Decay Of Nuclei Research Articles

Magnetically Aligned Grains as a Ubiquitous Source of Spin-polarized Electrons and Chiral-symmetry-breaking Agents

The unique biosignature of life on Earth is the homochirality of organic compounds, such as amino acids, proteins, and sugars. High-energy spin-polarized (spinup or spindown) electrons (SPEs) from the β decay of radioactive nuclei have been proposed as a source of symmetry breaking, leading to homochirality; however, their exact role is much debated. Here, we propose magnetically aligned dust grains as a new source of SPEs, due to the photoemission of electrons having aligned spins by the Barnett effect. For the interstellar UV radiation field of strength G UV, we find that the SPE emission rate is ΓpeSPE∼10−14GUV electrons per second per H, the fraction of spin-polarized to total photoelectrons is ∼10%, and the SPE yield (photoelectron number per UV photon) can reach ∼1%, using the modern theory of grain alignment. SPEs emitted from aligned grains could play an important role in chiral-induced spin-selectivity-driven reduction chemistry in the icy grain mantles, producing an enantiomer excess of chiral molecules formed on the grain mantle. Finally, we suggest magnetically aligned grains could directly impact the enantio-selectivity through the chiral-induced spin-selective adsorption effect and exchange interaction. We estimate the disalignment of electron spins and depolarization by elastic scattering using the Mott theory and find that these effects are negligible for low-energy SPEs, so that the spins of SPEs remain well aligned during their journey through dust grains and the gas. Our proposed mechanism might explain the chiral asymmetry of prebiotic molecules detected in numerous comets, asteroids, and meteorites.

Giant quadrupole resonances within neutron-induced α-particle emission?

The particular conditions for the recent measurement of 91Zr(n,α)88Sr reaction cross sections at incident energies below 5.3 MeV [Phys. Rev. C 106, 064602 (2022)] as well as a previous detailed analysis of other reaction channels involving neutrons incident on 91Zr, using a consistent set of model parameters, have two main advantages. First, the close agreement between the calculated and experimentally obtained data for the incident energy associated mainly with the ground-state activation provides strong support for the α-particle optical potential involved in this analysis. Second, a further underestimation of the cross section is observed around the energy corresponding to the isoscalar giant quadrupole resonance (ISGQR), beyond any model parameter uncertainty. This underestimation is consistent with previous observations of ISGQR-like α-particle decay of excited nuclei for neutron-induced reactions in the mass range 54≤A≤98. To phenomenologically identify the ISGQR-like behavior, a comparison is made between their strengths and the ISGQR strengths measured through the (γ,α) reaction and inelastic scattering of 3He and α-particles. Additionally, an isotope effect, possibly related to the decrease in Q-value with the target-nuclei asymmetry parameter, supports the observation of a low energy-weighted sum rule (EWSR) fraction for the ISGQR-like strength function in the excited nucleus 92Zr.

Study of [formula omitted]/EC-decay properties of [formula omitted] shell nuclei using nuclear shell model

Our study employs the nuclear shell model to systematically compute the half-lives of β-decay for nuclei in the mass range of A=18−39, encompassing the majority of sd shell nuclei. This analysis utilizes the USDB and SDNN Hamiltonians. The theoretical outcomes contain calculations of various parameters such as Q-values, half-lives, excitation energy, logft values, and branching ratios. We explore these results with axial–vector coupling constant for weak interactions, denoted as gA(=1.27), and κ value (=6289). We perform calculations of Gamow Teller matrix elements for 116 decay processes to calculate the quenching factor; we found a quenching factor of q=0.794±0.05 for the USDB interaction and q=0.815±0.04 for the SDNN interaction. We have also calculated superallowed transitions 0+→0+ for seven nuclei. Further, we have also included the electron capture phase space factor for the required nuclei to calculate the half-lives. This inclusion leads to small contribution in results, particularly for nuclei where electron capture (EC) plays a significant role. The overall results are in agreement with the experimental data.

Radioactive Gamma-Ray Lines from Long-lived Neutron Star Merger Remnants

The observation of a kilonova AT2017gfo associated with the gravitational wave event GW170817 provides the first strong evidence that neutron star mergers are dominant contributors to the production of heavy r-process elements. Radioactive gamma-ray lines emitted from neutron star merger remnants provide a unique probe for investigating the nuclide composition and tracking its evolution. In this work, we studied the gamma-ray line features arising from the radioactive decay of heavy nuclei in the merger remnants based on the r-process nuclear reaction network and the astrophysical inputs derived from numerical relativity simulations. The decay chain of 50126 Sn (T 1/2 = 230 kyr) → 51126 Sb (T 1/2 = 12.35 days) → 52126 Te (stable) produces several bright gamma-ray lines with energies of 415, 667, and 695 keV, making it the most promising decay chain during the remnant phase. The photon fluxes of these bright gamma-ray lines reach ∼10−5 γ cm−2 s−1 for Galactic merger remnants with ages less than 100 kyr, which can be detected by the high energy resolution MeV gamma-ray detectors like the MASS mission.

Modeling of Cluster Decay of Light Nuclei by the Interaction of the 9Be Nucleus with Fast Neutrons in an Ionization Chamber

Modeling of Cluster Decay of Light Nuclei by the Interaction of the 9Be Nucleus with Fast Neutrons in an Ionization Chamber

Nuclear matrix elements of neutrinoless double-beta decay in covariant density functional theory with different mechanisms

Nuclear matrix elements (NMEs) for neutrinoless double-beta (0νββ) decay in candidate nuclei play a crucial role in interpreting results from current experiments and in designing future ones. Accurate NME values serve as important nuclear inputs for constraining parameters in new physics, such as neutrino mass and the Wilson coefficients of lepton-number-violating (LNV) operators. In this study, we present a comprehensive calculation of NMEs for 0νββ decay in 76Ge, 82Se, 100Mo, 130Te, and 136Xe, using nuclear wave functions obtained from multi-reference covariant density functional theory (MR-CDFT). We employ three types of transition potentials at the leading order in chiral effective field theory. Our results, along with recent data, are utilized to constrain the coefficients of LNV operators. The results demonstrate that the combined NMEs based on the Feynman diagrams at the hadronic scale for the nonstandard mechanisms leads to the uncertainty by different nuclear models comparable to that for the standard mechanism. The use of NMEs from various nuclear models does not dramatically change the parameter space intervals for the coefficients, although MR-CDFT yields the most stringent constraint. Furthermore, our NMEs can also be used to perform a more comprehensive analysis with multiple isotopes.

Radioassay of the materials for AMoRE-II experiment

The AMoRE-II experiment will search for the 0νββ decay of 100Mo nuclei using molybdate crystal scintillators, operating at milli-Kelvin (mK) temperatures, with a total of 80 kg of 100Mo. The background goal for the experiment is 10–4 counts/keV/kg/year in the region of interest around the 0νββ decay Q-value of 3,034 keV. To achieve this level, the rate of background signals arising from emissions produced by decays of radioactive impurities in the detector and shielding materials must be strictly controlled. To do this, concentrations of such impurities are measured and are controlled through materials selection and purification. In this paper, we describe the design and the construction materials used to build the AMoRE-II detector and shielding system, including active and passive shielding, the cryostat, and the detector holders and instrumentation, and we report on measurements of radioactive impurities within candidate and selected materials.

Relativistic model-free prediction for neutrinoless double beta decay at leading order

Starting from a manifestly Lorentz-invariant chiral Lagrangian, we present a model-free prediction for the transition amplitude of the process nn→ppe−e− induced by light Majorana neutrinos, which is a key process of the neutrinoless double beta decay (0νββ) in heavy nuclei employed in large-scale searches. Contrary to the nonrelativistic case, we show that the transition amplitude can be renormalized at leading order without any uncertain contact operators. The predicted amplitude defines a stringent benchmark for the previous estimation with model-dependent inputs, and greatly reduces the uncertainty of 0νββ transition operator in the calculations of nuclear matrix elements. Generalizations of the present framework could also help to address the uncertainties in 0νββ decay induced by other mechanisms. In addition, the present work motivates a relativistic ab initio calculation of 0νββ decay in light and medium-mass nuclei.

A Novel Model for the MeV Emission Line in GRB 221009A

Gamma-ray bursts (GRBs) have long been considered potential sources of ultrahigh-energy cosmic rays (UHECRs; with energy ≳1018 eV). In this work, we propose a novel model generating MeV emission lines in GRBs, which can constrain the properties of heavy nuclei that potentially exist in GRB jets. Specifically, we find that relativistic hydrogen-like high-atomic-number ions originating from the β decay of unstable nuclei and/or the recombination entrained in the GRB jet can generate narrow MeV emission lines through the de-excitation of excited electrons. This model can successfully explain the MeV emission line observed in the most luminous GRB ever recorded, GRB 221009A, with suitable parameters including a Lorentz factor γ ∼ 820–1700 and a total mass of heavy nuclei M tot ∼ 1023–1026 g. Especially, the emission line broadening can be reasonably attributed to both the expansion of the jet shell and the thermal motion of nuclei, naturally resulting in a narrow width (σ line/E line ≲ 0.2) consistent with the observation. Furthermore, we predict that different GRBs can exhibit lines in different bands with various evolving behaviors, which might be confirmed with further observations. Finally, our model provides indirect evidence that GRBs may be one of the sources of UHECRs.

Ab Initio Computation of Auger Decay in Heavy Metals: Zinc about It.

We report the first coupled-cluster study of Auger decay in heavy metals. The zinc atom is used as a case study due to its relevance to the Auger emission properties of the 67Ga radionuclide. Coupled-cluster theory combined with complex basis functions is used to describe the transient nature of the core-ionized zinc atom. We also introduce second-order Møller-Plesset perturbation theory as an alternative method for computing partial Auger decay widths. Scalar-relativistic effects are included in our approach for computing Auger electron energies by means of the spin-free exact two-component one-electron Hamiltonian, while spin-orbit coupling is treated by means of perturbation theory. We center our attention on the K-edge Auger decay of zinc dividing the spectrum into three parts (K-LL, K-LM, and K-MM) according to the shells involved in the decay. The computed Auger spectra are in good agreement with experimental results. The most intense peak is found at an Auger electron energy of 7432 eV, which corresponds to a 1D2 final state arising from K-L2L3 transitions. Our results highlight the importance of relativistic effects for describing Auger decay in heavier nuclei. Furthermore, the effect of a first solvation shell is studied by modeling Auger decay in the hexaaqua-zinc(II) complex. We find that K-edge Auger decay is slightly enhanced by the presence of the water molecules as compared to the bare atom.

Broken seniority symmetry in the semimagic proton mid-shell nucleus Rh95

Lifetime measurements of low-lying excited states in the semimagic (N=50) nucleus Rh95 have been performed by means of the fast-timing technique. The experiment was carried out using γ-ray detector arrays consisting of LaBr3(Ce) scintillators and germanium detectors integrated into the DESPEC experimental setup commissioned for the Facility for Antiproton and Ion Research () Phase-0, Darmstadt, Germany. The excited states in Rh95 were populated primarily via the β decays of Pd95 nuclei, produced in the projectile fragmentation of a 850 MeV/nucleon Xe124 beam impinging on a 4g/cm2Be9 target. The deduced electromagnetic E2 transition strengths for the γ-ray cascade within the multiplet structure depopulating from the isomeric Iπ=21/2+ state are found to exhibit strong deviations from predictions of standard shell model calculations which feature approximately conserved seniority symmetry. In particular, the observation of a strongly suppressed E2 strength for the 13/2+→9/2+ ground state transition cannot be explained by calculations employing standard interactions. This remarkable result may require revision of the nucleon-nucleon interactions employed in state-of-the-art theoretical model calculations, and might also point to the need for including three-body forces in the Hamiltonian. Published by the American Physical Society 2024

Neutrino at Different Epochs of the Friedmann Universe

At least two relics of the Big Bang have survived: the cosmological microwave background (CMB) and the cosmological neutrino background (CνB). Being the second most abundant particle in the universe, the neutrino has a significant impact on its evolution from the Big Bang to the present day. Neutrinos affect the following cosmological processes: the expansion rate of the universe, its chemical and isotopic composition, the CMB anisotropy and the formation of the large-scale structure of the universe. Another relic neutrino background is theoretically predicted, it consists of non-equilibrium antineutrinos of Primordial Nucleosynthesis arising as a result of the decay of neutrons and tritium nuclei. Such antineutrinos are an indicator of the baryon asymmetry of the universe. In addition to experimentally detectable active neutrinos, the existence of sterile neutrinos is theoretically predicted to generate neutrino masses and explain their oscillations. Sterile neutrinos can also solve such cosmological problems as the baryonic asymmetry of the universe and the nature of dark matter. The recent results of several independent experiments point to the possibility of the existence of a light sterile neutrino. However, the existence of such a neutrino is inconsistent with the predictions of the Standard Cosmological Model. The inclusion of a non-zero lepton asymmetry of the universe and/or increasing the energy density of active neutrinos can eliminate these contradictions and reconcile the possible existence of sterile neutrinos with Primordial Nucleosynthesis, the CMB anisotropy, and also reduce the H0-tension. In this brief review, we discuss the influence of the physical properties of active and sterile neutrinos on the evolution of the universe from the Big Bang to the present day.

A global study of $$\alpha $$-clusters decay in heavy and superheavy nuclei with half-life and preformation factor

A global study of $$\alpha $$-clusters decay in heavy and superheavy nuclei with half-life and preformation factor

Influence of strong laser field on nuclear <i>α</i> decay

With the development of pulse amplification and compression technology, the peak power of the pulse has been improved by several orders of magnitude, and it is possible for the ultra strong laser field to affect nuclei directly. The <i>α</i> decay, as one of the most major forms in nuclear reaction, is a critical research topic in nuclear physics. According to the theory of Gamow model explaining nuclear <i>α</i> decay in quantum mechanics, double folding model solving nuclear potential energy, and cluster model describing atomic nucleus, we present a complete set of solutions for the half-life of nuclear <i>α</i> decay to study the influence of ultra strong laser field on nuclear <i>α</i> decay. These half-lives of <i>α</i> decay of different nuclei from medium to heavy in the absence of laser field are obtained, which accord well with the experimental data. Subsequently, we introduce the effects of ultra strong laser field into our theoretical method to achieve the variations of the half-life of nuclear <i>α</i> decay. Considering that the optical period of the laser pulse is much longer than the theoretical tunneling time and the Lorentz force is much smaller than the Coulomb force, the laser field is treated as an electrostatic field. The results show that the half-life of nuclear <i>α</i> decay will reduce about 0.1% by the strong laser field with a peak power density of about 1.0×10<sup>26</sup> W/cm<sup>2</sup>, demonstrating that the half-life of nuclear <i>α</i> decay is effectively affected by the strong laser field. Furthermore, the influences of the nuclear parameters, e.g. total quantum number <i>G</i> describing <i>α</i> particle orbits, and <i>α</i> decay reaction energy <i>Q</i><sub><i>α</i></sub>, on the variations of these half-lives of <i>α</i> decay of different nuclei are discussed with the help of the calculation results. The dependence of the half-lives of nuclear <i>α</i> decay on the laser peak power density is also explained correspondingly. In summary, we provide a more accurate method of calculating the half-life of nuclear <i>α</i> decay, which is used to study the influences of ultra strong laser field on these half-lives of nuclear <i>α</i> decay of different nuclei. With the further construction of strong laser devices, more interesting phenomena and results will be found from the experiment on the atomic nucleus under strong laser field.

Microscopic modeling of direct pre-equilibrium emission: Impact on exclusive and inclusive (n,xn) and fission channels

We report on a microscopic modeling of the first order of multistep direct emission based on one phonon excitations, given by the QRPA model, and an effective in-medium nucleon nucleon interaction, described within the JLM folding model. The results of our coupled channels framework for deformed target are illustrated in the case of low energy discrete state excitations in 152Sm. Pre-equilibrium predictions and their impact on inclusive and exclusive (n,xn) cross sections and fission cross sections are discussed for actinides. We discuss the importance of i) collective excitations to describe the neutron emission spectra and of ii) spin distribution of the residual nucleus formed after the neutron pre-equilibrium emission, that is a key ingredient to model the residual nucleus decay.

RNA Pol II Assembly Affects ncRNA Expression.

RNA pol II assembly occurs in the cytoplasm before translocation of the enzyme to the nucleus. Affecting this assembly influences mRNA transcription in the nucleus and mRNA decay in the cytoplasm. However, very little is known about the consequences on ncRNA synthesis. In this work, we show that impairment of RNA pol II assembly leads to a decrease in cryptic non-coding RNAs (preferentially CUTs and SUTs). This alteration is partially restored upon overcoming the assembly defect. Notably, this drop in ncRNAs is only partially dependent on the nuclear exosome, which suggests a major specific effect of enzyme assembly. Our data also point out a defect in transcription termination, which leads us to propose that CTD phosphatase Rtr1 could be involved in this process.

Study on the decay of Z = 127 – 132 superheavy nuclei via emission of 1-n and 2-n halo nuclei

The barrier penetrability, decay constant and decay half-life of 1-n halo nuclei 11Be, 15,17,19C, 22N, 23O, 24,26F, 29,31Ne, 34,37Na, 35,37Mg, and 55Ca; and 2-n halo nuclei 22C, 27,29F, 34Ne, 36Na, and 46P from Z = 127 – 132 parents were calculated within the framework of the Coulomb and proximity potential model by calculating the Q-values using the finite-range droplet model. A comparison between the decay half-lives is made by considering the halo candidates as a normal cluster and as a deformed structure with a rms radius. Neutron shell closure at 190, 196, 198, 200, 204, and 208 are identified from the plot of decay half-lives versus the neutron number of daughter nuclei (NP). The calculation of alpha decay half-life and spontaneous decay half-life showed that the majority of the parent nuclei survive spontaneous fission and decay through alpha emission. The Geiger-Nuttall plots of log10T1/2 versus Q-1/2 and universal plots of log10T1/2 versus -lnP for the emission of all 1-n and 2-n halo nuclei from the parents considered here are linear and show the validity of Geiger - Nuttall law in the case of decay of halo nuclei from superheavy elements.

Periodic Variations of the Radon Concentration Measured by the Large Volume Detector at the Gran Sasso Underground Laboratory

Time series of gamma-ray photons from natural radioactivity measured with the Large Volume Detector (LVD) at the Gran Sasso underground laboratory (Laboratori Nazionali del Gran Sasso, Italy) have been analyzed. The instrument is used to detect neutrinos from gravitational collapses of stellar cores in the Galaxy. The background of the experiment is due to neutrons and gamma-ray photons from the decays of daughter nuclei of uranium and thorium. An analysis of periodic variations of the number of gamma-ray photons caused by the radon concentration in the underground laboratory has shown the presence of diurnal, weekly, monthly, and annual modulations. Data collected from 2004 to 2021, including a period of low activity in the hall of the Gran Sasso laboratory during the COVID-19 pandemic, have been reported.

Global comparison between experimentally measured isomeric yield ratios and nuclear model calculations

The level density steers transition probabilities between different states in the decay and de-excitation of excited nuclei. Reliable level density modelling is, therefore, key in describing, e.g., de-excitation of fission fragments, with implications on neutron and gamma-rays multiplicities, and also manifested in the population of isomeric states. We test six currently used level density models and the spin distribution in the level density by comparing calculations with measured isomeric yield ratios. The model calculations are performed with the TALYS code and experimental data for nuclear reactions populating spin isomers are retrieved from the EXFOR database. On average, calculations are in agreement with measured data. However, we find that the population of the high-spin state in an isomeric pair is clearly favoured in all of the six studied level density models. Further studies are then performed on the three used phenomenological level density models, to investigate the significance of their effect. We find that a significant reduction of the spin width distribution improves the agreement between calculated and experimentally observed isomeric yield ratios. This result is independent of the incident particle in the nuclear reaction. The needed reduction of the spin width distribution to comply with empirical data has, e.g., implications for studies in angular momentum generation in fission using isomeric yield rations, calculations of anti-neutrino spectra from nuclear reactors, as well as neutron and gamma-ray multiplicities in nuclear reactor calculations.

Determinants in laser-assisted deformed α decay

Laser manipulation of nuclear decay has extremely promising applications. In this study, cutting-edge Gaussian lasers were combined with the latest data on α decay to thoroughly investigate the factors that impact the penetration probability in laser-assisted α decay of nuclei, while considering the deformation of the nucleus. Our calculations reveal that using state-of-the-art laser fields can marginally alter the half-life of α decay by affecting the penetration probability within a narrow range. Moreover, our findings demonstrate two key points: (1) By deriving an analytical formula for the rate of change of the α decay penetration probability in an ultra-intense laser field, we unveil the negative correlation between the α decay energy and the rate of change of the α decay penetration probability. (2) We attribute the wavelength as the determinant of the effect of the average rate of change of the penetration probability, which we explain by reconstructing the laser pulse width and wavelength. This research offers a rapid method to estimate the rate of change of the α-decay penetration probability and serves as a valuable reference for future experimental investigations of laser-nuclear interactions.