Isospin effects and symmetry energy studies with INDRA

The equation of state of asymmetric nuclear matter is still controversial, as predictions at subsaturation as well as above normal density widely diverge. We discuss several experimental results measured in heavy-ion collisions with the INDRA array in the incident energy range 5-80 MeV/nucleon. In particular an estimate of the density dependence of the symmetry energy is derived from isospin diffusion results compared with a transport code: the potential part of the symmetry energy linearly increases with the density. We demonstrate that isospin equilibrium is reached in mid-central collisions for the two reactions Ni+Au at 52 MeV/nucleon and Xe+Sn at 32 MeV/nucleon. New possible variables and an improved modelization to investigate symmetry energy are discussed.Comment: Review for the special issue of EPJA on symmetry energy. 20 pages, 16 figure

Study of the neutron induced reaction 17O(n,α)14C^{17}O(n,\alpha)^{14}C at astrophysical energies via the Trojan Horse Method

International audienceNeutron induced reactions are fundamental for the nucleosynthesis of elements in the universe. Indeed, to correctly study the reactions involved in the well-known s-process in stars, which produce about half of the elements beyond the iron peak, it is mandatory to know the neutron abundance available in those stars. The 17O(n, a)14C reaction is one of the so-called “neutron poisons” for the pro- cess and it could play an important role in the balance of the neutron abundance. The reaction is therefore investigated in the energy range of astrophysical inter- est between 0 and 350 keV in the center of mass by applying the Trojan Horse Method to the three body reaction 2H(17O, a14C)H

Does the breakup process affect the reaction dynamics for the systems 17O, 17F + 58Ni at Coulomb barrier energies?

The scattering processes of two mirror projectiles, the well bound 17O (Sn = 4.143 MeV) and the loosely bound radioactive 17F (Sp = 0.600 MeV), on the proton closed shell target 58Ni were measured at several energies around the Coulomb barrier. The experimental data were analyzed within the framework of the optical model to extract the reaction cross section and to investigate the role played by direct reaction channels at near-barrier energies. The comparison shows a similar behaviour for the two A = 17 projectiles despite their very different binding energies and suggests a rather small effect of the 17F breakup channel on the reaction dynamics

Decay competition for IMF produced in the collisions 78Kr+40Ca and 86Kr+48Ca at 10 A.MeV

Decay modes of excited compound systems 118Ba and 134Ba, produced respectively in the 78Kr+40Ca and 86Kr+48Ca collisions at 10 A·MeV, are investigated. In particular, the competition between the various disintegration path of medium mass compound nuclei, formed by fusion processes, the production of the so referred Intermediate Mass Fragments (IMF), and the isospin dependence of the decay process are studied. Data were taken at the INFN-Laboratori Nazionali del Sud (LNS) by using the CHIMERA array. Data analysis is in progress; a first indication on the average-energy angular distributions suggests pre-equilibrium effects affecting the data and the presence of isotopical effects

Study of the 12^{12}C +16^{16}O fusion reaction in carbon burning via the Trojan Horse Method

International audience12C +12 C is the main reaction during core and shell carbon burning in massive stars, however, at temperatures higher than 109K when most of the carbon is depleted and its abundance is lower than 16O, the 12C +16 O fusion can also become relevant. Moreover, 12C +16 O reaction can ignite also in the scenario of explosive carbon burning. The astrophysical energy region of interest thus ranges from 3 to 7.2 MeV in the center-of-mass frame. There are various measurements of the cross-section available in the literature, however, they all stop around 4 MeV, making extrapolation necessary at lower energies. To try to solve this uncertainty and corroborate direct measurement the Trojan Horse Method was applied to three-body processes 16O(14N, α24Mg)2H and 16O(14N, p27Al)2H to study the 16O(12C, α)24Mg and 16O(12C, p)27Al reactions

Study of the 12^{12}C + 16^{16}O fusion via the Trojan Horse Method

International audienceThe 12C + 16O fusion reaction plays a role in the later stages of carbon burning, influencing the evolution of both massive stars and Type Ia Supernovae: when most of the carbon is depleted, by the main fusion reaction 12C + 12C, the abundance of 16O nuclei is significantly higher. Therefore 12C + 16O can indeed have a strong impact on the process. In this brief contribution, preliminary data analysis results of a new indirect measurement of the 12C + 16O, performed at astrophysical energies via the Trojan Horse Method, will be presented and discussed

Directionality for nuclear recoils in a Liquid Argon TPC

International audienceDirectional sensitivity to nuclear recoils would provide a smoking gun for a possible discovery of dark matter in the form of WIMPs (Weakly Interacting Massive Particles). A hint of directional dependence of the response of a dual-phase argon Time Projection Chamber (TPC) was found in the SCENE experiment. Given the potential importance of such a capability in the framework of dark matter searches, a new dedicated experiment, ReD (Recoil Directionality), was designed by the Global Argon Dark Matter Collaboration, in order to scrutinise this hint. A small dual-phase argon TPC was irradiated with neutrons produced by the p($^{7}$Li,$^{7}$Be)n reaction using the 15 MV TANDEM accelerator of the INFN - Laboratori Nazionali del Sud, Catania, Italy, so as to produce argon nuclear recoils in the range (20 - 100) keV of interest for dark matter searches. Energy and direction of nuclear recoils are inferred by the detection of the elastically-scattered neutron by a set of scintillation detectors. Events were selected by gating of the associated $^{7}$Be, which is detected by a telescope of Si detectors

Directionality for nuclear recoils in a LAr TPC

International audienceIn the direct searches for Weakly Interacting Massive Particles (WIMPs) as Dark Matter candidates, the sensitivity of the detector to the incom- ing particle direction could provide a smoking gun signature for an interesting event. The SCENE collaboration firstly suggested the possible directional de- pendence of a dual-phase argon Time Projection Chamber through the columnar recombination effect. The Recoil Directionality project (ReD) within the Global Argon Dark Matter Collaboration aims to characterize the light and charge re- sponse of a liquid Argon dual-phase TPC to neutron-induced nuclear recoils to probe for the hint by SCENE. In this work, the directional sensitivity of the de- tector in the energy range of interest for WIMPs (20-100 keV) is investigated with a data-driven analysis involving a Machine Learning algorithm

Constraining explosive nucleosynthesis by indirect reaction methods at storage rings using unstable beams in batch mode

International audienceNuclear reaction studies on unstable isotopes can strongly help in improving our understanding of nucleosynthesis in stars. Indirect approaches to determining astrophysical reaction rates are increasingly common-place and undergoing continuous refinement. Of particular interest is the use of such indirect techniques at storage rings, which, among other aspects, allow to recycle rare unstable beams. We propose to investigate the reaction rates of astrophysical interest using indirect methods (surrogate, Trojan horse, etc.) in reverse kinematics at the IMP-CAS storage ring. Long lived radioactive ion beams, produced remotely, can be accelerated, and made to interact with light targets. The proposed reactions are $^{85}$Kr(p, p’γ), $^{85}$Kr(d, pγ), constraining the neutron flux in an s-process branching point, $^{79}$Se(p, p’γ), $^{79}$Se(d, pγ), constraining the temperature in s-process nucleosyntheses, and $^{59}$Fe(d, pγ), constraining core collapse supernovae