Hot Nuclei Research Articles

Neutrinos from pre-supernova in the framework of TQRPA method

Abstract We propose a new method for calculating spectra and luminosities for (anti)neutrinos produced in the pre-supernova environment by weak processes with hot nuclei. It is based on the thermal quasiparticle random phase approximation (TQRPA), that allows microscopic thermodynamically consistent calculations of the weak-interaction response of nuclei at finite temperatures. For realistic representative pre-supernova conditions from the stellar evolution code MESA, we compute (anti)neutrino luminosities and spectra arising from neutral- and charged-current weak reactions with hot 56Fe and compare them with the contribution of thermal processes. We find that the TQRPA approach produces not only a higher total luminosity of electron neutrinos (mainly born in the electron capture reaction), compared to the standard technique based on the large-scale shell model (LSSM) weak-interaction rates, but also a harder neutrino spectrum. Besides, applying the TQRPA and LSSM, we find that in the context of electron antineutrino generation, the neutral-current nuclear de-excitation (ND) process via neutrino-antineutrino pair emission is at least as important as the electron-positron pair annihilation process. We also show that flavor oscillations enhance the high-energy contribution of the ND process to the electron antineutrino flux. This could potentially be important for pre-supernova antineutrino registration by the Earth’s detectors.

Classification of pairing phase transition in the hot nucleus

The hot nucleus [Formula: see text] is investigated using covariant density functional theory, where the shell-model-like approach treats the pairing correlation. Lee–Yang’s theorem is applied to classify the pairing phase transition by analyzing the distribution of zeros of the partition function in the complex temperature plane. The distribution of zeros of the partition function converges with increasing particle numbers and illustrates the characteristics of the phase transition. In our calculations, we determine the first-order of the phase transition near the critical temperature. Different seniority states show the pairing phase transition from a superfluid to a normal phase, ranging from fully paired states to completely unpaired states.

Expanding the limits of nuclear stability at finite temperature

Properties of nuclei in hot stellar environments such as supernovae or neutron star mergers are largely unexplored. Since it is poorly understood how many protons and neutrons can be bound together in hot nuclei, we investigate the limits of nuclear existence (drip lines) at finite temperature. Here, we present mapping of nuclear drip lines at temperatures up to around 20 billion kelvins using the relativistic energy density functional theory (REDF), including treatment of thermal scattering of nucleons in the continuum. With extensive computational effort, the drip lines are determined using several REDFs with different underlying interactions, demonstrating considerable alterations of the neutron drip line with temperature increase, especially near the magic numbers. At temperatures T ≲ 12 billion kelvins, the interplay between the properties of nuclear effective interaction, pairing, and temperature effects determines the nuclear binding. At higher temperatures, we find a surprizing result that the total number of bound nuclei increases with temperature due to thermal shell quenching. Our findings provide insight into nuclear landscape for hot nuclei, revealing that the nuclear drip lines should be viewed as limits that change dynamically with temperature.

Neutrino Spectrum and Energy Loss Rates Due to Weak Processes on Hot 56Fe in Pre-Supernova Environment

Applying TQRPA calculations of Gamow–Teller strength functions in hot nuclei, we compute the (anti)neutrino spectra and energy loss rates arising from weak processes on hot 56Fe under pre-supernova conditions. We use a realistic pre-supernova model calculated by the stellar evolution code MESA. Taking into account both charged and neutral current processes, we demonstrate that weak reactions with hot nuclei can produce high-energy (anti)neutrinos. We also show that, for hot nuclei, the energy loss via (anti)neutrino emission is significantly larger than that for nuclei in their ground state. It is found that the neutral current de-excitation via the νν¯-pair emission is presumably a dominant source of antineutrinos. In accordance with other studies, we confirm that the so-called single-state approximation for neutrino spectra might fail under certain pre-supernova conditions.

Description of temperature effects on proton radioactivity

Role of thermal effects of hot parent nuclei in the characteristics of proton emission process has been studied for the first time by analyzing the surface energy coefficient γ entering in the calculation of proximity potential for 15 experimentally detected proton emitters (67≤Z≤83) in the isomeric states. In the present work, the proton-nucleus interaction potentials are obtained by using one of the latest versions of proximity potential formalism proposed by Zhang et al. in 2013. In addition, the quantum mechanical tunneling probability and consequently the proton radioactivity half-lives are calculated within the framework of the semiclassical WKB method. We present a new temperature-dependent (TD) form of the coefficient γ based on thermal properties of hot proton emitters in the framework of the finite-temperature generalized liquid-drop model. By integrating temperature dependence into the surface energy coefficient of proximity potential Zhang 2013, a reasonable description of the experimental half-lives of proton radioactivity is achieved. We extend the modified form of the Zhang 2013 model to predict the proton radioactivity half-lives of 6 proton emitters in the isomeric states, whose proton radioactivity is energetically allowed or observed, but has not been quantified yet. The obtained results reveal that the predictions by our model are in good agreement with the other theoretical methods, namely UDLP proposed by Qi et al. (2012) [19] and NGNL proposed by Chen et al. (2019) [49]. In this work, we also attempt to introduce an empirical formula for estimating the half-lives of one-proton emission process from the excited states by taking into account both the thermal effects of all the available 15 hot proton emitters and the contribution of centrifugal potential. Our results indicate that the calculated proton radioactivity half-lives by the current formula are in good agreement with experimental data. This means that the correlation between the half-lives of proton decay processes and the nuclear temperature T of proton emitters can be suitable to deal with the proton radioactivity one-proton transition from isomeric states.

High-order partition function correction effect on the nuclear thermal quantities

Higher-order approximation based on Taylor expansion over the saddle point is employed to approach the partition function of a hot nucleus in the presence of the like-particle pairing correlations. Analytical expressions have been derived for the correction terms of different thermodynamic quantities such as energy, entropy and heat capacity. Furthermore, the theory has been applied to the schematic and realistic models. It is found that the correction terms are temperature-dependent functions and are more deeply sensitive to the pairing gap in the vicinity of the critical temperature.

Systematic analysis of the decay of Fl*287,288,290,292 formed in the complete fusion reactions Pu239,240,242,244+Ca48 including Skyrme forces

The fusion evaporation residue cross sections for the decay of the compound nuclear system $^{287,288,290,292}\mathrm{Fl}^{*}$ via $2n$- to $5n$-decay channels, synthesized in $^{239,240,242,244}\mathrm{Pu}+^{48}\mathrm{Ca}$, are studied using the dynamical cluster-decay model (DCM), including quadrupole deformations ${\ensuremath{\beta}}_{2i}$ for compact hot orientations ${\ensuremath{\theta}}_{i}$ at various excitation energies ${E}^{*}=32.5$ to 52.6 MeV. For the nucleus-nucleus interaction potentials, we have employed the Skyrme energy density functional based on the semiclassical extended Thomas-Fermi approach under frozen density approximation. Here, within the DCM, the Skyrme forces used are SLy4, ${\mathrm{SkM}}^{*}$, and, KDE0(v1). The DCM makes use of a single parameter, the neck-length parameter $\mathrm{\ensuremath{\Delta}}R$ that takes different values for different processes at a given temperature and provides an excellent fit to the measured data, independently of the choice of Skyrme force used. We make predictions of probable fusion-fission and quasifission mass regions of fragments and then calculate the evaporation residue cross sections ${\ensuremath{\sigma}}_{\mathrm{ER}}$ for experimentally unobserved neutron channels. Further, the product ${P}_{\mathrm{CN}}{P}_{\mathrm{surv}}$ of compound nucleus (CN) fusion probability ${P}_{\mathrm{CN}}$ and survival probability ${P}_{\mathrm{surv}}$ is calculated to determine the reduced evaporation residue cross section ${\ensuremath{\sigma}}_{\mathrm{ER}}/{\ensuremath{\sigma}}_{\mathrm{fusion}}$, denoted as ${\ensuremath{\sigma}}_{\mathrm{ER}}^{\mathrm{reduced}}$, and we have seen that ${P}_{\mathrm{surv}}$ is the main dominant factor in the product ${P}_{\mathrm{CN}}{P}_{\mathrm{surv}}$. To this end, we have analyzed the effects of mass asymmetry and isospin effect of target nucleus on the ${\ensuremath{\sigma}}_{\mathrm{ER}}$ and have found that the ${\ensuremath{\sigma}}_{\mathrm{ER}}$ for the production of superheavy element ${\mathrm{Fl}}^{*}$ increases slowly with increasing neutron number of the target nucleus. We have also searched for all possible target-projectile combinations forming the hot compound nucleus ${\mathrm{Fl}}^{*}$ at the excitation energy ${E}^{*}$ for compact-hot configurations and have also calculated the fusion evaporation residue cross sections for the proposed new reactions synthesizing Fl.

Superoperator Approach to the Theory of Hot Nuclei and Astrophysical Applications. III: Neutrino–Nucleus Reactions in Stars

Superoperator Approach to the Theory of Hot Nuclei and Astrophysical Applications. III: Neutrino–Nucleus Reactions in Stars

Superoperator Approach to the Theory of Hot Nuclei and Astrophysical Applications: I—Spectral Properties of Hot Nuclei

Superoperator Approach to the Theory of Hot Nuclei and Astrophysical Applications: I—Spectral Properties of Hot Nuclei

Superoperator Approach to the Theory of Hot Nuclei and Astrophysical Applications: II—Electron Capture in Stars

Superoperator Approach to the Theory of Hot Nuclei and Astrophysical Applications: II—Electron Capture in Stars

Correlation between nuclear temperature and symmetry energy in subsaturation nuclear matter density

Herein, a study of the correlation between nuclear temperature and symmetry energy is presented for heavy ion collisions at intermediate energies via the isospin-dependent quantum molecular-dynamics model. It is found that different symmetry energy parameters change the density and kinetic energy distribution of the hot nuclei. More importantly, nuclear temperatures that are based on kinetic energy properties can be used to study symmetry energy information.

Thermal properties of the superheavy nucleus of 292120172

The nuclear structure and thermal quantities of the superheavy nucleus of [Formula: see text] are studied in a recent developed framework of the Finite-Temperature Hartree–Fock–Bogoliubov (FT-HFB) by using a zero-range pairing and including the continuum effects. Analyzing the shell structure of this nucleus at both zero and finite temperature shows a dependence on the various Skyrme-type forces used and a shell closure occurrence at Z = 120 for protons and N = 172 for neutrons with a large gap energy where the pseudo-spin-orbit effects play a primordial role in the shell sequence at finite temperature which confirm the double magicity of [Formula: see text]. Thermodynamic quantities are also studied in the same framework where the results are qualitatively similar to what are obtained in case of the hot ordinary nuclei.

Angular momentum effects on the decay modes of hot compound nuclei formed in 86Kr+134,138Ba reactions

The dependence of decay modes of hot compound nuclei formed in [Formula: see text]Kr[Formula: see text]Ba reactions on the angular momentum has been analyzed using the dynamical cluster-decay model. This has been done by analyzing the change of fragmentation potential, preformation probability, penetrability and cross-section as a function of the fragment mass number at various values of the angular momentum. The evaporation residue cross-section calculated using dynamical cluster-decay model has been compared with the measured one for the channels: [Formula: see text], [Formula: see text], [Formula: see text] for the decay of [Formula: see text]U[Formula: see text] and [Formula: see text] for [Formula: see text]U[Formula: see text]. The summed up fragment cross-sections for the light particles, intermediate mass fragments and fission fragments as a function of angular momentum have been studied which gives an idea for the change of reaction mechanism with angular momentum. The charge distribution of the fission fragment cross-section shows an odd–even staggering, i.e., the probability of even-Z fission fragments is relatively higher than others. The mass distributions obtained within the dynamical cluster-decay model for the decay of [Formula: see text]U[Formula: see text] are in conformity with mass distributions determined by means of the double kinetic-energy technique in literature. The position of the most probable channel has been found to be fixed to a constant atomic number instead of mass number.

Properties of hot finite nuclei and associated correlations with infinite nuclear matter

This work aims to study the various thermal characteristics of nuclei in view of the saturation and critical behavior of infinite nuclear matter. The free energy of a nucleus is parametrized using the density and temperature-dependent liquid-drop model, and interaction among nucleons is worked out within the effective relativistic mean-field theory (E-RMF). The effective mass (${m}^{*}$) and critical temperature of infinite symmetric nuclear matter (${T}_{c}$) of a given E-RMF parameter force play a seminal role in the estimation of thermal properties. Larger ${m}^{*}$ and ${T}_{c}$ of the E-RMF set estimate larger excitation energy, level density, and limiting temperature $({T}_{l})$ for a given nucleus. The limiting temperature of a nucleus also depends on the behavior of the nuclear gas surrounding the nucleus, making the equation of state (EoS) at subsaturation densities an important input. A stiff EoS in the subsaturation region estimates a higher pressure of the nuclear gas, making it less stable. Since ${T}_{c}$ plays an important part in these calculations, we perform a Pearson correlation statistical study of twenty E-RMF parameter sets, satisfying the relevant constraint on the EoS. Effective mass seems to govern the thermal characteristics of infinite as well as finite nuclear matter in the framework of E-RMF theory.

Thermodynamically Consistent Description of One-Phonon States Fragmentation in Hot Nuclei

Thermodynamically Consistent Description of One-Phonon States Fragmentation in Hot Nuclei

Temperature effects on neutron-capture cross sections and rates through electric dipole transitions in hot nuclei

The temperature evolution of electric dipole transition strengths of Sn isotopes is studied using self-consistent quasiparticle random phase approximation (QRPA) and finite-temperature RPA models based on a relativistic density functional. For tin isotopes lighter than $^{132}\mathrm{Sn}$, temperature only shows its effect at high values of 2 MeV, while for neutron-rich tin isotopes heavier than $^{132}\mathrm{Sn}$, the low-lying strength distributions get fragmented and spread to the lower-energy region already at temperature of 1 MeV. Using these electric dipole transition strengths as inputs for the talys code, the temperature effects on $(n,\ensuremath{\gamma})$ cross sections are studied. For tin isotopes lighter than $^{132}\mathrm{Sn}$, temperature causes an enhancement of neutron-capture cross section at high temperatures of 2 MeV, while for neutron-rich tin isotopes heavier than $^{132}\mathrm{Sn}$, the cross section is largely enhanced already at temperature $T=1.0$ MeV, and the bump of cross section caused by the pygmy dipole resonance also becomes broader. The change in neutron-capture rate can be as large as 70% for $^{136}\mathrm{Sn}$, considering the temperature effects on electric dipole transition strength in the final compound nucleus with a temperature of 0.86 MeV (corresponding to $T=10$ GK in the astrophysical environment). The change is around 20% for tin isotopes lighter than $^{132}\mathrm{Sn}$ and above 40% for those heavier than $^{132}\mathrm{Sn}$.

Characteristics of Jupiter's X‐Ray Auroral Hot Spot Emissions Using Chandra

AbstractTo help understand and determine the driver of jovian auroral X‐rays, we present the first statistical study to focus on the morphology and dynamics of the jovian northern hot spot (NHS) using Chandra data. The catalog we explore dates from December 18, 2000 up to and including September 8, 2019. Using a numerical criterion, we characterize the typical and extreme behavior of the concentrated NHS emissions across the catalog. The mean power of the NHS is found to be 1.91 GW with a maximum brightness of 2.02 Rayleighs (R), representing by far the brightest parts of the jovian X‐ray spectrum. We report a statistically significant region of emissions at the NHS center which is always present, the averaged hot spot nucleus (AHSNuc), with mean power of 0.57 GW and inferred average brightness of 1.2 R. We use a flux equivalence mapping model to link this distinct region of X‐ray output to a likely source location and find that the majority of mappable NHS photons emanate from the pre‐dusk to pre‐midnight sector, coincident with the dusk flank boundary. A smaller cluster maps to the noon magnetopause boundary, dominated by the AHSNuc, suggesting that there may be multiple drivers of X‐ray emissions. On application of timing analysis techniques (Rayleigh, Monte Carlo, Jackknife), we identify several instances of statistically significant quasi‐periodic oscillations (QPOs) in the NHS photons ranging from 2.3 to 36.4 min, suggesting possible links with ultra‐low frequency activity on the magnetopause boundary (e.g., dayside reconnection, Kelvin‐Helmholtz instabilities).

Spitzer/IRAC Tarafından Seçilen AGN'lerin X-ışın Özellikleri

Spitzer/IRAC color selection is a powerful tool to identify hot accreting nuclei, that is to say AGN, in galaxies. In this study, mid-infrared detected candidate 36 AGNs are used that are selected from the Spitzer Survey of Stellar Structures in Galaxies (S4G) sample consisting of more than 2500 galaxies together with its extension sample of more than 400 galaxies by İkiz et al., (2020). Mid-infrared color selection method is tested by examining the X-ray properties of the galaxies via the XMM-Newton and Chandra. Using the X-ray data, we demonstrate that galaxies displaying hot mid-infrared nuclei stand out as (candidate) active galaxies. 64% of mid-infrared-selected AGN are detected at X-ray energies in XMM-Newton and Chandra data. It has been hypothesized that IRAC sources with AGN colors that lack X-ray detections are predominantly high-luminosity AGN that are obscure.

Thermodynamics of pairing transition for odd- A nuclei

The hot nucleus $^{171}$Yb is investigated by the covariant density functional theory with the PC-PK1 effective interaction. The thermodynamic quantities are evaluated with the canonical ensemble theory. The pairing correlations is treated by the shell-model-like approach, in which the particle numbers are conserved strictly and in which the blocking effect is handled exactly. An S-shaped heat capacity versus temperature of $^{171}$Yb appears. It has been studied in terms of the blocking effect, the single-particle levels, the pairing gap, and defined seniority components, and compared to the heat capacity of $^{172}$Yb. The pairing transition from the superfluid state to the normal state can result in the S-shaped heat capacity of $^{172}$Yb where the one-pair-broken and two-pair-broken states dominate, while the single-particle level structure near the Fermi surface is associated with the S-shaped heat capacity of $^{171}$Yb. For odd-A nuclei, although the one-pair-broken and two-pair-broken states still contribute, the pairing gap and the pairing transition is relatively weak. The S-shaped heat capacity could be affected due to the blocking of the single-particle level near the Fermi surface.

Proton entropy excess and possible signature of pairing reentrance in hot nuclei

The entropy excess caused by one proton (proton entropy excess) has been extracted for several pairs of medium and heavy mass nuclei such as (237U and 238Np), (231Th and 232Pa), (211Po and 212At), (196Pt and 197Au), and (90Y and 91Zr) using the available nuclear level density data. The nature of entropy excess as a function of excitation energy E⁎ is found in a reasonable agreement with the microscopic calculations based on the exact pairing plus independent-particle model at finite temperature (EP+IPM). It is observed that the proton entropy excess is ∼0.1−0.5kB for the spherical systems and ∼1.0−1.2kB for the deformed ones, which is notably smaller than that of neutron entropy excess (∼1.3−2.0kB). This is due to the effect of Coulomb interaction as well as the single-particle level density of protons, which is less than that of neutrons. Moreover, a peak-like structure in the entropy excess observed at low E⁎<1 MeV is possibly associated with the pairing reentrance phenomenon caused by the weakening of blocking effect in odd nuclei at low temperature within the EP+IPM. However, this peak-like structure, which is more pronounced in the spherical nuclei than in the deformed isotopes, is not well supported by experimental observation due to strong fluctuations of the measured data. Hence, further experimental and theoretical studies are called in order to understand this effect.