Gamow-Teller Strength Research Articles

Decay spectroscopy of Cd129

Excited states of $^{129}$In populated following the $\beta$-decay of $^{129}$Cd were experimentally studied with the GRIFFIN spectrometer at the ISAC facility of TRIUMF, Canada. A 480-MeV proton beam was impinged on a uranium carbide target and $^{129}$Cd was extracted using the Ion Guide Laser Ion Source (IG-LIS). $\beta$- and $\gamma$-rays following the decay of $^{129}$Cd were detected with the GRIFFIN spectrometer comprising the plastic scintillator SCEPTAR and 16 high-purity germanium (HPGe) clover-type detectors. %, along with the $\beta$-particles were detected with SCEPTAR. From the $\beta$-$\gamma$-$\gamma$ coincidence analysis, 32 new transitions and 7 new excited states were established, expanding the previously known level scheme of $^{129}$In. The $\log ft$ values deduced from the $\beta$-feeding intensities suggest that some of the high-lying states were populated by the $\nu 0 g_{7/2} \rightarrow \pi 0 g_{9/2}$ allowed Gamow-Teller (GT) transition, which indicates that the allowed GT transition is more dominant in the $^{129}$Cd decay than previously reported. Observation of fragmented Gamow-Teller strengths is consistent with theoretical calculations.

Nuclear structure properties of even-even chromium isotopes and the effect of deformation on calculated electron capture cross sections

In this study, we investigate the role of the nuclear deformation on the calculated electron capture cross section (ECC) of even-even chromium (Cr) isotopes. We first determined the nuclear structure properties of these nuclei within the interacting boson model-1 (IBM-1). The energy spectra and E2 transition probabilities were calculated by fitting the parameters in the model formalism. The analysis of the potential energy surface were also performed to predict the geometric shape of the Cr nuclei by plotting their contour plot in the plane of (β, γ) deformation parameters. Later, we calculated the ECC within the proton-neutron quasiparticle random phase approximation (pn-QRPA) model. In particular we studied how the calculated ECC changed with different values of nuclear deformation parameter. The calculated Gamow-Teller (GT) strength distributions were widely spread among the daughter states. The total GT strength decreased with increasing value of the β parameter. The computed ECC values, however, increased with increase in the β value of the Cr isotopes.

Gamow-teller strength and electron capture cross-section calculation by pn-QRPA for selected fp-shell nuclei

The allowed Gamow-Teller (GT) strengths and associated weak interaction rates on fp-shell nuclides are the most familiar processes of spin-isospin (στ) type. These rates play a crucial role in several astrophysical processes, particularly in nuclear synthesis and supernova-explosions. As per simulation consequences, the electron capture cross-section on medium-heavy nuclei has a key impact on decreasing the ratio of electron-to-baryon of the stellar matter during the late stages of stars formation. Stellar model based on the theoretical approaches should be tested against the available measured data. In the current work we present calculated Gamow-Teller strength distributions by pn-QRPA model for selected fp-shell nuclei (42Ti, 46Cr, 50Fe and 54Ni) and compare our results with available measured data. The Gamow-Teller strength distributions are well fragmented over the energy range 0-12 MeV and have a good comparison with experimental data. We calculate the electron capture cross-section for selected nuclei at temperature 0.5 MeV, 1.0 MeV and 1.5 MeV that shows the temperature dependence of calculated electron capture cross-section for astrophysical applications.

Effect of deformation on gamow-teller strength and electron capture cross-section for chromium isotopes

In this work, we explore the role of deformation parameter (β) on the calculated Gamow-Teller (GT) strength distributions and electron capture cross-sections (ECC) for 46,48,50Cr isotopes within the formalism of the proton neutron-quasi-particle random phase approximation (pn-QRPA). Three different β parameters were used in the present study. Two of them were calculated by using the interacting boson model (IBM) and the macroscopic-microscopic (Mac-mic) models. The third one is the experimental β values obtained by employing its relation with the experimental B(E2)↑ values. The GT strength distributions were widely dispersed among all the daughter states of the given isotopes. They were found to have an inverse relation with the β parameter i.e decreasing with increasing the β value. The ECC was computed as a function of the β parameter and the results suggest that the calculated ECC decreased with decreasing value of the β for the selected cases.

Low-energy super Gamow–Teller (LeSGT) and anti-LeSGT transitions

The LS-closed doubly-magic nuclei (DMN) $^{4}_{2}\mathrm{He}_{2}$, $^{16}_{\;\, 8}{\mathrm{O}}_{8}$, and $^{40}_{20}{\mathrm{Ca}}_{20}$ behave as inert cores for Gamow–Teller (GT) excitations. It is known that GT transition strengths from nuclei with DMN + identical two-nucleon particles (2p) to nuclei with DMN + proton-neutron particles ($\pi p$-$\nu p$), i.e., $^{6}_{2}{\mathrm{He}}_{4}\rightarrow ^{6}_{3}{\mathrm{Li}}_{3}$, $^{18}_{\;\, 8}{\mathrm{O}}_{10}$ (or $^{18}_{10}{\mathrm{Ne}}_{8}$) $\rightarrow ^{18}_{\;\, 9}{\mathrm{F}}_{9}$, and $^{42}_{20}{\mathrm{Ca}}_{22}$ (or $^{42}_{22}{\mathrm{Ti}}_{20}$) $\rightarrow ^{42}_{21}{\mathrm{Sc}}_{21}$, concentrate in the lowest GT states called the Low-energy Super GT (LeSGT) states. On the other hand, we notice that the GT strengths from nuclei with DMN + identical two-nucleon holes (2h) to nuclei with DMN + proton-neutron holes ($\pi h$-$\nu h$), i.e., $^{14}_{\;\, 6}{\mathrm{C}}_{8}$ (or $^{14}_{\;\, 8}{\mathrm{O}}_{6}$) $\rightarrow ^{14}_{\;\, 7}{\mathrm{N}}_{7}$, and $^{38}_{18}{\mathrm{Ar}}_{20}$ (or $^{38}_{20}{\mathrm{Ca}}_{18}$) $\rightarrow ^{38}_{19}{\mathrm{K}}_{19}$, concentrate in the second GT states. Accordingly, the lowest GT states, which can be called the anti-LeSGT states, are poorly excited. We find that this seesaw-like GT strength distributions in the 2p and 2h systems are the key to understand the hindered $\beta $ decay of $^{14}$C. The origin of the “Seesaw Mechanism” is analyzed by means of shell-model (SM) calculations.

Gamow-Teller strengths of some sd-shell nuclei in the shell model framework

The nuclear Gamow-Teller (GT) transition strength distributions B(GT)have been studied for some sd-shell nuclei in the (3He, t) charge-exchangereactions. The shell model calculations were performed by employing theUSDA and USDB effective interactions in the sd-model space. The results of B(GT) calculations reproduce the the experimental Gamow-Tellerstrength distributions well, while the calculated distribution of summedGT transition strengths were closely reproduce the observed ones.

Effect of deformation, particle-hole and particle-particle interaction on Gamow-Teller transitions of 76Ge

Gamow-Teller (GT) transitions for 76Ge using QRPA methods in this article are calculated, which play an essential role in the supernovae. Three different QRPA models are used to the GT strength distributions. QRPA models namely single quasi-particle (sqp), Pyatov Method (PM) and the Schematic Model (SM). Gamow-Teller distribution, ΣB(GT)-, the centroid of energy, the width of energy and ISR are calculated by using these models. The effect of particle-particle interaction on spherical nuclei and deformed nuclei on Gamow-Teller transitions is wanted to show. Deformed Woods-Saxon potential is used in calculations of Single-particle energies and wave functions. The results are also compared with previous theoretical calculations and measured strength distributions wherever available. It is expected that the current study of GT features would be helpful and may guide to a better knowledge of the presupernova progression of massive stars.

On Statistical Properties of the Gamow–Teller Strength Distribution in $${}^{\mathbf{60}}$$Ca

The $$\beta$$ -decay half-life and the delayed neutron emission of $${}^{60}$$ Ca are studied within a microscopic model, which is based on the Skyrme interaction T45 to construct single-particle and phonon spaces. We observe a redistribution of the Gamow–Teller strength due to the phonon-phonon coupling and the tensor correlations, considered in the model. For $${}^{60}$$ Sc, the spin-parity of the ground state is found to be $$1^{+}$$ . We predict that the half-life of $${}^{60}$$ Ca is 0.3 ms, while the total probabilities of the $$\beta xn$$ emission is 6.1%. To elucidate the obtained results, the random matrix theory has been applied to analyse the statistical properties of the $$1^{+}$$ spectrum populated in the $$\beta$$ -decay. We found a remarkable agreement between the GT strength distribution, obtained within the microscopic approach, and the ones, generated by means of the random coupling between the one- and two-phonon configurations.

Tensor Interaction Effects on Stellar Electron Capture and Beta-Decay Rates

The Gamow–Teller strength functions as well as electron capture and $$\beta$$ decay rates for $${}^{56,78}$$ Ni in hot stellar environment are calculated within a thermodynamically consistent approach based on the thermal quasiparticle RPA. We present a thorough analysis of the tensor interaction effects on the GT strength functions at zero and finite temperatures. To this aim we use self-consistent calculations with the Skyrme interaction. Several Skyrme interactions are used in order to verify the sensitivity of the obtained results to the Skyrme force parameters. It is pointed out that finite temperature amplifies the effect of tensor correlations on the GT strength functions. Our calculations of electron capture and $$\beta$$ decay rates demonstrate the importance of the tensor interaction for simulation of supernova weak-interaction processes.

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.

Gamow-Teller transitions to Zr93 via the Nb93(t,He3+γ ) reaction at 115 MeV/u and its application to the stellar electron-capture rates

Electron-capture reactions play important roles in the late evolution of core-collapse supernovae. The electron-capture rates used in astrophysical simulations rely on theoretical calculations which have to be tested against and guided by experimental data. We report on the measurement of the Gamow-Teller strength distribution of the odd-mass nucleus $^{93}\mathrm{Nb}$ via the ($t,^{3}\mathrm{He}$ + $\ensuremath{\gamma}$) charge-exchange reaction at a beam energy of 115 MeV/u. The Gamow-Teller strength distributions were extracted up to an excitation energy in $^{93}\mathrm{Zr}$ of 10 MeV. The results were compared with shell-model and quasiparticle random-phase approximation (QRPA) calculations. The theoretical calculations fail to describe the details of the strength distribution, but estimate reasonably well the integrated Gamow-Teller transition strength. Electron-capture rates derived from the measured and theoretical strength distributions match reasonably well, especially at the higher stellar densities of importance for deleptonization during the collapse of the stellar core, since the electron-capture $Q$ value is close to zero and the Fermi energy sufficiently high to ensure that the details of the strength distribution do not have a strong impact on the derived rates. At stellar densities in excess of ${10}^{9}$ g/${\mathrm{cm}}^{3}$, the electron-capture rate based on a single-state approximation used in astrophysical simulations is slightly higher than the rates based on the data and the shell-model and QRPA calculations, likely due to the fact that the approximation includes temperature-dependent effects, which increase the rates. However, the difference is much smaller than that observed in recent studies of nuclei with $Zl40$ near $N=50$, suggesting that the single-state approximation does not account for Pauli-blocking effects for nuclei with $Zl40$ that are much stronger than those for $^{93}\mathrm{Nb}$ with $Z=41$.

Quenching factor of Gamow-Teller and spin dipole giant resonances

Gamow-Teller (GT) and spin-dipole (SD) strength distributions of four doubly magic nuclei $^{48}$Ca, $^{90}$Zr, $^{132}$Sn and $^{208}$Pb are studied by the self-consistent Hartree-Fock plus random phase approximation (RPA) method. The Skyrme forces SAMi and SAMi-T without/with tensor interactions are adopted in our calculations. The calculated strengths are compared with available experimental data. The RPA results of GT and SD strengths of all four nuclei show fine agreement with observed GT and SD resonances in energy. A small GT peak below the main GT resonance is better described by the Skyrme interaction SAMi-T with the tensor terms. The quenching factors for GT and SD are extracted from the comparisons between RPA results and experimental strengths. It is pointed out that the quenching effect on experimental SD peaks is somewhat modest compared with that on GT peaks in the four nuclei.

Tritium β decay in pionless effective field theory

We calculate the $\beta$-decay of tritium at next-to-leading order in pionless effective field theory. At this order, a low-energy parameter $L_{1, A}$ enters the calculation that is also relevant for a high-accuracy prediction of the solar proton-proton fusion rate. We use the tritium half-life to determine this parameter and provide uncertainty estimates. We show proper renormalization of our calculation analyzing the residual cutoff dependence of observables. We find that next-to-leading order corrections contribute about $4\%$ to the triton decay Gamow-Teller strength. We show that these conclusions are insensitive to different arrangements of the effective range expansion.

Constraints for stellar electron-capture rates on Kr86 via the Kr86(t,He3+γ)Br86 reaction and the implications for core-collapse supernovae

In the late stages of stellar core-collapse, prior to core bounce, electron captures on medium-heavy nuclei drive deleptonization and simulations require the use of accurate reaction rates. Nuclei with neutron number near $N=50$, just above atomic number $Z=28$, play an important role, but rates used in astrophysical simulations rely primarily on a relatively simple single-state approximation. In order to improve the accuracy of astrophysical simulations, experimental data are needed to test the electron-capture rates and to guide the development of better theoretical models. This work presents the results of the $^{86}$Kr($t$,$^{3}$He+$\gamma$) experiment at the NSCL, from which an upper limit for the Gamow-Teller strength up to an excitation energy in $^{86}$Br of 5 MeV is extracted. The derived upper limit for the electron-capture rate on $^{86}$Kr indicates that the rate estimated through the single-state approximation is too high and that rates based on Gamow-Teller strengths estimated in shell-model and QRPA calculations are more accurate. The QRPA calculations tested in this manner were used for estimating the electron capture rates for 78 isotopes near $N=50$ and above $Z=28$. The impact of using these new electron-capture rates in simulations of supernovae instead of the rates based on the single-state approximation is investigated, indicating a significant reduction in the deleptonization that affects multi-messenger signals, such as the emission of neutrinos and gravitational waves.

Effect of nuclear deformation on electron capture cross-section on chromium isotopes

The electron capture plays significant role in the presupernova and supernova evolutions of massive stars which in turn are of great importance in synthesizing heavy elements beyond iron. In this paper, we study the effect of nuclear deformation on the computed electron capture cross-section on selected even–even chromium isotopes ([Formula: see text]Cr). The nuclear deformation parameters were computed using two different theoretical models: Interacting Boson Model (IBM-1) and Macroscopic (Yukawa-plus-exponential)–microscopic (Folded–Yukawa) model (Mac–mic model). A third value of deformation parameter was adopted from experimental data. We chose the pn-QRPA model to perform our calculations. The predictive power of the chosen model was first tested by calculating Gamow–Teller (GT) strength distributions of selected [Formula: see text]-shell nuclei where measured GT data was available. The calculated GT strength distributions were well-fragmented over the energy range 0–12[Formula: see text]MeV and were noted to be in decent agreement with experimental data. The total GT strength was found to increase (decrease) with decrease (increase) in the value of deformation parameter for the three chromium isotopes. The computed GT strength distributions satisfied the model-independent Ikeda sum rule. The ECC were calculated as a function of the deformation parameter at core temperature 1.0[Formula: see text]MeV. Our results show that the calculated ECC increased with increasing value of nuclear deformation.

Competition of deformation and neutron–proton pairing in Gamow–Teller transitions for 56,58Ni and 62,64Ni

We investigate effects of unlike-pairing correlations by neutron–proton (np) pairs on Gamow–Teller strength distributions for even–even Ni isotopes, 56,58,60,62,64Ni, by taking into account nuclear deformation in a deformed Woods–Saxon mean field. Our calculations based on a deformed Bardeen–Cooper–Schriffer approach which preserves the axial and the time-reversal symmetry are performed within a deformed quasiparticle random phase approximation, in which we explicitly include the deformation and the unlike-pairing as well as the like-pairing correlations by neutron–neutron and proton–proton pairs. Competition of these two effects, the deformation and the pairing correlations, is shown to be able to affect more or less the GT strength distributions of the even–even Ni isotopes.

Co69,71 β -decay strength distributions from total absorption spectroscopy

Background: The rapid neutron capture process is one of the main nucleosynthesis processes of elements heavier than Fe. Uncertainties in nuclear properties, such as masses, half-lives, and $\ensuremath{\beta}$-delayed neutron probabilities can cause orders of magnitude of variation within astrophysical $r$-process simulations. Presently, theoretical models are used to make global predictions of various nuclear properties for the thousands of nuclei required for these simulations, and measurements are required to benchmark these models, especially far from stability.Purpose: $\ensuremath{\beta}$-decay strength distributions can be used to not only inform astrophysical $r$-process simulations, but also to provide a stringent test for theoretical calculations. The aim of this work is to provide accurate strength distributions for $^{69,71}\mathrm{Co}\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$ decay.Method: The technique of total absorption spectroscopy was used to measure the $\ensuremath{\beta}$ decay of $^{69,71}\mathrm{Co}$ for the first time at the National Superconducting Cyclotron Laboratory. The ions were implanted in a double-sided silicon strip detector at the center of the Summing NaI(Tl) detector and identified using standard particle identification methods. The response of the detection system to the $\ensuremath{\beta}$-decay electron and subsequent $\ensuremath{\gamma}$-ray radiation was fit to the observed experimental data using a ${\ensuremath{\chi}}^{2}$-minimization technique.Results: $\ensuremath{\beta}$-feeding intensities and Gamow-Teller strength distributions were extracted from the fits of the experimental data. The $\ensuremath{\beta}$-decay intensities show that there is a large percentage of feeding to levels above 2 MeV, which have not been observed in previous studies. The resultant $\ensuremath{\beta}$-feeding intensities and Gamow-Teller strength distributions were compared to shell model and quasiparticle random phase approximation (QRPA) calculations.Conclusions: Comparing experimentally determined $\ensuremath{\beta}$-decay strength distributions provides a test of models, which are commonly used for global $\ensuremath{\beta}$-decay properties for astrophysical calculations. This work highlights the importance of performing detailed comparisons of models to experimental data, particularly far from stability and as close to the $r$-process path as possible.

β− decay of Tz=+112 isotopes Al37 and Si39 : Understanding Gamow-Teller strength distribution in neutron-rich nuclei

${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of ${T}_{z}=+\frac{11}{2}$ nuclei $^{37}\mathrm{Al}$ and $^{39}\mathrm{Si}$ was studied to obtain information about excited states in the daughter and granddaughter nuclei. New information on excited states has been obtained for $^{37,39}\mathrm{P}$, whereas level schemes for $^{37}\mathrm{Si}$ and $^{37,39}\mathrm{S}$ were confirmed and expanded on as compared to the most recent investigations. For the nuclei studied, the valence proton and neutron occupy different major shells with opposite parities, hence, the ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay preferentially and primarily populates core-excited $1p1h$ intruder states with a parity opposite to the ground state of the daughter nucleus. These low-lying intruder states shed light on the $N=20$ shell gap and its evolution with neutron number. The ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of very neutron-rich nuclei also illustrates how the Gamow-Teller (GT) strength distribution changes with neutron excess. Comparing ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of $^{37,39}\mathrm{Si}$ presented here with $^{38,40}\mathrm{Si}$ from a previous study, we clearly see an even-odd effect in the GT strength distribution with the decay from even-even nuclei showing strong low-lying strength whereas for the odd $A$ being very fragmented. Configuration interaction shell-model calculations with the state-of-art SDPFSDG-MU effective interaction were performed to understand the structure of the $1p1h$ states and explore the GT strength distribution.

Electron capture cross sections and nuclear partition functions for fp-shell nuclei

We present calculation of electron capture cross sections (ECC), in the limit of zero momentum transfer, using the pn-QRPA model in stellar matter. Towards this aim we make use of our recently introduced recipe for estimation of nuclear partition functions. For low momentum transfer (), the nuclear matrix elements of the operator provide the leading contribution to the total cross section which we estimate using the pn-QRPA model in a multi-shell single-particle space with a schematic interaction. Key fp-shell nuclei (odd-A, even–even and odd–odd) bearing astrophysical importance were selected for the calculation of ECC in stellar environment. These fp-shell nuclei play a crucial role in presupernova evolution of massive stars and core collapse. We further present microscopic calculation of ground and excited states Gamow–Teller strength distributions and stellar electron capture rates on these suite of nuclei. We used two different sets of empirically determined pairing gaps to calculate the ECC and electron capture rates. Results are compared with experimental data and previous computations. Our calculated ECC are systematically smaller at low electron incident energies as compared to the shell-model results.

High-resolution study of the Gamow-Teller ( GT− ) strength in the Zn64(He3,t)Ga64 reaction

Gamow-Teller (GT) transitions starting from the ${T}_{z}=+2$ nucleus $^{64}\mathrm{Zn}$ to the ${T}_{z}=+1$ nucleus $^{64}\mathrm{Ga}$ were studied in a ($p,n$)-type ($^{3}\mathrm{He},t$) charge-exchange reaction at a beam energy of 140 MeV/nucleon and scattering angles close to ${0}^{\ensuremath{\circ}}$. Here, ${T}_{z}$ is the $z$ component of the isospin $T$. The experiment was conducted at the Research Center for Nuclear Physics (RCNP) in Osaka, Japan. An energy resolution of $\ensuremath{\approx}34$ keV was achieved by applying beam matching techniques to the Grand Raiden magnetic spectrometer system. With our good resolution, we could observe GT strength fragmented in many states up to an excitation energy of $\ensuremath{\approx}11$ MeV. By performing angular distribution analysis, we could identify states in $^{64}\mathrm{Ga}$ excited by GT transitions. The reduced GT transition strengths [$B$(GT) values] were calculated assuming the proportionality between the cross sections and the $B$(GT) values. Shell-model calculations using the GXPF1J interaction reproduced the $B$(GT) strength distribution throughout the spectrum. States with isospin $T=3$ were identified by comparing the $^{64}\mathrm{Zn}\text{(}{}^{3}\text{He,}t{\text{)}}^{64}\text{Ga}$ spectrum with a $^{64}\mathrm{Zn}(d,^{2}\mathrm{He})^{64}\mathrm{Cu}$ spectrum. Relative excitation energies of the corresponding structures are in good agreement, supporting the robustness of isospin symmetry in the mass number $A=64$ nuclei.