arXiv subjects

Jameel-Un Nabi

Publications and source records attributed to Jameel-Un Nabi.

At least 37 records · Page 2Linked to original sources

arXiv2025

$β$-decay properties of some astrophysically important Sc-isotopes

In the late progressive stages of heavy stars, electron capture and $β^\pm$-decay are the governing processes. The weak rates are essential inputs for modeling the stages of high-mass stars before supernova explosions. As per results obtained from previous simulations, weak rates of Scandium isotopes contribute substantially in changing the lepton-to-baryon ratio ($Y_e$) of the nuclear matter in the core. In the present analysis, we report important $β^-$-decay properties of crucial Sc isotopes in an astrophysical environment with mass numbers $49 \leq A \leq 54$. The investigation includes Gamow-Teller (GT) strength distributions, terrestrial half-lives, and stellar rates of electron capture (EC) and $β^-$-decay reactions. The calculations are performed using the proton-neutron (pn) quasi-particle random phase approximation (QRPA) model over a wide temperature range ($10^7$-$3 \times 10^{10}$ K) and density range ($10^1 - 10^{11}$ g/cm$^3$). Additionally, we compare our calculated results with available experimental and theoretical data. A good agreement is observed between our calculated half-lives and experimentally measured values. Our weak $β^-$-decay and EC rates are compared with those from the Independent-Particle Model (IPM) and Large-Scale Shell Model (LSSM). At high stellar temperatures and densities, our calculated $β^-$-decay rates are smaller than those from the other models.

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arXiv2025

Lepton emission rates of 43-64V isotopes under stellar conditions

In astrophysical conditions prevalent during the late times of stellar evolution, lepton ($e^-$ and $e^+$) emission processes compete with the corresponding lepton capture processes. Prior to the collapse, lepton emissions significantly affect the cooling of the core and reduce its entropy. Therefore, the lepton emission rates for Fe-group nuclei serve as an important input for core-collapse simulations of high-mass stars. From earlier simulation studies, isotopes of vanadium (V) have great astrophysical significance in regard to their weak-decay rates, which substantially affect $Y_e$ (fraction of lepton to baryon number) during the final developmental stages of massive stars. The current study involves the computation of the weak lepton emission (LE) rates for V isotopes by employing the improved deformed proton-neutron Quasi-particle Random Phase Approximation (pn-QRPA) model. The mass numbers of the selected isotopes range from 43 to 64. The LE rates on these isotopes have been estimated for a broad spectrum of density and temperature under astrophysical conditions. The ranges considered for density and temperature are $10^1$ to $10^{11}$ (g/cm$^3$) and $10^7$ to $3 \times 10^{11}$ (K), respectively. The lepton emission rates from the present study were also compared to the rates previously estimated by using the independent-particle model (IPM) and large-scale shell model (LSSM). IPM rates are generally bigger than QRPA rates, while LSSM rates overall show a good comparison with the reported rates.

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arXiv2025

$β$-decay of N=126 isotones for the r-process nucleosynthesis

The $β$-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 $β$-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 $β$-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 $β$-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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arXiv2025

Effect of nuclear deformation on Gamow-Teller strength distributions of Hg isotopes

Recent studies \cite{1,2} predicted the sensitivity of the Gamow-Teller (GT) strength distributions to nuclear deformation in neutron-deficient Hg isotopes. Motivated by this work, we investigate nuclear ground-state properties and GT strength distributions for neutron-deficient Hg isotopes ($^{177\hbox{-}193}$Hg). The nuclear deformation ($β(E2)$) values were calculated using the **Relativistic Mean Field (RMF)** model. The RMF approach, with different density-dependent interactions (**DD-ME2** and **DD-PC1**), was employed to compute nuclear shape parameters. These computed deformation values were then used within the framework of the **deformed proton-neutron quasi-particle random phase approximation (pn-QRPA)** model, with a separable interaction, to calculate the allowed GT strength distributions for these Hg isotopes. Our calculations validate the findings of \cite{1} and confirm the effect of deformation on GT strength distributions. This study may further provide a complementary signature for nuclear shape isomers. Noticeable differences are highlighted between our results and previous calculations. The study of \cite{1} suggests that $^{177\hbox{-}182}$Hg possess prolate shapes, while $^{184\hbox{-}196}$Hg exhibit oblate shapes. In contrast, our calculations predict **prolate** shapes for $^{177\hbox{-}188}$Hg and **oblate** shapes for $^{189\hbox{-}193}$Hg isotopes.

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arXiv2025

Investigation of pairing correlations on computed Gamow-Teller strength distributions and associated $β$-decay half-lives

We investigate the effect of pairing correlations on the computed Gamow-Teller (GT) strength distributions and corresponding $β$-decay half-lives. The calculations are performed for a total of 47 sd-shell nuclei, for $20 < A < 30$, employing the pn-QRPA model. Our calculations use three different values of pairing gaps computed using three different empirical formulae. The GT strength distribution and centroid values change considerably with a change in the pairing gap values. This, in turn, leads to differences in computed half-lives. The pairing gaps computed using the mass-dependent formula result in the calculated half-lives being in better agreement with the measured data.

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arXiv2025

$β$-Decay Properties of Neutron-rich Yttrium Isotopes

In this study, we have reported key nuclear properties of weak $β$-decay processes on Yttrium isotopes for the mass number range $A = 101 - 108$. This mass region is important in astrophysical $r$-process abundances. Our study might be helpful in $r$-process simulations. We have computed charge-changing strength distributions, $β$-decay half-lives, $β$-delayed neutron emission probabilities, and $β^{-}$ (EC) weak rates under stellar conditions. We have performed microscopic calculations based on deformed proton-neutron quasi-particle random phase approximation (pn-QRPA) over a wide temperature ($10^7 - 3 \times 10^{10}$) K and density ($10 - 10^{11}$) g/cm$^3$ domain. Unique first-forbidden (U1F) transitions have been included in the calculations in addition to the allowed transitions. A significant decrease in calculated half-lives in certain cases, e.g., in $^{107}$Y ($^{108}$Y) by about 67\% (42\%), has been observed because of the contribution from U1F transitions. We have compared present results with measured and theoretical works. A good agreement of our half-lives with experimental data is observed.

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arXiv2025

Investigation of effects of pairing correlations on calculated $β$-decay half-lives of fp-shell nuclei

Pairing of nucleons plays a key role in solving various nuclear physics problems. We investigate the probable effects of pairing correlations on the calculated Gamow-Teller (GT) strength distributions and the associated $β$-decay half-lives. Computations are performed for a total of 35 fp-shell nuclei using the proton-neutron quasiparticle random phase approximation (pn-QRPA) model. The nuclei were selected because of their importance in various astrophysical environments. Pairing gaps are one of the key parameters in the pn-QRPA model to compute GT transitions. We employed three different values of the pairing gaps obtained from three different empirical formulae in our calculation. The GT strength distributions changed significantly as the pairing gap values changed. This in turn resulted in contrasting centroid and total strength values of the calculated GT distributions and led to differences in calculated half-lives using the three schemes. The half-life values computed via the three-term pairing formula, based on separation energies of nucleons, were in best agreement with the measured data. We conclude that the traditional choice of pairing gap values, $Δ_p = Δ_n = 12/\sqrt{A}$, may not lead to half-life values in good agreement with measured data. The findings of this study are interesting but warrant further investigation.

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arXiv2025

Electron capture and \b{eta}-decay rates for nuclei with A=65-80

Recently, a list of the 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 $A = 65\text{--}80$, 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 previous pn-QRPA and independent particle model (IPM) results is presented for the first time. The reported EC rates are nearly the same when compared with the previous pn-QRPA calculation. On the other hand, the reported BD rates are generally smaller by up to an order of magnitude. Comparison with IPM results shows that our calculated rates are larger by two orders of magnitude. The current calculation may contribute to a more realistic simulation of the late phases of stellar evolution and the modeling of X-ray bursts.

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arXiv2025

Investigation of $β$-decay properties of neutron-rich Cerium isotopes

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 $120 \leq A \leq 157$ 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 changes 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.

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arXiv2025

Study of \b{eta}-Decay, log ft Values and Nuclear Structure Properties of Neutron-rich Ge Nuclei

We use the relativistic mean field (RMF) model to conduct a thorough analysis of the ground-state properties of $^{67\text{--}80}$Ge nuclei. Binding energies and neutron skin thicknesses are computed for a total of 14 neutron-rich Ge isotopes. This study provides a comprehensive overview of the RMF model's explanation of nuclear ground-state properties. Furthermore, we examine the $\log ft$ values of the allowed $β^\pm$ decays and electron/positron capture rates on Ge isotopes in the mass region $A = 67\text{--}80$. The proton-neutron quasiparticle random phase approximation (pn-QRPA) method was employed to calculate the $β$-decay properties of selected Ge isotopes. The calculated $\log ft$ values show good consistency with the measured data. The predicted $β$-decay half-lives are within a factor of 2 of the measured values. For high temperature and density conditions in the core of massive stars, the calculated pn-QRPA stellar rates are up to an order of magnitude larger than the independent shell model rates. The findings reported in this study could be valuable for simulating the late-stage stellar evolution of massive stars.

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arXiv2025

Energy rates due to Fe isotopes during presupernova evolution of massive stars

This work presents the microscopic calculation of energy rates (γ ray heating and (anti)neutrino cooling rates) due to weak decay of selected Fe isotopes. The isotopes have astrophysical significance during the presupernova evolution of massive stars. The energy rates are calculated using the pn QRPA model and compared with the independent particle model (IPM), large scale shell model (LSSM) and recent shell model calculation (GXPF1J). The reported (anti)neutrino cooling rates are smaller by up to two orders of magnitude at low core temperature values than the IPM rates. The two calculations compare well at T = 30 GK. The comparison of cooling rates with the LSSM is interesting. The pn QRPA cooling rates due to even even Fe isotopes are smaller (up to 2 orders of magnitude). For the odd A isotopes, the reported rates are bigger up to an order of magnitude. The pn QRPA computed cooling rates are, up to 2 orders of magnitude, bigger when compared with the GXPF1J calculation. The γ ray heating rates due to electron capture rates rise with the temperature and density values of the stellar core. On the other hand, the γ ray heating due to \b{eta} decay increases with the core temperature values but decreases by orders of magnitude when the stellar core stiffens. The pn QRPA computed γ heating rates are bigger (up to 3 orders of magnitude) at high temperatures and densities (for the case of 55 56Fe) when compared with the recent shell model results. Owing to the importance of energy rates, this study may contribute to a realistic simulation of presupernova evolution of massive stars.

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arXiv2025

$β^-$-decay half-lives of even-even nuclei using the recently introduced phase space recipe

We present the beta decay half-lives calculation for selected even even nuclei that decay through electron emission. The kinematical portion of the half-life calculation was performed using a recently introduced technique for computation of phase space factors (PSFs). The dynamical portion of our calculation was performed within the proton neutron quasiparticle random phase approximation (pn QRPA) model. Six nuclei (20O, 24Ne, 34Si, 54Ti, 62Fe, and 98Zr) were selected for the present calculation. We compare the calculated PSFs for these cases against the traditionally used recipe. In our new approach, the Dirac equation was numerically solved employing a Coulomb potential. This potential was adopted from a more realistic proton distribution of the daughter nucleus. Thus, the finite size of the nucleus and the diffuse nuclear surface corrections are taken into account. Moreover, a screened Coulomb potential was constructed to account for the effect of atomic screening. The power series technique was used for the numerical solution. The calculated values of half-lives, employing the recently developed method for computation of PSFs, were in good agreement with the experimental data.

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arXiv2025

Nuclear Structure Properties and Stellar Weak Rates for 76Se: Unblocking of the Gamow Teller Strength

At finite temperatures ($\geq 10^7$K), $^{76}$Se is abundant in the core of massive stars and electron capture on $^{76}$Se 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 $^{76}$Se 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 $^{76}$Se can be envisioned within the formalism of the potential energy surface based on the classical limit of the IBM-1 model. In the second phase, we reconfirm the unblocking of the Gamow-Teller (GT) strength in $^{76}$Se (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 $^{76}$Se. 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 $β$-delayed neutrons and emission probabilities are also calculated. Our study suggests that at high stellar temperatures and low densities, the $β^+$-decay on $^{76}$Se should not be neglected and needs to be taken into consideration along with electron capture rates for simulation of presupernova evolution of massive stars.

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arXiv2025

Effect of Nuclear Deformation on Electron Capture Cross-section on Chromium Isotopes

The electron capture plays significant role in the pre supernova and supernova evolutions of massive stars which in turn are of great importance in synthesizing heavy elements beyond iron. In this paper we study the effect of nuclear deformation on the computed electron capture cross section on selected even even chromium isotopes (464850Cr). The nuclear deformation parameters were computed using two different theoretical models: Interacting Boson Model (IBM 1) and Macroscopic (Yukawa plus exponential) microscopic (Folded Yukawa) model (Mac mic model). A third value of deformation parameter was adopted from experimental data. We chose the pn QRPA model to perform our calculations. The predictive power of the chosen model was first tested by calculating Gamow Teller (GT) strength distributions of selected fp shell nuclei where measured GT data was available. The calculated GT strength distributions were well fragmented over the energy range 0 12 MeV and were noted to be in decent agreement with experimental data. The total GT strength was found to increase (decrease) with decrease (increase) in the value of deformation parameter for the three chromium isotopes. The computed GT strength distributions satisfied the model independent Ikeda sum rule. The ECC were calculated as a function of the deformation parameter at core temperature 1.0 MeV. Our results show that the calculated ECC increased with increasing value of nuclear deformation.

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arXiv2025

Electron capture cross sections and nuclear partition functions for fp-shell nuclei

We present calculation of electron capture cross sections (ECC), in the limit of zero momentum transfer, using the pn QRPA model in stellar matter. Towards this aim we make use of our recently introduced recipe for estimation of nuclear partition functions. For low momentum transfer q tends to zero, the nuclear matrix elements of the Pστ plus operator provide the leading contribution to the total cross section which we estimate using the pn QRPA model in a multi shell single particle space with a schematic interaction. Key f p shell nuclei (odd A, even even and odd odd) bearing astrophysical importance were selected for the calculation of ECC in stellar environment. These f p shell nuclei play crucial role in pre supernova evolution of massive stars and core collapse. We further present microscopic calculation of ground and excited states Gamow Teller strength distributions and stellar electron capture rates on these suite of nuclei. We used two different sets of empirically determined pairing gaps to calculate the ECC and electron capture rates. Results are compared with experimental data and previous computations. Our calculated ECC are systematically smaller at low electron incident energies as compared to the shell model results.

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arXiv2025

Mass fractions in stellar interior during presupernova evolution

We assume nuclear statistical equilibrium (NSE) conditions and use Saha Equation to calculate mass fractions in stellar interior during presupernova evolution of massive stars. Our ensemble contains 728 nuclei. The distinguishing feature of our calculation is a state by state summation of nuclear level densities up to 10 MeV for all nuclei considered in our ensemble. This leads to a more realistic description of nuclear partition function which poses one of the largest uncertainties in the mass fraction calculations under conditions of NSE. The Coulomb correction term was taken into account for the calculation of ground state binding energies of the nucleons. Our calculated mass fractions are up to four orders of magnitude smaller than previous calculation. The current calculation could prove useful for study of stellar matter during presupernova phases of massive stars.

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arXiv2025

The nuclear ground-state properties and stellar electron emission rates of 76Fe, 78Ni, 80Zn, 126Ru, 128Pd and 130Cd using RMF and pn-QRPA models

Our study consists of investigations of nuclear ground state properties and weak transition rates of even even waiting point nuclei. The calculation was performed for N = 50 and N = 82 nuclei. The Relativistic Mean Field (RMF) model was used to explore the nuclear ground state properties of selected nuclei. The proton neutron quasi particle random phase (pnQRPA) model was used for the computation of allowed Gamow Teller (GT) and unique first forbidden (U1F) transitions of the selected waiting point nuclei. The RMF approach with different density dependent interactions, DD ME2 and DD PC1, was used to compute potential energy curves and surfaces, quadrupole moments, deformation parameters, binding energies, proton neutron separation energies, charge, and radii. The RMF computed deformation parameters were used in the pn QRPA model, as a free parameter, for the computation of GT and U1F weak transitions. We investigated three different sets of deformation parameter for the calculation of electron emission rates. The rates changed considerably with change in deformation parameter. We later investigated contribution of allowed GT and U1F rates and competition between positron capture and electron emission rates at high stellar temperatures. The computed positron capture rates were significant especially at low densities and high temperatures.

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arXiv2025

Investigation of Gamow-Teller strength of 186Hg within deformed pn-QRPA

Recently the the total absorption gamma spectroscopy technique was used to determine the Gamow Teller (GT) distribution of \b{eta} decay of 186Hg. It was concluded that the best description of the measured data was obtained with dominantly prolate components for both parent 186Hg and daughter 186Au. Motivated by the recent findings, we investigate the effect of nuclear deformation on the energy distribution of the GT strength of the decay of 186Hg into 186Au within the framework of pn QRPA based on the deformed Nilsson potential. To do the needful, we first calculate the energy levels and shape prediction of 186Hg within the interacting boson model. The computed GT strength distribution satisfied the model independent Ikeda sum rule 100 % (99.98 %) for the prolate (oblate) case. Based on the strength distributions, the deformed pn QRPA model with separable interaction prefers a prolate shape for the ground state of 186Hg and supports the shape coexistence for this nucleus.

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