Beta-decay Half-lives Research Articles

Decay Characteristics of Neutron Excess Scandium Nuclei

In neutron star mergers, neutron excess nuclei and the r-process are important factors governing the production of heavier nuclear systems. A single-particle model evaluation of Scandium nuclei suggests that the heaviest Z = 21 nucleus will have mass 71 with filling of the 1g9/2 neutron shell. A = 59 – 71 scandium isotopes have limited experimental half-life data, but the model predicts beta decay half-lives in the range of 0.312 – 7.60 ms. Based on previous calculations for Z = 9 - 20, 26, and 30 systems and comparisons to the 59Sc – 67Sc calculations, summarized in the Japanese Nuclear Data Compilation, the single-particle model results likely overestimate the half-lives of A = 59 – 71 neutron excess scandium nuclei.

Decay Characteristics of Neutron Excess Potassium Nuclei

In neutron star mergers, neutron excess nuclei and the r-process are important factors governing the production of heavy nuclear systems. A single-particle model evaluation of potassium nuclei suggests that the heaviest Z = 19 nucleus will have mass 69 with filling of the 1g9/2 neutron shell. A = 55 – 69 potassium isotopes have limited experimental half-life data, but the model predicts beta decay half-lives in the range of 0.315 – 9.23 ms. Based on previous calculations for Z = 9 - 18, 20, 26, and 30 systems and comparisons to the 55K – 59K, 61K, and 63K calculations, summarized in the Japanese Nuclear Data Compilation, the single-particle model results likely overestimate the half-lives of A = 55 – 69 neutron excess potassium nuclei.

A study of decay chains of radioactive actinium isotopes

In this paper, we systematically studied half-lives of the different decay modes using various theoretical models such as the unified fission model (UFM) and the effective liquid drop model. Beta-decay half-lives were evaluated using semi-empirical formulae available in the literature. We compared half-lives of all the studied decay modes and identified shorter half-lives among the same in [Formula: see text]Ac nuclei. We investigated the actinium series which is similar to the thorium series. Among these decay series, alpha-emitting isotopes show great promise for cancer treatment because of their short path length and high-energy transfer of radiation. Furthermore, we predicted the decay chains of the actinium isotopes. All the decay series of actinium ends with the formation of stable nuclei or with longer half-lives. The predicted decay series and new isotopes during the decay process are helpful in the field of medicine and radiotherapy.

Decay Characteristics of Neutron Excess Argon Nuclei

Bevelacqua Resources, 7531 Flint Crossing Circle SE, Owens Cross Roads, AL 35763 USA bevelresou@aol.com In neutron star mergers, neutron excess nuclei and the r-process are important factors governing the production of heavier nuclear systems. A single-particle model evaluation of argon nuclei suggests that the heaviest Z = 18 nucleus will have mass 69 with filling of the 3s1/2 neutron shell. A = 51 – 69 argon isotopes have limited experimental half-life data, but the model predicts beta decay half-lives in the range of 0.473 – 20.3 ms. Based on previous calculations for Z = 9 - 17, 20, 26, and 30 systems and comparisons to the 51Ar - 56Ar, 58Ar, and 60Ar calculations, summarized in the Japanese Nuclear Data Compilation, the single-particle model results likely overestimate the half-lives of A = 51 – 69 neutron excess argon nuclei.

Decay Characteristics of Neutron Excess Chlorine Nuclei

In neutron star mergers, neutron excess nuclei and the r-process are important factors governing the production of heavier nuclear systems. A single-particle model evaluation of chlorine nuclei suggests that the heaviest Z = 17 nucleus will have mass 62 with filling of the 1g9/2 neutron shell. A = 48 – 62 chlorine isotopes have limited experimental half-life data, but the model predicts beta decay half-lives in the range of 0.535 – 51.9 ms. Based on previous calculations for Z = 9 - 16, 20, 26, and 30 systems and comparisons to the 48Cl - 53Cl, and 55Cl calculations, summarized in the Japanese Nuclear Data Compilation, the single-particle model results likely overestimate the half-lives of A = 48 – 62 neutron excess chlorine nuclei.

Nuclear Spin-Isospin Response within the Fayans Functional

An effective approximation to a fully self-consistent global description of the total force function of b decay within the framework of the theory of finite Fermi systems is presented, based on the calculation of ground states within the framework of the modified energy density functional of Fayans et al. (DF3-f) and the continuum quasiparticle random phase approximation (CQRPA). The isovector parameter ℎ2− of the volume part of the functional has been refined, the permissible range of which was determined earlier by us from restrictions on the parameters of the equation of state for nuclear matter—the symmetry energy and its derivative at equilibrium density, obtained from a joint analysis of the value of the ‘‘neutron skin’’ ΔRnp of the nuclei 208Pb and 48Ca, found in the PREX-II and CREX experiments, results of ab initio calculations of the properties of the ground states of nuclei with the interaction of N3LO and systematics of data on the masses of neutron stars from astrophysical observations. New calculations of the Gamow–Teller strength functions for the reference doubly magic nuclei 208Pb and 132Sn, as well as for the nucleus 130Sn with developed neutron pairing have been carried out. In the proposed model, the global DF3-a + CQRPA calculations of beta-decay half-lives of heavy (quasi)spherical nuclei with Z = 81–83 and T1/2 240 s are conducted. Experimental lifetimes are described with accuracy up to factor 5.

Double Beta Decay: A Shell Model Approach

Studies of weak interaction in nuclei are important tools for testing different aspects of the fundamental symmetries of the Standard Model. Neutrinoless double beta decay offers an unique venue of investigating the possibility that neutrinos are Majorana fermions and that the lepton number conservation law is violated. Here, I use a shell model approach to calculate the nuclear matrix elements needed to extract the lepton-number-violating parameters of a few nuclei of experimental interest from the latest experimental lower limits of neutrinoless double beta decay half-lives. The analysis presented here could reveal valuable information regarding the dominant neutrinoless double beta decay mechanism if experimental half-life data become available for different isotopes. A complementary shell model analysis of the two-neutrino double beta decay nuclear matrix elements and half-lives is also presented.

Beta-decay half-lives of the isotopes close to the neutron drip line and astrophysical implications

In this paper, we examined the β −-decay half-lives of 94 extremely neutron-rich isotopes with Z = 26 − 57 close to the neutron drip line, which are important for the r-process calculations. The half-lives were calculated using four semi-empirical models and compared to those based on the FRDM+QRPA approach and available measured data. The impact of the difference in the models on the half-life predictions was investigated. We found that theoretical calculations for the β-decay half-life have a large deviation, up to 60%, which is mostly similar to that in measurements. The half-lives of the investigated nuclei are ranging from a few to hundreds of milliseconds. The r-process abundances in various astrophysical scenarios were calculated by using the predicted half-lives. The half-life uncertainty due to different models results in a large deviation in the isotopic abundance, specially for the isotopes in the mass range of A > 210. The shell closures in 76Fe is still a doubt due to the discrepancy in the trends of the half-life and paring gap while a closed-shell at N = 82 in 127Rh is possible. The results of this study also notice that it is a challenge for measuring precisely the masses of 106Rb, 116,117Nb, 122Tc, and 128Rh because of their short half-lives.

Beta-decay half-lives of the extremely neutron-rich nuclei in the closed-shell N = 50, 82, 126 groups

The β −-decay half-lives of extremely neutron-rich nuclei are important for understanding nucleosynthesis in the rapid neutron capture process (r-process). However, most of their half-lives are unknown or very uncertain, leading to the need for reliable calculations. In this study, we updated the coefficients in recent semi-empirical formulae using the newly updated mass (AME2020) and half-life (NUBASE2020) databases to improve the accuracy of the half-life prediction. In particular, we developed a new empirical model for better calculations of the β −-decay half-lives of isotopes ranging in Z = 10–80 and N = 15–130. We examined the β −-decay half-lives of the extremely neutron-rich isotopes at and around the neutron magic numbers of N = 50, 82, and 126 using either five different semi-empirical models or finite-range droplet model and quasi-particle random phase approximation method. The β −-decay rates derived from the estimated half-lives were used in calculations to evaluate the impact of the half-life uncertainties of the investigated nuclei on the abundance of the r-process. The results show that the half-lives mostly range in 0.001 < T 1/2 < 100 s for the nuclei with a ratio of N/Z < 1.9; however, they differ significantly for those with the ratio of N/Z > 1.9. The half-life differences among the models were found to range from a few factors (for N/Z < 1.9 nuclei) to four orders of magnitude (for N/Z > 1.9). These discrepancies lead to a large uncertainty, which is up to four orders of magnitude, in the r-process abundance of isotopes. We also found that the multiple-reflection time-of-flight technique is preferable for precise mass measurements because its measuring timescale applies to the half-lives of the investigated nuclei. Finally, the results of this study are useful for studies on the β-decay of unstable isotopes and astrophysical simulations.

Decay characteristics of neutron excess iron nuclei

In neutron star mergers, neutron excess nuclei and the r-process are important factors governing the production of heavy nuclear systems. An evaluation of iron nuclei suggests that the heaviest Z = 26 nucleus will have mass 76 with filling of the 1g9/2 neutron shell. A = 73‐76 iron isotopes have limited experimental half-life data, but the model predicts beta decay half-lives in the range of 20‐30 ms. Based on comparisons to Z = 20 and lighter Z = 26 systems, these results likely overestimate the experimental half-lives of these A = 73‐76 neutron excess iron nuclei.

Data from multi year and multi radiation detector measurements of different radiation sources with environmental data.

The data described consists of radiation measurement outputs from several different detectors located in Abu Dhabi, UAE, for the duration of 30 November 2014 through 13 December 2016. This data could be useful for anyone studying radiation count rate or spectroscopic changes over a multi year period from various radiation sources and measurement systems. The outputs of the measurement systems include 1) counts per 20 min from a Geiger–Muller detector measuring 90Sr, 2) counts per 20 min from a Geiger–Muller detector measuring 204Tl, 3) radiation spectra per 30 min from a NaI detector measuring 60Co, 4) radiation spectra per 30 min from a NaI detector measuring 54Mn, 5) radiation spectra per 30 min from a liquid scintillation detector measuring 226Ra, 6) counts per 30 min from a liquid scintillation detector measuring 14C, and room pressure, temperature, and humidity data every 10 min. A detailed description of the setup of each of these measurement systems can be found in “Experimental Setup and Commissioning Baseline Study in Search of Time-Variations in Beta-Decay Half-Lives” [1].

A new reference database for beta-delayed neutrons

A new database containing all available experimental and evaluated β-delayed neutron data is presented in this paper. The database is the product of an international effort coordinated by the International Atomic Energy Agency. It comprises a microscopic section including all available experimental data on beta-decay half-lives, β-delayed neutron emission probabilities and spectra, as well as new systematics and global theoretical calculations for comparison. The beta-delayed neutron data for individual precursors have been benchmarked against available data on macroscopic properties such as total delayed-neutron yields and spectra, delayed-neutron decay curves and time-dependent group parameters using the summation method. All available measured macroscopic data have also been compiled in the macroscopic section of the database. The dedicated database is available online on the IAEA server (URL:http://www-nds.iaea.org/beta-delayed-neutron/database.html).

Statistical Global Modeling of β−-Decay Halflives Systematics Using Multilayer Feedforward Neural Networks and Support Vector Machines

In this work, the beta-decay halflives problem is dealt as a nonlinear optimiza- tion problem, which is resolved in the statistical framework of Machine Learning (LM). Continuing past similar approaches, we have constructed sophisticated Artificial Neural Networks (ANNs) and Support Vector Regression Machines (SV Ms) for each class with even-odd character in Z and N to global model the systemat- ics of nuclei that decay 100% by the β−-mode in their ground states. The arising large-scale lifetime calculations generated by both types of machines are discussed and compared with each other, with the available experimental data, with previous results obtained with neural networks, as well as with estimates coming from tradi- tional global nuclear models. Particular attention is paid on the estimates for exotic and halo nuclei and we focus to those nuclides that are involved in the r-process nucleosynthesis. It is found that statistical models based on LM can at least match or even surpass the predictive performance of the best conventional models of β-decay systematics and can complement the latter.

Neutron rich matter in the laboratory and in the heavens after GW170817

The historic observations of the neutron star merger GW170817 advanced our understanding of r-process nucleosynthesis and the equation of state (EOS) of neutron rich matter. Simple neutrino physics suggests that supernovae are not the site of the main r-process. Instead, the very red color of the kilonova associated with GW170817 shows that neutron star (NS) mergers are an important r-process site. We now need to measure the masses and beta decay half-lives of very neutron rich heavy nuclei so that we can more accurately predict the abundances of heavy elements that are produced. This can be done with new radioactive beam accelerators such as the Facility for Rare Isotope Beams (FRIB). GW170817 provided information on the deformability of NS and the equation of state of dense matter. The PREX II experiment will measure the neutron skin of 208Pb and help constrain the low density EOS. As the sensitivity of gravitational wave detectors improve, we expect to observe many more events. We look forward to exciting advances and surprises!

R-process 130Cd Waiting Point

Most of the elements heavier than Fe in the universe were produced by the so-called r-process. Its mechanism is based on a rapid neutron capture by the nuclei, so that the neutron capture rates are much faster than those of β -decay. When r-process reaches nuclei with magic neutron numbers, the neutron separation or binding energies increase and the process slows down, it has to wait for several β decays to produce heavier nuclei. These magic nuclei are the waiting points. Information about r-process are steel missing and it requires knowledge of the nuclear structure of the neutron rich nuclei. However, the nuclear properties of these nuclei are not sufficiently well understood due to the experimental difficulties in their production. The A=130 isobars with N=82 present one of the most interesting waiting points, because of their positions far from β stability and near the doubly magic 132Sn core, for which theoretical and experimental studies give important information about beta decay half-lives. In this context, we focus on the study of even-even 130 Cd waiting point nuclear properties. We have performed some spectroscopic calculations for energetic spectrum, β -decay half-life evolution in terms of temperature, using recent experimental data, by means of Oxbash nuclear structure code. The getting spectrum is in a reasonably agreement with the available experimental data. However, the calculated β-decay half-life for the studied waiting point is short in comparison with the experimental one.

Calculations of β-decay half-lives for neutron rich tin isotopes

Many of the nuclei made temporarily during r-process nucleosynthesis are currently inaccessible to experiment. Their properties, however, help determine the abundances of stable elements which we observe in the solar system. Beta decay half-lives and rates are among the most important of these properties. Nuclei with 50 ≤Z≤ 56 and 82 ≤ N ≤ 88 in the π(gdsh) ⊕ν(hfpi) valence space above the 132Sn core lie on or close to the path of astrophysical r-process flow. The even-N neutron-rich Sn isotopes are the classical “waiting point” nuclei in the A=130 solar system abundance peak under typical r-process conditions. With respect to the r-process, N=86 isotope is an important waiting-point nucleus for moderate neutron densities to drive the r-process flow beyond A-130 peak. For such systems, the consideration of the three-body monopole effects is presently a relevant issue in nuclear structure calculations in order to reproduce their experimental studies. In the present work, the total β-decay half-lives and rates of the exotic Sn isotopes above the 132Sn core are calculated using monopole interaction at different temperatures. The calculation has been realized using Oxbash code in the frame work of the nuclear shell model.

Double β Decay and the Axial Strength

Quenching of the weak axial strength g_A is discussed and relations of this quenching to the nuclear matrix elements of double beta decays are highlighted. An analysis of Gamow-Teller transitions in the mass range A=62-142 is presented and its results are compared with those of many previous works. The enhancement of the axial charge is discussed for first-forbidden pseudoscalar beta transitions. Higher-forbidden beta transitions are introduced and their role in determining the effective value of g_A is examined, in particular from the point of view of rge beta-decay half-lives and the shapes of electron spectra of forbidden non-unique beta transitions.

Neutrino cooling rates due to nickel isotopes for presupernova evolution of massive stars

As per simulation studies, the weak reaction rates on nickel isotopes play a substantial role in affecting the ratio of electron-to-baryon content of stellar interior during the late stages of core evolution. (Anti)neutrinos are produced in weak-decay processes, and escape from the stellar content having densities less than 1011 g cm−3. They take away energy and reduce the stellar core entropy. In this paper we report on the microscopic calculation of neutrino and antineutrino cooling rates due to weak rates on nickel isotopes in mass range 56 ≤ A ≤ 71. The calculations are accomplished by employing the deformed pn-QRPA model. Recent studies on GT strength properties of nickel isotopes show that the deformed pn-QRPA model well explained the experimental charge-changing transitions. Our calculated beta decay half-lives for selected nickel isotopes are in excellent comparison with experimental data. The (anti)neutrino cooling rates are determined over temperatures in the range of 0.01 × 109 – 30 × 109 K and densities in the range of 10 – 1011 g cm−3 domain. The computed rates are compared with previous theoretical calculations. For neutron rich nuclide, at high temperatures, our computed cooling rates are enhanced as compared to previous calculations.

Effect of Dynamical Pairing of the Beta-Decay Properties of Neutron-Rich Nuclei

The influence of an effective spin—isospin interaction in the particle—particle channel on the beta-decay half-lives and multineutron-emission probabilities is studied. The contributions of tensor correlations and coupling of the one- and two-phonon configurations are taken into account within a self-consistent approach that relies on the quasiparticle random-phase approximation and which employs Skyrme interaction. The beta-decay properties of neutron-rich cadmium isotopes are calculated.

Coupling charge-exchange vibrations to nucleons in a relativistic framework: Effect on Gamow-Teller transitions and β-decay half-lives

The nuclear response theory for isospin-transfer modes in the relativistic particle-vibration coupling framework is extended to include coupling of single nucleons to isospin-flip (charge-exchange) phonons, in addition to the usual neutral vibrations. This new coupling introduces dynamical pion and rho-meson exchange, beyond the Hartree-Fock approximation, up to infinite order. We investigate the impact of this new mechanism on the Gamow-Teller response of a few doubly-magic neutron-rich nuclei, namely $^{48}$Ca, $^{78}$Ni, $^{132}$Sn and $^{208}$Pb. It is found that the coupling to isospin-flip vibrations can have a non negligible impact on the strength distribution and quenching of the giant resonance, globally improving the agreement with the experimental data. The corresponding beta-decay half-lives of $^{78}$Ni and $^{132}$Sn are also calculated, and found to be decreased by a factor $\sim 2$ by the inclusion of the new phonons.