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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, $$\beta ^-$$ 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 $$\beta ^-$$ decay rates are in good agreement with large-scale shell model calculations.

In this paper, fabrication and characterization of Cu/PTB7-Th (35 mass%)/PC $$_{61}$$ BM (35 mass%)/graphene (30 mass%)/Ag thin-film composite cells are given. First of all, Ag and Cu electrodes were deposited on flat glass substrate by vacuum evaporation with 130- $$\upmu $$ m inter-electrode gap. The PTB7-Th (35 mass%) composite and PC $$_{61}$$ BM (35 mass%) composite in chlorobenzene and graphene (30 mass%) were deposited on the inter-electrode gap by drop-casting technique, and film thickness of 8–12 $$\upmu $$ m was achieved. The dependence of forward and reverse bias resistance of the cells versus temperature in the range of 25–75 $${^{\circ }}$$ C, humidity in the range of 47–90 %RH and pressure in the range of 0–7.7 kN m $$^{-2}$$ was measured. The average temperature resistance coefficients were equal to (− 1.03)% $${^{\circ }}\hbox {C}^{-1}$$ and $$(-\,1.14)\%\ {^{\circ }}\hbox {C}^{-1}$$ for forward and reverse bias resistances, respectively. The reverse and forward bias resistances decreased 1.29 and 1.27 times due to $$\%\mathrm{RH}$$ , and due to pressure, it decreased by 9.0–9.2%. Impedance (Z) of the sample was also measured at different frequencies (100 Hz, 1 kHz, 10 kHz and 100 kHz) which decreased from 1.23 to 1.04 times. The obtained results are explained, firstly, by transfer of charges between donors and acceptors molecules and effect of water molecules on the PTB7-Th (35 mass%):PC $$_{61}$$ BM (35 mass%):graphene composite.

In this paper the fabrication of built–in rubber graphene and CNT based elastic composite samples under uniaxial compressive displacements is presented along with the investigation of their resisti...

The total cross-section, astrophysical S-factor, and rate of radiative capture reaction 12C(p, γ)13N are calculated using the potential model. In this work, we take into account the capture of protons through s1/2 → p1/2 and d3/2 → p1/2 single-particle transitions, fine-tune the values of the depth and nuclear radius of the Woods-Saxon potential to achieve better comparison with the measured data. The results for the elastic scattering phase shift, astrophysical S-factor, and rates are compared with the previously reported results of the calculations and experimental data.

As per simulation studies, the weak reaction rates on nickel isotopes play a substantial role in affecting the ratio of electron-to-baryon content of stellar interior during the late stages of core evolution. (Anti)neutrinos are produced in weak-decay processes, and escape from the stellar content having densities less than 1011 g cm − 3 . They take away energy and reduce the stellar core entropy. In this paper we report on the microscopic calculation of neutrino and antineutrino cooling rates due to weak rates on nickel isotopes in mass range 56 ≤ A ≤ 71. The calculations are accomplished by employing the deformed pn-QRPA model. Recent studies on GT strength properties of nickel isotopes show that the deformed pn-QRPA model well explained the experimental charge-changing transitions. Our calculated beta decay half-lives for selected nickel isotopes are in excellent comparison with experimental data. The (anti)neutrino cooling rates are determined over temperatures in the range of 0.01 × 109 – 30 × 109 K and densities in the range of 10 – 1011 g cm − 3 domain. The computed rates are compared with previous theoretical calculations. For neutron rich nuclide, at high temperatures, our computed cooling rates are enhanced as compared to previous calculations.

This project aims to investigate the most important weak interaction nuclei in the presupernova evolution of massive stars. To achieve this goal, an ensemble containing 728 nuclei in the mass range of A = 1–100 was considered. We computed the mass fractions of these nuclei using Saha’s equation for predetermined values of T, ρ, and Y e and assuming nuclear statistical equilibrium. The nuclear partition functions were obtained using a newly introduced recipe where excited states, up to 10 MeV, were treated as discrete. The weak interaction rates (electron capture (ec) and β-decay (bd)) were calculated in a totally microscopic fashion using the proton–neutron quasiparticle random phase approximation model and without assuming the Brink–Axel hypothesis. The calculated rates were coupled with the computed mass fractions to investigate the time rate of change of lepton to baryon fraction of the stellar matter. We compare our results with the previous calculations reported in the literature. Noticeable differences up to orders of magnitude are reported with previous calculations. These differences may influence the evolution of the star in the later stages of presupernova. We present a list of the top 50 ec and bd nuclei, which have the largest effect on Y e for conditions after silicon core burning. The competition between the ec and bd rates in the stellar core was investigated and it was found that Y e = 0.424–0.455 is the interval where the bd results are bigger than the ec rates.

Lepton (electron and positron) capture rates on iron-regime nuclei are an essential element for modeling the late stages of progression of massive stars that become core collapse and thermonuclear supernova. As per previous simulation studies, lepton capture (LC) rates on isotopes of vanadium are believed to have a substantial effect in regulating the Ye (lepton to baryon fraction) during the final evolutionary phases. The present work involves the calculation of lepton capture rates for 22 isotopes of vanadium by making use of the proton-neutron (pn-) quasiparticle random phase approximation (QRPA) model. The covered mass range is from A = 43 to 64. The LC rates have been computed over stellar densities ranging from $10^{1}$ to $10^{11}$ (g/cm3) and for the temperature range $10^{7} - 3 \times 10^{10}$ (K). A comparison of our calculated LC rates to the rates computed using other models (IPM and LSSM) has also been presented. As compared to the rates calculated by other models, pn-QRPA rates at high temperature ( $3 \times 10^{10}$ K) are larger by up to 1-2 orders of magnitude.

Radiative capture $p + {}^{13}\mathrm{C}\rightarrow {}^{14}\mathrm{N}+\gamma $ at energies bearing astrophysical consequences is one of the important processes in the CNO cycle. We focus on the possibility of describing the main contribution to the total cross section of the radiative capture process in the framework of the single-particle potential model without separation into direct and resonant transitions. In case where the single-particle potential model fails to describe other partial components, we use the R-matrix approach. The partial components of the astrophysical S-factor are calculated for all possible electric dipole transitions. The calculated value of the total S-factor at zero energy is in good agreement with earlier reported values. Based on the value of total astrophysical S-factor depending on the collision energy, we calculate the nuclear reaction rates for ${p} + {^{13}\mathrm{C}} \rightarrow {^{14}\mathrm{{N}}}+\gamma $ .

Electron capture and $\beta ^{-}$ decay are the dominant decay processes during late phases of evolution of heavy stars. Previous simulation results show that weak rates on isotopes of Molybdenum (Mo) have a meaningful contribution during the development of phases of stars before they go supernova. The relative abundance coupled with the stellar weak rates on Mo isotopes may change the lepton-to-baryon content of the core material. Here we report on the calculation of nuclear structure properties of 82−138Mo isotopes employing the RMF model. Later we calculate the weak decay rates of these isotopes. We use the pn-QRPA model to compute these rates. In the first step, the ground-state nuclear properties of Mo isotopes such as binding energy per nucleon, neutron and proton separation energies, charge radii, total electric quadrupole moments and deformation parameter of electric quadrupole moments have been calculated using density dependent version of RMF model with DD-PC1 and DD-ME2 functionals. The calculated electric quadrupole deformation parameters have been used in a deformed pn-QRPA calculation in the second phase of this work to calculate half-lives and weak decay rates for these Mo isotopes in stellar matter. We calculate the electron capture and $\beta $-decay rates over an extensive range of temperature ($0.01\times 10^{9}$ K to $30\times 10^{9}$ K) and density (10 to $10^{11}$) g/cm3. Our study can prove useful for simulation of presupernova evolution processes of stars.

The neutrino cooling and gamma heating rates are considered as an important input needed to study the final phases of the evolution of high-mass stars. The weak-interaction mediated processes, namely the $\beta $-decay and electron capture, significantly change the lepton to baryon ratio and accelerate the contraction of the core. The emission of resulting neutrinos/antineutrinos tend to cool the stellar core. On the other hand gamma rays are produced because of electron capture and $\beta $-decay to excited states in daughter nuclei. These gamma rays heat the core and contribute to increase of entropy which may cause convection to occur. In the present work, the weak-interaction heating and cooling rates on a chain of twenty two isotopes of vanadium having mass in the range 43–64 have been estimated using the proton-neutron quasiparticle random phase approximation theory. The rates have been computed for the temperature ranging from ($10^{7}\mbox{--}3\times 10^{10}$) K and for the density range $(10\mbox{--}10^{11})~\mbox{g/cm}^{3}$. Our calculated neutrino energy loss rates have also been compared with the previously reported rates calculated using other theoretical models. At high stellar temperatures, our rates are larger by 1–2 orders of magnitude as compared to previous results.

Weak rates in nickel isotopes play an integral role in the dynamics of supernovae. Electron capture and β-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, Ni 56 – 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.

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 × 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 are overall in good comparison with the reported rates. We attribute these differences to correct placement of GT centroid in LSSM and QRPA models.

WOS: 000411536200001 At 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. Higher Education Commission (Pakistan) through HEC [20-3099, 5557/KPK/NRPU/RD/HEC/2016] J.-U. Nabi wishes to acknowledge the support provided by the Higher Education Commission (Pakistan) through HEC Projects No. 20-3099 and 5557/KPK/NRPU/R&D/HEC/2016.

WOS: 000390830600001 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 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. Higher Education Commission (Pakistan) through the HEC Project [20-3099] J.-U. Nabi wishes to acknowledge the support provided by the Higher Education Commission (Pakistan) through the HEC Project No. 20-3099.

In this paper, 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 ( 20 O, 24 Ne, 34 Si, 54 Ti, 62 Fe and 98 Zr) 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 by 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.

We investigate even-even nuclei in the $A\sim70$ mass region within the framework of the proton-neutron quasi-particle random phase approximation (\mbox{pn-QRPA}) and the interacting boson model-1 (\mbox{IBM-1}). Our work includes calculation of the energy spectra and the potential energy surfaces $V(\beta,\gamma)$ of Zn, Ge, Se, Kr and Sr nuclei with the same proton and neutron number, $N = Z$. The parametrization of the \mbox{IBM-1} Hamiltonian was performed for the calculation of the energy levels in the ground state bands. Geometric shape of the nuclei was predicted by plotting the potential energy surfaces $V(\beta,\gamma)$ obtained from the \mbox{IBM-1} Hamiltonian in the classical limit. The \mbox{pn-QRPA} model was later used to compute half-lives of the neutron-deficient nuclei which were found to be in very good agreement with the measured ones. The \mbox{pn-QRPA} model was also used to calculate the Gamow-Teller strength distributions and was found to be in decent agreement with the measured data. We further calculate the electron capture and positron decay rates for these $N$ = $Z$ waiting point (WP) nuclei in the stellar environment employing the \mbox{pn-QRPA} model. For the $rp$-process conditions, our total weak rates are within a factor two compared with the Skyrme HF+BCS+QRPA calculation. All calculated electron capture rates are comparable to the competing positron decay rates under $rp$-process conditions. Our study confirms the finding that electron capture rates form an integral part of the weak rates under $rp$-process conditions and should not be neglected in the nuclear network calculations., Comment: 25 pages, 13 figures, 5 tables

In this paper we show that the proton-neutron residual interaction can play an important role in the reliability of calculated β-decay half-lives. It may also improve the prediction power of the quasiparticle random phase approximation (QRPA) model. We further demonstrate that a reasonable choice of the particle-particle (attractive) and particle-hole force (repulsive) parameters can result in calculated half-lives in very good comparison with the measured ones. Pairing gaps have affect on calculated half-lives which we explore in this paper. We present our half-lives calculation using the proton-neutron QRPA (pn-QRPA) model possessing a multi-shell single-particle deformed space including a schematic interaction for some medium mass neutron-deficient nuclei undergoing β + /EC decay. Our study shows a better agreement with the available experimental data as compared to former calculations.

Within the framework of potential cluster model, astrophysical S-factor of radiative capture reaction $^{12}\mathrm{C} (\mathrm{p},\gamma)^{13}\mathrm{N}$ has been calculated in the two body cluster model for the energy range 0–1 MeV. The nuclear interaction in the initial and final states is described by the Woods–Saxon potential. The calculated astrophysical S-factor and rates are compared with known experimental results.

A new algorithm for the asymptotic nuclear coefficients calculation, which we call the $\mathrm{\ensuremath{\Delta}}$ method, is proved and developed. This method was proposed by Ram\'{\i}rez Su\'arez and Sparenberg (arXiv:1602.04082.) but no proof was given. We apply it to the bound state situated near the channel threshold when the Sommerfeld parameter is quite large within the experimental energy region. As a result, the value of the conventional effective-range function ${K}_{l}({k}^{2})$ is actually defined by the Coulomb term. One of the resulting effects is a wrong description of the energy behavior of the elastic scattering phase shift ${\ensuremath{\delta}}_{l}$ reproduced from the fitted total effective-range function ${K}_{l}({k}^{2})$. This leads to an improper value of the asymptotic normalization coefficient (ANC) value. No such problem arises if we fit only the nuclear term. The difference between the total effective-range function and the Coulomb part at real energies is the same as the nuclear term. Then we can proceed using just this $\mathrm{\ensuremath{\Delta}}$ method to calculate the pole position values and the ANC. We apply it to the vertices $^{4}\mathrm{He}+^{12}\mathrm{C}\ensuremath{\leftrightarrow}^{16}\mathrm{O}$ and $^{3}\mathrm{He}+^{4}\mathrm{He}\ensuremath{\leftrightarrow}^{7}\mathrm{Be}$. The calculated ANCs can be used to find the radiative capture reaction cross sections of the transfers to the $^{16}\mathrm{O}$ bound final states as well as to the $^{7}\mathrm{Be}$.

Gamma ray heating and neutrino cooling rates, due to weak interaction processes, on $sd$ -shell nuclei in stellar core are calculated using the proton neutron quasiparticle random phase approximation theory. The recent extensive experimental mass compilation of Wang et al. (Chin. Phys. C 36:1603, 2012), other improved model input parameters including nuclear quadrupole deformation (Raman et al. in At. Data Nucl. Data Tables 78(1):1–128, 2001; Moller et al. in At. Data Nucl. Data Tables 109:1–204, 2016) and physical constants are taken into account in the current calculation. The purpose of this work is two fold, one is to improve the earlier calculation of weak rates performed by Nabi and Klapdor-Kleingrothaus (At. Data Nucl. Data Tables 71:149, 1999a) using the same theory. We further compare our results with previous calculations. The selected $sd$ -shell nuclei, considered in this work, are of special interest for the evolution of O–Ne–Mg core in 8–10 $\mbox{M}_{\odot }$ stars due to competitive gamma ray heating rates and cooling by URCA processes. The outcome of these competitions is to determine, whether the stars end up as a white dwarf (Nabi in Phys. Rev. C 78(4):045801, 2008b), an electron-capture supernova (Jones et al. in Astrophys. J. 772(2):150, 2013) or Fe core-collapse supernova (Suzuki et al. in Astrophys. J. 817(2):163, 2016). The selected $sd$ -shell nuclei for calculation of associated weak-interaction rates include $^{20,23}\mathrm{O}$ , $^{20,23}\mathrm{F}$ , $^{20,23,24}\mathrm{Ne}$ , ${}^{20,23\mbox{--}25}\mathrm{Na}$ , and ${}^{23\mbox{--}25}\mathrm{Mg}$ . The cooling and heating rates are calculated for density range ( $10 \leq \rho\ (\mbox{g}\,\mbox{cm}^{-3}) \leq 10^{11}$ ) and temperature range ( $0.01\times 10^{9}\leq T(K)\leq 30\times 10^{9}$ ). The calculated gamma heating rates are orders of magnitude bigger than the shell model rates (except for $^{25}\mathrm{Mg}$ at low densities). At high temperatures the gamma heating rates are in reasonable agreement. The calculated cooling rates are up to an order of magnitude bigger for odd-A nuclei.

The allowed charge-changing transitions are the most common weak interaction processes of spin-isospin form that play a crucial role in several nuclear/astrophysical processes. The first-forbidden (FF) transition becomes important, in the circumstances where allowed Gamow-Teller (GT) transitions are unfavored, specifically for neutron-rich nuclei due to phase space considerations. In this paper deformed proton-neutron quasi-particle random phase approximation (pn-QRPA) model is applied, for the first time, for the estimation of allowed GT and unique first-forbidden (U1F) transitions ( $|\Delta J| = 2$ ) of neutron rich copper isotopes in mass range $72 \leq A \leq 82$ under stellar conditions. We compared our computed terrestrial $\beta$ -decay half-life values with previous calculations and experimental results. It was concluded that the pn-QRPA calculation is in good accordance with measured data. Our study suggests that the addition of rank (0 and 1) operators in FF transitions can further improve the comparison which remain unattended at this stage. The deformed pn-QRPA model was employed for the estimation of GT and U1F stellar electron emission ( $\beta^{-}$ -decay) rates over wide range of stellar temperature (0.01 GK–30 GK) and density ( $10\mbox{--}10^{11}\mbox{ g}/\mbox{cm}^{3}$ ) domains for astrophysical applications. Our study shows that, in high density and low temperature regions, the contribution of U1F rates to total electron emission rates of neutron-rich copper nuclei is negligible.

Gamma ray heating rates are thought to play a crucial role during the pre-supernova stage of high mass stars. Gamma ray heating rates, due to β±-decay and electron (positron) capture on chromium isotopes, are calculated using proton-neutron quasiparticle random phase approximation theory. The electron capture significantly affects the lepton fraction (Ye) and accelerates the core contraction. The gamma rays emitted as a result of weak processes heat the core and tend to hinder the cooling and contraction due to electron capture and neutrino emission. The emitted gamma rays tend to produce enormous entropy and set the convection to play its role at this stage. The gamma heating rates, on 50-60Cr, are calculated for the density range 10 < ρ (g.cm-3) < 1011 and temperature range 107 < T (K) < 3.0×1010.

The structure and the weak interaction mediated rates of the heavy waiting point (WP) nuclei 80Zr, 84Mo, 88Ru, 92Pd and 96Cd along $N = Z$ line were studied within the interacting boson model-1 (IBM-1) and the proton-neutron quasi-particle random phase approximation (pn-QRPA). The energy levels of the $N = Z$ WP nuclei were calculated by fitting the essential parameters of IBM-1 Hamiltonian and their geometric shapes were predicted by plotting potential energy surfaces (PESs). Half-lives, continuum electron capture rates, positron decay rates, electron capture cross sections of WP nuclei, energy rates of $\beta$ -delayed protons and their emission probabilities were later calculated using the pn-QRPA. The calculated Gamow-Teller strength distributions were compared with previous calculation. We present positron decay and continuum electron capture rates on these WP nuclei under $\mathit{rp}$ -process conditions using the same model. For the $\mathit{rp}$ -process conditions, the calculated total weak rates are twice the Skyrme $\mbox{HF}+\mbox{BCS}+\mbox{QRPA}$ rates for 80Zr. For remaining nuclei the two calculations compare well. The electron capture rates are significant and compete well with the corresponding positron decay rates under $\mathit{rp}$ -process conditions. The finding of the present study supports that electron capture rates form an integral part of the weak rates under $\mathit{rp}$ -process conditions and has an important role for the nuclear model calculations.

The temperature dependences of resistance, impedance and capacitance of semitransparent sensor having structure ITO/PTB7-Th:PC[Formula: see text]BM/Graphene composite (semisurface type) were investigated. The transparency of the sensor was 58–60%. The dependences of the resistance, impedance and capacitance at different frequencies 100 Hz, 1 kHz, 10 kHz, 100 kHz and 200 kHz and temperature in the range of 23.8–80[Formula: see text]C for the sensor were studied. It was observed that as the temperature increased from 23.8[Formula: see text]C to 80[Formula: see text]C, the resistance and impedance (at 1 kHz) of the samples decreased, on average, by a factor of 3.51 and 3.79, respectively. At same experimental conditions (1 kHz), the capacitances of the samples also decreased by a factor of 9.6. It was also noted that as frequency increased from 100 Hz to 200 kHz, the impedance of the sensor decreased by a factor of 21 and 12, at temperatures 24[Formula: see text]C and 58[Formula: see text]C, respectively. Under the same conditions, the capacitance decreased by a factor of 30 and 28, respectively. The temperature resistance coefficients were measured to be −1.31%/[Formula: see text]C, −1.30%/[Formula: see text]C, −1.27%/[Formula: see text]C, −0.84%/[Formula: see text]C, −0.72%/[Formula: see text]C and −0.33%/[Formula: see text]C for R, Z (100 Hz), Z (1 kHz), Z (10 kHz), Z (100 kHz) and Z (200 kHz), respectively. For capacitance measurement, the temperature capacitance coefficients were measured as −1.39%/[Formula: see text]C, −1.38%/[Formula: see text]C, −1.37%/[Formula: see text]C, −1.36%/[Formula: see text]C and −1.34%/[Formula: see text]C, respectively. The semitransparent PTB7-Th- and PC[Formula: see text]BM-based temperature sensor can be used for measurement of the temperature as a teaching aid in situations where visual control of illumination and light intensity is required.

We revisit the computation of the phase space factors (PSF) involved in the positron decay and EC processes for a large number of nuclei of experimental interest. To obtain the electron/positron wave functions, we develop a code for solving accurately the Dirac equation with a nuclear potential derived from a realistic proton density distribution in the nucleus. The finite nuclear size (FNS) and screening effects are included through recipes which differ from those used in previous calculations. Comparing our results with previous calculations, performed with the same Q-values, we find a close agreement for positron decays, while, for the EC process, there are relevant differences. For the EC process, we also find that the screening effect has a notable influence on the computed PSF values especially for light nuclei. Further, we recomputed the same PSF values but using the most recent Q-values reported in literature. In several cases, the new Q-values differ significantly from the older ones, leading to large differences in the PSF values as compared with previous results. Our new PSF values can contribute to more reliable calculations of the beta-decay rates, used in the study of nuclei far from the stability line and stellar evolution.

We calculate Gamow–Teller strength distributions for $\beta \beta$ -decay nuclei ${}^{76}\mbox{Ge}$ and ${}^{82}\mbox{Se}$ using the deformed pn-QRPA model. We use a deformed Nilsson basis and consider pairing correlations within the deformed BCS theory. Ground state correlations and two-particle and two-hole mixing states were included in our pn-QRPA model. Our calculated strength distributions were compared with experimental data and previous calculation. The total Gamow–Teller strength and centroid placement calculated in our model compares well with the measured value. We calculate $\beta$ -decay and positron capture rates on ${}^{76}\mbox{Ge}$ and ${}^{82}\mbox{Se}$ in supernovae environments and compare them to those obtained from experimental data and previous calculation. Our study shows that positron capture rates command the total weak rates at high stellar temperatures. We also calculate energy rates of $\beta$ -delayed neutrons and their emission probabilities.

Gamow-Teller transitions in isotopes of chromium play a consequential role in the presupernova evolution of massive stars. $\beta$-decay and electron capture rates on chromium isotopes significantly affect the time rate of change of lepton fraction ($\dot{Y_{e}}$). Fine-tuning of this parameter is one of the key for simulating a successful supernova explosion. The (anti)neutrinos produced as a result of electron capture and $\beta$-decay are transparent to stellar matter during presupernova phases. They carry away energy and this result in cooling the stellar core. In this paper we present the calculations of Gamow-Teller strength distributions and (anti)neutrino energy loss rates due to weak interactions on chromium isotopes of astrophysical importance. We compare our results with measured data and previous calculations wherever available., Comment: 22 pages, 12 figures, 5 tables. arXiv admin note: text overlap with arXiv:1602.06134

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., Comment: 22 pages, 10 figures, 7 tables. arXiv admin note: text overlap with arXiv:1301.5225 by other authors

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.

In a recent study by Cole et al. [A. L. Cole et al., Phys. Rev. C 86 (2012) 015809], it was concluded that quasi-particle random phase approximation (QRPA) calculations show larger deviations and overestimate the total experimental Gamow–Teller (GT) strength. It was also concluded that QRPA calculated electron capture rates exhibit larger deviation than those derived from the measured GT strength distributions. The main purpose of this study is to probe the findings of the Cole et al. paper. This study gives useful information on the performance of QRPA-based nuclear models. As per simulation results, the capturing of electrons that occur on medium heavy isotopes have a significant role in decreasing the ratio of electron-to-baryon content of the stellar interior during the late stages of core evolution. We report the calculation of allowed charge-changing transitions strength for odd-[Formula: see text] [Formula: see text]-shell nuclei ([Formula: see text]Sc and [Formula: see text]Mn) by employing the deformed pn-QRPA approach. The computed GT transition strength is compared with previous theoretical calculations and measured data. For stellar applications, the corresponding electron capture rates are computed and compared with rates using previously calculated and measured GT values. Our finding shows that our calculated results are in decent accordance with measured data. At higher stellar temperature, our calculated electron capture rates are larger than those calculated by independent particle model (IPM) and shell model. It was further concluded that at low temperature and high density regions, the positron emission weak-rates from [Formula: see text]Sc and [Formula: see text]Mn may be neglected in simulation codes.

Charge-changing transitions play a significant role in stellar weak-decay processes. The fate of the massive stars is decided by these weak-decay rates including lepton (positron and electron) captures rates, which play a consequential role in the dynamics of core collapse. As per previous simulation results, weak interaction rates on nickel (Ni) isotopes have significant influence on the stellar core vis-à-vis controlling the lepton content of stellar matter throughout the silicon shell burning phases of high mass stars up to the presupernova stages. In this paper, we perform a microscopic calculation of Gamow–Teller (GT) charge-changing transitions, in the [Formula: see text]-decay and electron capture (EC) directions, for neutron-rich Ni isotopes ([Formula: see text]Ni). We further compute the associated weak-decay rates for these selected Ni isotopes in stellar environment. The computations are accomplished by employing the deformed proton–neutron quasiparticle random phase approximation (pn-QRPA) model. A recent study showed that the deformed pn-QRPA theory is well suited for the estimation of GT transitions. The astral weak-decay rates are determined over densities in the range of 10–10[Formula: see text][Formula: see text]g/cm3and temperatures in the range of 0.01[Formula: see text]–30[Formula: see text][Formula: see text]K. The calculated lepton capture rates are compared with the previous calculation of Pruet and Fuller (PF). The overall comparison demonstrates that, at low stellar densities and high temperatures, our EC rates are bigger by as much as two orders of magnitude. Our results show that, at higher temperatures, the lepton capture rates are the dominant mode for the stellar weak rates and the corresponding lepton emission rates may be neglected.

We calculate the temperature-dependent nuclear partition functions (TDNPFs) and nuclear abundances for 728 nuclei, assuming nuclear statistical equilibrium (NSE). The theories of stellar evolution support NSE. Discrete nuclear energy levels have been calculated microscopically, using the pn-QRPA theory, up to an excitation energy of 10 MeV in the calculation of the TDNPFs. This feature of our paper distinguishes it from previous calculations. Experimental data is also incorporated wherever available to ensure the reliability of our results. Beyond 10 MeV, we employ a simple Fermi gas model and perform integration over the nuclear level densities to approximate the TDNPFs. We calculate nuclidic abundances, using the Saha equation, as a function of three parameters: stellar density, stellar temperature and the lepton-to-baryon content of stellar matter. All these physical parameters are considered to be extremely important in the stellar interior. The results obtained in this paper show that the equilibrium configuration of nuclei remains unaltered by increasing the stellar density (only the calculated nuclear abundances increase by roughly the same order of magnitude). Increasing the stellar temperature smoothes the equilibrium configuration showing peaks at the neutron-number magic nuclei.