arXiv subjects

G. Martínez-Pinedo

Publications and source records attributed to G. Martínez-Pinedo.

At least 19 recordsLinked to original sources

arXiv2026

Late-time emission-line profiles from kilonova models

Numerical simulations suggest that neutron star mergers eject material with complex, non-spherical density and composition distributions. Here we use two-dimensional configurations of merger ejecta obtained from long-term hydrodynamic simulations to quantify the influence of such ejecta structure on the shapes of spectral lines in the optically thin limit. We consider three example elements of interest for kilonova modelling (selenium, tellurium and tungsten) and illustrate profile shapes for a sample of models and observer orientations. Many of our calculations yield complex profile shapes, including cases with multiple peaks and/or extended wings on scales large enough to be relevant to interpreting observations. For selenium and tellurium, our late-phase profile shapes are most sensitive to the structure of the low-velocity ejecta (~0.1c) launched after the merger from the relic black-hole torus system, while for heavier elements the contribution from the more rapidly expanding and more neutron-rich dynamical ejecta launched right after the merger is more significant and leads to broader line shapes. We also find that the dynamical influence of heating due to the decay of r-process elements can lead to considerably broader peaks than suggested by models that neglect this effect. Although idealised, our calculations demonstrate that line shapes are sensitive to the ejecta structure and could therefore constrain the polar observation angle or underlying properties of the merger that determine the spatial distributions of elements in the ejecta components, such as the binary mass ratio or even the equation of state of high-density matter.

astro-ph.HE↗

arXiv2025

Luminosity predictions for the first three ionisation stages of W, Pt and Au to probe potential sources of emission in kilonova

A large number of R-matrix calculations of electron impact excitation for heavy elements (Z > 70) have been performed in recent years for applications in fusion and astrophysics research. With the expanding interest in heavy ions due to kilonova (KN) events such as AT2017gfo and AT2023vfi, this new data can be utilised for the diagnosis and study of observed KN spectra. In this work recently computed electron-impact excitation effective collision strengths are used, for the first three ionisation stages of tungsten (W, Z = 74), platinum (Pt, Z = 78) and gold (Au, Z = 79), to construct basic collisional radiative models tailored for the late stage nebular phases of KN. Line luminosities are calculated at a range of electron temperatures and densities and the strengths of these lines for a representative ion mass are compared. For the case of W III, these optically thin intensities are additionally used to constrain the mass of this ion in both AT2017gfo and AT2023vfi. Comparing with theoretical predictions of nucleosynthesis yields from neutron-star merger simulations, broad agreement with the inferred ion masses of W is found. Furthermore, we highlight the value of W measurements by showing that the abundance of other groups of elements and outflow properties are constrained by exploiting theoretically motivated correlations between the abundance of W and that of lanthanides or third r-process peak elements. Based on simple estimates, we also show that constraints on the distribution of tungsten in the ejecta may be accessible through the line shape, which may also yield information on the neutron-star merger remnant evolution.

physics.atom-ph↗

arXiv2025

Bound-State Beta Decay of $\mathbf{\mathrm{^{205}{Tl}^{81+}}}$ Ions and the LOREX Project

Stable $^{205}$Tl ions have the lowest known energy threshold for capturing electron neutrinos ($ν_e$) of ${ E}_{ν_e}\ge50.6$\,keV. The Lorandite Experiment (LOREX), proposed in the 1980s, aims at obtaining the longtime averaged solar neutrino flux by utilizing natural deposits of Tl-bearing lorandite ores. To determine the $ν_e$ capture cross section, it is required to know the strength of the weak transition connecting the ground state of $^{205}$Tl and the 2.3 keV first excited state in $^{205}$Pb. The only way to experimentally address this transition is to measure the bound-state beta decay ($β_{b}$) of fully ionized $\mathrm{^{205}Tl^{81+}}$ ions. After three decades of meticulous preparation, the half-life of the $β_{b}$ decay of $\mathrm{^{205}Tl^{81+}}$ has been measured to be $291_{-27}^{+33}$ days using the Experimental Storage Ring (ESR) at GSI, Darmstadt. The longer measured half-life compared to theoretical estimates reduces the expected signal-to-noise ratio in the LOREX, thus challenging its feasibility.

nucl-ex↗

arXiv2024

High-temperature $^{205}$Tl decay clarifies $^{205}$Pb dating in early Solar System

Radioactive nuclei with lifetimes on the order of millions of years can reveal the formation history of the Sun and active nucleosynthesis occurring at the time and place of its birth. Among such nuclei whose decay signatures are found in the oldest meteorites, $^{205}$Pb is a powerful example, as it is produced exclusively by slow neutron captures (the s process), with most being synthesized in asymptotic giant branch (AGB) stars. However, making accurate abundance predictions for $^{205}$Pb has so far been impossible because the weak decay rates of $^{205}$Pb and $^{205}$Tl are very uncertain at stellar temperatures. To constrain these decay rates, we measured for the first time the bound-state $β^-$ decay of fully ionized $^{205}$Tl$^{81+}$, an exotic decay mode that only occurs in highly charged ions. The measured half-life is 4.7 times longer than the previous theoretical estimate and our 10% experimental uncertainty has eliminated the main nuclear-physics limitation. With new, experimentally backed decay rates, we used AGB stellar models to calculate $^{205}$Pb yields. Propagating those yields with basic galactic chemical evolution (GCE) and comparing with the $^{205}$Pb/$^{204}$Pb ratio from meteorites, we determined the isolation time of solar material inside its parent molecular cloud. We find positive isolation times that are consistent with the other s-process short-lived radioactive nuclei found in the early Solar System. Our results reaffirm the site of the Sun's birth as a long-lived, giant molecular cloud and support the use of the $^{205}$Pb--$^{205}$Tl decay system as a chronometer in the early Solar System.

nucl-ex↗

arXiv2024

Electric and magnetic dipole strength in $^{58}$Ni from forward-angle inelastic proton scattering

The aim of the present work is a state-by-state analysis of possible E1 and M1 transitions in $^{58}$Ni with a high-resolution (p,p') experiment at 295 MeV and very forward angles including 0° and a comparison to results from studies of the dipole strength with the $(γ,γ')$ and (e,e') reactions. The E1 and M1 cross sections of individual peaks in the spectra are deduced with a multipole decomposition analysis and converted to reduced E1 and spin-M1 transition strengths using the virtual photon and the unit cross-section method, respectively. Despite the high level density good agreement is obtained for the deduced excitation energies of J = 1 states in the three types of experiments indicating that the same states are excited. The B(E1) and B(M1) strengths from the $(γ,γ^\prime)$ experiments are systematically smaller than in the present work because of the lack of information on branching ratios to lower-lying excited states and the competition of particle emission. Fair agreement with the B(M1) strengths extracted from the (e,e') data is obtained after removal of E1 transitions uniquely assigned in the present work, which belong to a low-energy toroidal mode with unusual properties mimicking M1 excitations in electron scattering. The experimental M1 strength distribution is compared to large-scale shell-model calculations with the effective GXPF1A and KB3G interactions. They provide a good description of the isospin splitting and the running sum of the M1 strength. A quenching factor 0.74 for the spin-isospin part of the M1 operator is needed to attain quantitative agreement with the data.

nucl-ex↗

arXiv2023

The nuclear reaction network WinNet

We present the state-of-the-art single-zone nuclear reaction network WinNet that is capable of calculating the nucleosynthetic yields of a large variety of astrophysical environments and conditions. This ranges from the calculation of the primordial nucleosynthesis, where only a few nuclei are considered, to the ejecta of neutron star mergers with several thousands of involved nuclei. Here we describe the underlying physics and implementation details of the reaction network. We additionally present the numerical implementation of two different integration methods, the implicit Euler method and Gears method along with their advantages and disadvantages. We furthermore describe basic example cases of thermodynamic conditions that we provide together with the network and demonstrate the reliability of the code by using simple test cases. With this publication, WinNet is publicly available and open source at GitHub and Zenodo.

astro-ph.IM↗

arXiv2023

Opacities of Singly and Doubly Ionised Neodymium and Uranium for Kilonova Emission Modeling

Even though the electromagnetic counterpart AT2017gfo to the binary neutron star merger GW170817 is powered by the radioactive decay of r-process nuclei, only few tentative identifications of light r-process elements have been made so far. One of the major limitations for the identification of heavy nuclei is incomplete or missing atomic data. While substantial progress has been made on lanthanide atomic data over the last few years, for actinides there has been less emphasis, with the first complete set of opacity data only recently published. We perform atomic structure calculations of neodymium $(Z=60)$ as well as the corresponding actinide uranium $(Z=92)$. Using two different codes (FAC and HFR) for the calculation of the atomic data, we investigate the accuracy of the calculated data (energy levels and electric dipole transitions) and their effect on kilonova opacities. For the FAC calculations, we optimise the local central potential and the number of included configurations and use a dedicated calibration technique to improve the agreement between theoretical and available experimental atomic energy levels (AELs). For ions with vast amounts of experimental data available, the presented opacities agree quite well with previous estimations. On the other hand, the optimisation and calibration method cannot be used for ions with only few available AELs. For these cases, where no experimental nor benchmarked calculations are available, a large spread in the opacities estimated from the atomic data obtained with the various atomic structure codes is observed.We find that the opacity of uranium is almost double the neodymium opacity.

astro-ph.HE↗

arXiv2021

Forbidden electron capture on $^{24}$Na and $^{27}$Al in degenerate oxygen-neon cores

Stars with an initial mass of $\sim 7$-11 solar masses form degenerate oxygen-neon cores following carbon burning. Electron captures in such cores can trigger runaway oxygen burning, resulting in either a collapse or a thermonuclear explosion. We provide a detailed description of the formalism used in previous work and apply it to two further forbidden transitions that are relevant to degenerate oxygen-neon cores: the $4^+_\text{g.s.}\rightarrow{}2^+_1$ transition in $^{24}\text{Na}(e^-,ν_e)^{24}\text{Ne}$ and the ${5/2^+_{\text{g.s.}} \rightarrow{} 1/2^+_{\text{g.s.}}}$ transition in $^{27}\text{Al}(e^-,ν_e)^{27}\text{Mg}$. The relevant nuclear matrix elements are determined through shell model calculations and constraints from CVC theory. We then investigate the astrophysical impact using the stellar evolution code MESA and through timescale arguments. In the relevant temperature range, the forbidden transitions substantially reduce the threshold densities for $^{24}\text{Na}(e^-,ν_e)^{24}\text{Ne}$ and $^{27}\text{Al}(e^-,ν_e)^{27}\text{Mg}$. In the MESA models, $^{24}\text{Na}(e^-,ν_e)^{24}\text{Ne}$ now occurs immediately following the onset of $^{24}\text{Mg}(e^-,ν_e)^{24}\text{Na}$. The impact on the overall evolution is uncertain: this is due to known difficulties in accounting for convective instabilities triggered by the $A=24$ electron captures. The transition between $^{27}\text{Al}$ and $^{27}\text{Mg}$ may have a minor effect on the early evolution but is unlikely to affect the outcome. The studied transitions should be included when calculating weak interaction rates between $^{24}$Na and $^{24}$Ne for temperatures $\log_{10}(T[\text{K}])\lesssim8.5$ and between $^{27}$Al and $^{27}$Mg for $\log_{10}(T[\text{K}])\lesssim8.8$.

nucl-th↗

arXiv2020

Unblocking of stellar electron capture for neutron-rich $N=50$ nuclei at finite temperature

We have calculated electron capture rates for neutron-rich $N=50$ nuclei ($^{78}$Ni, $^{82}$Ge, $^{86}$Kr, $^{88}$Sr) within the Thermal QRPA approach at temperatures $T=0$, corresponding to capture on the ground-state, and at $T=10$ GK (0.86 MeV), which is a typical temperature at which the $N=50$ nuclei are abundant during a supernova collapse. In agreement with recent experiments, we find no Gamow-Teller (GT$_+$) strength at low excitation energies, $E<7$ MeV, caused by Pauli blocking induced by the $N=50$ shell gap. At the astrophysically relevant temperatures this Pauli blocking of the GT$_+$ strength is overcome by thermal excitations across the $Z=40$ proton and $N=50$ neutron shell gaps, leading to a sizable GT contribution to the electron capture. At the high densities, at which the $N=50$ nuclei are important for stellar electron capture, forbidden transitions contribute noticeably to the capture rate. Our results indicate that the neutron-rich $N=50$ nuclei do not serve as an obstacle of electron capture during the supernova collapse.

nucl-th↗

arXiv2020

Mass Measurements of Neutron-Rich Gallium Isotopes Refine Production of Nuclei of the First r-Process Abundance Peak in Neutron Star Merger Calculations

We report mass measurements of neutron-rich Ga isotopes $^{80-85}$Ga with TRIUMF's Ion Trap for Atomic and Nuclear science (TITAN). The measurements determine the masses of $^{80-83}$Ga in good agreement with previous measurements. The masses of $^{84}$Ga and $^{85}$Ga were measured for the first time. Uncertainties between $25-48$ keV were reached. The new mass values reduce the nuclear uncertainties associated with the production of A $\approx$ 84 isotopes by the \emph{r}-process for astrophysical conditions that might be consistent with a binary neutron star (BNS) merger producing a blue kilonova. Our nucleosynthesis simulations confirm that BNS merger may contribute to the first abundance peak under moderate neutron-rich conditions with electron fractions $Y_e=0.35-0.38$.

nucl-ex↗

arXiv2019

A Survey of Nuclear Pasta in the Intermediate Density Regime: Structure Functions for Neutrino Scattering

Background: Nuclear pasta matter, emerging due to the competition between the long-range Coulomb force and the short-range strong force, is believed to be present in astrophysical scenarios, such as neutron stars and core-collapse supernovae. Its structure can have a high impact e.g. on neutrino transport or the tidal deformability of neutron stars. Purpose: We investigate the impact of nuclear pasta on neutrino interactions and compare the results to uniform matter. Method: We calculate the elastic and inelastic static structure factors for nuclear pasta matter using density functional theory (DFT), which contain the main nuclear input for neutrino scattering. Results: Each pasta structure leaves a unique imprint in the elastic structure factor and it is largely enhanced. The inelastic structure factors are very similar for all configurations. Conclusion: Nuclear pasta has a noticeable impact on neutrino neutral-current scattering opacities. While for inelastic reactions the cross section is reduced, the elastic coherent scattering increases dramatically. The effect can be of importance for the cooling of neutron stars as well as for core-collapse supernova models.

nucl-th↗

arXiv2019

Measurement of the $2^+\rightarrow 0^+$ ground-state transition in the $β$ decay of $^{20}$F

We report the first detection of the second-forbidden, non-unique, $2^+\rightarrow 0^+$, ground-state transition in the $β$ decay of $^{20}$F. A low-energy, mass-separated $^{20}\rm{F}^+$ beam produced at the IGISOL facility in Jyväskylä, Finland, was implanted in a thin carbon foil and the $β$ spectrum measured using a magnetic transporter and a plastic-scintillator detector. The $β$-decay branching ratio inferred from the measurement is $b_β = [ 0.41\pm 0.08\textrm{(stat)}\pm 0.07\textrm{(sys)}] \times 10^{-5}$ corresponding to $\log ft = 10.89(11)$, making this one of the strongest second-forbidden, non-unique $β$ transitions ever measured. The experimental result is supported by shell-model calculations and has significant implications for the final evolution of stars that develop degenerate oxygen-neon cores. Using the new experimental data, we argue that the astrophysical electron-capture rate on $^{20}$Ne is now known to within better than 25% at the relevant temperatures and densities.

nucl-ex↗

arXiv2019

Discovery of an Exceptionally Strong $β$-Decay Transition of $^{20}$F and Implications for the Fate of Intermediate-Mass Stars

A significant fraction of stars between 7-11 solar masses are thought to become supernovae, but the explosion mechanism is unclear. The answer depends critically on the rate of electron capture on $^{20}$Ne in the degenerate oxygen-neon stellar core. However, due to the unknown strength of the transition between the ground states of $^{20}$Ne and $^{20}$F, it has not previously been possible to fully constrain the rate. By measuring the transition, we have established that its strength is exceptionally large and enhances the capture rate by several orders of magnitude. This has a decisive impact on the evolution of the core, increasing the likelihood that the star is (partially) disrupted by a thermonuclear explosion rather than collapsing to form a neutron star. Importantly, our measurement resolves the last remaining nuclear physics uncertainty in the final evolution of degenerate oxygen-neon stellar cores, allowing future studies to address the critical role of convection, which at present is poorly understood.

astro-ph.SR↗

arXiv2019

A Survey of Nuclear Pasta in the Intermediate Density Regime I: Shapes and Energies

Background: Nuclear pasta, emerging due to the competition between the long-range Coulomb force and the short-range strong force, is believed to be present in astrophysical scenarios, such as neutron stars and core-collapse supernovae. Its structure can have a high impact e.g. on neutrino transport or the tidal deformability of neutron stars. Purpose: We study several possible pasta configurations, all of them minimal surface configurations, which are expected to appear in the mid-density regime of nuclear pasta, i.e. around 40% of the nuclear saturation density. In particular we are interested in the energy spectrum for different pasta configurations considered. Method: Employing the density functional theory (DFT) approach, we calculate the binding energy of the different configurations for three values of the proton content XP = 1/10, 1/3 and 1/2, by optimizing their periodic length. We study finite temperature effects and the impact of electron screening. Results: Nuclear pasta lowers the energy significantly compared to uniform matter, especially for $X_P \geq 1/3$. However, the different configurations have very similar binding energies. For large proton content, $X_P \geq 1/3$, the pasta configurations are very stable, for lower proton content temperatures of a few MeV are enough for the transition to uniform matter. Electron screening has a small influence on the binding energy of nuclear pasta, but increases its periodic length. Conclusion: Nuclear pasta in the mid-density regime lowers the energy of the matter for all proton fractions under study. It can survive even large temperatures of several MeV. Since various configurations have very similar energy, it is to expected that many configurations can coexist simultaneously already at small temperatures.

nucl-th↗

arXiv2019

Self-consistent calculation of the reactor antineutrino spectra including forbidden transitions

With the goal of determining the $θ_{13}$ neutrino oscillation mixing angle, the measurements of reactor antineutrino fluxes at the Double Chooz, RENO and Daya Bay experimental facilities have uncovered a systematic discrepancy between the number of observed events and theoretical expectations. In the \emph{ab initio} approach, the total reactor antineutrino spectrum is a weighted sum of spectra resulting from all $β$ branches of all fission products in the reactor core. At all three facilities a systematic deviation of the number of observed events from the number of predicted events was noticed, i.e., approximately 6\% of the predicted neutrinos were not observed. This discrepancy was named the reactor neutrino anomaly. In theoretical studies it is assumed that all the decays are allowed in shape, but a quarter of all transitions are actually forbidden and may have a complex energy dependence that will affect the total reactor antineutrino spectrum. In order to estimate the effect of forbidden transitions, we perform a fully self-consistent calculation of spectra from all contributing transitions and compare the results with a purely allowed approximation.

nucl-th↗

arXiv2018

The $ν$ process in the light of an improved understanding of supernova neutrino spectra

We study the neutrino-induced production of nuclides in explosive supernova nucleosynthesis for progenitor stars with solar metallicity including neutrino nucleus reactions for all nuclei with charge numbers $Z < 76$ with average neutrino energies in agreement with modern Supernova simulations. Considering progenitors with initial main sequence masses between 13~M$_\odot$ and 30~M$_\odot$, we find a significant production of $^{11}$B, $^{138}$La, and $^{180}$Ta by neutrino nucleosynthesis, despite the significantly reduced neutrino energies. The production of $^{19}$F turns out to be more sensitive to the progenitor mass and structure than to the $ν$ process. With our complete set of cross sections we have identified effects of the $ν$~process on several stable nuclei including $^{33}$S, $^{40}$Ar, $^{41}$K, $^{59}$Co, and $^{113}$In at the 10\% level. Neutrino-induced reactions contribute to a similar extent to the production of radioactive ${}^{26}$Al and increase the yield of $^{22}$Na by 50\%. Future $γ$~ray astronomy missions may reach the precision at which the contribution from the $ν$~process becomes relevant. We find that the production of $^{22}$Na by the $ν$~process could explain the Ne-E(L) component of meteoritic graphite grains. The $ν$~process enhances the yield of $^{36}$Cl and we point out that the resulting $^{36}$Cl/$^{35}$Cl ratio is in agreement with the values infrerred for the early solar system. Our extended set of neutrino-nucleus interactions also allows us to exclude any further effects of the $ν$ process on stable nuclei and to quantify the effects on numerous, hitherto unconsidered radioactive nuclei, e.g., $^{36}$Cl, $^{72}$As, $^{84}$Rb, and $^{88}$Y.

astro-ph.HE↗

arXiv2018

Mass Measurements of Neutron-Deficient Y, Zr, and Nb Isotopes and Their Impact on $rp$ and $νp$ Nucleosynthesis Processes

Using isochronous mass spectrometry at the experimental storage ring CSRe in Lanzhou, the masses of $^{82}$Zr and $^{84}$Nb were measured for the first time with an uncertainty of $\sim 10$ keV, and the masses of $^{79}$Y, $^{81}$Zr, and $^{83}$Nb were re-determined with a higher precision. %The latter differ significantly from their literature values. The latter are significantly less bound than their literature values. Our new and accurate masses remove the irregularities of the mass surface in this region of the nuclear chart. Our results do not support the predicted island of pronounced low $α$ separation energies for neutron-deficient Mo and Tc isotopes, making the formation of Zr-Nb cycle in the $rp$-process unlikely. The new proton separation energy of $^{83}$Nb was determined to be 490(400)~keV smaller than that in the Atomic Mass Evaluation 2012. This partly removes the overproduction of the $p$-nucleus $^{84}$Sr relative to the neutron-deficient molybdenum isotopes in the previous $νp$-process simulations.

nucl-ex↗

arXiv2016

Thermal QRPA with Skyrme interactions and supernova neutral-current neutrino-nucleus reactions

The Thermal Quasiparticle Random-Phase Approximation is combined with the Skyrme energy density functional method (Skyrme-TQRPA) to study the response of a hot nucleus to an external perturbation. For the sample nuclei, $^{56}$Fe and $^{82}$Ge, the Skyrme-TQRPA is applied to analyze thermal effects on the strength function of charge-neutral Gamow-Teller transitions which dominate neutrino-nucleus reactions at $E_ν\lesssim 20$~MeV. For the relevant supernova temperatures we calculate the cross sections for inelastic neutrino scattering. We also apply the method to examine the rate of neutrino-antineutrino pair emission by hot nuclei. The cross sections and rates are compared with those obtained earlier from the TQRPA calculations based on the phenomenological Quasiparticle-Phonon Model Hamiltonian. For inelastic neutrino scattering on $^{56}$Fe we also compare the Skyrme-TQRPA results to those obtained earlier from a hybrid approach that combines shell-model and RPA calculations.

nucl-th↗