Stellar neutron capture cross sections of ⁴¹K and ⁴⁵Sc

The neutron capture cross sections of light nuclei (

Stellar (n,γ) cross sections of ²³Na

The cross section of the ²³Na(n,γ)²⁴Na reaction has been measured via the activation method at the Karlsruhe 3.7 MV Van de Graaff accelerator. NaCl samples were exposed to quasistellar neutron spectra at kT = 5.1 and 25 keV produced via the ¹⁸O(p,n)¹⁸F and ⁷Li(p,n)⁷Be reactions, respectively. The derived capture cross sections (σ)kT=5keV = 9.1 ± 0.3mb and (σ)kT=25keV = 2.03 ± 0.05 mb are significantly lower than reported in literature. These results were used to substantially revise the radiative width of the first ²³Na resonance and to establish an improved set of Maxwellian average cross sections. The implications of the lower capture cross section for current models of s-process nucleosynthesis are discussed

Stellar neutron capture cross sections of ²⁰ ²¹ ²²Ne

The stellar (n,γ) cross sections of the Ne isotopes are important for a number of astrophysical quests, i.e., for the interpretation of abundance patterns in presolar material or with respect to the s-process neutron balance in red giant stars. This paper presents resonance studies of experimental data in the keV range, which had not been fully analyzed before. The analyses were carried out with the R-matrix code sammy. With these results for the resonant part and by adding the components due to direct radiative capture, improved Maxwellian-averaged cross sections (MACS) could be determined. At kT=30keV thermal energy we obtain MACS values of 240±29,1263±160, and 53.2±2.7 μbarn for ²⁰Ne,²¹Ne, and ²²Ne, respectively. In earlier work the stellar rates of ²⁰Ne and ²¹Ne had been grossly overestimated. ²²Ne and ²⁰Ne are significant neutron poisons for the s process in stars because their very small MACS values are compensated by their large abundances

Direct radiative capture of p-wave neutrons

The neutron direct radiative capture (DRC) process is investigated, highlighting the role of incident p-wave neutrons. A set of calculations is shown for the 12-C(n,gamma) process at incoming neutron energies up to 500 keV, a crucial region for astrophysics. The cross section for neutron capture leading to loosely bound s, p and d orbits of 13-C is well reproduced by the DRC model demonstrating the feasibility of using this reaction channel to study the properties of nuclear wave functions on and outside the nuclear surface. A sensitivity analysis of the results on the neutron-nucleus interaction is performed for incident s- as well as p-waves. It turned out that the DRC cross section for p-wave neutrons is insensitive to this interaction, contrary to the case of incident s-wave neutrons. PACS number(s): 25.40Lw,21.10Gv,23.40.HcComment: 16 pages, REVTeX file, PostScript file, .dvi fil

Search for the γ decay of the narrow near-threshold proton resonance in 11B

The γ decay of the elusive narrow, near-threshold proton resonance in 11B was investigated at Laboratori Nazionali di Legnaro (INFN) in a particle-γ coincidence experiment, using the 6Li(6Li,pγ) fusion-evaporation reaction and the GALILEO-GALTRACE setup. No clear signature was found for a possible E1 decay to the 1/2 , first-excited state of 11B, predicted by the Shell Model Embedded in the Continuum (SMEC) with a branching of with respect to the dominant particle-decaying modes. The statistical analysis of the γ-ray spectrum provided an average upper limit of for this γ-ray branching, with a global significance of 5σ. On the other hand, by imposing a global confidence level of 3σ, a significant excess of counts was observed for E keV, corresponding to a resonance energy of 11429(20) keV (namely 200(20) keV above the proton separation energy of 11B) and a γ-ray branching of . This result is compatible with the SMEC calculations, potentially supporting the existence of a near-threshold proton resonance in 11B.This work was supported by the Italian Istituto Nazionale di Fisica Nucleare, the Polish National Science Centre, Poland under research project No. 2020/39/D/ST2/03443 , the PRIN2017 call for funding, under the project 2017P8KMFT CTADIR from the Italian Ministry of Education, University and Research, the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, grant no. 2020R1A6A3A03039081 , the MCIN/AEI/10.13039/501100011033, Spain with grant PID2020-118265GB-C42 , by Generalitat Valenciana, Spain with grant CIAPOS/2021/114 and by the EU FEDER funds.Departamento de Física Aplicad

Level density and gamma strength function in 162-Dy from inelastic 3-He scattering

Complementary measurements have been performed for the level density and gamma strength function in 162-Dy using inelastic 3-He scattering. Comparing these results to previous measurements using the 163-Dy(3-He,alpha) reaction, reveals that the measured quantities above 1.5 MeV do not depend significantly on the nuclear reaction chosen.Comment: 15 pages, including 7 figure

The 14C(n,g) cross section between 10 keV and 1 MeV

The neutron capture cross section of 14C is of relevance for several nucleosynthesis scenarios such as inhomogeneous Big Bang models, neutron induced CNO cycles, and neutrino driven wind models for the r process. The 14C(n,g) reaction is also important for the validation of the Coulomb dissociation method, where the (n,g) cross section can be indirectly obtained via the time-reversed process. So far, the example of 14C is the only case with neutrons where both, direct measurement and indirect Coulomb dissociation, have been applied. Unfortunately, the interpretation is obscured by discrepancies between several experiments and theory. Therefore, we report on new direct measurements of the 14C(n,g) reaction with neutron energies ranging from 20 to 800 keV

Role and regulation of ACC deaminase gene in Sinorhizobium meliloti: Is it a symbiotic, rhizospheric or endophytic gene?

Plant-associated bacteria exhibit a number of different strategies and specific genes allow bacteria to communicate and metabolically interact with plant tissues. Among the genes found in the genomes of plant-associated bacteria, the gene encoding the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase (acdS) is one of the most diffused. This gene is supposed to be involved in the cleaving of plant-produced ACC, the precursor of the plant stress-hormone ethylene toning down the plant response to infection. However, few reports are present on the actual role in rhizobia, one of the most investigated groups of plant-associated bacteria. In particular, still unclear is the origin and the role of acdS in symbiotic competitiveness and on the selective benefit it may confer to plant symbiotic rhizobia. Here we present a phylogenetic and functional analysis of acdS orthologs in the rhizobium model-species Sinorhizobium meliloti. Results showed that acdS orthologs present in S. meliloti pangenome have polyphyletic origin and likely spread through horizontal gene transfer, mediated by mobile genetic elements. When acdS ortholog from AK83 strain was cloned and assayed in S. meliloti 1021 (lacking acdS), no modulation of plant ethylene levels was detected, as well as no increase in fitness for nodule occupancy was found in the acdS-derivative strain compared to the parental one. Surprisingly, AcdS was shown to confer the ability to utilize formamide and some dipeptides as sole nitrogen source. Finally, acdS was shown to be negatively regulated by a putative leucine-responsive regulator (LrpL) located upstream to acdS sequence (acdR). acdS expression was induced by root exudates of both legumes and non-leguminous plants. We conclude that acdS in S. meliloti is not directly related to symbiotic interaction, but it could likely be involved in the rhizospheric colonization or in the endophytic behavior

Design study for a new spallation target of the n_TOF facility at CERN

The n_TOF facility is a time of flight spectrometer dedicated to measuring neutron capture and fission cross sections. The neutron source consists on a lead target bombarded by a high energetic proton beam. After finishing a successful period of data taking by the end of 2004, it has been decided to upgrade the neutron spallation source with a cladded target. In this study, Monte Carlo simulations are reported for the assessment and comparison of the neutron and gamma fluxes from different target configurations. In addition, the plans for a second vertical measuring station with a flight path of 20 m above the spallation target have been considered in the simulations as well. Results for the energy deposition and the target heating are also presented

Identification and rejection of scattered neutrons in AGATA

Gamma rays and neutrons, emitted following spontaneous fission of 252Cf, were measured in an AGATA experiment performed at INFN Laboratori Nazionali di Legnaro in Italy. The setup consisted of four AGATA triple cluster detectors (12 36-fold segmented high-purity germanium crystals), placed at a distance of 50 cm from the source, and 16 HELENA BaF2 detectors. The aim of the experiment was to study the interaction of neutrons in the segmented high-purity germanium detectors of AGATA and to investigate the possibility to discriminate neutrons and gamma rays with the gamma-ray tracking technique. The BaF2 detectors were used for a time-of-flight measurement, which gave an independent discrimination of neutrons and gamma rays and which was used to optimise the gamma-ray tracking-based neutron rejection methods. It was found that standard gamma-ray tracking, without any additional neutron rejection features, eliminates effectively most of the interaction points due to recoiling Ge nuclei after elastic scattering of neutrons. Standard tracking rejects also a significant amount of the events due to inelastic scattering of neutrons in the germanium crystals. Further enhancements of the neutron rejection was obtained by setting conditions on the following quantities, which were evaluated for each event by the tracking algorithm: energy of the first and second interaction point, difference in the calculated incoming direction of the gamma ray, figure-of-merit value. The experimental results of tracking with neutron rejection agree rather well with Geant4 simulations