arXiv subjects

O. Niţescu

Publications and source records attributed to O. Niţescu.

3 recordsLinked to original sources

arXiv2023

Atomic corrections for the unique first forbidden $β$ transition of $^{187}$Re

In this paper, we reexamine one of the most promising candidates for determining the neutrino mass scale -- the unique first forbidden $β$ transition from $^{187}$Re($5/2^+$) to $^{187}$Os($1/2^-$). With the lowest-known ground-state to ground-state $Q$-value for a $β$ transition at $2.4709$ keV, rhenium's $β$ decay can offer insights into the neutrino mass scale puzzle. However, understanding its electron spectrum is a complex task. Besides involving a mixture of $s_{1/2}$-state and $p_{3/2}$-state electrons, the rhenium $β$ spectrum could be strongly influenced by various atomic corrections. In addition to our previous paper, we have incorporated finite nuclear size, diffuse nuclear surface, screening, and exchange corrections into the rhenium $β$ decay model. We have accounted for the last two effects within the framework of the Dirac-Hartree-Fock-Slater self-consistent method. We have discovered that both screening and exchange effects significantly alter the partial decay rates for the $s_{1/2}$- and $p_{3/2}$-state emission channels, while still maintaining the experimentally confirmed dominance of the $p_{3/2}$-state emission. The ratio between the respective decay rates has been found to be approximately $10^4$. When compared to the other corrections, the exchange effect stands out due to the modification it induces in the spectrum shape. We demonstrate that calculations with and without the exchange effect lead to entirely different shape factors for the decay spectrum. Finally, we illustrate that to preserve the linearity of the Kurie plot, it is essential to include the exchange correction in its definition. We conclude that atomic effects, especially the exchange effect, should be taken into account in current and future investigations of the neutrino mass scale from $β$ decays.

nucl-th↗

arXiv2023

Self-consistent calculations for atomic electron capture

We present a comprehensive investigation of electron capture (EC) ratios spanning a broad range of atomic numbers. The study employs a self-consistent computational method that incorporates electron screening, electron correlations, overlap and exchange corrections, as well as shake-up and shake-off atomic effects. The electronic wave functions are computed with the Dirac-Hartree-Fock-Slater (DHFS) method, chosen following a systematic comparison of binding energies, atomic relaxation energies and Coulomb amplitudes against other existing methods and experimental data. A novel feature in the calculations is the use of an energy balance employing atomic masses, which avoids approximating the electron total binding energy and allows a more precise determination of the neutrino energy. This leads to a better agreement of our predictions for capture ratios in comparison with the experimental ones, especially for low-energy transitions. We expand the assessment of EC observables uncertainties by incorporating atomic relaxation energy uncertainties, in contrast to previous studies focusing only on Q-value and nuclear level energies. Detailed results are presented for nuclei of practical interest in both nuclear medicine and exotic physics searches involving liquid Xenon detectors ($^{67}\mathrm{Ga}$, $^{111}\mathrm{In}$, $^{123}\mathrm{I}$, $^{125}\mathrm{I}$ and $^{125}\mathrm{Xe}$). Our study can be relevant for astrophysical, nuclear, and medical applications.

nucl-th↗

arXiv2023

Exchange correction for allowed $β$-decay

We investigate the exchange effect between the final atom's bound electrons and those emitted in the allowed $β$-decay of the initial nucleus. The electron wave functions are obtained with the Dirac-Hartree-Fock-Slater self-consistent method, and we ensure the orthogonality between the continuum and bound electron states, in the potential of the final atom, by modifying the last iteration of the self-consistent method. We show that orthogonality plays an essential role in calculating the exchange correction. After imposing the orthogonality, we found considerable differences in magnitude and energy dependence compared to previous results. We argue that our findings can solve the mismatch between the previous predictions and experimental measurements in the low-energy region of the $β$ spectrum. First, we calculate the exchange effect for the low-energy $β$ transitions in $^{14}$C, $^{45}$Ca, $^{63}$Ni, and $^{241}$Pu, recently investigated in the literature. Next, we compute the total exchange correction for a large number of $β$ emitters, with $Z$ from $1$ to $102$. From the systematic study, we found that for ultra-low energy, i.e., $5$ eV, the $Z$ dependence of total exchange effect is affected by $s_{1/2}$ and $p_{1/2}$ orbitals closure. We also show that the contributions from orbitals higher than $2s_{1/2}$ orbital are essential for correctly calculating the total effect, especially for low energies and heavy $β$ emitters. Finally, we provide an analytical expression of the total exchange correction for each atomic number for easy implementation in experimental investigations.

physics.atom-ph↗