Number Of Neutrons Research Articles

Fictitious neutron sinks to trace radiative s-process nucleosynthesis

Context. Asymptotic giant branch (AGB) stars are strong producers of s-process elements, which are synthesized by successive slow neutron captures on elements heavier than iron. The nucleosynthesis calculation involves solving large nuclear networks with hundreds of nuclei, which in a stellar evolution code can greatly extend the computational time. However, the s-process is often measured using a handful of elements located on the neutron magic shells and grouped into tracers called ls, hs, and vhs. Aims. We propose a fictitious network that approximates the production of ls, hs, and vhs species at a minimal computational expense. The network is specifically designed for the radiative s-process in AGB stars. It is an alternative to methods using large networks that can be used as a fast exploratory tool to trace the production of s-elements. Methods. The fictitious network was constructed by assembling species with Z ≥ 18 into seven fictitious particles whose abundances and reaction rates model the effective properties of the corresponding groups. The effective reaction rates were tabulated as a function of neutron density and number of neutrons captured per initial heavy seed (Ncapt) using single-zone nucleosynthesis calculations. The accuracy of our network was tested by comparing the abundances obtained with the fictitious and large networks during the radiative burning of 13C during the interpulse period of a 2 M⊙, [Fe/H] = −2 star. Results. The fictitious network reliably reproduces the abundances of ls, hs, and vhs species during the radiative s-process. The accuracy of the method increases with the strength of the nucleosynthesis as measured by Ncapt, but diminishes when the nuclear distribution is different from the initial distribution. This network is well suited to follow the s-process nucleosynthesis in low-mass AGB stars where neutrons are mainly produced below the envelope by the 13C(α, n) reaction.

Post-Neutron Mass Yield Distribution in the Epi-Cadmium Neutron-Induced Fission of 245Cm

The cumulative and independent yields of various fission products within the mass ranges of 83 to 117 and 123 to 161 have been measured in the epi-cadmium neutron-induced fission of 245Cm by using an off-line gamma-ray spectrometric technique. Charge distribution correction was applied on the cumulative yields to obtain the post-neutron mass yield distribution. From the mass yield distribution data, the full-width at tenth-maximum of light and heavy mass wings, average light mass <AL> and heavy mass <AH>, average neutron number <ν>, and peak-to-valley ratio were obtained for the first time. Comparison of mass yield distributions was made between the epi-cadmium and thermal neutron–induced fission of 245Cm to examine the role of excitation energy on the nuclear structure effect and P/V ratio.

Fusion enhancement within a collective clusterization approach applied to the isotopic chain of neutron-rich light-mass compound nuclei

The dynamics of neutron-rich light-mass compound nuclei $^{24,25,26,27}\mathrm{Mg}^{*}$ formed in $^{12,13,14,15}\mathrm{C}+^{12}\mathrm{C}$ fusion reactions, respectively, is explored at different ${E}_{\mathrm{c}.\mathrm{m}.}$ values within the dynamical cluster decay model (DCM). DCM is based on the quantum mechanical fragmentation theory, which treats the binary fragmentation of emitting compound nucleus as light particles (LPs), intermediate mass fragments (IMFs), as well as symmetric mass fragments (SMFs), on equal footing, which is not the case with other fission and statistical models. All calculations are made for spherical considerations and angular momenta taken up to the $\ensuremath{\ell}$-critical value for the respective reactions. A fusion enhancement is observed as we go from compound nuclei (CN) having an even number of neutrons ($^{24,26}\mathrm{Mg}^{*}$) to CN with the odd number of neutrons ($^{25,27}\mathrm{Mg}^{*}$). Interestingly, we find that the only parameter of the DCM, the neck-length parameter $\mathrm{\ensuremath{\Delta}}R$ related to the barrier lowering, is in linear relation with ${\ensuremath{\sigma}}_{\mathrm{Fusion}}$ at chosen incident laboratory energy. The fusion enhancement is found to be larger for odd neutron number nuclei, which indicates the influence of unpaired neutrons on fusion cross sections. Within the formalism of DCM, the phenomenon of fusion enhancement finds its base in the process of collective clusterization, which is quite evident from the larger values of summed-up preformation probability for the reactions having odd mass projectiles or forming odd mass CN. The DCM calculated fusion cross sections are in good agreement with the available experimental data for the given reactions.

Post-Neutron Mass Yield Distribution in the Epi-Cadmium Neutron-Induced Fission of 229Th

In the epi-cadmium neutron-induced fission of 229Th, cumulative yields of relatively long-lived fission products within the mass range of 77 to 151 were measured by using an off-line gamma-ray spectrometric technique. The mass yields were obtained from the cumulative fission product yields by using charge distribution correction. The peak-to-valley (P/V) ratio, full-width at tenth-maximum of light and heavy mass wings, average light mass <AL> and heavy mass <AH>, and average neutron number <ν> were obtained. The P/V ratio was obtained for the first time and was found to be about three times lower in the epi-cadmium neutron fission than in the thermal neutron fission of 229Th, which shows the role of excitation energy. The fine structure of the mass yield distribution in the 229Th(nf,f) reaction was explained from the viewpoint of nuclear structure effect and the Standard I and Standard II asymmetric modes of fission.

Systematic analysis of the decay of Fl*287,288,290,292 formed in the complete fusion reactions Pu239,240,242,244+Ca48 including Skyrme forces

The fusion evaporation residue cross sections for the decay of the compound nuclear system $^{287,288,290,292}\mathrm{Fl}^{*}$ via $2n$- to $5n$-decay channels, synthesized in $^{239,240,242,244}\mathrm{Pu}+^{48}\mathrm{Ca}$, are studied using the dynamical cluster-decay model (DCM), including quadrupole deformations ${\ensuremath{\beta}}_{2i}$ for compact hot orientations ${\ensuremath{\theta}}_{i}$ at various excitation energies ${E}^{*}=32.5$ to 52.6 MeV. For the nucleus-nucleus interaction potentials, we have employed the Skyrme energy density functional based on the semiclassical extended Thomas-Fermi approach under frozen density approximation. Here, within the DCM, the Skyrme forces used are SLy4, ${\mathrm{SkM}}^{*}$, and, KDE0(v1). The DCM makes use of a single parameter, the neck-length parameter $\mathrm{\ensuremath{\Delta}}R$ that takes different values for different processes at a given temperature and provides an excellent fit to the measured data, independently of the choice of Skyrme force used. We make predictions of probable fusion-fission and quasifission mass regions of fragments and then calculate the evaporation residue cross sections ${\ensuremath{\sigma}}_{\mathrm{ER}}$ for experimentally unobserved neutron channels. Further, the product ${P}_{\mathrm{CN}}{P}_{\mathrm{surv}}$ of compound nucleus (CN) fusion probability ${P}_{\mathrm{CN}}$ and survival probability ${P}_{\mathrm{surv}}$ is calculated to determine the reduced evaporation residue cross section ${\ensuremath{\sigma}}_{\mathrm{ER}}/{\ensuremath{\sigma}}_{\mathrm{fusion}}$, denoted as ${\ensuremath{\sigma}}_{\mathrm{ER}}^{\mathrm{reduced}}$, and we have seen that ${P}_{\mathrm{surv}}$ is the main dominant factor in the product ${P}_{\mathrm{CN}}{P}_{\mathrm{surv}}$. To this end, we have analyzed the effects of mass asymmetry and isospin effect of target nucleus on the ${\ensuremath{\sigma}}_{\mathrm{ER}}$ and have found that the ${\ensuremath{\sigma}}_{\mathrm{ER}}$ for the production of superheavy element ${\mathrm{Fl}}^{*}$ increases slowly with increasing neutron number of the target nucleus. We have also searched for all possible target-projectile combinations forming the hot compound nucleus ${\mathrm{Fl}}^{*}$ at the excitation energy ${E}^{*}$ for compact-hot configurations and have also calculated the fusion evaporation residue cross sections for the proposed new reactions synthesizing Fl.

Personal neutron dosimetry: State-of-the-art and new technologies

Neutron personal dosimetry is necessary for the monitoring of exposed workers, not only in nuclear industry and related activities but also in the growing number of neutron producing facilities, so new techniques and devices are continuously developed and improved. This article provides a review of the present state-of-the-art as well as the main new results and innovative developments in neutron personal dosimetry using electronic personal dosimeters (EPDs), track dosimeters (etched track dosimeters, FNTD), luminescent dosimeters (TL, OSL, RPL), superheated drop dosimeters and direct ion storage (DIS) dosimeters.

Nuclear Structure Investigations of Even–Even Hf Isotopes

The mass region of rare-earth nuclei in the nuclear chart is riddled with well-deformed nuclei, exhibiting rotational properties and many interesting nuclear structure-related phenomena. The scarcity of experimental data as the neutron number increases and the exotic phenomena such as shape coexistence, which are strongly connected with the underlying symmetries of the Hamiltonian and are predicted to take place in this region, make this mass region a fertile ground for experimental and theoretical studies of nuclear structure. In this work, we investigate the structure of the even–even 162–184Hf (hafnium) isotopes through a calculation of various observables such as B(E2;01+→21+) reduced transition matrix elements and quadrupole moments. Six different nuclear models are employed in the calculations of the observables for these nuclei, the shapes of which deviate from spherical symmetry, and as such, are characterized by Hamiltonians, which break the rotational invariance of the exact nuclear many-body Hamiltonian. The results of the present study are expected to establish some concrete guidelines for current and future experimental endeavors. Along these lines, the results for the 162–180Hf isotopes are compared with existing experimental data where available, showing an overall good agreement.

Comprehensive investigation of lattice dynamics of neutron multiplier beryllides: vibrational spectra and thermal performances

In order to realize tritium self-sufficiency during the operation of fusion reactors, neutron multiplier materials are needed to multiply the number of neutrons. Beryllium (Be) and beryllides (Be12V, Be12Ti) are considered as candidates for neutron multiplier materials in the tritium breeding blanket. Thermal performances are essential data to evaluate the service performance of materials in future fusion reactors. Due to the toxicity of beryllium, the preparation and analysis of neutron multiplier materials are challenging. As a result, the performance data of neutron multiplier materials are limited. It is essential to adopt the theoretical method to get the basic parameters for the design of a tritium breeding blanket and optimization of neutron multiplier. In the present work, the electron structure, vibrational spectra, and thermal performances have been theoretically investigated to understand thermal expansion and thermal conductivity properties. Experimental data are also included to compare with the calculated results and detailed analysis is presented. Due to the reactivity with water, BeO will form on the surface of Be. Therefore, BeO was studied as well. The bulk modulus of Be is the smallest of the four materials, while BeO is the largest. Higher bulk modulus has a better ability to restrain the deformation due to pressure. The c-axis of the Be12V has the largest thermal expansion coefficient, while the c-axis of the Be12Ti is the smallest. It has been found that the larger the lattice constant of crystal axes, the smaller the linear thermal expansion coefficient in same material. Electrons play a major role in the heat transfer of Be12V and Be12Ti. At high temperatures, phonon and electron coupling must be considered. Isotopeenrichment and enlarging the grain size cannot significantly improve the phonon thermal conductivity when the temperature is higher than room temperature. The calculated values can be adopted to predict the materials’ performances and support future fusion reactors’ neutron multiplier material preparation.

Study of multinucleon knockout reactions of exotic nuclei in the region of Sn

The experimental data collected during the S515 experiment performed by the R3B collaboration at GSI/FAIR represent a great opportunity to investigate nucleon knockout reactions of exotic nuclei in the region of Sn using complete kinematics measurements. These cross sections can be used in the future to investigate the quenching in the knockout of the minority species (neutrons or protons) in nuclei far from stability. Some of the arguments put forward are the underestimation of the knockout of deeply bound nucleons, final state interactions or the role of short-range correlations (SRC). Recently, several works based on inclusive measurements have shown that these SRCs could reduce the single nucleon knockout cross sections by around 50%, depending on the neutron excess (N/Z) of the initial projectile. The S515 data can help us to go further in this investigation because it allows to correlate the knockout cross sections of one, two or more nucleons with the number of protons and neutrons emitted from the target and which can be detected by the CALIFA and NeuLAND detectors, respectively, and perform complete kinematical studies on the nature of the event (SRC, evaporation, emission of clusters, final-state interactions...). Here the results obtained for the charge distribution of reaction residues are presented, which is one of the first steps of the still on-going analysis.

Conceptual design of a GEM (gas electron multiplier) based gas Cherenkov detector for measurement of 17MeV gamma rays from T(D, γ)5He in magnetic confinement fusion plasmas.

The only method for assessing the fusion power throughput of a deuterium-tritium (DT) reactor presently relies on determining the absolute number of 14MeV neutrons produced in the DT plasma. An independent method, developed and investigated during the recent DT campaign at the Joint European Torus, is based on the absolute counting of 17MeV gamma rays produced by the competing T(D, γ)5He reaction that features a very weak branching ratio (about 3-6 × 10-6) when compared to the main T(D,n)4He reaction. The state-of-the-art spectrometer used for gamma-ray measurements in magnetic confinement fusion plasmas is LaBr3(Ce) scintillator detectors, although they require significant neutron shielding to extract a relatively weak gamma-ray signal from a much more abundant neutron field. A better approach relies on a gamma-ray detector that is intrinsically insensitive to neutrons. We have advanced the design of a gamma-ray counter based on the Cherenkov effect for gamma-rays whose energy exceeds 11MeV, optimized to work in the neutron-rich environment of a steady-state, magnetically confined fusion plasma device. The gamma-rays interact with an aluminum window and extract electrons that move into the radiator emitting photons via the Cherenkov effect. Since the Cherenkov light consists of few photons (25 on average) in the far UV band (100-200nm), a pre-amplifier is required to transport the photons to the neutron-shielded location, which may be a few meters away, where the readout elements of the detector, either a silicon or standard photomultiplier tube, are placed. The present work focuses on the development of a scintillating GEM (Gas Electron Multiplier) based pre-amplifier that acts as a Cherenkov photon pre-amplifier and wavelength shifter. This paper presents the result of a set of Garfield++ simulations developed to find the optimal GEM working parameters. A photon gain of 100 is obtained by biasing a single GEM foil to 1kV.

New developments in fission studies within the time-dependent density functional theory framework

We have extended significantly the microscopic description of the fission process by examining a larger set of observables. We extract neutron and proton numbers of fission fragments, their spins and fission fragment relative orbital angular momentum and their correlations, investigate neutrons emitted at or shortly after scission, excitation energy sharing mechanism, total kinetic energy of fission fragments, and the entanglement entropy. I will present a short overview of our simulations obtained with two independent nuclear energy density functionals.

Study for the long-lived gamma background due to neutron emitting calibration reactions

In this article, a detailed theoretical investigation has been done on the long-lived gamma background due to neutron emitting reactions. It mainly focused on the experiments that will be used to calibrate energy with the terminal voltage of an upcoming Facility for Research in Experimental Nuclear Astrophysics (FRENA). Many reactions like (p, n), (p, γ) have been utilized in various accelerator facilities around the globe for energy calibration purposes. Neutron emitting reactions like 7Li(p, n), 13C(p, n), 19F(p, n), 27Al(p, n), etc. have been very commonly used. For such reactions, a significant number of neutrons produced from such experiments can interact with surrounding elements like copper, tantalum, stainless steel (SS304 and SS316), concrete materials,etc. These interactions may create long-lived gamma activity in the vicinity of the accelerator and detection area. Background gammas from these radioactive isotopes can interfere with gamma measurements in future experiments. The present study has been done to investigate those possibilities of gamma background which may occur due to the calibration study by neutron emitting experiments. Here 7Li(p, n), 13C(p, n), 19F(p, n) and 27Al(p, n) reactions having neutron threshold energies 1.8803, 3.2355, 4.2351, 5.8036 MeV respectively are chosen keeping in mind the proton energy available at the facility.

Nucleus density based new relationship of nuclear charge radius

In this paper we predict and evaluate the value of the nuclear charge radius by analyzing the relationship between nuclear mass and nuclear charge radius.We obtain 884 nuclei (&lt;i&gt;Z&lt;/i&gt;, &lt;i&gt;N&lt;/i&gt; ≥ 8) with known mass and known charge radii by combining AME2020 database with CR2013 database, and calculate the mass densities &lt;inline-formula&gt;&lt;tex-math id="M3"&gt;\begin{document}$ \rho_\text{m} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20230126_M3.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20230126_M3.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; of the 884 nuclei. We aim to obtain an empirical formula of one constant which is useful in describing and predicting nuclear charge radius. With the empirical formula and the AME2020 database, the root-mean-square deviation (RMSD) of the nuclear charge radius of &lt;inline-formula&gt;&lt;tex-math id="M5"&gt;\begin{document}$ \sigma = 0.093 $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20230126_M5.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20230126_M5.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; fm is successfully obtained.Considering the influence of neutron numbers on &lt;inline-formula&gt;&lt;tex-math id="M6"&gt;\begin{document}$\rho_{\rm{m}}$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20230126_M6.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20230126_M6.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, we use the neutron factor &lt;inline-formula&gt;&lt;tex-math id="M7"&gt;\begin{document}${1}/{N} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20230126_M7.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20230126_M7.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; to correct the empirical formula, and the RMSD is reduced to &lt;i&gt;σ&lt;/i&gt; = 0.047 fm (the accuracy is increased by about 50%). The second correction is shell effect of neutrons. The results show that the RMSD of nuclear charge radius is reduced to 0.034 fm based on shell effect of neutrons. We use the empirical formula with corrections to predict the nuclear charge radius (1573 nuclear charge radius with &lt;i&gt;Z&lt;/i&gt;, &lt;i&gt;N&lt;/i&gt; ≥ 8) which is difficult to measure experimentally. The difference between our predicted values based on AME2020 database and the experimental values measured in recent years is in the allowable range of deviation. The result shows that the new relation for nuclear charge radius is simple and reliable. In addition, the RMSD of the calculation value for 791 nuclei is reduced to σ = 0.032 fm after we have removed some nuclei with special shell effect and isotope chains. These results show that the new relation proposed in this paper can be comparable to &lt;inline-formula&gt;&lt;tex-math id="M8"&gt;\begin{document}$ A^{1/3} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20230126_M8.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20230126_M8.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; and &lt;inline-formula&gt;&lt;tex-math id="M9"&gt;\begin{document}$ Z^{1/3} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20230126_M9.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20230126_M9.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; formulas with corrections.Moreover, we study the 884 and 791 nuclear mass densities by using L-M neural network method to build description and prediction models. Comparing with CR2013, the RMSDs of nuclear charge radius are &lt;i&gt;σ&lt;/i&gt; = 0.018 fm and &lt;i&gt;σ&lt;/i&gt; = 0.014 fm, respectively. The RMSDs are reduced by about 50% compared with that from the empirical formula with corrections, and the predicted values are closer to the experimental values measured in recent years.

Importance of deuteron breakup in the deuteron knockout reaction

Background: An isoscalar $pn$ pair is expected to emerge in nuclei that have similar proton and neutron numbers and it may be a candidate for a deuteron ``cluster.'' There is, however, no experimental evidence for it.Purpose: The purpose of this paper is to construct a new reaction model for the $(p,pd)$ reaction including the deuteron breakup in the elementary process and the deuteron reformation by the final-state interactions. How these processes contribute to the observables of the reaction is investigated.Methods: The distorted wave impulse approximation is extended twofold. The elementary processes of the $(p,pd)$, i.e., the $p\text{\ensuremath{-}}d$ elastic scattering and the $d(p,p)pn$ reaction, are described with an impulse picture employing a nucleon-nucleon effective interaction. The three-body scattering waves in the final state of the $(p,pd)$ reaction are calculated with the continuum-discretized coupled-channels method. The triple-differential cross section (TDX) of the $(p,pd)$ reaction is calculated with the new model.Results: The elementary processes are described reasonably well with the present model. As for the $(p,pd)$ reaction, the deuteron reformation can either increase or decrease the TDX height depending on the interference between the elastic and breakup channels of deuteron, while the back-coupling effect always decreases it.Conclusions: It is shown that the deuteron reformation significantly changes the TDX of the $(p,pd)$ reaction through the interference. It is important to include this process to quantitatively discuss the $(p,pd)$ cross sections in view of the deuteron formation in nuclei. For more quantitative discussion regarding the experimental data, further improvement will be necessary.

Alpha Decay Half-Lives Calculation of Even-Even Nuclei in the62≤Z≤100Region using Woods-Saxon Potential

Alpha decay properties of even-even nuclei in the 62 ≤ Z ≤ 100 region are investigated within the Unified Fission Model based on a Modified Woods-Saxon potential. The computed alpha decay half-lives are compared to experimental data and are found to be in good agreement with it. The acquired pattern of the variation of alpha decay half-lives as a function of neutron number are explained by the nuclear shell effect. The experimental alpha decay energy Q is found to have an inverse relation with the alpha decay half-lives. This work has shown that the Unified Fission Model based on a Modified Woods-Saxon potential is sufficient to obtain the values of alpha decay half-lives.

Extended p_{3/2} Neutron Orbital and the N=32 Shell Closure in ^{52}Ca.

The one-neutron knockout from ^{52}Ca in inverse kinematics onto a proton target was performed at ∼230 MeV/nucleon combined with prompt γ spectroscopy. Exclusive quasifree scattering cross sections to bound states in ^{51}Ca and the momentum distributions corresponding to the removal of 1f_{7/2} and 2p_{3/2} neutrons were measured. The cross sections, interpreted within the distorted-wave impulse approximation reaction framework, are consistent with a shell closure at the neutron number N=32, found as strong as at N=28 and N=34 in Ca isotopes from the same observables. The analysis of the momentum distributions leads to a difference of the root-mean-square radii of the neutron 1f_{7/2} and 2p_{3/2} orbitals of 0.61(23)fm, in agreement with the modified-shell-model prediction of 0.7fm suggesting that the large root-mean-square radius of the 2p_{3/2} orbital in neutron-rich Ca isotopes is responsible for the unexpected linear increase of the charge radius with the neutron number.

Fission-stability of high-K states in superheavy nuclei

Fission is the one of the primary radioactive decay modes for the heaviest nuclei and ultimately determines the existence of the heaviest elements on a macroscopic time scale, e.g., ge 10^{-14} s. The present experimental data on the decay properties of the heaviest nuclei with proton numbers 102–118 and/or of neutron numbers up to 177 show that fission occurs occasionally. This confirms that shell structure plays an essential role for their stability against fission. The shell effect on fission manifests in both collective and single-particle ways, which can experimentally be studied in decays of even–even, odd-A and odd–odd nuclei. At the same time, high-K states formed in couplings of quasiparticles are also known to be stable against fission. However, detailed knowledge and theoretical descriptions on a retardation effect/strength of high-K quantum number on fission are still scarce. In the present work, fission from high-K states are discussed and described within the semi-empirical approach. Fission half-lives are calculated for various high-K states, which have been theoretically predicted to exist in Fm-Rf (Z = 100–104) and Hs-Ds (Z = 108–112). The results are found to be in line with the available experimental findings, and also leading to different intriguing predictions, e.g., high-K states in superheavy nuclei tend to be more stable against fission compared to their ground states.

Structure and α decay for the neutron-deficient nuclei with 89≤Z≤94 in the density-dependent cluster model combined with a relativistic mean-field approach

The density-dependent cluster model combined with relativistic mean-field theory is used to explore the structure and $\ensuremath{\alpha}$ decay for the neutron-deficient nuclei with $89\ensuremath{\le}Z\ensuremath{\le}94$, including two newly discovered nuclei $^{207}\mathrm{Th}$ [Phys. Rev. C 105, L051302 (2022)] and $^{214}\mathrm{U}$ [Phys. Rev. Lett. 126, 152502 (2021)]. The effective nucleon-nucleon interactions and matter density distributions from the relativistic mean field are employed to construct the $\ensuremath{\alpha}$-daughter potential with a double-folding model. The Pauli blocking effect is considered by normalizing the strength of the $\ensuremath{\alpha}$-daughter potential with the Bohr-Sommerfeld quantization condition. The $\ensuremath{\alpha}$-preformation factor is calculated with the cluster formation model. The calculated $\ensuremath{\alpha}$-decay half-lives for the 106 observed nuclei with $89\ensuremath{\le}Z\ensuremath{\le}94$ are in excellent agreement with experimental data. Extending this model to the unknown nuclei $^{201--204}\mathrm{Ac}$, $^{205--206}\mathrm{Th}$, $^{209--210}\mathrm{Pa}$, $^{212--213,220}\mathrm{U}$, $^{215--218,221}\mathrm{Np}$, and $^{220--227}\mathrm{Pu}$, the evolution of the $N=126$ shell closure with neutron number is explored for the high-$Z$ isotopes. The available $\ensuremath{\alpha}$-decay energies, preformation factors, and $\ensuremath{\alpha}$-decay half-lives show a regular change with increasing neutron number. Especially, the robustness of the $N=126$ shell closure is shown up to the Pu isotopes.

Alpha decay of thermally excited nuclei

One of the prominent decay modes of heavy nuclei which are produced in astrophysical environments at temperatures of the order of 109 K is the α (4He) decay. Thermally enhanced α decay rates are evaluated within the standard scheme of a tunneling decay where the α particle tunnels through the potential barrier formed by its interaction with the daughter nucleus. Following the observation that there exists several excited levels with the possibility of an α decay when the daughter nucleus is at a shell closure, we focus in particular on decays producing daughter nuclei with the neutron number, N = 126. Within a statistical approach we find that the half-lives, t 1/2(T), for temperatures ranging from T = 0 to 2.4 GK can decrease by 1–2 orders of magnitude with the exception of the decay of 212Po which decays to the doubly magic daughter 208Pb, where t 1/2(T) decreases by 5 orders of magnitude. The effect of these thermally enhanced α decays on the r-process nucleosynthesis can be significant in view of the mass build-up at the waiting point nuclei with closed neutron shells.

A new relation for nuclear masses based on the nuclide chain with the same number of neutrons

There are many studies in Odd–Even staggering (OES) of nuclear masses, but the research on nuclear masses by using the systematicness of OES is indeed very few. In this work, we analyze the relationship among the four neighboring nuclei based on the OES of nuclide chain with the same number of neutrons in atomic mass evaluation database (AME2016 database). Our purpose in this paper is to describe an empirical formula with one constant for OES of nuclear masses that can be useful in describing and predicting nuclear masses with mass number [Formula: see text]. With the empirical formula and AME2016 database, the root-mean-square deviation (RMSD) of the nuclei that we have successfully obtained 172[Formula: see text]keV for [Formula: see text] (the RMSD is 140[Formula: see text]keV for [Formula: see text]). This paper also uses Levenberg–Marquart (L-M) neural network approach to study the OES of nuclear masses ([Formula: see text], RMSD [Formula: see text][Formula: see text]keV; [Formula: see text], RMSD [Formula: see text][Formula: see text]keV). The results show that the RMSD of nuclear masses for [Formula: see text] based on neural network approach 30[Formula: see text]keV decreases than that based on empirical formula (the accuracy is increased by about 17%). In addition, the predicted values based on the empirical formula and L-M neural network approach are consistent with the values in AME2020 database, and the difference between our predicted values based on AME2016 database and experimental values measured in recent years is small. These results show that the new relation for nuclear masses has good simplicity, accuracy and reliability. Accurate nuclear mass is helpful to the research of nuclear physics, nuclear technology and astrophysics.