Neutron Capture on the s-Process Branching Point 171^{171}Tm via Time-of-Flight and Activation

The neutron capture cross sections of several unstable nuclides acting as branching points in the s process are crucial for stellar nucleosynthesis studies. The unstable $^{171}$Tm(t$_{1/2}$=1.92 yr) is part of the branching around mass A∼170 but its neutron capture cross section as a function of the neutron energy is not known to date. In this work, following the production for the first time of more than 5 mg of $^{171}$Tm at the high-flux reactor Institut Laue-Langevin in France, a sample was produced at the Paul Scherrer Institute in Switzerland. Two complementary experiments were carried out at the neutron time-of-flight facility (n_TOF) at CERN in Switzerland and at the SARAF liquid lithium target facility at Soreq Nuclear Research Center in Israel by time of flight and activation, respectively. The result of the time-of-flight experiment consists of the first ever set of resonance parameters and the corresponding average resonance parameters, allowing us to make an estimation of the Maxwellian-averaged cross sections (MACS) by extrapolation. The activation measurement provides a direct and more precise measurement of the MACS at 30 keV: 384(40) mb, with which the estimation from the n_TOF data agree at the limit of 1 standard deviation. This value is 2.6 times lower than the JEFF-3.3 and ENDF/B-VIII evaluations, 25% lower than that of the Bao et al. compilation, and 1.6 times larger than the value recommended in the KADoNiS (v1) database, based on the only previous experiment. Our result affects the nucleosynthesis at the A∼170 branching, namely, the $^{171}$Yb abundance increases in the material lost by asymptotic giant branch stars, providing a better match to the available pre-solar SiC grain measurements compared to the calculations based on the current JEFF-3.3 model-based evaluation

The s -process in the Nd-Pm-Sm region: Neutron activation of 147^{147}Pm

International audienceThe Nd-Pm-Sm branching is of interest for the study of the s -process, related to the production of heavy elements in stars. As 148 Sm and 150 Sm are s -only isotopes, the understanding of the branching allows constraining the s -process neutron density. In this context the key physics input needed is the cross section of the three unstable nuclides in the region: 147 Nd (10.98 d half-life), 147 Pm (2.62 yr) and 148 Pm (5.37 d). This paper reports on the activation measurement of 147 Pm, the longest-lived of the three nuclides. The cross section measurement has been carried out by activation at the SARAF LiLiT facility using a 56(2) μg target. Compared to the single previous measurement of 147 Pm, the measurement presented herein benefits from a target 2000 times more massive. The resulting Maxwellian Averaged Cross Section (MACS) to the ground and metastable states in 148 Pm are 469(50) mb and 357(27) mb. These values are 41% higher (to the ground state) and 15% lower (to the metastable state) than the values reported so far, leading however to a total cross section of 826(107) mb consistent within uncertainties with the previous result and hence leaving unchanged the previous calculation of the s -process neutron density

Measurements of fusion reactions of low-intensity radioactive carbon beams on 12C and their implications for the understanding of x-ray bursts

The interaction between neutron-rich nuclei plays an important role for understanding the reaction mechanism of the fusion process as well as for the energy production through pycnonuclear reactions in the crust of neutron stars. We have performed the first measurements of the total fusion cross sections in the systems C10,14,15+C12 using a new active target-detector system. In the energy region accessible with existing radioactive beams, a good agreement between the experimental and theoretical cross sections is observed. This gives confidence in our ability to calculate fusion cross sections for systems which are outside the range of today's radioactive beam facilities.Fil: Carnelli, Patricio Francisco Florencio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; Argentina. Argonne National Laboratory; Estados UnidosFil: Almaraz Calderon, S.. Argonne National Laboratory; Estados UnidosFil: Rehm, K. E.. Argonne National Laboratory; Estados UnidosFil: Albers, M.. Argonne National Laboratory; Estados UnidosFil: Alcorta, M.. Argonne National Laboratory; Estados UnidosFil: Bertone, P. F.. Argonne National Laboratory; Estados UnidosFil: Digiovine, B.. Argonne National Laboratory; Estados UnidosFil: Esbensen, H.. Argonne National Laboratory; Estados UnidosFil: Fernandez Niello, Jorge Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; Argentina. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; ArgentinaFil: Henderson, D.. Argonne National Laboratory; Estados UnidosFil: Jiang, C. L.. Argonne National Laboratory; Estados UnidosFil: Lai, J.. Louisiana State University; Estados UnidosFil: Marley, S. T.. Argonne National Laboratory; Estados UnidosFil: Nusair, O.. Argonne National Laboratory; Estados UnidosFil: Palchan Hazan, T.. Argonne National Laboratory; Estados UnidosFil: Pardo, R. C.. Argonne National Laboratory; Estados UnidosFil: Paul, M.. The Hebrew University of Jerusalem; IsraelFil: Ugalde, C.. Argonne National Laboratory; Estados Unido

A Multi-Sampling Ionization Chamber (MUSIC) for measurements of fusion reactions with radioactive beams

A detection technique for high-efficiency measurements of fusion reactions with low-intensity radioactive beams was developed. The technique is based on a Multi-Sampling Ionization Chamber (MUSIC) operating as an active target and detection system, where the ionization gas acts as both target and counting gas. In this way, we can sample an excitation function in an energy range determined by the gas pressure, without changing the beam energy. The detector provides internal normalization to the incident beam and drastically reduces the measuring time. In a first experiment we tested the performance of the technique by measuring the 10,13,15C+12C fusion reactions at energies around the Coulomb barrier.Fil: Carnelli, Patricio Francisco Florencio. Argonne National Laboratory; Estados Unidos. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia Física (Centro Atómico Constituyentes). Proyecto Tandar; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Almaraz Calderón, S.. Argonne National Laboratory; Estados UnidosFil: Rehm, K. E.. Argonne National Laboratory; Estados UnidosFil: Albers, M.. Argonne National Laboratory; Estados UnidosFil: Alcorta, M.. Argonne National Laboratory; Estados UnidosFil: Bertone, P. F.. Argonne National Laboratory; Estados UnidosFil: Digiovine, B.. Argonne National Laboratory; Estados UnidosFil: Esbensen, H.. Argonne National Laboratory; Estados UnidosFil: Fernandez Niello, Jorge Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia Física (Centro Atómico Constituyentes). Proyecto Tandar; ArgentinaFil: Henderson, D.. Argonne National Laboratory; Estados UnidosFil: Jiang, C. L.. Argonne National Laboratory; Estados UnidosFil: Lai, J.. Argonne National Laboratory; Estados UnidosFil: Marley, S. T.. Argonne National Laboratory; Estados UnidosFil: Nusair, O.. Argonne National Laboratory; Estados UnidosFil: Palchan Hazan, T.. Argonne National Laboratory; Estados UnidosFil: Pardo, R.. Argonne National Laboratory; Estados UnidosFil: Paul, M.. The Hebrew University of Jerusalem; IsraelFil: Ugalde, C.. Argonne National Laboratory; Estados Unido

C+C Fusion Cross Sections Measurements for Nuclear Astrophysics

Total fusion cross section of carbon isotopes were obtained using the newly developed MUSIC detector. MUSIC is a highly efficient, active target-detector system designed to measure fusion excitation functions with radioactive beams. The present measurements are relevant for understanding x-ray superbursts. The results of the first MUSIC campaign as well as the astrophysical implications are presented in this work

C+C Fusion Cross Sections Measurements for Nuclear Astrophysics

Total fusion cross section of carbon isotopes were obtained using the newly developed MUSIC detector. MUSIC is a highly efficient, active target-detector system designed to measure fusion excitation functions with radioactive beams. The present measurements are relevant for understanding x-ray superbursts. The results of the first MUSIC campaign as well as the astrophysical implications are presented in this work