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Öğe Nuclear structure properties and stellar weak rates for Se-76: Unblocking of the Gamow Teller strength(Elsevier Science Bv, 2017) Nabi, Jameel-Un; Ishfaq, Mavra; Boyukata, Mahmut; Riaz, MuhammadAt finite temperatures (>= 10(7)K), Se-76 is abundant in the core of massive stars and electron capture on Se-76 has a consequential role to play in the dynamics of core-collapse. The present work may be classified into two main categories. In the first phase we study the nuclear structure properties of Se-76 using the interacting boson model-1 (IBM-1). The IBM-1 investigations include the energy levels, B (E2) values and the prediction of the geometry. We performed the extended consistent-Q formalism (ECQF) calculation and later the triaxial formalism calculation (constructed by adding the cubic term to the ECQF). The geometry of Se-76 can be envisioned within the formalism of the potential energy surface based on the classical limit of IBM-1 model. In the second phase, we reconfirm the unblocking of the Gamow Teller (GT) strength in Se-76 (a test case for nuclei having N > 40 and Z < 40). Using the deformed pn-QRPA model we calculate GT transitions, stellar electron capture cross section (within the limit of low momentum transfer) and stellar weak rates for Se-76. The distinguishing feature of our calculation is a state-by-state evaluation of stellar weak rates in a fully microscopic fashion. Results are compared with experimental data and previous calculations. The calculated GT distribution fulfills the Ikeda sum rule. Rates for, beta-delayed neutrons and emission probabilities are also calculated. Our study suggests that at high stellar temperatures and low densities, the beta(+)-decay on Se-76 should not be neglected and needs to be taken into consideration along with electron capture rates for simulation of presupernova evolution of massive stars. (C) 2017 Elsevier B.V. All rights reserved.Öğe Nuclear structure properties and weak interaction rates of even-even Fe isotopes(Elsevier, 2024) Nabi, Jameel-Un; Boyukata, Mahmut; Ullah, Asim; Riaz, MuhammadNuclear structure properties and weak interaction rates of neutron -rich even-even iron (Fe) isotopes (A = 50 - 70) are investigated using the Interacting Boson Model -1 (IBM -1) and the proton-neutron Quasiparticle Random Phase Approximation (pn-QRPA) model. The IBM -1 is used for the calculation of energy levels and the B(E2) values of neutron -rich Fe isotopes. Later their geometry was predicted within the potential energy formalism of the IBM -1 model. Weak interaction rates on neutron -rich nuclei are needed for the modeling and simulation of presupernova evolution of massive stars. In the current study, we investigate the possible effect of nuclear deformation on stellar rates of even-even Fe isotopes. The pn-QRPA model is applied to calculate the weak interaction rates of selected Fe isotopes using three different values of deformation parameter. It is noted that, in general, bigger deformation values led to smaller total strength and larger centroid values of the resulting Gamow-Teller distributions. This later translated to smaller computed weak interaction rates. The current finding warrants further investigation before it may be generalized. The reported stellar rates are up to 4 orders of magnitude smaller than previous calculations and may bear astrophysical significance.Öğe Nuclear structure properties of even-even chromium isotopes and the effect of deformation on calculated electron capture cross sections(ELSEVIER, 2020) Nabi, Jameel-Un; Boyukata, Mahmut; Ullah, Asim; Riaz, MuhammadIn this study, we investigate the role of the nuclear deformation on the calculated electron capture cross section (ECC) of even-even chromium (Cr) isotopes. We first determined the nuclear structure properties of these nuclei within the interacting boson model-1 (IBM-1). The energy spectra and E2 transition probabilities were calculated by fitting the parameters in the model formalism. The analysis of the potential energy surface were also performed to predict the geometric shape of the Cr nuclei by plotting their contour plot in the plane of (beta, gamma ) deformation parameters. Later, we calculated the ECC within the proton-neutron quasiparticle random phase approximation (pn-QRPA) model. In particular we studied how the calculated ECC changed with different values of nuclear deformation parameter. The calculated Gamow-Teller (GT) strength distributions were widely spread among the daughter states. The total GT strength decreased with increasing value of the beta parameter. The computed ECC values, however, increased with increase in the beta value of the Cr isotopes. (c) 2020 Elsevier B.V. All rights reserved.Öğe Re-examination of β-decay in Hg, Pb and PoIsotopes(Iop Publishing Ltd, 2023) Nabi, Jameel-Un; Bayram, Tuncay; Riaz, Muhammad; Ullah, Asim; Hayder, Anes; Şentürk, Şevki; Böyükata, MahmutThis study re-examines the effect of nuclear deformation on the calculated Gamow-Teller (GT) strength distributions of neutron-deficient (Hg178-192, Pb185-194 and Po196-206) nuclei. The nuclear ground state properties and shape parameters were calculated using the Relativistic Mean Field model. Three different density-dependent interactions ((DC)-C-3, DD-ME2 and DD-PC1) were used in the calculation. Estimated shape parameters were later used within the framework of deformed proton-neutron quasi-random phase approximations model, with a separable interaction, to calculate the GT strength distributions, half-lives and branching ratios for these neutron-deficient isotopes. It was concluded that half-lives and GT strength distributions vary considerably with change in shape parameter.
