Search

Several experiments around the world are looking for a new particle, named Dark Boson, which may do the link between the Ordinary Matter (which forms basically stars, planets, interstellar gas...) and the Hidden Sectors of the Universe. This particle, if it exists, would act as the messenger of a new fundamental interaction of nature. In this paper, the underlying Dark Sectors theory will be introduced first. A non-exhaustive summary of experimental studies carried out to date and foreseen in the incoming years will be presented after,including the 8Be anomaly. The last section will provide a status of the New JEDI**** project which aims to investigate the existence or not of a Dark Boson in the MeV range.

Nuclear deexcitation lines are regularly observed in the $\ensuremath{\gamma}$-ray emission spectra of strong solar flares. The most prominent lines are produced by interactions of protons and $\ensuremath{\alpha}$ particles, accelerated up to hundreds of MeV, with abundant nuclei of the solar atmosphere. Analysis and interpretation of these lines, which carry valuable information on the solar flare properties, need cross-section data for the $\ensuremath{\gamma}$-ray line emission in these interactions for a wide particle energy range. To this purpose, we measured the $\ensuremath{\gamma}$-ray emission in interactions of $\ensuremath{\alpha}$-particle beams of ${E}_{\ensuremath{\alpha}}=50\text{--}90$ MeV with target foils of C, Mg, Si, and Fe at the center for proton therapy of the Helmholtz-Zentrum Berlin. Setups of three high-purity Ge detectors and one $\mathrm{La}{\mathrm{Br}}_{3}$:Ce detector have been employed to detect the $\ensuremath{\gamma}$ rays in two experiment campaigns. Relatively large distances of the detectors from the target and pulsed beams with sub-ns-wide pulses allowed the separation of beam-induced prompt $\ensuremath{\gamma}$-ray emission from the targets from other $\ensuremath{\gamma}$ rays and neutron-induced background. $\ensuremath{\gamma}$-ray production cross sections for about 60 deexcitation lines from excited target nuclei or reaction products have been determined. For the strongest deexcitation lines from the major target isotopes, $^{12}\mathrm{C}$, $^{24}\mathrm{Mg}$, $^{28}\mathrm{Si}$, $^{56}\mathrm{Fe}$, there are now measured cross-section data from reaction threshold to ${E}_{\ensuremath{\alpha}}=90$ MeV that can be directly used for astrophysical applications like solar flares. Comparison of the results with a cross-section compilation for strong $\ensuremath{\gamma}$-ray lines in solar flare emissions and the predictions of the talys nuclear reaction code were done. They underline the importance of cross-section determinations at accelerator laboratories for the establishment of an accurate cross-section data base in a wide projectile energy range.

International audience; For the next generation of MeV range gamma-ray telescopes, position sensitive calorimeters based on a monolithic scintillator coupled to a pixelated photodetector could be an important building block. In this paper, we present the optimization of the position reconstruction algorithms using machine learning, for a detector based on a 51×51×10mm3 CeBr 3 crystal. For that purpose, we used an automated test bench and collimated radioactive sources to generate experimental data of known energy and position by irradiating the detector with gamma rays. We found in these data different gamma-ray interaction morphologies for which position reconstruction algorithms perform differently, and we developed an algorithm to automatically classify them. We also conducted an extensive optimization of the artificial neural networks that perform the 3D position reconstruction using the Keras Python library with Theano backend. We found that at 662keV , 90% of events have a morphology that facilitates position reconstruction. The optimized position reconstruction algorithms give for those events a rms error in the plane of the detector of 1.8mm on each axis. The rms error in the depth of the crystal is found to be 2mm .

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.

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 International Gamma-Ray Astrophysics Laboratory (INTEGRAL) is a European Space Agency hard X-ray/γ-ray observatory for astrophysics, covering photon energies from 15 keV to 10 MeV. It was launched in 2002, and since then the Bismuth Germanate (BGO) detectors of the Anti-Coincidence Shield (ACS) of the Spectrometer on INTEGRAL (SPI) have detected many hard X-ray (HXR) bursts from the Sun, producing light curves at photon energies above ≈ 100 keV. The spacecraft has a highly elliptical orbit, providing long uninterrupted observing (about 90 % of the orbital period) with nearly constant background due to the shorter time needed to cross Earth's radiation belts. However, because of technical constraints, INTEGRAL cannot be pointed at the Sun, and high-energy solar photons are always detected in nonstandard observation conditions. To make the data useable for solar studies, we have undertaken a major effort to specify the observing conditions through Monte Carlo simulations of the response of ACS for several selected flares. We checked the performance of the model employed for the Monte Carlo simulations using the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observations for the same sample of solar flares. We conclude that although INTEGRAL was not designed to perform solar observations, ACS is a useful instrument for solar-flare research. In particular, its relatively large effective area allows determining good-quality HXR/γ-ray light curves for X- and M-class solar flares and, in some cases, probably also for C-class flares.

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

26Al was the first cosmic radioactivity ever detected in the galaxy as well as one of the first extinct radioactivity observed in refractory phases of meteorites. Its nucleosynthesis in massive stars is still uncertain mainly due to the lack of nuclear information concerning the 26Al(n,p)26Mg and 26Al(n,α)23Na reactions. We report on a single and coincidence measurement of the 27Al(p,p’)27Al(p)26Mg and 27Al(p,p’)27Al(α)23Na reactions performed at the Orsay TANDEM facility aiming at the spectroscopy study of 27Al above the neutron threshold. Fourteen states are observed for the first time within 350 keV above the 26Al+n threshold.

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.

Uncertainties in the thermonuclear rates of the $^{15}\text{O}(\ensuremath{\alpha},\ensuremath{\gamma}){}^{19}\text{Ne}$ and ${}^{18}\text{F}(p,\ensuremath{\alpha}){}^{15}\text{O}$ reactions affect model predictions of light curves from type I x-ray bursts and the amount of the observable radioisotope $^{18}\text{F}$ produced in classical novae, respectively. To address these uncertainties, we have studied the nuclear structure of $^{19}\text{Ne}$ over ${E}_{x}=4.0\ensuremath{-}5.1$ and 6.1--7.3 MeV using the $^{19}\text{F}(^{3}\text{He},t)^{19}\text{Ne}$ reaction. We find the ${J}^{\ensuremath{\pi}}$ values of the 4.14- and 4.20-MeV levels to be consistent with $9/{2}^{\ensuremath{-}}$ and $7/{2}^{\ensuremath{-}}$, respectively, in contrast to previous assumptions. We confirm the recently observed triplet of states around 6.4 MeV and find evidence that the state at 6.29 MeV, just below the proton threshold, is either broad or a doublet. Our data also suggest that predicted but yet unobserved levels may exist near the 6.86-MeV state. Higher resolution experiments are urgently needed to further clarify the structure of $^{19}\text{Ne}$ around the proton threshold before a reliable ${}^{18}\text{F}(p,\ensuremath{\alpha}){}^{15}\text{O}$ rate for nova models can be determined.

In this review, we emphasize the interplay between astrophysical observations, modeling, and nuclear physics laboratory experiments. Several important nuclear cross sections for astrophysics have long been identified e.g. 12C(alpha,gamma)16O for stellar evolution, or 13C(alpha,n)16O and 22Ne(alpha,n)25Mg as neutron sources for the s-process. More recently, observations of lithium abundances in the oldest stars, or of nuclear gamma-ray lines from space, have required new laboratory experiments. New evaluation of thermonuclear reaction rates now includes the associated rate uncertainties that are used in astrophysical models to i) estimate final uncertainties on nucleosynthesis yields and ii) identify those reactions that require further experimental investigation. Sometimes direct cross section measurements are possible, but more generally the use of indirect methods is compulsory in view of the very low cross sections. Non-thermal processes are often overlooked but are also important for nuclear astrophysics, e.g. in gamma-ray emission from solar flares or in the interaction of cosmic rays with matter, and also motivate laboratory experiments. Finally, we show that beyond the historical motivations of nuclear astrophysics, understanding i) the energy sources that drive stellar evolution and ii) the origin of the elements can also be used to give new insights into physics beyond the standard model., 38 pages, 33 Figures, invited review

The response of a scintillation detector with a cylindrical 1.5-inch LaBr3:Ce crystal to incident neutrons has been measured in the energy range En = 2-12 MeV. Neutrons were produced by proton irradiation of a Li target at Ep = 5-14.6 MeV with pulsed proton beams. Using the time-of-flight information between target and detector, energy spectra of the LaBr3:Ce detector resulting from fast neutron interactions have been obtained at 4 different neutron energies. Neutron-induced gamma rays emitted by the LaBr3:Ce crystal were also measured in a nearby Ge detector at the lowest proton beam energy. In addition, we obtained data for neutron irradiation of a large-volume high-purity Ge detector and of a NE-213 liquid scintillator detector, both serving as monitor detectors in the experiment. Monte-Carlo type simulations for neutron interactions in the liquid scintillator, the Ge and LaBr3:Ce crystals have been performed and compared with measured data. Good agreement being obtained with the data, we present the results of simulations to predict the response of LaBr3:Ce detectors for a range of crystal sizes to neutron irradiation in the energy range En = 0.5-10 MeV, Comment: 28 pages, 10 figures, 4 Tables

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.

SEPServer is a three-year collaborative project funded by the seventh framework programme (FP7-SPACE) of the European Union. The objective of the project is to provide access to state-of-the-art observations and analysis tools for the scientific community on solar energetic particle (SEP) events and related electromagnetic (EM) emissions. The project will eventually lead to better understanding of the particle acceleration and transport processes at the Sun and in the inner heliosphere. These processes lead to SEP events that form one of the key elements of space weather. In this paper we present the first results from the systematic analysis work performed on the following datasets: SOHO/ERNE, SOHO/EPHIN, ACE/EPAM, Wind/WAVES and GOES X-rays. A catalogue of SEP events at 1 AU, with complete coverage over solar cycle 23, based on high-energy (~68-MeV) protons from SOHO/ERNE and electron recordings of the events by SOHO/EPHIN and ACE/EPAM are presented. A total of 115 energetic particle events have been identified and analysed using velocity dispersion analysis (VDA) for protons and time-shifting analysis (TSA) for electrons and protons in order to infer the SEP release times at the Sun. EM observations during the times of the SEP event onset have been gathered and compared to the release time estimates of particles. Data from those events that occurred during the European day-time, i.e., those that also have observations from ground-based observatories included in SEPServer, are listed and a preliminary analysis of their associations is presented. We find that VDA results for protons can be a useful tool for the analysis of proton release times, but if the derived proton path length is out of a range of 1 AU

The decay of $^{19}$O($\beta^-$) and $^{19}$Ne($\beta^+$) implanted in niobium in its superconducting and metallic phase was measured using purified radioactive beams produced by the SPIRAL/GANIL facility. Half-lives and branching ratios measured in the two phases are consistent within one-sigma error bar. This measurement casts strong doubts on the predicted strong electron screening in superconductor, the so-called superscreening. The measured difference in screening potential energy is 110(90) eV for $^{19}$Ne and 400(320) eV for $^{19}$O. Precise determinations of the half-lives were obtained for $^{19}$O: 26.476(9) s and $^{19}$Ne: 17.254(5) s., Comment: 4 pages, 3 figures, accepted for publication in Physical Review Letters

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.

Expérience GANIL E521aS/SPIRAL; International audience; The unbound nucleus $^{18}$Na, the intermediate nucleus in the two-proton radioactivity of $^{19}$Mg, was studied by the measurement of the resonant elastic scattering reaction $^{17}$Ne(p,$^{17}$Ne)p performed at 4 A.MeV. Spectroscopic properties of the low-lying states were obtained in a R-matrix analysis of the excitation function. Using these new results, we show that the lifetime of the $^{19}$Mg radioactivity can be understood assuming a sequential emission of two protons via low energy tails of $^{18}$Na resonances.

International audience; The abundance calculations of the p-nuclei produced in explosive stellar sites rely on the Hauser-Feshbach (HF) theory with the alpha-article optical model potential (α-OMP) one of its major ingredients. To date, most of the (α, γ) cross sections measured show that HF calculations can be wrong by a factor of ten or more especially when phenomenological α-OMP are employed. To investigate the relevant uncertainties entering the HF calculations and furthermore develop global microscopic α-OMPs, systematic (α, γ) cross-section measurements are necessary. This led us to perform a feasibility study of (α, γ) measurements in inverse kinematics that will allow us to employ also radioactive beams in the future. Hence, the 4He(78Kr,γ)82Sr reaction was studied using the LISE3 spectrometer to separate the 82Sr recoils from the primary 78Kr beam. Although an excellent rejection factor > 1010 was achieved, the position of the ions of interest was unexpectedly masked by a secondary beam of high intensity. Given these, new setup improvements are proposed to remove the pollutant ions. Recently, many experiments were conducted in order to study the influence of the environment (especially in a metallic material) on the decay probability of radioactive nuclei. Additionally, hydrogen-like fusion reactions were performed indicating a change in the cross-section due to the influence of the Coulomb field screening induced by quasi-free electrons in metals. This was explained by the Debye screening model which treats metallic electrons within Maxwell-Boltzmann statistics. We measured the decay rate of 19O in metallic, insulating and superconducting environments whereas the electrons in the superconductors should obey the Bose-Einstein statistics. The decay rate measurement was supported by a branching ratios measurement. We found that the effect on the decay rate, if any, is less than the 0.1%, far below the theoretical predictions.

$\ensuremath{\gamma}$-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.

A fast-timing setup has been developed to measure the nuclear-state half-lives of neutron-rich nuclei. The first on-line measurements were performed on 137, 139Cs obtained from the β decay of 137, 139Xe. These neutron-rich Xe nuclei were produced by the 238U photofission induced by the 50MeV electron beam delivered by the ALTO facility. The half-lives of the first excited state in 137Cs and of six excited states in 139Cs were measured for the first time. Taking into account new information given by the deduced transition probabilities, we discuss the structure of the first excited states in 137, 139Cs : it is shown that, in both nuclei, the first excited $$\tfrac{5} {2}^ +$$ level corresponds mainly to the one-proton state issued from the π2d 5/2 orbital and that the most probable spin values for the states located at 289.8, 393.5, and 393.8keV in 139Cs are $$\tfrac{5} {2}^ +$$ , $$\tfrac{3} {2}^ +$$ , and $$\tfrac{1} {2}^ +$$ , respectively.

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.

International audience; The nucleosynthesis of the light elements Li, Be and B by galactic cosmic rays is presented. Observations of cosmic rays and the nuclear reactions responsible for Li, Be and B nucleosynthesis are described, followed by some words on propagation. At the end, some open questions concerning galactic cosmic rays are discussed.

In order to perform half-life measurements at Alto, we developed a fast-timing setup using fast scintillators : LaBr3. The main components of our setup and their characteristics (timing properties) are presented. The resulting time resolution, obtained after optimization, and measured off-line with radioactive sources is discussed. This set-up was tested on-line by measuring using the slope method half-lives of 137-139Cs levels fed by the β- decay of 137-139Xe. The neutron-rich Xe nuclei were produced by 238U photofission using, at low intensity, the electron beam and the line of the future facility ALTO. Our results show the ability of such a fast-timing system to measure half-lives lower than the total time resolution. Off-line and on-line results are discussed. Fil: Deloncle, I.. Université Paris Sud; Francia. Centre National de la Recherche Scientifique; Francia Fil: Roussière, B.. Centre National de la Recherche Scientifique; Francia. Université Paris Sud; Francia Fil: Cardona, Maria Angelica. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comision Nacional de Energia Atomica. Gerencia D/area Invest y Aplicaciones No Nucleares. Gerencia Fisica (cac). Departamento de Física de la Materia Condensada.; Argentina Fil: Hojman, Daniel Leonardo. Comision Nacional de Energia Atomica. Gerencia D/area Invest y Aplicaciones No Nucleares. Gerencia Fisica (cac). Departamento de Física de la Materia Condensada.; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Kiener, J.. Université Paris Sud; Francia. Centre National de la Recherche Scientifique; Francia Fil: Petkov, P.. Institue of Nuclear Research and Nuclear Energy; Bulgaria Fil: Tonev, D.. Institue of Nuclear Research and Nuclear Energy; Bulgaria Fil: Venkova, Ts.. Institue of Nuclear Research and Nuclear Energy; Bulgaria

Six proton-emitting states in $^{19}\mathrm{Ne}$ were studied through the inelastic scattering reaction $\mathrm{H}(^{19}\mathrm{Ne},p)^{19}\mathrm{Ne}^{*}(p)^{18}\mathrm{F}$. Their energies and widths were derived from the protons detected at zero degree, while proton-proton angular correlations between the detector at zero degree and a segmented annular detector were used to determine their spin value. In addition to the known states, a new broad $J=\frac{1}{2}$ resonance has been evidenced at ${E}_{x}\ensuremath{\approx}7.9\text{ }\text{ }\mathrm{MeV}$, $\ensuremath{\approx}1.45\text{ }\text{ }\mathrm{MeV}$ above the proton emission threshold. By introducing this resonance, the $^{18}\mathrm{F}(p,\ensuremath{\alpha})^{15}\mathrm{O}$ destruction rate in novae is significantly enhanced. This reduces the chance to observe the cosmic $\ensuremath{\gamma}$-ray emission of $^{18}\mathrm{F}$ from novae in space telescopes.

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 nucleosynthetic origin of $^{26}\mathrm{Al}$ (${t}_{1/2}=0.72$ Myr) in the early solar system is still an open question. Several models predict that short-lived radionuclides could be produced by irradiation of circumsolar material by light charged particles emitted by the young sun. Within some models, most of the $^{26}\mathrm{Al}$ is produced by $^{3}\mathrm{He}$-induced reactions on $^{24}\mathrm{Mg}$. Little experimental data exist on $^{3}\mathrm{He}$ reactions so that irradiation models have had to rely on theoretical cross sections deduced from statistical nuclear reaction codes. We performed a direct measurement of the $^{26}\mathrm{Al}$ production on Mg target by means of $\ensuremath{\gamma}$ ray spectroscopy and accelerator mass spectrometry (AMS). The data indicate that the theoretical cross section used in previous approaches was overestimated by a factor of 3. Taking the particle spectra considered in theoretical approaches these data lead to a net reduction of the $^{26}\mathrm{Al}$ production of a factor of 2. We calculated the relative contribution of the different $^{26}\mathrm{Al}$ production channels depending on the irradiation scenario. We show that extremely large particles fluxes would be necessary to reach the canonical ${}^{26}\mathrm{Al}{/}^{27}\mathrm{Al}$ $=5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ in solids that were present in the early solar system. An in situ origin of this important isotopic chronometer by irradiation is unlikely.

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

{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.

Gamma-ray angular distributions for the resonances at Ep = 550 keV and 1747 keV of the radiative capture reaction 13-C(p,g)14-N have been measured, using intense proton beams on isotopically pure 13-C targets. Relative intensities for the strongest transitions were extracted with an accuracy of typically five per cent, making these resonances new useful gamma-ray standards for efficiency calibration in the energy range Egamma = 1.6 to 9 MeV., Comment: 17 pages, 6 figures, Nuclear Instruments and Methods, Sec. A, accepted

On Oct. 17, 2002, the ESA INTEGRAL observatory was launched into a highly elliptical orbit. SPI, a high resolution Ge spectrometer covering an energy range of 20-8000 keV, is one of its two main instruments. We use data recorded early in the mission (i.e. in March 2003) to characterize the instrumental background, in particular the many gamma-ray lines produced by cosmic-ray interactions in the instrument and spacecraft materials. More than 300 lines and spectral features are observed, for about 220 of which we provide identifications. An electronic version of this list, which will be updated continuously, is available for download at CESR. We also report first results from our efforts to model these lines by ab initio Monte Carlo simulation.

The reduced transition probability B(E2: 01 +→ 2+) of 72Zn has been measured for the first time by Coulomb excitation at intermediate energy. The result B(E2: 01 +→ 2+) = 1740±210 e2fm4, corresponds to the deformation parameter β2 of 0.23, in close agreement with expectations derived from the neighboring nucleus 73Zn. A discussion of the evolution of the N = 40 sub-shell closure as a function of Z is presented.

We calculated in detail the angular distribution of \ensuremath{\gamma} rays and the resulting shape of the \ensuremath{\gamma}-ray line produced by the nuclear deexcitation of the 4.439 MeV state of ${}^{12}\mathrm{C}$ following proton and \ensuremath{\alpha}-particle interactions with ${}^{12}\mathrm{C}$ and ${}^{16}\mathrm{O}$ in the energy range from threshold to 100 MeV per nucleon, making use of available experimental data. In the proton energy range from 8.6 to 20 MeV, the extensive data set of a recent accelerator experiment on \ensuremath{\gamma}-ray line shapes and angular distributions was used to deduce parametrizations for the \ensuremath{\gamma}-ray emission of the ${2}^{+},$ 4.439 MeV state of ${}^{12}\mathrm{C}$ following inelastic proton scattering off ${}^{12}\mathrm{C}$ and proton induced spallation of ${}^{16}\mathrm{O}.$ At higher proton energies and for \ensuremath{\alpha}-particle induced reactions, optical model calculations were the main source to obtain the needed reaction parameters for the calculation of \ensuremath{\gamma}-ray line shapes and angular distributions. Line shapes are predicted for various interaction scenarios of accelerated protons and \ensuremath{\alpha} particles in solar flares.

Recent observations of high ionization rates of molecular hydrogen in diffuse interstellar clouds point to a distinct low-energy cosmic-ray component. Supposing that this component is made of nuclei, two models for the origin of such particles are explored and low-energy cosmic-ray spectra are calculated, which, added to the standard cosmic-ray spectra, produce the observed ionization rates. The clearest evidence of the presence of such low-energy nuclei between a few MeV nucleon{sup -1} and several hundred MeV nucleon{sup -1} in the interstellar medium would be a detection of nuclear {gamma}-ray line emission in the range E {sub {gamma}} {approx} 0.1-10 MeV, which is strongly produced in their collisions with the interstellar gas and dust. Using a recent {gamma}-ray cross section compilation for nuclear collisions, {gamma}-ray line emission spectra are calculated alongside the high-energy {gamma}-ray emission due to {pi}{sup 0} decay, the latter providing normalization of the absolute fluxes by comparison with Fermi-LAT observations of the diffuse emission above E {sub {gamma}} = 0.1 GeV. Our predicted fluxes of strong nuclear {gamma}-ray lines from the inner Galaxy are well below the detection sensitivities of the International Gamma-Ray Astrophysics Laboratory, but a detection, especially of the 4.4 MeV line, seems possible with new-generationmore » {gamma}-ray telescopes based on available technology. We also predict strong {gamma}-ray continuum emission in the 1-8 MeV range, which, in a large part of our model space for low-energy cosmic rays, considerably exceeds the estimated instrument sensitivities of future telescopes.« less

Fast-timing measurements were performed on 137,139Cs obtained from the ?? decay of 137'139Xe. The neutron-rich Xe nuclei were produced by the 238IJ photofission induced by the 50 MeV electron beam delivered by the ALTO facility. The half-lives of the first excited state in 137Cs and of six excited states in 139Cs were measured for the first time. These T1/2 results give new information on the structure of the 137,13955Cs82,84 nuclei located near the neutron closed shell N = 82. In particular, it is shown that, in both nuclei, the first excited 5/2+ level corresponds mainly to the one-proton state issued from the ?2d5/2 orbital. From the comparison with other N = 84 isotones, the most probable spin values for the states located at 289.8, 393.5, and 393.8 keV in 139Cs appear to be 5/2+, 3/2+, and 1/2+.

We propose to perform a continuously scanning all-sky survey from 200 keV to 80 MeV achieving a sensitivity which is better by a factor of 40 or more compared to the previous missions in this energy range. The Gamma-Ray Imaging, Polarimetry and Spectroscopy (GRIPS) mission addresses fundamental questions in ESA's Cosmic Vision plan. Among the major themes of the strategic plan, GRIPS has its focus on the evolving, violent Universe, exploring a unique energy window. We propose to investigate $\gamma$-ray bursts and blazars, the mechanisms behind supernova explosions, nucleosynthesis and spallation, the enigmatic origin of positrons in our Galaxy, and the nature of radiation processes and particle acceleration in extreme cosmic sources including pulsars and magnetars. The natural energy scale for these non-thermal processes is of the order of MeV. Although they can be partially and indirectly studied using other methods, only the proposed GRIPS measurements will provide direct access to their primary photons. GRIPS will be a driver for the study of transient sources in the era of neutrino and gravitational wave observatories such as IceCUBE and LISA, establishing a new type of diagnostics in relativistic and nuclear astrophysics. This will support extrapolations to investigate star formation, galaxy evolution, and black hole formation at high redshifts., Comment: to appear in Exp. Astron., special vol. on M3-Call of ESA's Cosmic Vision 2010; 25 p., 25 figs; see also www.grips-mission.eu