Browsing by Subject "FP-SHELL"

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    Investigation of Gamow Teller transition properties in 56-64Ni isotopes using QRPA methods
    (ELSEVIER SCIENCE BV) Cakmak, S; Nabi, JU; Babacan, T
    Weak rates in nickel isotopes play an integral role in the dynamics of supernovae. Electron capture and beta-decay of nickel isotopes, dictated by Gamow-Teller transitions, significantly alter the lepton fraction of the stellar matter. In this paper we calculate Gamow-Teller (GT) transitions for isotopes of nickel, Ni56-64, using QRPA methods. The GT strength distributions were calculated using four different QRPA models. Our results are also compared with previous theoretical calculations and measured strength distributions wherever available. Our investigation concluded that amongst all RPA models, the pn-QRPA(C) model best described the measured GT distributions (including total GT strength and centroid placement). It is hoped that the current investigation of GT properties would prove handy and may lead to a better understanding of the presupernova evolution of massive stars. (C) 2017 Elsevier B.V. All rights reserved.
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    Study of Gamow-Teller transitions in isotopes of titanium within the quasi particle random phase approximation
    (SPRINGER) Cakmak, S; Nabi, JU; Babacan, T; Selam, C
    The Gamow-Teller (GT) transition is inarguably one of the most important nuclear weak transitions of the spin-isospin sigma tau type. It has many applications in nuclear and astrophysics. These include, but are not limited to, r-process beta-decays, stellar electron captures, neutrino cooling rates, neutrino absorption and inelastic scattering on nuclei. The quasiparticle random phase approximation (QRPA) is an efficient way to generate GT strength distribution. In order to better understand both theoretical systematics and uncertainties, we compare the GT strength distributions, centroid and width calculations for isotopes, using the pn-QRPA, Pyatov method (PM) and the Schematic model (SM). The pn-QRPA and SM are further sub-divided into three categories in order to highlight the role of particle-particle (pp) force and deformation of the nucleus in the GT strength calculations. In PM, we study only the influence of the pp force in the calculation. We also compare with experimental results and other calculations where available. We found that the inclusion of pp force and deformation significantly improves the performance of SM and pn-QRPA models. Incorporation of pp force leads to pinning down the centroid value in the PM. The calculated GT strength functions using the pn-QRPA (C) and SM (C) models are in reasonable agreement with measured data.
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    Spin-isospin transitions in chromium isotopes within the quasiparticle random phase approximation
    (ELSEVIER SCI LTD) Cakmak, S; Nabi, JU; Babacan, T; Maras, I
    Beta decay and electron capture on isotopes of chromium are advocated to play a key role in the stellar evolution process. In this paper we endeavor to study charge-changing transitions for 24 isotopes of chromium (Cr42-65). These include neutron-rich and neutron-deficient isotopes of chromium. Three different models from the QRPA genre, namely the pn-QRPA, the Pyatov method (PM) and the Schematic model (SM), were selected to calculate and study the Gamow Teller (GT) transitions in chromium isotopes. The SM was employed separately in the particle particle (pp) and pp + particle-hole (ph) channels. To study the effect of deformation, the SM was first used assuming the nuclei to be spherical and later to be deformed. The PM was used both in pp and pp + ph channels but only for the case of spherical nuclei. The pn-QRPA calculation was done by considering both pp and ph forces and taking deformation of nucleus into consideration. A recent study proved this version of pn-QRPA to be the best for calculation of GT strength distributions amongst the QRPA models. The pn-QRPA model calculated GT distributions had low-lying centroids and small widths as compared to other QRPA models. Our calculation results were also compared with other theoretical models and measurements wherever available. Our results are in decent agreement with previous measurements and shell model calculations. (C) 2014 COSPAR. Published by Elsevier Ltd. All rights reserved.