Number Of Neutrons Research Articles

Peeling away neutron skin in ultracentral collisions of relativistic nuclei

In heavy nuclei the ratio between local densities of neutrons and protons increases towards the nuclear periphery. The excess of neutrons is known as the neutron skin (NS) with a subtle difference ($<0.5$~fm) between the r.m.s radii of the distributions of neutrons and protons. We show that the presence of NS in $^{208}$Pb leads to extra spectator neutrons in ultracentral $^{208}$Pb--$^{208}$Pb collisions at the CERN SPS and LHC. The yields of spectator neutrons and protons were calculated within a new version of Abrasion-Ablation Monte Carlo for Colliders model (AAMCC-MST) taking into account NS and pre-equilibrium clustering of spectator matter. While the average numbers of spectator neutrons and protons in ultracentral collisions vary insignificantly, the cross sections of emission of certain numbers of spectator neutrons in events with 0,1,...5 spectator protons are changed by 50--250\%, depending on the thickness of NS. These cross sections are less sensitive to other parameters in calculations, and their measurements in the ALICE experiment at the LHC will make it possible to restrict the existing variety of neutron density parameterizations in $^{208}$Pb.

Octupole shape phase transitions and critical points in neutron rich actinides

The evolution of octupole shapes and shape phase transitions in neutron rich actinides is studied within the covariant density functional framework. Octupole constrained energy surfaces, and spectroscopic observables of four isotopic chains of: Cm, Cf, Fm and No with neutron numbers 186le N le 200 are analysed using a collective quadrupole–octupole Hamiltonian (QOCH). The parameters of the Hamiltonian are determined by axially reflection-asymmetric relativistic Hartree–Bogoliubov calculations based on the energy density functional DD-PC1, and a finite-range pairing interaction. The results suggest quantum phase transitions from non-octupole to octupole deformed shapes and to octupole vibrations with increasing neutron number. ^{288}Cm is possibly close to the critical point of a simultaneous phase transition from spherical to prolate deformed and from non-octupole to stable octupole deformed configurations.

αdecay of Po and Rn isotopes using different choices of impinging frequency

A comprehensive study of $\ensuremath{\alpha}$ particle emergence from $^{188\text{--}218}\mathrm{Po}$ isotopes is carried out within the framework of the preformed cluster model (PCM). The mass asymmetry coordinate and the interfragment separation play crucial roles in the identification of the most probable decay channel and the barrier penetration of decay fragments. First, the barrier characteristics are studied using two choices of radii [with surface diffuseness (${C}_{i}$) and without surface diffuseness (${R}_{i}$)]. The fragmentation behavior of $^{188}\mathrm{Po}$, $^{202}\mathrm{Po}$, and $^{218}\mathrm{Po}$ isotopes is explored for the identification of the most probable decay channel in view of the structure of the fragmentation potential. The $\ensuremath{\alpha}$ decay is found to be the most prominent decay mode in the chosen set of isotopes. The preformation and penetrative probability of the decay fragments is studied with respect to increase in the neutron number of the parent nucleus. The $\ensuremath{\alpha}$ decay half-lives of polonium isotopes are calculated using classical assault frequency (${\ensuremath{\nu}}_{c}$) and quantum mechanical assault frequency (${\ensuremath{\nu}}_{q}$) and a comparison is made with the experimental data. Here, the term assault frequency is basically the impinging frequency of an $\ensuremath{\alpha}$ particle near the surface of the parent nucleus. Further, the $\ensuremath{\alpha}$ decay half-lives of the $^{198\text{--}220}\mathrm{Rn}$ isotopes are calculated using the effective assault frequency (${\ensuremath{\nu}}_{e}$) parameter, and a comparison is made with the available experimental data.

Attempts to produce new americium isotopes near N=126

Searches for new americium isotopes with neutron number around 126 are made in bombardments of $^{191,193}\mathrm{Ir}$ targets with $^{40}\mathrm{Ar}$ ions by employing the gas-filled recoil separator SHANS and the recoil-$\ensuremath{\alpha}$ correlation technique. No evidence for nuclides of interest is obtained, and the upper limits of the cross sections producing the evaporation residues are estimated to be 31.4 pb and 5.4 pb for the reactions of $^{40}\mathrm{Ar}+^{193}\mathrm{Ir}$ and $^{40}\mathrm{Ar}+^{191}\mathrm{Ir}$, respectively. We have performed microscopic finite-temperature Skyrme Hartree-Fock$+$ (Bardeen- Cooper- Schripffer theory) BCS calculations, and found that the fission barriers of compound nuclei in this region decrease rapidly with increasing proton number. The non-observation of new americium isotopes would be attributed to small survival probabilities of the $^{231}\mathrm{Am}$ and $^{233}\mathrm{Am}$ compound nuclei due to their much reduced fission barriers at high excitations.

The Milne Problem with the Anlı-Güngör Scattering

Recently developed the Anlı-Güngör scattering function is applied to the Milne problem in this study. It is the function of Legendre polynomials with t parameter which can be called as scattering parameter. The extrapolation distance values are calculated for varying t parameters and varying secondary neutron numbers with the HN method. The numerical results are calculated by 40th approximation in order to get high precision results. The calculated extrapolation distance results are very convergence. Since there is no a similar study for the Milne problem with the Anlı-Güngör scattering in the literature, the interpolation technique is applied to the HN method results. Thus, the isotropic scattering results could be determined by t → 0 limit.

Determination of biological radioprotective characteristics of some natural organic compounds for radiation shielding applications

Abstract Ionizing radiation is used in many fields in energy, medicine, and industrial applications. Those who are in these areas or cancer patients receiving radiotherapy are at risk for acute or long-term exposure to radiation damage due to these ionizing radiations. Non-toxic new agents are needed to protect intact tissue and cells. In this study, we aimed to determine the gamma and neutron radiation attenuation characteristics of seven different natural compounds (quercetin, menadione, naphthol, caffeine, quinine sulphate, cholesterol and riboflavin) to help users in radiation applications. Gamma radiation attenuation parameters such as the mean free path, mass attenuation coefficient, effective atom number, linear attenuation coefficient, and half-value layer were calculated theoretically with WinXCom software for the energy range 0.015–15 MeV. Fast neutron attenuation criteria, such as mean free path, half-value layer, effective removal cross-sections and transmission neutron number, were theoretically determined with Monte Carlo simulation codes (Geant4). Neutron absorption measurement experiments were also applied in addition to the theoretical results. The neutron radiation absorption capacities were determined for samples with an 241Am-Be 4.5 MeV energy neutron source and portatif-type Canberra brand BF3 gas neutron detector. Neutron attenuation parameters were compared with paraffin to determine the absorption capability of the samples. It was found that the dose 1.1094 (μSv/h) from the source was absorbed by the samples to the following extent: 31.76% (Quercetin), 21.85% (Menadione), 28.85% (Naphthol), 22.94% (Caffeine), 12.51% (Quinine sulphate), 40.44% (Cholesterol) and 20.94% (Riboflavin). From the results, it can be clearly seen that all these drug samples had a good neutron radiation attenuation capacity. This revealed that the examined samples had radiation absorption abilities. It was found that the cholesterol sample had an especially excellent absorption power for both neutron and gamma radiation. The samples investigated in this study could be used to develop radiation-protective drugs.

Dependence of (n,γ)−(γ,n) equilibrium r -process abundances on nuclear physics properties

In most $r$-process expansions, the dominant nuclear evolution occurs in an $(n,\ensuremath{\gamma})\text{\ensuremath{-}}(\ensuremath{\gamma},n)$ equilibrium in which nuclei rapidly exchange neutrons but change charge much more slowly by beta decay. Freeze-out from this equilibrium shapes the final abundances but does not significantly alter the overall global abundance pattern; therefore, it is important to understand the details of $(n,\ensuremath{\gamma})\text{\ensuremath{-}}(\ensuremath{\gamma},n)$ equilibrium both because it is the main evolution phase that determines the final abundance pattern and because it is the starting point for the freeze-out. Through use of a simple but realistic phenomenological nuclear physics model, we show that isotopic abundances versus neutron number in $(n,\ensuremath{\gamma})\text{\ensuremath{-}}(\ensuremath{\gamma},n)$ equilibrium are well approximated as Gaussians. Nuclear pairing causes isotopic abundances to alternate between two Gaussians, and shell effects cause the isotopic abundances to shift from one Gaussian to another when the neutron number crosses a magic number. More complex neutron-separation energy curves versus mass number can be generated by adding a spike function to a linearly declining curve. In such a case, the equilibrium abundance curve jumps from one Gaussian to another for each added spike. Insights from our model can help shed light on how detailed theoretical or experimental nuclear data affect $r$-process nucleosynthesis during the $(n,\ensuremath{\gamma})\text{\ensuremath{-}}(\ensuremath{\gamma},n)$ equilibrium phase.

Neutron star crust properties: comparison between the compressible liquid-drop model and the extended Thomas-Fermi approach

We present a detailed analysis of three models predicting the properties of non-uniform matter in the crust of neutron stars: the compressible liquid-drop model, the fourth order Extended Thomas Fermi (ETF) method, and ETF plus Strutinsky integral (ETFSI) correction. The former treats the nuclear clusters as uniform hard spheres, the second takes into account the density distribution which can be different for neutrons and protons, and the last one includes the proton shell effects within the Strutinsky approach. The purpose of this work is to understand the importance of the improvements in the nuclear modeling and to analyze the quantities which are the most sensitive to them. We find that thermodynamic quantities such as pressure, energy and chemical potential, as well as the electron fraction, are in very good agreement among the three models. This confirms previous results where we have shown that the improvement in the finite-size description of the nuclear clusters has a small impact on these quantities, since they are mainly constrained by the bulk properties. The refinements in the finite-size modeling are shown to impact mostly the composition of the nuclear clusters (Z cl, N cl) in an ordering which ranks according to the leptodermous expansion. This analysis is performed considering both the r-cluster and the e-cluster representations. The proton shell effects are shown to stabilize Z cl, which consequently impacts the neutron number N cl as well.

Shape Changes in Odd-Even Osmium Isotopes

This paper has calculated the energy levels of 185-187-189Os isotopes using the projected shell model (PSM). Yrast Spectrum, nucleus rotation frequency and the ratio of reduced electromagnetic transition probabilities, B(E2)/B(M1) plots versus spin for understanding the structure of multi-quasiparticle band up to the spins 47/2+, 33/2+ and 31/2+ for these isotopes, are plotted, respectively. It was found that in the spin ranges 35/2+-39/2+, 31/2+-33/2+, and 27/2+-29/2+, due to 3-quasiparticle band-crossing, simultaneously by increasing rotational inertia of the nucleus, nucleus rotation frequency decreases greatly and as an important result, B(E2)/B(M1) ratio, the electrical properties of the nucleus in these spins increase. Indeed, in these isotopes, observed that by increasing neutron number, the deformation parameter, ε2 decreases as well, and by increasing spin in especial spins, due to nucleon alignment phenomenon, the nucleus rotational behavior decreases inverse the vibration mode.

Role of dynamic pairing correlations in fission dynamics. II. Fermium and nobelium isotopes

The competition between the quenching of pairing due to the repulsive Coulomb interaction and dynamic pairing correlations added by particle number symmetry restoration has been studied in a selected set of Fermium and Nobelium isotopes by using a hierarchy of Hartree-Fock-Bogoliubov--based approximations and a restricted variation after particle number projection, all of them based on the $\mathrm{D}1{\mathrm{M}}^{*}$ parametrization of the Gogny force. It is found that Coulomb antipairing is partially compensated by beyond-mean-field pairing correlations. However, the compensation is not perfect and a modulation of the spontaneous fission half-lives, as functions of the neutron number, indicates that the combined effect on fission dynamics of Coulomb antipairing and restricted particle number symmetry restoration cannot be overlooked. Neither can it be accounted for by the Coulomb Slater approximation.

Ab initio predictions link the neutron skin of 208Pb to nuclear forces

Heavy atomic nuclei have an excess of neutrons over protons, which leads to the formation of a neutron skin whose thickness is sensitive to details of the nuclear force. This links atomic nuclei to properties of neutron stars, thereby relating objects that differ in size by orders of magnitude. The nucleus 208Pb is of particular interest because it exhibits a simple structure and is experimentally accessible. However, computing such a heavy nucleus has been out of reach for ab initio theory. By combining advances in quantum many-body methods, statistical tools and emulator technology, we make quantitative predictions for the properties of 208Pb starting from nuclear forces that are consistent with symmetries of low-energy quantum chromodynamics. We explore 109 different nuclear force parameterizations via history matching, confront them with data in select light nuclei and arrive at an importance-weighted ensemble of interactions. We accurately reproduce bulk properties of 208Pb and determine the neutron skin thickness, which is smaller and more precise than a recent extraction from parity-violating electron scattering but in agreement with other experimental probes. This work demonstrates how realistic two- and three-nucleon forces act in a heavy nucleus and allows us to make quantitative predictions across the nuclear landscape.

Bubble nuclei: Single-particle versus Coulomb interaction effects

The detailed investigation of microscopic mechanisms leading to the formation of bubble structures in nuclei is performed in the framework of covariant density functional theory. The main emphasis of this study is on the role of single-particle degrees of freedom and Coulomb interaction. In general, the formation of bubbles lowers the Coulomb energy. However, in nuclei this trend is counteracted by the quantum nature of the single-particle states: only specific single-particle states with specific density profiles can be occupied with increasing proton and neutron numbers. A significant role of the central classically forbidden region at the bottom of the wine bottle potentials in the formation of nuclear bubbles (via primarily the reduction of the densities of the $s$ states at $r=0$) is revealed for the first time. Their formation also depends on the availability of low-$l$ single-particle states for occupation since single-particle densities represent the basic building blocks of total densities. Nucleonic potentials disfavor the occupation of such states in hyperheavy nuclei and this contributes to the formation of bubbles in such nuclei. Existing bubble indicators are strongly affected by single-particle properties and thus they cannot be reliable measures of bulk properties (such as the Coulomb interaction). An additivity rule for densities is proposed for the first time. It was shown that the differences in the densities of bubble and flat density nuclei follow this rule in the $A\ensuremath{\approx}40$ mass region and in superheavy nuclei with comparable accuracy. This strongly suggests the same mechanism of the formation of central depression in bubble nuclei of these two mass regions. Nuclear saturation mechanisms and self-consistency effects also affect the formation of bubble structures. The detailed analysis of different aspects of bubble physics strongly suggests that the formation of bubble structures in superheavy nuclei is dominated by single-particle effects. The role of the Coulomb interaction increases in hyperheavy nuclei but even for such systems we do not find strong arguments that the formation of bubble structures is dominated by it.

Gamma and Neutron Shielding Parameters of Polyester-based composites reinforced with boron and tin nanopowders

The usage of composites as the shielding materials are highly recommended since they could be used in order to attenuate the undesired radiation with unique properties and advantages in the areas where the radiation is prevalent. In this context, not only are their radiation shielding properties important but also their flexibility, durability and low cost. Due to the mentioned superior characteristics, the polyester based composites are among the most preferred materials. With the aim of creating unique and novel radiation shielding materials, this study investigates gamma and neutron shielding capabilities of the polyester composites reinforced with Boron and Tin nanopowders at different proportions (0–50%, 10–40%, 20–30%, 30-20% and 40-10%, 50-0%). The gamma shielding abilities of the prepared polyester composite materials were evaluated using an HPGe detector system, WinXCOM computer program and different simulation tools (FLUKA and GEANT4) at the energies varying from 59.5 to 1332.5 keV. The experimental, theoretical and simulation results showed remarkable agreement between each other, and the addition of Sn enhances the gamma attenuation performance of the chosen polyester composite materials. In addition to gamma analysis results, neutron shielding properties of the proposed composites are further determined. On this purpose, the transmitted neutron numbers through the samples (as functions of neutron energy and the sample thickness) and effective neutron removal cross sections were evaluated. The neutron shielding performance of the samples showed that the prepared composites could be alternative materials to the existing neutron shields in the literature.

Finite-range simple effective interaction including tensor terms

The prediction of single particle level crossing phenomenon between $2p_{3/2}$ and $1f_{5/2}$ orbitals in $Ni$- and $Cu$-isotopic chains by the finite range simple effective interaction without requiring the tensor part is discussed. In this case the experimentally observed crossing could be studied as a function of nuclear matter incompressibility, $K(\rho_0)$. The estimated crossing for the neutron number $N$=46 could be reproduced by the equation of state corresponding to $K(\rho_0)$=240 MeV. However, the observed proton gaps between the $1h_{11/2}$ and $1g_{7/2}$ shells in $Sn$ and $Sb$ isotopic chain, and the neutron gaps between the $1i_{13/2}$ and $1h_{9/2}$ shells in $N$=82 isotones, as well as the shell closure properties at $N$=28 require explicit consideration of a tensor part as the central contribution is not enough to initiate the required level splittings.

Modern Trends in Neutron Scattering Instrument Technologies

This article reviews some current trends that can be observed in the development of neutron scattering instrument technologies. While the number of neutron scattering facilities worldwide and the number of beam days they offer are largely stable, their scientific impact is increasing through improving instrumental capabilities, new and more versatile instruments, and more efficient data collection protocols. Neutron beams are becoming smaller but more intense, and instruments are being designed to utilize more ‘useful’ neutrons in unit time. This article picks and discusses a few recent developments in the areas of integrated source and instrument design, use of computational tools, new detectors, and experiment automation.

Impact of tensor force on quantum shell effects in quasifission reactions

Quantum shell effects drive many aspects of many-body quantal systems and their interactions. Among these are the quasifission reactions that impede the formation of a compound nucleus in superheavy element (SHE) searches. Fragment production in quasifission is influenced by shell effects as a nontrivial manifestation of microscopic dynamics hindering the full equilibration of the composite system to form the compound nucleus. In this Letter, we use the microscopic time-dependent Hartree-Fock (TDHF) theory to study 48Ca+249Bk collisions to investigate the influence of the tensor component of the effective nucleon-nucleon interaction. The results show that the inclusion of the tensor force causes the spherical shell effect to become more prominent, particularly for the neutron number yield whose peak is exactly at magic number N=126. This suggests that the tensor force plays a compelling role in the evolution of dynamical shell effects in nuclear reactions, influencing the competition between spherical and deformed shell gaps.

Isthmus connecting mainland and island of stability of superheavy nuclei

For the $^{48}\mathrm{Ca}$ and Ra/actinide-based complete fusion reactions, the excitation functions for the production of isotopes of superheavy nuclei with charge numbers 108--116 are calculated and compared to the available experimental data. The calculated production cross sections clearly indicate the border nucleus Ds between the island of stability of superheavy nuclei and the mainland with a relatively large number of neutrons.

Effect of Coriolis mixing on lifetime of isomeric states in heavy nuclei

The effect of Coriolis $K$ mixing on the $\ensuremath{\gamma}$ decay of one-quasiparticle isomeric states is examined in transfermium nuclei with neutron number $N=153$. We consider a core-plus-quasiparticle coupling in which the $K$ mixing sharply increases if the isomeric quasiparticle state closely approaches the rotational state with the same angular momentum $I$, but built on another quasiparticle state which is either directly coupled to the isomeric ($\mathrm{\ensuremath{\Delta}}K=1$) or connected with it through the intermediate mixing quasiparticle orbitals ($\mathrm{\ensuremath{\Delta}}K&gt;1$). This mechanism is likely to explain the 38-ns ${K}^{\ensuremath{\pi}}=7/{2}^{+}$ isomer in $^{251}\mathrm{Cf}$ which is quasidegenerated with an ${I}^{\ensuremath{\pi}}=7/{2}^{+}$ rotation state built on ${K}^{\ensuremath{\pi}}=1/{2}^{+}$. Our model explains the enhancement of its decay by three orders of magnitude compared to the ${K}^{\ensuremath{\pi}}=7/{2}^{+}$ isomer in $^{249}\mathrm{Cm}$. We suggest that the same mechanism could be of general importance for the isomer decay properties in a wide range of heavy odd-mass nuclei.

Assessment of the Photon and Neutron Source Term for the NPP Krško Spent Fuel

Accurate knowledge of the fuel nuclide inventory is important after reactor shut down, during the fuel storage and subsequent reprocessing or disposal to provide adequate shielding from the photon and neutron radiation. In this paper possibility to calculate the NPP Krško photon and neutron source term with the Serpent code has been analysed. Some deficiencies in the supplied ENDF/B-VII.0 decay library have been observed. In addition, Serpent reports only spontaneous fission rates without (α, n) and (β, n) contributions. To get neutron emission, spontaneous fission rates had to be multiplied with the average number of neutrons born for each particular nuclide manually. Comparison with the Origen code has shown acceptable agreement of the ENDF/B-VII.1 results. Influence of several factors such as fuel burnup, enrichment, temperature, moderator temperature (density), soluble boron concentration, average power, and burnable absorbers has been analysed. In addition, it was demonstrated that, except for the burnup and enrichment, averaging of all other parameters is acceptable approach. IFBA fuel should be accounted for explicitly due to relative high impact on the photon and neutron emissions.

Statistical correlations of nuclear quadrupole deformations and charge radii

Shape deformations and charge radii, basic properties of atomic nuclei, are influenced by both the global features of the nuclear force and the nucleonic shell structure. As functions of proton and neutron number, both quantities show regular patterns and, for nuclei away from magic numbers, they change very smoothly from nucleus to nucleus. In this paper, we explain how the local shell effects are impacting the statistical correlations between quadrupole deformations and charge radii in well-deformed even-even Er, Yb, and Hf isotopes. This implies, in turn, that sudden changes in correlations can be useful indicators of underlying shell effects. Our theoretical analysis is performed in the framework of self-consistent mean-field theory using quantified energy density functionals and density-dependent pairing forces. The statistical analysis is carried out by means of the linear least-square regression. The local variations of nuclear quadrupole deformations and charge radii, explained in terms of occupations individual deformed Hartree-Fock orbits, make and imprint on statistical correlations of computed observables. While the calculated deformations or charge radii are, in some cases, correlated with those of their even-even neighbors, the correlations seem to deteriorate rapidly with particle number. The statistical correlations between nuclear deformations and charge radii of different nuclei are affected by the underlying shell structure. Even for well deformed and superfluid nuclei for which these observables change smoothly, the correlation range usually does not exceed $\Delta N=4$ and $\Delta Z=4$, i.e., it is rather short. This result suggests that the frequently made assumption of reduced statistical errors for the differences between smoothly-varying observables cannot be generally justified.