Ground-state Nuclear Properties of Neutron-rich Copper Isotopes and Lepton Capture Rates in Stellar Matter

Abstract

This study essentially consists of two separate investigations where we study neutron-rich isotopes of copper. Two different nuclear models were selected to perform the two investigations. In the first part of this paper, the nuclear ground-state properties of neutron-rich copper isotopes (72 ≤ A ≤ 82) have been studied with the help of the relativistic mean field (RMF) model. The second portion of this paper is dedicated to calculation of lepton capture rates in stellar environment. Ground and excited states of GT and U1F strength functions were calculated in a microscopic way employing the deformed proton-neutron quasiparticle random phase approximation (pn-QRPA) model. The lepton capture rates were computed on a wide temperature range of (0.01-30)×10 9 K and stellar density range of (10-10 11) g/cm 3. We compared our computed half-lives (GT + U1F) with previous theoretical and measured results. Our calculated terrestrial half-lives agree well with the measured ones. Our study shows that, at high stellar temperatures, allowed GT and, specially, U1F positron capture rates dominate the competing β-decay rates. For a better description of presupernova evolutionary phases of massive stars, simulators are recommended to take into account lepton capture rates on neutron-rich copper isotopes presented in this work.

Electron Capture on Nuclei in Stellar Environment

“…As discussed before, stellar electron capture plays a crucial role in the late stages of evolution of a massive star, in both the pre-supernova and supernova phases [1,3,17,18]. In the pre-supernova phase, electrons are captured by nuclei with A ≤ 60-65 [8,10,12,19,22,25], while the collapse-phase electron capture is carried out on heavier and more neutron-rich nuclei, with Z < 40 and N ≥ 40 [12,13,[20][21][22]. The above findings have been taken into account in choosing the set of the nuclear systems studied below.…”

“…After a comparison of these two Tables, we conclude that as the mass number A increases and moves to heavier nuclear isotopes, for a given incident electron energy E e , the partial cross-sections also increase. During the core-collapse phase (densities at ρ ≥ 10 10 g cm −3 and temperatures at T 1.0 MeV), the electron-capture process took place on heavier and more neutron-rich nuclei, with Z < 40 and N ≥ 40 [12,13,[20][21][22]. In this sub-section, cross-section results for the stellar electron capture on the 66 Zn and 90 Zr parent nuclei are presented and discussed.…”

“…Motivated by this effect, many authors emphasized the calculation of e − -capture rates based on the GT-type contributions (at momentum transfer q → 0) and evaluated them on the basis of the dominance of GT transitions [8,10,12,19,22,25]. In our previous work [7], by considering momentum-dependent operators, we saw that in addition to GT transitions, the Fermi (as well as the first-and second-forbidden) transitions hlmay also contribute non-negligible e − -capture rates [8,11,20,22,26].…”

“…Furthermore, the Fermi energy of the degenerate electron gas is sufficiently large compared to the threshold energy E thr (the negative Q value of the reactions involved) in the interior of the stars [19] and leads to appreciable e − -capture on nuclei that reduces the Y e [8,20]. It is worth noting that the nuclear matter in the stellar core is neutronized, and in this way, the electron pressure is reduced while the energy as well as the entropy decrease.…”

“…This means that for sufficiently low entropy, the matter composition is dominated by the nuclei with very high binding energy [2]. Under these conditions, e − -capture occurs in more neutron-rich and heavier nuclei, A ≥ 65 [12,13,[20][21][22][27][28][29], and as a consequence, the nuclear composition is shifted to more neutron-rich and heavier nuclei [2,3,22].…”