Narrow Results

Self-consistent theory frameworks have been introduced for description of excitations in nuclei at finite temperature, based on energy density functionals formulated using i) relativistic mean field Lagrangian with density dependent meson-nucleon vertex functions, and ii) Skyrme-type functionals. Finite temperature random phase approximation (FTRPA) has been employed in description of multipole excitations and charge-exchange modes. It is shown that in the temperature range T = 1–2 MeV additional transition strength appears at low energies due to thermal unblocking of single-particle orbitals close to the Fermi level. Within the finite temperature Hartree-Fock+RPA based on Skyrme functionals, the electron capture cross sections have been studied for target nuclei at temperatures relevant in modeling the supernova evolution.

The influence of strong electron screening (SES) on electron capture (EC) plays a key role in supernovae explosions. We investigate the influence of SES on EC of iron group nuclei by the linear response theory model (LRTM) and the plasma sphere theory model (PSTM). The corrections of the Q-value, the electron chemical potential, electron energy, the Coulomb wave correction factor, and nuclear blinding energy by SES are considered. The screening rates even decrease by $\sim 81.89\%$ and $\sim 78.32\%$ by PSTM and LRTM, respectively. We compare our screening results with those of Fuller et al. (FFN), Aufderheide et al. (AUFD), Nabi et al. (NKK), and Martinez-Pinedo et al. (MLD). Our screening rates can be lowered about by $1\sim 2$, 2, and 1 orders of magnitude than those of AUFD (FFN), NKK, and MLD, respectively.

The cross-section ratios R of transfer ionization to single electron capture of Helium atom induced by fluorine ions in the strong-interaction region were measured by means of the position-sensitive-detection and the time-of-flight (TOF) technologies. The velocity and charge state dependence of R were studied. It is found that the R decreases when the 2q/v increases, where q and v are the charge state and velocity of projectile respectively. In this energy region the transfer ionization can be look as Two-Step process that one target electron is captured, and another electron is ionized.

The Cosmic Microwave Background (CMB) yields information about our Universe at around 380,000 years after the Big Bang (BB). Due to the weak interaction of the neutrinos with matter, the Cosmic Neutrino Background (CNB) should give information about a much earlier time of our Universe, around one second after the BB. Probably, the most promising method to “see” the CNB is the capture of the electron neutrinos from the Background by Tritium, which then decays into ³He and an electron with the energy of the the $Q$-value $=$ 18.562keV plus the electron neutrino rest mass. The “KArlsruhe TRItium Neutrino” (KATRIN) experiment, which is in preparation, seems presently the most sensitive proposed method for measuring the electron antineutrino mass. At the same time, KATRIN can also look by the reaction ${\nu }_e(\sim 1.95\mathrm{\text{K}}){+}^3\mathrm{\text{H}}{\to }^3\mathrm{\text{He}}+e^{-}(Q=18.6\mathrm{\text{keV}}+m_{\nu e}{c}^2)$. The capture of the Cosmic Background Neutrinos (CNB) should show in the electron spectrum as a peak by the electron neutrino rest mass above $Q$. Here, the possibility to see the CNB with KATRIN is studied. A detection of the CNB by KATRIN seems not to be possible at the moment. But KATRIN should be able to determine an upper limit for the local electron neutrino density of the CNB.

In this study, efforts were made to propose a semi-empirical equation for electron capture within the atomic number range $7\le Z\le 103$ and the mass number range of $12\le A\le 252$. About 753 nuclei were considered for the same. These nuclei were categorized into four groups based on the parities of both protons and neutrons: even(Z)–even(N), even(Z)–odd(N), odd(Z)–even(N) and odd(Z)–odd(N). Comparative analysis was carried out between the formula’s predictions and experimental data. The improved semi-empirical formula for electron capture belongs to the first category, requiring only the daughter nucleus’s atomic number and decay energy, making them a valuable tool for predicting electron capture half-lives. The present formula effectively describes even-Z-even-N cases. However, significant discrepancies occur when either Z or N is odd in nuclei, indicating that further refinement is necessary to improve.

Electron captures by atomic nuclei in dense matter are among the most important processes governing the late evolution of stars, limiting in particular the stability of white dwarfs. Despite considerable progress in the determination of the equation of state of dense Coulomb plasmas, the threshold electron Fermi energies are still generally estimated from the corresponding Q values in vacuum. Moreover, most studies have focused on nonmagnetized matter. However, some white dwarfs are endowed with magnetic fields reaching 10⁹ G. Even more extreme magnetic fields might exist in super Chandrasekhar white dwarfs, the progenitors of overluminous type Ia supernovae like SN 2006gz and SN 2009dc. The roles of the dense stellar medium and magnetic fields on the onset of electron captures and on the structure of white dwarfs are briefly reviewed. New analytical formulas are derived to evaluate the threshold density for the onset of electron captures for arbitrary magnetic fields. Their influence on the structure of white dwarfs is illustrated by simple analytical formulas and numerical calculations.

The Cosmic Microwave Background (CMB) yields information about our Universe at around 380,000 years after the Big Bang (BB). Due to the weak interaction of the neutrinos with matter, the Cosmic Neutrino Background (CNB) should give information about a much earlier time of our Universe, around one second after the BB. Probably, the most promising method to “see” the CNB is the capture of the electron neutrinos from the Background by Tritium, which then decays into ³He and an electron with the energy of the the Q-value = 18.562 keV plus the electron neutrino rest mass. The “KArlsruhe TRItium Neutrino” (KATRIN) experiment, which is in preparation, seems presently the most sensitive proposed method for measuring the electron antineutrino mass. At the same time, KATRIN can also look by the reaction ${\nu }_e(\sim 1.95\mathrm{\text{K}}){+}^3\mathrm{\text{H}}{\to }^3\mathrm{\text{He}}+e^{-}(Q=18.6\mathrm{\text{keV}}+m_{\nu e}{c}^2)$. The capture of the Cosmic Background Neutrinos (CNB) should show in the electron spectrum as a peak by the electron neutrino rest mass above $Q$. Here, the possibility to see the CNB with KATRIN is studied. A detection of the CNB by KATRIN seems not to be possible at the moment. But KATRIN should be able to determine an upper limit for the local electron neutrino density of the CNB.

Gamow-Teller transitions and stellar electron-capture rates in hot nuclei are computed using the self-consistent finite-temperature relativistic random-phase approximation (FTRRPA). The predicted electron-capture rates in stellar environment for ^54,56Fe are consistent with those obtained in the shellmodel approach. The FTRRPA provides an efficient and accurate theoretical framework for large-scale calculations of stellar electron-capture rates.