Search

3He(d,γ)5Li is important in the Big Bang Nucleosynthesis (BBN), as it provides seeds for the 6Li formation. Within the framework of the potential model the 3He(d,γ)5Li is analyzed. In the present investigation the nuclear width , nuclear cross-sections, astrophysical S-factor, and nuclear reaction rates have been computed. The present study is in better agreement with the observed data.

Reliable and precise knowledge of the β-decay properties of neutron-rich nuclei is important for a better understanding of the r-process. We report the computation of β-decay properties of neutron-rich Cerium isotopes calculated within the proton-neutron quasiparticle random phase approximation (pn-QRPA) approach. A total of 34 isotopes of Ce in the mass range 120 ≤ A ≤ 157 were considered in our calculation. Pairing gaps are recognized amongst the key parameters in the pn-QRPA model to compute Gamow-Teller (GT) transitions. We employed two different values of the pairing gaps obtained from two different empirical formulae in our computation. The GT strength distributions changed considerably with a change in the pairing gap values. This in turn resulted in contrasting centroid and total strength values of the GT distributions and led to differences in calculated half-lives using the two schemes. The traditional pairing gaps resulted in significant fragmentation of GT strength. However, the pairing gaps, calculated employing the formula based on separation energies of neutron and proton, led to computed half-lives in better agreement with the measured data.

β-decay is amongst the key properties of nuclei required for the modeling of r-process nucleosynthesis. It also governs the flow of abundances among neighboring isotopic chains of high-mass elements. In the present work, a simple proton-neutron quasi particle random phase approximation (p–n-QRPA) model has been used for the calculation of β-decay half-lives of Rb, Sr, Y and Zr neutron-rich isotopes. For 97−103Rb, 98−107Sr, 101−109Y and 104−112Zr, where the experimental data were available, the half-life values are reproduced with reasonable accuracy. The same set of model parameters are later used to predict half-lives for few neutron-rich nuclei (104−112Rb, 108−113Sr, 110−114Y and 113−115Zr) where measured data is not available. The p–n-QRPA results (including only allowed transitions) are compared with previous calculations (allowed plus forbidden) and exhibit agreement within a factor of 2.0 when compared with the recent available experimental data.

Recently a list of top 50 most important electron capture (ec) and β-decay (bd) nuclei, averaged throughout the stellar trajectory for 0.500 > Y e > 0.400, was published. The current study presents the calculation of ec and bd rates, from the published list with A = 65–80, on a detailed temperature-density grid. The ec and bd rates were calculated using the proton-neutron quasiparticle random phase approximation model (pn-QRPA). Our calculation did not employ the Brink-Axel hypothesis. A systematic comparison of the current calculation with the previous pn-QRPA and independent particle model (IPM) results is presented for the first time. The reported ec rates are almost the same when compared with the previous pn-QRPA calculation. On the other hand, the reported bd rates are generally smaller up to an order of magnitude. Comparison with IPM results show that our calculated rates are bigger, by two orders of magnitude. The current calculation may contribute to a more realistic simulation of late phases of stellar evolution and modeling of x-ray bursts.

The proton radiative capture reactions are crucial in nuclear astrophysics. 9Be(p,γ)10B is important in stellar and primordial nucleosynthesis. In the present work, we compute the astrophysical S-factor for 9Be(p,γ)10B by employing the potential model (PM) for the magnetic transitions. Moreover, we revised the nuclear structure features and spectroscopic properties of the 10B nucleus under the PM approach.

Within the framework of the modified potential model, we computed the astrophysical S-factor of the proton radiative capture p + 11C → 12N + γ. At energies bearing astrophysical importance, radiative capture is a key process in the spectroscopic study of 12N. In this work, we consider the radiative capture cross-section for the proton capture by 11C within the framework of the potential model. For the possible electric and magnetic dipole transitions, we computed the partial components of the astrophysical S-factor within the energy range E = (0.01–0.8) MeV. The computed value of the S-factor at zero energy shows satisfactory agreement with the reported results. Furthermore, we computed the radiative capture rates for the selected reaction, which shows a better comparison with the reported data.

We explore the effectiveness of the Brink–Axel hypothesis (BAH) for the computation of stellar electron capture (EC) and β-decay (BD) rates, namely that the transition strength function depends only upon the transition energy and not upon the details of the initial state. For this purpose, we calculated Gamow–Teller (GT) strength distributions for a selection of sd-shell nuclides, using two different microscopic models, namely the proton–neutron quasiparticle random phase approximation and the full configuration-interaction shell model, taking into account the first 100 states of both the initial and final nuclides. The GT transition strengths among these levels evolve with initial state energy. These transition strength functions we folded into weak-interaction mediated rates in stellar matter, specifically EC and BD rates, for a range of densities 10 g cm−3 ⩽ ρ ⩽ 1011 g cm−3 and range of temperatures 1 GK ⩽ T ⩽ 30 GK. When transitions from excited states were approximated using the BAH, augmented by so-called ‘back-resonance’ transitions, the rates were affected by up to three orders of magnitude or more at high temperatures and densities. Thus the BAH is not a reliable approximation for the calculation of stellar rates, especially in high temperature–density environments.

Radiative capture p + 9Be → 10B + γ at energies bearing astrophysical importance is a key process for the spectroscopic study of 10B. In this work, we consider the radiative capture cross-section for the 9Be(p, γ)10B within the framework of the potential model and the R-matrix method for the multi-entrance channel cases. In certain cases, when the potential fails, therefore, the R-matrix approach is better to use for the description of partial components of the cross-section that have sharp or broad resonances. For all possible electric and magnetic dipole transitions, partial components of the astrophysical S-factor are computed. The computed value of the total S-factor at zero energy is consistent with the reported results.

Radiative capture p + 13N → 14O + γ at energies bearing astrophysical importance is one of the key processes in the hot CNO cycle. The transition from normal CNO to hot CNO takes place when the proton capture rates on 13N are higher than the β decay rates of 13N. The hot CNO cycle initiates at stellar temperature T ≥ 0.11 ×109 K. Within the frame work of potential model, we calculate the nuclear reaction rates and astrophysical S-factor for the reaction 13N(p, γ)14O. It is to be noted that the nuclear cross-section is calculated for the first resonance of p–13N system within the proton energy range (0–1) MeV, where the E1 transition plays a dominant role. Our calculated radiative capture rates are in nice comparison with the existing data. Based on the radiative capture rates we further estimate the temperature at which the normal CNO turns into a hot CNO cycle

Rates for (anti-)neutrino energy loss on nickel isotopes, due to interactions involving weak decays (β±-decay and lepton captures) are regarded as having fundamental importance during late evolutionary stages of massive stars. These rates substantially affect the leptonic ratio (Ye) of stellar interior. For the densities less than 1011 g/cm3, weak processes produce (anti-)neutrinos which cause reduction in the stellar core’s entropy. In this paper, rates for neutrino and anti-neutrino energy loss on nickel neutron-rich isotopes (66-71Ni) have been presented. Rates for energy loss have been determined by applying the deformed pn-QRPA model. The ranges for temperature and density, have been used to determine the rates, are from 0.01 to 30 (109 K) and 101 to 1011 (g/cm3), respectively. Our computed rates for energy loss, at higher temperature regions, are enhanced in comparison with previously reported rates of Pruet and Fuller (PF).

Radiative capture p + 13C → 14N + γ at energies of astrophysical interest is one of the important process in the CNO cycle. We focus the reader’s attention on the possibility of describing this reaction within the framework of a single-particle potential model even when the reaction has a resonant characteristic. The partial components of the astrophysical S-factor are calculated for electric dipole transition. The calculated value of S-factor is in good agreement with experimental data both at low and high energy from the resonance position.

We calculate the temperature-dependent nuclear partition functions (TDNPFs) and nuclear abundances for 728 nuclei, assuming nuclear statistical equilibrium (NSE). The theories of stellar evolution support NSE. Discrete nuclear energy levels have been calculated microscopically, using the pn-QRPA theory, up to an excitation energy of 10 MeV in the calculation of the TDNPFs. This feature of our paper distinguishes it from previous calculations. Experimental data is also incorporated wherever available to ensure the reliability of our results. Beyond 10 MeV, we employ a simple Fermi gas model and perform integration over the nuclear level densities to approximate the TDNPFs. We calculate nuclidic abundances, using the Saha equation, as a function of three parameters: stellar density, stellar temperature and the lepton-to-baryon content of stellar matter. All these physical parameters are considered to be extremely important in the stellar interior. The results obtained in this paper show that the equilibrium configuration of nuclei remains unaltered by increasing the stellar density (only the calculated nuclear abundances increase by roughly the same order of magnitude). Increasing the stellar temperature smoothes the equilibrium configuration showing peaks at the neutron-number magic nuclei.

From the modeling and simulation results of presupernova evolution of massive stars, it was found that isotopes of iron, $^{54,55,56}$Fe, play a significant role inside the stellar cores, primarily decreasing the electron-to-baryon ratio ($Y_{e}$) mainly via electron capture processes thereby reducing the pressure support. The neutrinos produced, as a result of these capture processes, are transparent to the stellar matter and assist in cooling the core thereby reducing the entropy. The structure of the presupernova star is altered both by the changes in $Y_{e}$ and the entropy of the core material. Here we present the microscopic calculation of Gamow-Teller strength distributions for isotopes of iron. The calculation is also compared with other theoretical models and experimental data. Presented also are stellar electron capture rates and associated neutrino cooling rates, due to isotopes of iron, in a form suitable for simulation and modeling codes. It is hoped that the nuclear inputs presented here should assist core-collapse simulators in the process of fine-tuning of the $Y_{e}$ parameter during various phases of presupernova evolution of massive stars. A reliable and accurate time evolution of this parameter is a possible key to generate a successful explosion in modeling of core-collapse supernovae., 17 pages, 6 figures and 5 tables

The result of the experiment performed to measure the solar neutrino flux at one AU produced by the reaction (pep) was announced for the first time in 2012 by the Borexino collaboration. This neutrino flux was significantly greater than the flux predicted by Bahcall and May, who used two-body approaches for the calculation of this reaction. We have used the three-body model for the proton-proton-electron system in the continuous spectrum of energy to determine the rate of the pep reaction, and have estimated the neutrino flux. Our result for the neutrino flux is 25–40% more than the value predicted by Bachall et al and depends on the shape of the nucleon–nucleon (N N) potential. Moreover, the calculated flux lies within the confidence interval of the experimental data in the case of purely attractive potentials as well as when the potential is repulsive at small distances between nucleons.