Yazar "Nabi, Jameel-Un" seçeneğine göre listele

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    Allowed and forbidden ?-decay log ft values of neutron-rich Pb and Bi isotopes
    (Springer, 2024) Cakmak, Necla; Nabi, Jameel-Un; Mehmood, Arslan; Ullah, Asim; Tahir, Rubba
    The beta-decay log ft values for Pb210-215 -> Bi210-215 and Bi210-215 -> Po210-215 transitions in the north-east region of Pb-208 nuclei are estimated using the proton-neutron quasiparticle random phase approximation (pn-QRPA) model. The pn-QRPA equations were solved using the schematic model approach. The Woods-Saxon (WS) potential was inserted as a mean-field basis and nuclei were treated as spherical. Allowed Gamow-Teller (GT) and first-forbidden (FF) transitions were investigated in the particle-hole (ph) channel. The calculated log ft values of the allowed GT and FF transitions using the pn-QRPA model with WS potential were found closer to the experimental values. Later we performed calculation of beta-decay rates in stellar environment. Here we solved the random phase approximation (RPA) equations in deformed Nilsson basis, both in the particle-particle (pp) and particle-hole (ph) channels. Allowed beta-decay and unique first-forbidden (U1F) rates were calculated in stellar matter. For certain cases, the calculated U1F contribution was much more than the allowed beta-decay rates under prevailing stellar conditions, in line with previous findings. Increasing temperature of the stellar core affected the allowed GT rates more than the U1F rates.
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    ?-decay of N=126 isotones for the r-process nucleosynthesis
    (Iop Publishing Ltd, 2021) Nabi, Jameel-Un; Cakmak, Necla; Ullah, Asim; Ullah Khan, Asad
    The beta-decay properties of nuclei with neutron number N = 126 is investigated in this paper. Two different versions of the proton-neutron quasi particle random phase (pn-QRPA) model were employed to compute beta-decay rates and half-lives for the N = 126 isotones. The first set of calculation solves the pn-QRPA equations using the schematic model (SM) approach. The Woods-Saxon potential was employed as a mean-field basis. A spherical shape assigned for each waiting point nuclei throughout all simulations. Both allowed Gamow-Teller (GT) and first-forbidden (FF) transitions were considered in the particle-hole (ph) channel. The second set uses the pn-QRPA model in deformed Nilsson basis to calculate beta-decay rates for allowed GT and unique first-forbidden (U1F) transitions under terrestrial and stellar conditions. Our results are in agreement with shell model findings that first-forbidden transitions lead to a considerable decrement in the calculated half-lives of the isotones. Inclusion of the first-forbidden contribution led to a decent agreement of our computed terrestrial beta-decay half-lives with measured ones, much better than the previous calculations. The possible implication of the waiting point nuclei on r-process nucleosynthesis is discussed briefly.
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    First-forbidden ?-decay rates, energy rates of ?-delayed neutrons and probability of ?-delayed neutron emissions for neutron-rich nickel isotopes
    (Springer, 2016) Nabi, Jameel-Un; Cakmak, Necla; Iftikhar, Zafar
    First-forbidden (FF) transitions can play an important role in decreasing the calculated half-lives specially in environments where allowed Gamow-Teller (GT) transitions are unfavored. Of special mention is the case of neutron-rich nuclei where, due to phase-space amplification, FF transitions are much favored. We calculate the allowed GT transitions in various pn-QRPA models for even-even neutron-rich isotopes of nickel. Here we also study the effect of deformation on the calculated GT strengths. The FF transitions for even-even neutron-rich isotopes of nickel are calculated assuming the nuclei to be spherical. Later we take into account deformation of nuclei and calculate GT + unique FF transitions, stellar beta-decay rates, energy rate of beta-delayed neutrons and probability of beta-delayed neutron emissions. The calculated half-lives are in excellent agreement with measured ones and might contribute in speeding-up of the r-matter flow.
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    First-forbidden transitions and stellar ?-decay rates of Zn and Ge isotopes
    (Iop Publishing Ltd, 2015) Nabi, Jameel-Un; Cakmak, Necla; Stoica, Sabin; Iftikhar, Zafar
    First-forbidden (FF) charge-changing transitions become relatively important for nuclei as their proton number increases. This is because the strength of allowed Gamow-Teller (GT) transitions decreases with increasing Z. The FF transitions play an important role in reducing the half-lives compared to those calculated from taking the GT transitions alone into account. In this paper we calculate allowed GT as well as 0(+) -> 0(-) and 0(+) -> 2(-) transitions for neutron-rich Zn and Ge isotopes. Two different pn-QRPA models were used with a schematic separable interaction to calculate GT and FF transitions. Half-lives calculated after inclusion of FF transitions were in excellent agreement with the experimental data. Our calculations were also compared to previous QRPA calculations and were found to be in better agreement with measured data. Stellar beta-decay rates were calculated for these nuclei including allowed GT and unique FF transitions for astrophysical applications. Ge-86,Ge-88 has a sizeable contribution to the total stellar rate from unique FF transitions.
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    Unique first-forbidden ?-decay transitions in odd-odd and even-even heavy nuclei
    (Elsevier Science Bv, 2017) Nabi, Jameel-Un; Cakmak, Necla; Majid, Muhammad; Selam, Cevad
    The allowed Gamow Teller (GT) transitions are the most common weak nuclear processes of spin-isospin (sigma tau) type. These transitions play a key role in numerous processes in the domain of nuclear physics. Equally important is their contribution in astrophysics, particularly in nuclear synthesis and supernova explosions. In situations where allowed GT transitions are not favored, first-forbidden transitions become significant, specifically in medium heavy and heavy nuclei. For neutron-rich nuclei, first-forbidden transitions are favored mainly due to the phase-space amplification for these transitions. In this work we calculate the allowed GT as well as unique first-forbidden (U1F) vertical bar Delta J vertical bar = 2 transitions strength in odd odd and even-even nuclei in mass range 70 <= A <= 214. Two different pn-QRPA models were used with a schematic separable interaction to calculate GT and U1F transitions. The inclusion of U1F strength improved the overall comparison of calculated terrestrial beta-decay half-lives in both models. The ft values and reduced transition probabilities for the 2- <-> 0(+) transitions were also calculated. We compared our calculations with the previously reported correlated RPA calculation and experimental results. Our calculations are in better agreement with measured data. For stellar applications we further calculated the allowed GT and U1F weak rates. These include beta(+/-)-decay rates and electron/positron capture rates of heavy nuclei in stellar matter. Our study shows that positron and electron capture rates command the total weak rates of these heavy nuclei at high stellar temperatures. (C) 2016 Elsevier B.V. All rights reserved.