arXiv subjects

Jameel-Un Nabi

Publications and source records attributed to Jameel-Un Nabi.

At least 55 records · Page 3Linked to original sources

arXiv2025

Investigation of weak-rates for odd-A nuclei for presupernova simulations

Calculating weak decay rates under stellar conditions for studying presupernova evolution of massive stars is a challenging task. Here we show the importance of odd A nuclei for presupernova simulations. In order to calculate the required nuclear matrix elements we apply the pn QRPA model in a deformed basis. Nuclear deformation, thought to play an integral role in calculation of associated weak decay rates, is taken into account in our model. We calculate Gamow Teller (GT) strength distributions, emission and positron capture rates for selected odd A nuclei. Our model does not employ the Brink Axel hypothesis as used in previous calculations of weak decay rates and we perform a state by state microscopic calculation of GT strength distributions from all parent excited states. Our calculated decay rates are in good agreement with large scale shell model calculations.

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arXiv2025

Impact of Coulomb Correction Factor on Rate of Change of Lepton Fraction during Presupernova Evolution

We reexamine the weak interaction nuclei having largest contribution to the lepton to baryon fraction Ye by coupling the stellar weak rates and mass abundances for post silicon burning conditions during the presupernova evolution of massive stars. The stellar weak rates were recently calculated by Nabi et al. 2021 employing the fully microscopic pnQRPA model without invoking the Brink Axel hypothesis. We compute the mass abundances for a total of 728 nuclei, with A equal 1to 100, using Sahas equation and assuming nuclear statistical equilibrium with the incorporation of Coulomb correction factor to the chemical potential. We compile a list of top 50 electron capture ec and \b{eta} decay bd nuclei on the basis of largest contribution to Ye forpost silicon burning conditions where 11 percent ec and 6percent bd nuclei debuted dueto Coulomb corrections. The calculated mass abundances and corresponding Ye values are enhanced up to 3 orders of magnitude for heavier nuclei once Coulomb corrections were incorporated. This enhancement led to anincrement in total Y bde and Yece values, at Ye equal to 0.425 (\r{ho} equal 2.20 multiply 109 g/cm3 of 80percent and 91percent respectively. After incorporating the Coulomb corrections we propose a revised interval of Ye equal 0.423 0.455 where bd rates surpass thecompeting ec rates and is 3.2 percent bigger than the one suggested by Nabi et al. (2021).

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arXiv2025

Stellar Weak Rates and Mass Fractions of 20 Most Important $fp$-shell Nuclei with $A < 65$

This work presents stellar weak rates and mass fractions of 20 most important electron capture (ec) and beta decay (bd) nuclei with $A < 65$ according to a recent study during the presupernova evolution of massive stars. The mass fractions of these nuclei were calculated using the Sahas equation which assumes nuclear statistical equilibrium for a set of initial conditions ($T_9$, $ρ$ and $Y_e$) that represents the trajectory which a massive stars central region takes after its silicon core burns. Our computed mass fractions were found in decent comparison in most cases, and up to a factor 4 difference was noted when compared with the Independent Particle Model results. The weak interaction (ec and bd) rates were calculated in a totally microscopic fashion using the proton neutron quasiparticle random phase ap proximation model and without assuming the Brink Axel hypothesis. The rates were computed for a wide range of density ($10$-$10^{11}$) g/cm$^3$ and temperature (0.01-30) GK. In comparison with large scale shell model, our computed rates were found bigger at high values of core temperature. The current study may contribute in a more realistic simu lation of stellar evolution processes and modeling of core collapse supernovae.

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arXiv2024

Reexamination of nuclear structure properties and shape coexistence of nuclei around A70

We reexamine the nuclear structure properties of waiting point nuclei around A70 using the interacting boson model 1 (IBM 1) and the relativistic mean field (RMF) model. Effective density dependent meson exchange functional (DD ME2) and density dependent point coupling functional (DD PC1) were used for the RMF calculations. We calculated the energy levels, the geometric shapes, binding and separation energies of nucleons and quadrupole deformation parameters (\b{eta}2). The shape coexistence phenomena in A 70 nuclei (68Se, 70Se, 70Br, 70Kr, 72Kr, 74Kr, 74Rb, and 74Sr) was later investigated. Spherical and deformed shapes of the selected waiting point nuclei were computed using the IBM 1 and RMF models, respectively. The proton neutron quasiparticle random phase approximation (pn QRPA) model was used to calculate \b{eta} decay properties (Gamow Teller strength distributions, \b{eta} decay half lives, and branching ratios) of selected nuclei as a function of \b{eta}2. The results revealed a significant variation in calculated half lives and Gamow Teller strength distributions as the shape parameter was changed. The \b{eta}2 computed via DD ME2 functional resulted in half lives in best agreement with the measured data.

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arXiv2024

Validity of Brink Axel Hypothesis for calculations of allowed stellar weak rates of heavy nuclei

The knowledge of beta decay transitional probabilities and GamowTeller (GT) strength functions from highly excited states of nuclides is of particular importance for applications to astrophysical network calculations of nucleosynthesis in explosive stellar events. These quantities are challenging to achieve from measurements or computations using various nuclear models. Due to unavailability of feasible alternatives, many theoretical studies often rely on the Brink Axel (BA) hypothesis, that is, the response of strength functions depends merely on the transition energy of the parent nuclear ground state and is independent of the underlying details of the parent state, for the calculation of stellar rates. BA hypothesis has been used in many applications from nuclear structure determination to nucleosynthesis yield in the astrophysical matter.

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arXiv2024

Re examination of \b{eta} decay in Hg, Pb and Po Isotopes

This study re examines the effect of nuclear deformation on the calculated Gamow Teller (GT) strength distributions of neutron deficient (178 192Hg, 185 194Pb and 196 206Po) nuclei. The nuclear ground state properties and shape parameters were calculated using the Relativistic Mean Field model. Three different density dependent interactions 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.

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arXiv2024

Impact of the Brink Axel Hypothesis on Unique First Forbidden \b{eta} transitions for r process nuclei

Key nuclear inputs for the astrophysical r process simulations are the weak interaction rates. Consequently, the accuracy of these inputs directly affects the reliability of nucleosynthesis modeling. Majority of the stellar rates, used in simulation studies, are calculated invoking the Brink Axel (BA) hypothesis. The BA hypothesis assumes that the strength functions of all parent excited states are the same as for the ground state, only shifted in energies. However, BA hypothesis has to be tested against microscopically calculated state by state rates. In this project we study the impact of the BA hypothesis on calculated stellar \b{eta} decay and electron capture rates. Our investigation include both Unique First Forbidden (U1F) and allowed transitions for 106 neutron rich trans iron nuclei ([27, 77] less than equal to [Z, A] less than equal to [82, 208]). The calculations were performed using the deformed proton-neutron quasiparticle randomphase approximation (pn QRPA) model with a simple plus quadrupole separable and schematic interaction. Waiting-point and several key r process nuclei lie within the considered mass region of the nuclear chart.

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arXiv2024

Radiative Capture of proton 14N(p,γ) 15O at Low Energy

The CNO cycle is the main source of energy in stars more massive than our Sun. It defines the energy production and the duration contributes in determining the lifetime of massive stars. The cycle is an important tool for the determination of the age of globular clusters. Radiative capture p plus 14N 15O plus γ, at energies of astrophysical interest, is one of the important processes in the CNO cycle. In this project, we apply a potential model to describe both non resonant and resonant reactions in the channels where radiative capture occurs through electric E1 transitions. We employed the R matrix method to describe the reactions going via M1 resonant transitions, when it was not possible to correctly reproduce the experimental data by a potential model. The partial components of the astrophysical S factor are calculated for all possible electric and magnetic dipole transitions in 15O. The linear extrapolated S factor at zero energy (S(0)) is in good agreement with earlier reported values for all types of transitions considered in this work. Based on the value of the total astrophysical S factor, depending on the collision energy, we calculate the nuclear reaction rates for p plus 14N 15O plus γ. The computed rates are in good agreement with the results of the NACRE II Collaboration and the most recent existing measurements.

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arXiv2024

Re analysis of Temperature Dependent Neutron Capture Rates and Stellar \b{eta} decay Rates of 95 98Mo

The neutron capture rates and temperature dependent stellar beta decay rates of Mo isotopes are investigated within the framework of the statistical code (Talys v1.96) and proton neutron quasi particle random phase approximation (pnQRPA) models. The Maxwellian average cross section (MACS) and neutron capture rates for 95 98Mo(n,γ) 96 99Mo radiative capture processes are analyzed within the framework of statistical code Talys v1.96 based on the phenomenological nuclear level density (NLD) parameters and gamma strength functions (GSFs). The current model based computed data for MACS provide a good comparison with the existing measured data. The temperature dependent stellar \b{eta} decay rates of 95 98Mo are investigated at different densities within the framework of the pn-QRPA model. For the considered temperature range, the neutron capture rates were found to be higher, by orders of magnitude, than the stellar \b{eta} rates.

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arXiv2024

Nuclear structure properties and weak interaction rates of even-even Fe isotopes

Nuclear structure properties and weak interaction rates of neutron rich even even iron (Fe) isotopes (A = 50 70) are investigated using the Interacting Boson Model1 (IBM1) and the proton neutron Quasiparticle Random Phase Approximation (pnQRPA) model. The IBM1 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 IBM1 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 pnQRPA 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.

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arXiv2024

Re-analysis of the Gamow-Teller distributions for N=Z nuclei, 24Mg, 28Si, and 32S

The Gamow-Teller (GT) strength distributions of sd shell N=Z nuclei ($^{24}$Mg, $^{28}$Si, and $^{32}$S) are investigated within the framework of proton-neutron quasi particle random phase approximation (pn QRPA) using a deformed basis. The nuclear properties of these special nuclei were investigated by the Relativistic Mean Field (RMF) model. The RMF framework with density-dependent interactions (DD-PC1 and DD-ME2) was employed to compute ground-state deformation parameters (beta 2) using potential energy curves. The $β_2$ values computed from the RMF and the finite range droplet model (FRDM) were employed as a free parameter in the pn QRPA calculation to investigate the resulting GT strength distributions.The present model-based analyses compare well with the observed data.

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arXiv2024

Investigation of Nuclear Structure and $β$-decay Properties of As Isotopes

The nuclear ground state properties of 67 80As nuclei have been investigated within the framework of relativistic mean field (RMF) approach. The RMF model with density dependent (DDME2) interaction is utilized for the calculation of potential energy curves and the nuclear ground state deformation parameters $β_2$ of selected As isotopes. Later, the $β$ decay properties of As isotopes were studied using the proton neutron quasi particle random phase approximation pnQRPA model. These include Gamow Tellar (GT) strength distributions, log ft values, $β$ decay half lives, stellar $β$ plus minus decays and stellar electron positron capture rates. The $β_2$ values computed from RMF model were employed in the on QRPA model as an input parameter for the calculations of $β$-decay properties for 67 80As. The calculated log ft values were in decent agreement with the measured data. The predicted $β$-decay half lives matched the experimental values within a factor of 10. The stellar rates were compared with the shell model results. Only at high temperature and density values, the sum of $β$ plus and electron capture rates had a finite contribution. On the other hand, the sum of $β$ negative and positron capture rates were sizeable only at low density and high temperature values. For all such cases, the pn QRPA rates were found to be bigger than the shell model rates up to a factor of 33 or more. The findings reported in the current investigation could prove valuable for simulating the late stage stellar evolution of massive stars.

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arXiv2024

Re-investigation of neutron capture by 84Kr and 86Kr in the s-process nucleosynthesis

The thermonuclear reaction rates and Maxwellian averaged cross sections (MACS) for the 84Kr(n,γ) 85Kr and 86Kr(n,γ) 87Kr processes were examined using the statistical model code Talys v1.96. The effects of nuclear level densities (NLDs) on Maxwellian averaged cross sections and neutron capture rates are examined both quantitatively and qualitatively. The present Talys based MACS and radiative capture rates for 84Kr(n,γ) 85Kr and 86Kr(n,γ) 87Kr processes agree well with the earlier reported findings. The statistical models nuclear properties (level density and gamma ray strength) were fine tuned to reproduce the existing experimental nuclear data.

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arXiv2024

Investigation of 90,92Zr(n,γ) 91,93Zr in the s process nucleosynthesis

The neutron capture rates and Maxwellian averaged cross sections (MACS) for 90Zr(n,γ) 91Zr and 92Zr(n,γ) 93Zr processes have been computed within the framework of Talys v1.96. The effects of phenomenological nuclear level density (NLD) parameters and the gamma strength functions (GSFs) on Maxwellian averaged cross sections and neutron capture rates are examined both quantitatively and qualitatively. The present model based computed data for MACS and reaction rates gives a good comparison with the existing literature. The fine-tuning of the statistical models nuclear properties (level density and gamma-ray strength) to reproduce experimental data will allow the detailed investigation of the s process network.

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arXiv2024

Allowed and forbidden beta-decay log ft values of neutron-rich Pb and Bi isotopes

The beta-decay log ft values for 210 215Pb 210 215Bi and 210 215Bi 210 215Po transitions in the north east region of 208Pb nuclei are estimated using the proton neutron quasiparticle random phase approximation 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(WS) were found closer to the experimental values. Later we performed calculation of beta-decay rates in stellar environment. Here we solved the 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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arXiv2024

Investigating the effect of nuclear deformation on $β$-decay half-lives of neutron-rich nuclei

We examine the effect of nuclear deformation on the calculated $β$-decay half-lives of 55 neutron-rich nuclei. The deformation values were computed using DD-PC1 and DD-ME2 interactions in the Relativistic Hartree-Bogoliubov model. Yet another set of deformation was adopted from the Finite Range Droplet Model (FRDM). The model-dependent deformation values were used as a free parameter in the proton-neutron quasiparticle random phase approximation model to calculate the $β$-decay properties under terrestrial and stellar conditions. The Gamow-Teller strength distributions, branching ratios, half-lives and stellar weak rates of selected nuclei were later investigated. It was concluded that the $β$-decay properties of neutron-rich nuclei changed with nuclear deformation. The FRDM computed deformation values provided the best predictions for calculated half-lives followed by the DD-ME2 functional. The terrestrial $β$-decay half-lives changed up to 3 orders of magnitude and the stellar $β$-rates within a factor of 2 as the neutron-rich nuclei switched their geometrical configurations. For magic number nucleus $^{138}$Sn, the stellar rates changed substantially by more than 1 order of magnitude as the nucleus transitioned away from the spherical shape. Our investigation might prove useful for a realistic modeling of nucleosynthesis calculation.

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arXiv2022

Investigation of the neutron imaging applications using fine-grained nuclear emulsion

Neutron imaging is a non-destructive inspection technique with a wide range of applications. One of the important aspects concerning neutron imaging is achieving micrometer-scale spatial resolution. Developing a neutron detector with a high resolution is a challenging task. Neutron detectors, based on fine-grained nuclear emulsion, may be suitable for high resolution neutron imaging applications. High track density is a necessary requirement to improve the quality of neutron imaging. However, the available track analysis methods are difficult to apply under high track density conditions. Simulated images were used to determine the required track density for neutron imaging. It was concluded that a track density of the order of $10^4$ tracks per 100 $\times$ 100 $μ$m$^2$ is sufficient to utilize neutron detectors for imaging applications. The contrast resolution was also investigated for the image data sets with various track densities and neutron transmission rates. Moreover, experiments were performed for neutron imaging of the gadolinium-based gratings with known geometries. The structure of gratings was successfully resolved. The calculated 1$σ$ 10-90 \% edge response, using the gray scale optical images of the grating slit with a periodic structure of 9 $μ$m, was 0.945 $\pm$ 0.004 $μ$m.

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arXiv2022

Study on the reusability of fluorescent nuclear track detectors using optical bleaching

Fluorescent nuclear track detectors (FNTDs) based on Al${_2}$O${_3}$:C,Mg crystals are luminescent detectors that can be used for dosimetry and detection of charged particles and neutrons. These detectors can be utilised for imaging applications where a reasonably high track density, approximately of the order of 1 $\times$ $10^4$ tracks in an area of 100 $\times$ 100 $μ$m$^2$, is required. To investigate the reusability of FNTDs for imaging applications, we present an approach to perform optical bleaching under the required track density conditions. The reusability was assessed through seven irradiation-bleaching cycles. For the irradiation, the studied FNTD was exposed to alpha-particles from an $^{241}$Am radioactive source. The optical bleaching was performed by means of ultraviolet laser light with a wavelength of 355 nm. Three dedicated regions on a single FNTD with different accumulated track densities and bleaching conditions were investigated. After every irradiation-bleaching cycle, signal-to-noise ratio was calculated to evaluate FNTD performance. It is concluded that FNTDs can be reused at least seven times for applications where accumulation of a high track density is required.

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