Neutron capture reactions relevant to thesandpprocesses in the region of theN=50shell closure

Abstract

Radiative thermal neutron capture cross sections for nuclei participating in s-process and pprocess nucleosynthesis in and around N = 50 closed neutron shell have been calculated in statistical semi-microscopic Hauser-Feshbach approach for the energy range of astrophysical interest. A folded optical-model potential is constructed utilizing the standard DDM3Y real nucleon-nucleon interaction. The folding of the interaction with target radial matter densities, obtained from the relativistic-mean-field approach, is done in coordinate space using the spherical approximation. The standard nuclear reaction code TALYS1.8 is used for cross-section calculation. The cross sections are compared with experimental results and reasonable agreements are found for almost all cases. Maxwellian-averaged cross sections (MACS) for the nuclei are presented at a single thermal energy of 30 keV relevant to s-process. We have also presented the MACS values over a range of energy from 5 to 100 keV for neutron magic nuclei with (N = 50).PACS numbers: I. INTRODUCTIONElements heavier than iron are produced via two principle processes, namely, the slow neutron capture process (s-process) and the rapid neutron capture process (r-process), differing in the respective neutron capture timescales with respect to the β-decay half-lives. There is a minor contribution from another process, namely, pprocess, producing a subset of proton-rich isotopes. The detailed study of the heavy element nucleosynthesis was done in the fundamental work of Burbidge et al. [1] and also of Cameron [2]. Recently Käppeler et al. [3] presented a review of progress on the studies of s-process nucleosynthesis with advanced nuclear physics inputs, observational data, and stellar models.While the majority of the theory of the s-process is well-developed, uncertainty still remains in constraining the neutron capture rates of nuclei involved in nucleosynthesis chain. The capture cross sections are highly scattered and uncertain in the energy range appropriate for astrophysical applications. These uncertainties lead to significant errors in determining exact abundances of elements involved in different processes. Many works * Electronic address: saumidutta89@gmail.com † Electronic address: ggphy@caluniv.ac.in ‡ Electronic address: abhattacharyyacu@gmail.com have been devoted to this respect in order to measure the thermal neutron capture cross sections relevant to s-process temperature. However, reactions on some important nuclei are still not available due to their unavailability in the terrestrial laboratory. Käppeler et al. [4] showed the present status of the uncertainty of stellar (n, γ) cross sections and commented that improvements are certainly necessary especially in the mass region below A=120 and above A=180. Some reactions are of significant importance, basically those with closed neutron shells acting as bottlenecks to the s-process reaction flow. They have very low cross-sections and in some scenarios, the s-process reaction flow cannot overcome these bottlen...

Microscopic folding model analysis of the radiative(n,γ)reactions near theZ=28shell closure and the weaksprocess

“…Two potentials give different results for cross section values. Our microscopic potential has also been found to predict results different from JLM potential in our earlier studies near the N = 82 and the N = 50 closed neutron core [9,10]. This suggests that the statistical model calculation of (n, γ) cross sections are indeed sensitive to the neutron optical potential.…”

“…3 -7 and from presented values in table II that the cross sections can be reasonably described with unnormalized potential depths. This was also the case in our previous studies [9,10]. Moreover, it is convenient to establish a uniquely parameterized potential model instead of individual fit as it can reflect a more general and global behavior.…”

“…Experiments are not possible at all energies and hence, theoretical extrapolations are evidently needed. In our earlier studies, this theory was found to be successful in the study of the neutron capture reactions for several nuclei those take part in heavy element nucleosynthesis near the N = 82 as well as the N = 50 shell closures [9,10]. Some more details on theoretical description can also be available there.…”

Importance of α-induced reactions and the inverse (γ,α) process on p-nuclei

“…Similar calculations had been implemented successfully to calculate single folded potentials (proton-nucleus potential, neutron-nucleus potential etc.) in our earlier works [8,9,10,11] and in Dutta et al [12].…”

“…In the present work we have employed the FSU Gold Lagrangian density [16] to calculate the density distribution ρ( r 2 ) . This set of parameters have been successfully used in earlier works where semi-microscopic optical potential for proton-nucleus [8,9,10,11] and neutron-nucleus [12] was calculated using single folding method.…”