13(α,p)O16 reaction rate used in stellar evolution calculations comes from the Caughlan and Fowler compilation with very scarce information on the origin of this rate and with no associated uncertainty. The goal of this work is to provide a recommended N13(α,p)O16 reaction rate, based on available experimental data, with a meaningful statistical uncertainty. Method: Unbound nuclear states in the F17 compound nucleus were studied using the spectroscopic information of the analog states in O17 nucleus that were measured at the Tandem-Alto facility using the C13(Li7,t)O17 α-particle-transfer reaction. The α-particle spectroscopic factors were derived using a finite-range distorted-wave Born approximation analysis. This spectroscopic information was used to calculate a recommended N13(α,p)O16 reaction rate with meaningful uncertainty using a Monte Carlo approach. Results: The N13(α,p)O16 reaction rate from the present work is found to be within a factor of two of the previous evaluation in the temperature range of interest, with a typical uncertainty of a factor ≈2-3. The source of this uncertainty has been identified to come from the three main contributing resonances at Erc.m.=221, 741, and 959 keV. This new error estimation translates to an overall uncertainty in the C13 production of a factor of 50 when using the lower and upper reaction rates in the conditions relevant for the N13(α,p)O16 activation. Conclusions: The main source of uncertainty on the re-evaluated N13(α,p)O16 reaction rate currently comes from the uncertain α-particle width of relevant F17 states.

It has been suggested that hydrogen ingestion into the helium shell of massive stars could lead to high $^{13}$C and $^{15}$N excesses when the shock of a core-collapse supernova passes through its helium shell. This prediction questions the origin of extremely high $^{13}$C and $^{15}$N abundances observed in rare presolar SiC grains which is usually attributed to classical novae. In this context $^{13}$N($��$,p)$^{16}$O the reaction plays an important role since it is in competition with $^{13}$N $��^+$-decay to $^{13}$C. The $^{13}$N($��$,p)$^{16}$O reaction rate used in stellar evolution calculations comes from the CF88 compilation with very scarce information on the origin of this rate. The goal of this work is to provide a recommended $^{13}$N($��$,p)$^{16}$O reaction rate, based on available experimental data. Unbound nuclear states in the $^{17}$F compound nucleus were studied using the spectroscopic information of the analog states in $^{17}$O nucleus that were measured at the Alto facility using the $^{13}$C($^7$Li,t)$^{17}$O alpha-transfer reaction, and spectroscopic factors were derived using a DWBA analysis. This spectroscopic information was used to calculate a recommended $^{13}$N($��$,p)$^{16}$O reaction rate with meaningful uncertainty using a Monte Carlo approach. The present $^{13}$N($��$,p)$^{16}$O reaction rate is found to be within a factor of two of the previous evaluation, with a typical uncertainty of a factor 2-3. The source of this uncertainty comes from the three resonances at $E_r^{c.m.} = 221$, 741 and 959 keV. This new error estimation translates to an overall uncertainty in the $^{13}$C production of a factor of 50. The main source of uncertainty on the re-evaluated $^{13}$N($��$,p)$^{16}$O reaction rate currently comes from the uncertain alpha-width of relevant $^{17}$F states.

Classical novae result from thermonuclear explosions producing several $��$-ray emitters which are prime targets for satellites observing in the MeV range. The early 511 keV gamma-ray emission depends critically on the $^{18}$F(p,$��$)$^{15}$O reaction rate which, despite many experimental and theoretical efforts, still remains uncertain. One of the main uncertainties in the $^{18}$F(p,$��$)$^{15}$O reaction rate is the contribution in the Gamow window of interference between sub-threshold $^{19}$Ne states and known broad states at higher energies. Therefore the goal of this work is to clarify the existence and the nature of these sub-threshold states. States in the $^{19}$Ne compound nucleus were studied at the Tandem-ALTO facility using the $^{19}$F($^3$He,t)$^{19}$Ne charge exchange reaction. Tritons were detected with an Enge Split-pole spectrometer while decaying protons or $��$-particles from unbound $^{19}$Ne states were collected, in coincidence, with a double-sided silicon strip detector array. Angular correlations were extracted and constraints on the spin and parity of decaying states established. The coincidence yield at $E_x$ = 6.29 MeV was observed to be high spin, supporting the conclusion that it is indeed a doublet consisting of high spin and low spin components. Evidence for a broad, low spin state was observed around 6 MeV. Branching ratios were extracted for several states above the proton threshold and were found to be consistent with the literature. R-matrix calculations show the relative contribution of sub-threshold states to the astrophysically important energy region above the proton threshold. The levels schemes of $^{19}$Ne and $^{19}$F are still not sufficiently well known and further studies of the analogue assignments are needed. The tentative broad state at 6 MeV may only play a role if the reduced proton width is large.

Neutron-capture reactions on $^{18}$F in the helium-burning shell play an important role in the production of $^{15}$N during core-collapse supernovae. The competition between the $^{18}$F($n,p/\alpha$)$^{18}$O/$^{15}$N reactions controls the amount of $^{15}$N produced. The strengths of these reactions depend on the decay branching ratios of states in $^{19}$F above the neutron threshold. We report on an experiment investigating the decay branching ratios of these states in order to better constrain the strengths of the reactions., Comment: Submitted as part of the Proceedings of NIC 2018

The angular distributions of $^{8}\mathrm{Be}$ states in the excitation energy region ${E}_{x}\ensuremath{\sim}(16.5\text{--}18.2)$ MeV produced in the $^{7}\mathrm{Li}(^{3}\mathrm{He},d)^{8}\mathrm{Be}$ proton transfer reaction have been measured at the Orsay $14.8\ensuremath{-}\mathrm{MV}$ tandem accelerator for $^{3}\mathrm{He}^{2+}$ ion bombarding energy, ${E}_{\text{lab}}\phantom{\rule{4pt}{0ex}}=20$ MeV, and forward angular range, ${\ensuremath{\theta}}_{\text{lab}}=5{}^{\ensuremath{\circ}}\text{--}50{}^{\ensuremath{\circ}}$. A high energy resolution detection system composed of a split-pole magnetic spectrometer and a $\mathrm{\ensuremath{\Delta}}E\ensuremath{-}E$, position-sensitive drift chamber was used to record the energy spectra of outgoing deuterons. The measured cross section data for the direct reaction component have been separated from the compound nucleus one, then analyzed in the framework of the nonlocal, finite-range (FR)--distorted-wave Born approximation (DWBA) theory. New values of the ${C}^{2}S$ and (${S}_{p1/2},\phantom{\rule{4pt}{0ex}}{S}_{p3/2})$ proton absolute and partial spectroscopic factors and related ${\ensuremath{\gamma}}_{p}^{2}(a)$ proton reduced widths versus the $p+^{7}\mathrm{Li}$ channel radius have been extracted for the ${2}^{+}(16.626)$ and ${2}^{+}(16.922),T=0+1$ isospin-mixed loosely bound states of astrophysical interest and the ${1}^{+}(17.640)$, $T=1$ unbound state of $^{8}\mathrm{Be}$. They are compared to sparse earlier experimental values and to shell-model-predicted ones from the literature, and are discussed. In particular, the status of the spectroscopic information on the ${2}^{+}$ isospin-mixed doublet is reviewed and updated. The application in nuclear astrophysics of the DWBA derived results is emphasized.

The angular distributions of $^{8}$Be states in the excitation energy region, E$_{x}$ $\ \sim$($16.5-18.2$) MeV, produced in the $^{7}$Li($^{3}% $He,d)$^{8}$Be proton transfer reaction have been measured at the Orsay 14.8$-$MV tandem accelerator for $^{3}$He$^{2+}$ ion bombarding energy, E$_{lab}$ $=20$ MeV, and forward anglular range, $\theta_{lab}=5^{\circ}-50^{\circ}$. A high energy resolution detection system composed of a split-pole magnetic spectrometer and a $\Delta E-E$,\ position-sensitive drift chamber was used to record the energy spectra of outgoing deuterons. The measured cross section data for the direct reaction component have been separated from the compound nucleus one, then analyzed in the framework of the non local, FR-DWBA theory. New values of the $C^{2}S$ and ($S_{p1/2},$ $S_{p3/2})$ proton absolute and partial spectroscopic factors and related $\gamma_{p}^{2}(a)$\ proton reduced widths versus the p $+$ $^{7}$Li channel radius have been extracted for the $2^{+}(16.626)$ and $2^{+}(16.922),T=0+1$ isospin-mixed loosely bound states of astrophysical interest and the $1^{+}(17.640)$, $T=1$ unbound state of $^{8}$Be. They are compared to sparse earlier experimental values and to shell-model predicted ones from the literature, and are discussed. In particular, the status of the spectroscopic information on the $2^{+}$ isospin-mixed doublet is reviewed and up-dated. The application in nuclear astrophysics of the DWBA derived results is emphasised.

Intense and purified radioactive beam of post-accelerated $^{14}$O was used to study the low-lying states in the unbound $^{15}$F nucleus. Exploiting resonant elastic scattering in inverse kinematics with a thick target, the second excited state, a resonance at E$\_R$=4.757(6)(10)~MeV with a width of $\Gamma$=36(5)(14)~keV was measured for the first time with high precision. The structure of this narrow above-barrier state in a nucleus located two neutrons beyond the proton drip line was investigated using the Gamow Shell Model in the coupled channel representation with a $^{12}$C core and three valence protons. It is found that it is an almost pure wave function of two quasi-bound protons in the $2s\_{1/2}$ shell., Comment: 8 pages, 2 figures, 1 table, Submitted to Phys. Lett. B

The full-energy peak efficiency calibration and the energy resolution measurements of the 2 in . × 2 in . LaBr 3 γ -ray detector are presented for γ -ray energies in the 700 keV–17.6 MeV range. Measurements were done using a combination of proton-capture nuclear reactions on Al 27 , Na 23 , K 39 , Li 7 and B 11 for high-energy γ -rays, and radioactive sources such as Co 60 and Eu 152 for the lowest energies. At high energies, two γ -rays in a cascade from proton resonance capture were employed using Al, Na 2 WO 4 , K 2 SO 4 and LiBO 2 targets. The obtained results were compared to the simulations performed using a GEANT4 code.

The early E ⩽ 511 keV gamma-ray emission from novae depends critically on the F 18 ( p , α ) O 15 reaction. Unfortunately the reaction rate of the F 18 ( p , α ) O 15 reaction is still largely uncertain due to the unknown strengths of low-lying proton resonances near the F 18 + p threshold which play an important role in the nova temperature regime. We report here our last results concerning the study of the d ( F 18 , p ) F 19 ( α ) N 15 transfer reaction. We show in particular that these two low-lying resonances cannot be neglected. These results are then used to perform a careful study of the remaining uncertainties associated to the F 18 ( p , α ) O 15 and F 18 ( p , γ ) Ne 19 reaction rates.

Radioactive beams of $^{14}\mathrm{O}$ and $^{15}\mathrm{O}$ were used to populate the resonant states ${1/2}^{+}$, ${5/2}^{+}$ and ${0}^{\ensuremath{-}},{1}^{\ensuremath{-}},{2}^{\ensuremath{-}}$ in the unbound $^{15}\mathrm{F}$ and $^{16}\mathrm{F}$ nuclei, respectively, by means of proton elastic scattering reactions in inverse kinematics. Based on their large proton spectroscopic factor values, the resonant states in $^{16}\mathrm{F}$ can be viewed as a core of $^{14}\mathrm{O}$ plus a proton in the $2{s}_{1/2}$ or $1{d}_{5/2}$ shell and a neutron in $1{p}_{1/2}$. Experimental energies were used to derive the strength of the $2{s}_{1/2}$-$1{p}_{1/2}$ and $1{d}_{5/2}$-$1{p}_{1/2}$ proton-neutron interactions. It is found that the former changes by 40% compared with the mirror nucleus $^{16}\mathrm{N}$, and the latter changes by 10%. This apparent symmetry breaking of the nuclear force between mirror nuclei finds explanation in the role of the large coupling to the continuum for the states built on an $\ensuremath{\ell}=0$ proton configuration.

The ${}^{26}\mathrm{Al}$ radioisotope is of great importance for understanding the chemical and dynamical evolution of our galaxy. Among the possible stellar sources, massive stars are believed to be the main producer of this radioisotope. Understanding ${}^{26}\mathrm{Al}$ nucleosynthesis in massive stars requires estimates of the thermonuclear reaction rates of the $^{26}\mathrm{Al}$${(n,p)}^{26}$Mg, $^{26}\mathrm{Al}$${(n,\ensuremath{\alpha})}^{23}$Na, and $^{23}\mathrm{Na}$${(\ensuremath{\alpha},p)}^{26}$Mg reactions. These reaction rates depend on the spectroscopic properties of ${}^{27}\mathrm{Al}$ states above the neutron and alpha thresholds. In this context, the $^{27}\mathrm{Al}$${(p,{p}^{\ensuremath{'}})}^{27}$Al* reaction was studied at 18 MeV using a high-resolution Enge Split-Pole spectrometer. States from the ground state up to excitation energies of $\ensuremath{\approx}$14 MeV were populated. While up to the ${}^{23}\mathrm{Na}$ + $\ensuremath{\alpha}$ threshold no additional states are observed, we report for the first time 30 new levels above the ${}^{23}\mathrm{Na}$ + $\ensuremath{\alpha}$ threshold and more than 30 new states above the ${}^{26}\mathrm{Al}$ + n threshold for which excitation energies are determined with an uncertainty of 4--5 keV.

The observed primordial ${}^{7}$Li abundance in metal-poor halo stars is found to be lower than its Big-Bang nucleosynthesis (BBN) calculated value by a factor of approximately three. Some recent works suggested the possibility that this discrepancy originates from missing resonant reactions which would destroy ${}^{7}$Be, parent of ${}^{7}$Li. The most promising candidate resonances which were found include a possibly missed 1${}^{\ensuremath{-}}$ or 2${}^{\ensuremath{-}}$ narrow state around 15 MeV in the compound nucleus ${}^{10}$C formed by ${}^{7}$Be+${}^{3}$He and a state close to 7.8 MeV in the compound nucleus ${}^{11}$C formed by ${}^{7}$Be+${}^{4}$He. In this work, we studied the high excitation energy region of ${}^{10}$C and the low excitation energy region in ${}^{11}$C via the reactions ${}^{10}$B(${}^{3}$He,$t$)${}^{10}$C and ${}^{11}$B(${}^{3}$He,$t$)${}^{11}$C, respectively, at the incident energy of 35 MeV. Our results for ${}^{10}$C do not support ${}^{7}$Be+${}^{3}$He as a possible solution for the ${}^{7}$Li problem. Concerning ${}^{11}$C results, the data show no new resonances in the excitation energy region of interest and this excludes the ${}^{7}$Be+${}^{4}$He reaction channel as an explanation for the ${}^{7}$Li deficit.

The radiative capture reaction 12C(α,γ)16O plays an important role in helium burning in massive stars and their subsequent evolution [1]. However, despite various experimental studies, the cross section of this reaction at stellar energies remains highly uncertain. The extrapolation down to stellar energy (Ecm∼300 keV) of the measured cross sections at higher energies is made difficult by the overlap of various contributions of which some are badly known such as that of the 2+ (Ex=6.92 MeV) and 1- (Ex=7.12 MeV) sub-threshold states of 16O. Hence, to further investigate the contribution of these two-subthreshold resonances to the 12C(α,γ)16O cross section, a new determination of their a-reduced widths and so their a- spectroscopic-factors was performed using 12C(7Li,t)16O transfer reaction measurements at two incident energies and a detailed DWBA analysis of the data [2]. The measured and calculated differential cross sections are presented as well as the obtained spectroscopic factors and the a- reduced widths as well as the assymptotic normalization constants (ANC) for the 2+ and 1- subthreshold states. Finally, the results obtained from the R-matrix calculations of the 12C(α,γ)16O cross section using our obtained a-reduced widths for the two sub-threshold resonances are presented and discussed., SCOPUS: cp.j, info:eu-repo/semantics/published

The ${}^{12}$C($\ensuremath{\alpha}$,$\ensuremath{\gamma}$)${}^{16}$O reaction plays a crucial role in stellar evolution. The rate of this reaction determines directly the ${}^{12}$C-to-${}^{16}$O abundance ratio at the end of the helium burning phase of stars and consequently has a big effect on the subsequent nucleosynthesis and even on the evolution of massive stars. However, despite many experimental studies, the low-energy cross section of ${}^{12}$C($\ensuremath{\alpha}$,$\ensuremath{\gamma}$)${}^{16}$O remains uncertain. The extrapolation of the measured cross sections to stellar energies ($E\ensuremath{\sim}300$ keV) is made particularly difficult by the presence of the 2${}^{+}$ (${E}_{x}=6.92$ MeV) and 1${}^{\ensuremath{-}}$ (${E}_{x}=7.12$ MeV)subthreshold states of ${}^{16}$O. To further investigate the contribution of these two subthreshold resonances to the ${}^{12}$C($\ensuremath{\alpha}$,$\ensuremath{\gamma}$)${}^{16}$O cross section, we determine their $\ensuremath{\alpha}$-reduced widths via a measurement of the transfer reaction ${}^{12}$C(${}^{7}$Li, $t$)${}^{16}$O at two incident energies, 28 and 34 MeV. The uncertainties on the determined $\ensuremath{\alpha}$-spectroscopic factors and the $\ensuremath{\alpha}$-reduced widths were reduced thanks to a detailed distorted-wave Born approximation analysis of the transfer angular distributions measured at the two incident energies. The $R$-matrix calculations of ${}^{12}$C($\ensuremath{\alpha}$,$\ensuremath{\gamma}$)${}^{16}$O cross section using our obtained $\ensuremath{\alpha}$-reduced widths for the 2${}^{+}$ and 1${}^{\ensuremath{-}}$ subthreshold resonances lead to an $E1$ $S$ factor at 300 keV of $100\ifmmode\pm\else\textpm\fi{}28$ keV b, which is consistent with values obtained in most of the direct and indirect measurements as well as the NACRE collaboration compilation while the result for the $E2$ component ${S}_{E2}\phantom{\rule{0.28em}{0ex}}(300\phantom{\rule{4.pt}{0ex}}\text{keV})=50\ifmmode\pm\else\textpm\fi{}19$ keV b disagrees with the NACRE adopted value.

The unbound nucleus Na-18, the intermediate nucleus in the two-proton radioactivity of Mg-19, was studied by the measurement of the resonant elastic scattering reaction H(Ne-17,p)Ne-17 performed at 4 A.MeV using a radioactive beam from the SPIRAL Facility. Spectroscopic properties of the low-lying states were obtained in an R-matrix analysis of the excitation function. (C) 2012 Elsevier B.V. All rights reserved. Preprint available at: [https://arxiv.org/pdf/1110.1236.pdf]

$\ensuremath{\gamma}$-ray production cross sections have been measured in proton irradiations of N, Ne, and Si and $\ensuremath{\alpha}$-particle irradiations of N and Ne. In the same experiment we extracted also line shapes for strong $\ensuremath{\gamma}$-ray lines of $^{16}\mathrm{O}$ produced in proton and $\ensuremath{\alpha}$-particle irradiations of O. For the measurements gas targets were used for N, O, and Ne and a thick foil for Si. All targets were of natural isotopic composition. Beams in the energy range up to 26 MeV for protons and 39 MeV for $\ensuremath{\alpha}$ particles were delivered by the Institut de Physique Nucl\'eaire--Orsay tandem accelerator. The $\ensuremath{\gamma}$ rays were detected with four high-purity Ge detectors in the angular range ${30}^{\ifmmode^\circ\else\textdegree\fi{}}$ to ${135}^{\ifmmode^\circ\else\textdegree\fi{}}$. We extracted 36 cross-section excitation functions for proton reactions and 14 for $\ensuremath{\alpha}$-particle reactions. For the majority of the excitation functions no other data exist to our knowledge. Where comparison with existing data was possible, usually a very good agreement was found. It is shown that these data are very interesting for constraining nuclear reaction models. In particular, the agreement of cross section calculations in the nuclear reaction code talys with the measured data could be improved by adjusting the coupling schemes of collective levels in the target nuclei $^{14}\mathrm{N}$, $^{20,22}\mathrm{Ne}$, and $^{28}\mathrm{Si}$. The importance of these results for the modeling of nuclear $\ensuremath{\gamma}$-ray line emission in astrophysical sites is discussed.

$\gamma$-ray production cross sections have been measured in proton irradiations of N, Ne and Si and $\alpha$-particle irradiations of N and Ne. In the same experiment we extracted also line shapes for strong $\gamma$-ray lines of $^{16}$O produced in proton and $\alpha$-particle irradiations of O. For the measurements gas targets were used for N, O and Ne and a thick foil was used for Si. All targets were of natural isotopic composition. Beams in the energy range up to 26 MeV for protons and 39 MeV for $\alpha$-particles have been delivered by the IPN-Orsay tandem accelerator. The $\gamma$ rays have been detected with four HP-Ge detectors in the angular range 30$^{\circ}$ to 135$^{\circ}$. We extracted 36 cross section excitation functions for proton reactions and 14 for $\alpha$-particle reactions. For the majority of the excitation functions no other data exist to our knowledge. Where comparison with existing data was possible usually a very good agreement was found. It is shown that these data are very interesting for constraining nuclear reaction models. In particular the agreement of cross section calculations in the nuclear reaction code TALYS with the measured data could be improved by adjusting the coupling schemes of collective levels in the target nuclei $^{14}$N, $^{20,22}$Ne and $^{28}$Si. The importance of these results for the modeling of nuclear $\gamma$-ray line emission in astrophysical sites is discussed., Comment: 42 pages, 12 figures, 7 tables, submitted to Phys. Rev. C

The unbound nucleus 18 Na , the intermediate nucleus in the two-proton radioactivity of 19 Mg , is studied through the resonant elastic scattering 17 Ne ( p ,17 Ne ) p . The spectroscopic information obtained in this experiment is discussed and put in perspective with previous measurements and the structure of the mirror nucleus 18 N .

International audience; The 18F nucleus is one of the radioactive isotopes produced during nova explosions. It is of particular interest since it is mainly responsible for the 511 keV gamma-ray emission of novae that could be detected with the INTEGRAL satellite or future gamma-ray telescopes. The amount of 18F synthesised still suffers from large uncertainties coming from missing nuclear information concerning the 18F destruction reaction 18F(p,a)15O. In particular, the interference sign between three 3/2+ resonances in 19Ne, situated slightly above the proton threshold (8 keV and/or 38 keV) and at higher energy (665 keV), is unknown. The maximum effect of these interferences is lying in the energy range corresponding to the Gamow peak region and has a strong impact on the 18F(p,a)15O reaction rate. We report here on the direct measurement at low energy (down to 400 keV in the center-of-mass) of the 18F(p,a)15O total cross section that we performed at the Louvain-la-Neuve CRC-RIB facility with the high-intensity and -purity 18F radioactive beam (T1/2 = 110 min). The total cross section for the different incident energies will be presented and compared to previous experimental data.

$��$-ray production cross sections have been measured in proton irradiations of N, Ne and Si and $��$-particle irradiations of N and Ne. In the same experiment we extracted also line shapes for strong $��$-ray lines of $^{16}$O produced in proton and $��$-particle irradiations of O. For the measurements gas targets were used for N, O and Ne and a thick foil was used for Si. All targets were of natural isotopic composition. Beams in the energy range up to 26 MeV for protons and 39 MeV for $��$-particles have been delivered by the IPN-Orsay tandem accelerator. The $��$ rays have been detected with four HP-Ge detectors in the angular range 30$^{\circ}$ to 135$^{\circ}$. We extracted 36 cross section excitation functions for proton reactions and 14 for $��$-particle reactions. For the majority of the excitation functions no other data exist to our knowledge. Where comparison with existing data was possible usually a very good agreement was found. It is shown that these data are very interesting for constraining nuclear reaction models. In particular the agreement of cross section calculations in the nuclear reaction code TALYS with the measured data could be improved by adjusting the coupling schemes of collective levels in the target nuclei $^{14}$N, $^{20,22}$Ne and $^{28}$Si. The importance of these results for the modeling of nuclear $��$-ray line emission in astrophysical sites is discussed., 42 pages, 12 figures, 7 tables, submitted to Phys. Rev. C

During nova outbursts the decay of {sup 18}F is the main source of {gamma}-ray emission at and below 511 keV. In spite of much experimental effort, the quantity of {sup 18}F synthesized still suffers from large uncertainties which arise mainly from the {sup 18}F(p, {alpha}){sup 15}O reaction cross section at low energies. We report here on a new direct measurement carried out at the Louvain-la-Neuve RIB facility of Louvain-la-Neuve using an isobarically pure {sup 18}F beam impinging on a thin polyethylene target. Cross sections down to a center-of-mass energy of 400 keV have been obtained and the results together with previous experimental data were compared to R-matrix calculations. The effect of the relative contribution of the two low-lying 3/2{sup +} resonances as well as the sensitivity of the calculations to the R-matrix radius is studied in detail.

The $^{13}\mathrm{C}$($\ensuremath{\alpha},n$)$^{16}\mathrm{O}$ reaction is considered the main neutron source for the s process in low mass asymptotic giant branch (AGB) stars. In the Gamow peak, the cross section sensitively depends on the $1/{2}^{+}$ subthreshold state of $^{17}\mathrm{O}$ (${E}_{x}=6.356$ MeV). In this work, we determined the astrophysical $S$ factor through an evaluation of the \ensuremath{\alpha} spectroscopic factor and the corresponding asymptotic normalization factor (ANC) of the 6.356 MeV state using the transfer reaction $^{13}\mathrm{C}$($^{7}\mathrm{Li}$,$t$)$^{17}\mathrm{O}$ at two different incident energies. Our result confirms that the contribution of the $1/{2}^{+}$ state is dominant at astrophysical energies. Our reaction rate at $T=0.09$ GK is slightly lower than the value adopted in the Nuclear Astrophysics Compilation of REaction rates (NACRE), but two times larger than the one obtained in a recent ANC measurement.

The reaction 13C(α,n)16O is considered as the main neutron source for s‐process in low‐mass asymptotic giant branch stars. At low energies of astrophysical interest, the contribution of the subthreshold state 6.356 MeV of 17O to the 13C(α,n)16O cross section should be taken into account. However, the results of previous studies of this contribution lead to different conclusions.Hence, we investigated the effect of this resonance on the astrophysical S‐factor through a new precise measurement of the alpha spectroscopic factor, Sα, of the 6.356 MeV state using the transfer reaction 13C(7Li,t)17O at two different incident energies. The measured angular distributions and the obtained spectroscopic factors will be presented as well as their impact on C(α,n)16O cross section and reaction rate.

{gamma}-ray production cross sections for proton and {alpha}-particle interactions with {sup 12}C, {sup 16}O, {sup 24}Mg, and Fe have been measured in the energy range 5-25 MeV with proton beams and 5-40 MeV with {alpha}-particle beams. Isotopically pure foils of {sup 24}Mg and foils of natural isotopical composition of C, MgO, and Fe have been used. {gamma}-ray angular distributions were obtained with five high-purity Ge detectors with bismuth germanate Compton shields placed at angles of 45 deg. to 157.5 deg. Cross sections for more than 50 different {gamma}-ray transitions were extracted, and for many of them no data have been published before. Comparison of present data with data available in the literature shows mostly good to excellent agreement. In addition to the production cross sections, high-statistics, low-background line shapes of the 4.438 MeV {sup 12}C {gamma} ray from inelastic scattering off {sup 12}C and spallation of {sup 16}O were obtained. Comparison with nuclear reaction calculations shows that these data place interesting constraints on nuclear reaction models.

The {sup 17}O(p,{alpha}){sup 14}N and {sup 17}O(p,{gamma}){sup 18}F reactions are of major importance to hydrogen-burning nucleosynthesis in a number of different stellar sites. In particular, {sup 17}O and {sup 18}F nucleosynthesis in classical novae is strongly dependent on the thermonuclear rates of these two reactions. The previously estimated rate for {sup 17}O(p,{alpha}){sup 14}N carries very large uncertainties in the temperature range of classical novae (T=0.01-0.4 GK), whereas a recent measurement has reduced the uncertainty of the {sup 17}O(p,{gamma}){sup 18}F rate. We report on the observation of a previously undiscovered resonance at E{sub c.m.}=183.3 keV in the {sup 17}O(p,{alpha}){sup 14}N reaction, with a measured resonance strength {omega}{gamma}{sub p{alpha}}=(1.6{+-}0.2)x10{sup -3} eV. We studied in the same experiment the {sup 17}O(p,{gamma}){sup 18}F reaction by an activation method, and the resonance strength was found to amount to {omega}{gamma}{sub p{gamma}}=(2.2{+-}0.4)x10{sup -6} eV. The excitation energy of the corresponding level in {sup 18}F was determined to be 5789.8{+-}0.3 keV in a Doppler shift attenuation method measurement, which yielded a value of {tau}

A new experiment to determine the thermonuclear cross section of the C-12(alpha,gamma)O-16 reaction has been performed in regular kinematics using an intense alpha-particle beam of up to 340 mu A from the Stuttgart DYNAMITRON. For the first time, a 4 pi-germanium-detector setup has been used to measure the angular distribution of the gamma rays at all angles simultaneously. It consisted of an array of nine EUROGAM high-purity Ge detectors in close geometry, actively shielded individually with bismuth germanate crystals. The C-12 targets were isotopically enriched by magnetic separation during implantation. The depth profiles of the implanted carbon in the C-12 targets were determined by Rutherford backscattering for purposes of cross-section normalization and absolute determination of the E1 and E2 S factors. Angular distributions of the gamma decay to the O-16 ground state were measured in the energy range E-c.m.=1.30-2.78 MeV and in the angular range (lab.) 30 degrees-130 degrees. From these distributions, astrophysical E1 and E2 S-factor functions vs energy were calculated, both of which are indispensable to the modeling of this reaction and the extrapolation toward lower energies. The separation of the E1 and E2 capture channels was done both by taking the phase value phi(12) as a free parameter and by fixing it using the results of elastic alpha-particle scattering on C-12 in the same energy range.

We investigated the proton‐capture reactions on 17O occuring in classical nova explosions. We observed a previously undiscovered resonance at ERlab=194.1±0.6 keV in the 17O(p,α)14N reaction, with a measured resonance strength ωγpα=1.6±0.2 meV. We studied in the same experiment the 17O(p,γ)18F reaction by an activation method and the resonance‐strength ratio was found to be ωγpα/ωγpγ=470±50. The corresponding excitation energy in the 18F compound nucleus was determined to be 5789.8±0.3 keV by γ‐ray measurements using the 14N(α,γ)18F reaction. These new resonance properties have important consequences for 17O nucleosynthesis and γ‐ray astronomy of classical novae.

We report on the observation of a previously unknown resonance at E=194.1+/-0.6 keV (lab) in the 17-O(p,alpha)14-N reaction, with a measured resonance strength omega_gamma(p,alpha)=1.6+/-0.2 meV. We studied in the same experiment the 17-O(p,gamma)18-F reaction by an activation method and the resonance-strength ratio was found to be omega_gamma(p,alpha)/omega_gamma(p,gamma)=470+/-50. The corresponding excitation energy in the 18-F compound nucleus was determined to be 5789.8+/-0.3 keV by gamma-ray measurements using the 14-N(alpha,gamma)18-F reaction. These new resonance properties have important consequences for 17-O nucleosynthesis and gamma-ray astronomy of classical novae., 4 pages, 4 figures. Accepted for publication in Physical Review Letters

International audience; 26Al was the first cosmic radioactivity ever detected in the galaxy. Its nucleosynthesis in novae outbursts is still uncertain mainly due to the lack of nuclear information concerning the 25Al(p,g )26Si reaction. We report here on a neutron-gamma coincidence measurement of the 24Mg(3He,ng )26Si reaction performed at the Orsay TANDEM facility aiming at the spectroscopic study of astrophysically important 26Si states. A new level in the Gamow peak is observed at EX = 5:888 MeV and the gamma-ray decay scheme of all levels below the proton threshold is confirmed.