Number Of Neutrons Research Articles

Study on the basic of spallation target for accelerator driven system

A study on the basic of spallation target for Accelerator Driven System (ADS) has been done. ADS is a subcritical assembly combined with a high-power proton accelerator. In the center of the subcritical assembly, there is a spallation target for producing primary neutrons that will be multiplied by the subcritical core surrounding it. The neutrons are produced via spallation reaction which occurs when the spallation target is bombarded by high-energy protons. The spallation target has to be designed so that the number of neutrons escaping from the target per incident proton is maximum and the power density deposited on it is high (~1 MW/litter). The spallation target can be made of a solid or liquid material such as Pb, Hg, U, W, Ta, or Pb-Bi which are the most preferred materials for spallation targets. But, today Pb-Bi is the reference material for ADS applications. The spallation target has a large thermal load due to the conversion of about 10 MW proton into a neutron. Therefore, the target needs a cooling system; there are two options that can be considered i.e., cooling by means of the subcritical reactor primary system coolant and cooling by means of an independent loop.

Hexadecapole strength in the rare isotopes 74,76Kr

In the Ge-Sr mass region, isotopes with neutron number N≤40 are known to feature rapid shape changes with both nucleon number and angular momentum. To gain new insights into their structure, inelastic proton scattering experiments in inverse kinematics were performed on the rare isotopes 74,76Kr. This work focuses on observables related to the Jπ=41+ states of the Kr isotopes and, in particular, on the hexadecapole degree of freedom. By performing coupled-channels calculations, hexadecapole deformation parameters β4 were determined for the Jπ=41+ states of 74,76Kr from inelastic proton scattering cross sections. Two possible coupled-channels solutions were found. A comparison to predictions from nuclear energy density functional theory, employing both non-relativistic and relativistic functionals, clearly favors the large, positive β4 solutions. These β4 values are unambiguously linked to the well deformed prolate configuration. Given the β2−β4 trend, established in this work, it appears that β4 values could provide a sensitive measure of the nuclear shell structure.

Collapse of the N=28 shell closure in the newly discovered Na39 nucleus and the development of deformed halos towards the neutron dripline

Halos and changes of nuclear magicities have been extensively investigated in exotic nuclei during past decades. The newly discovered $^{39}\mathrm{Na}$ with the neutron number $N=28$ provides a new platform to explore such novel phenomena near the neutron dripline of the sodium isotopic chain. We study the shell property and the possible halo structure in $^{39}\mathrm{Na}$ within the deformed relativistic Hartree-Bogoliubov theory in continuum. It is found that the lowering of $2p$ orbitals in the spherical limit results in the collapse of the $N=28$ shell closure in $^{39}\mathrm{Na}$, and a well-deformed ground state is established. The pairing correlations and the mixing of $pf$ components driven by deformation lead to the occupation of weakly bound or continuum $p$-wave neutron orbitals. An oblate halo is therefore formed around the prolate core in $^{39,41}\mathrm{Na}$, making $^{39}\mathrm{Na}$ a single nucleus with the coexistence of several exotic structures, including the quenched $N=28$ shell closure, Borromean structure, deformed halo, and shape decoupling. The microscopic mechanisms behind the shape decoupling phenomenon and the development of halos towards dripline are revealed.

Enhanced α decays to negative-parity states in even-even nuclei with octupole deformation

The $\ensuremath{\alpha}$ decays of even-even Ra, Th, U, and Pu isotopes to ground and excited states of daughter nuclei with neutron numbers of $N=130--140$ are investigated. These nuclei show some enhanced $\ensuremath{\alpha}$-branching ratios to negative-parity states $({1}^{\ensuremath{-}},$ ${3}^{\ensuremath{-}})$, compared with the decays to positive-parity states $({4}^{+})$ of comparable energy. This enhancement correlates with appearance of static octupole deformation, rather than spherical nuclear shapes or dynamic asymmetric vibrational states. The highly enhanced branching ratios occur for $\ensuremath{\alpha}$ decays to the ${1}^{\ensuremath{-}}$ and ${3}^{\ensuremath{-}}$ states of the Ra isotopes with $N=134, 136, 138$, then to ${1}^{\ensuremath{-}}$ state in Th $(N=134--140)$ and to the ${3}^{\ensuremath{-}}$ state in Rn $(N=132--136)$ isotopes.

Merging of the island of inversion at N = 40 and N = 50

We performed a quantitative study of the nuclei with proton numbers from Z=20 (Ca) to Z=28 (Ni) and neutron numbers ranging from N=38 to 52 using the realistic shell model, which merged the descriptions of nuclei around N=40 and N=50 within an extended model space. The 21+ excitation energy (E(21+)) is calculated for neutron-rich Cr, Fe, and Ni isotopes. The results suggest that the islands of inversion at N=40 and N=50 merge around the Cr chain, and the N=50island of inversion is located below 78Ni. To demonstrate the prediction of the N=50island of inversion, we calculated and compared the E(21+), B(E2;01+→21+), effective single-particle energies (ESPEs), the probability of particle-hole excitation, and the average occupations in the N=40 and N=50 isotones. Similar parabolic trends of E(21+) and B(E2;01+→21+) in the N=40 and 50 isotones are obtained. The calculated ESPEs give that the N=40 and N=50 shell gaps both increase with the variation of proton number from Z=20 (Ca) to Z=28 (Ni). However, our calculations indicate that different particle-hole excitations dominate in the ground states of the N=40 and N=50islands of inversion, with 2p2h and 4p4h configurations being prominent in N=40 isotones, whereas 2p2h excitations are most important in the N=50 isotones. Furthermore, large occupations of the intruder quadrupole partner orbitals are also obtained in N=40 and N=50 isotones in our realistic shell model calculations.

First spectroscopic study of odd-odd Cu78

Nuclei in the vicinity of Ni78 are important benchmarks for nuclear structure, which can reveal changes in the shell structure far from stability. Spectroscopy of the odd-odd isotope Cu78 was performed for the first time in an experiment with the EURICA setup at the Radioactive Isotope Beam Factory at RIKEN Nishina Center. Excited states in the neutron-rich isotope were populated following the β decay of Ni78 produced by in-flight fission and separated by the BigRIPS separator. A level scheme based on the analysis of γ−γ coincidences is presented. Tentative spin and parity assignments were made when possible based on the β-decay feeding intensities and γ-decay properties of the excited states. Time correlations between β and γ decay show clear indications of an isomeric state with a half-life of 3.8(4) ms. Large-scale Monte Carlo shell-model calculations were performed using the A3DA-m interaction and a valence space comprising the full fp shell and the 1g9/2 and 2d5/2 orbitals for both protons and neutrons. The comparison of the experimental results with the shell-model calculations allows interpreting the excited states in terms of spin multiplets arising from the proton-neutron interaction. The results provide further insight into the evolution of the proton single-particle orbitals as a function of neutron number, and quantitative information about the proton-neutron interaction outside the doubly magic Ni78 core.Received 6 October 2022Revised 3 January 2023Accepted 9 January 2023DOI:https://doi.org/10.1103/PhysRevC.107.044301©2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBeta decayEnergy levels & level densitiesIsomer decaysNuclear spin & parityNuclear structure & decaysNucleon-nucleon interactionsShell modelProperties59 ≤ A ≤ 89Nuclear Physics

Isospin-Symmetry Breaking within the Nuclear Shell Model: Present Status and Developments

The paper reviews the recent progress in the description of isospin-symmetry breaking within the nuclear shell model and applications to actual problems related to the structure and decay of exotic neutron-deficient nuclei and nuclei along the N=Z line, where N is the neutron number and Z the atomic number. The review recalls the fundamentals of the isospin formalism for two-nucleon and many-nucleon systems, including quantum numbers, the spectrum’s structure and selection rules for weak and electromagnetic transitions; and at the end, summarizes experimental signatures of isospin-symmetry breaking effects, which motivated efforts towards the creation of a relevant theoretical framework to describe those phenomena. The main approaches to construct accurate isospin-nonconserving Hamiltonians within the shell model are briefly described and recent advances in the description of the structure and (isospin-forbidden) decay modes of neutron-deficient nuclei are highlighted. The paper reviews major implications of the developed theoretical tools to (i) the fundamental interaction studies on nuclear decays and (ii) the estimation of the rates of nuclear reactions that are important for nuclear astrophysics. The shell model is shown to be one of the most suitable approaches to describing isospin-symmetry breaking in nuclear states at low energies. Further efforts in extending and refining the description to larger model spaces, and in developing first-principle theories to deal with isospin-symmetry breaking in many-nucleon systems, seem to be indispensable steps towards our better understanding of nuclear properties in the precision era.

Experimental review of octupole correlations in the A≈80 mass region

This review presents the nuclei with octupole correlations in the [Formula: see text] mass region. The status of experimental data on the behavior of the energy displacement, the [Formula: see text] transition probability and intrinsic electric dipole moment have been reviewed. The evolutions of the octupole strength with the numbers of protons and neutrons are discussed.

Spectral features of vibrational Te isotopes

The variation of collective vibrational spectra with varying $N$ displayed by the $Z=52$ Te isotopes, for less than $N=82$ closed shell, are of special interest. The spectral features of the ground band and the two and three phonon excited multiplets in $^{118--128}\mathrm{Te}$, are studied here empirically. The state energy $E({2}_{1}{}^{+})$ increases, and the energy ratio ${R}_{4/2}$ decreases with increasing neutron number $N$. Also the ${0}_{2}{}^{+}$ state rises up sharply, and the ${0}_{3}{}^{+}$ state follows it, unlike their relation in the E(5) symmetry. It is shown that $^{120}\mathrm{Te}$ isotope displays the weakly deformed status, and the heavier isotopes move towards the spherical harmonic vibrator status. The interacting boson model (IBM-1) is used to reproduce these spectral features of $^{118--124}\mathrm{Te}$, with use of slight variation of boson energy \ensuremath{\epsilon} and of the quadrupole interaction strength. In the microscopic approach, the dynamic pairing plus quadrupole model of Kumar and Baranger also reproduces these basic spectral features.

Predicting β -decay energy with machine learning

${Q}_{\ensuremath{\beta}}$ represents one of the most important factors characterizing unstable nuclei, as it can lead to a better understanding of nuclei behavior and the origin of heavy atoms. Recently, machine learning methods have been shown to be a powerful tool to increase accuracy in the prediction of diverse atomic properties such as energies, atomic charges, and volumes, among others. Nonetheless, these methods are often used as a black box not allowing unraveling insights into the phenomena under analysis. Here, the state-of-the-art precision of the $\ensuremath{\beta}$-decay energy on experimental data is outperformed by means of an ensemble of machine-learning models. The explainability tools implemented to eliminate the black box concern allowed to identify proton and neutron numbers as the most relevant characteristics to predict ${Q}_{\ensuremath{\beta}}$ energies. Furthermore, a physics-informed feature addition improved models' robustness and raised vital characteristics of theoretical models of the nuclear structure.

Space-Dependent Calculation of the Multiplicity Moments for Shells With the Inclusion of Scattering

In recent work, we extended the methodology of multiplicity counting in nuclear safeguards by elaborating the one-speed stochastic transport theory of the calculation of the so-called multiplicity moments, i.e., the factorial moments of the number of neutrons emitted from a fissile item, following a source event from an internal neutron source [spontaneous fission and () reactions]. Calculations were made for solid spheres and cylinders, with the source being homogeneously distributed within the item. Recent measurements of the Rocky Flats Shells during the Measurement of Uranium Subcritical and Critical (MUSIC) campaign conducted by Los Alamos National Laboratory and assisted by the University of Michigan inspired us to extend the model to spherical shell geometry with a point source in the middle of the central cavity. Comparison of the calculated results with the experimental ones indicated that accounting for fission as the only neutron reaction (the standard procedure in the point model, adapted also in our work so far) was not sufficient for reaching good agreement with measurements. The model was therefore extended to include elastic scattering into the one-speed formalism, whereas the effect of inelastic scattering was accounted for in an empirical way. After these extensions, good agreement was found between the calculated and the measured values. The paper describes the extension of the theory and provides concrete quantitative results.

Nuclear structure properties of Si and P isotopes with the microscopic effective interactions

In the present work, we have reported comprehensive study of the sd-shell nuclei Si and P with neutron number varying from N=9 to N=20 using the microscopic effective valence shell interactions, namely, N3LO, JISP16 and DJ16A. These effective sd-shell interactions are developed using the ab initio no-core shell model wave functions and the Okubo-Lee-Suzuki transformation method. For comparison, we have also performed shell model calculations with the empirical USDB interaction. Energy spectra and electromagnetic properties of these isotopic chains have been studied. Theoretically calculated shell model results are compared with the available experimental data, to check the predictive strength of these microscopic interactions. It is found that the binding energies of the ground states are better reproduced with the DJ16A interaction as compared to other microscopic interactions and a proton subshell closure at Z=14 is obtained in Si. Spin-tensor decomposition of two-body interaction is presented to understand the contributions from central, vector and tensor components into these interactions. Spectroscopic strengths of 23Al(d,n)24Si are examined for the newly performed experiment at NSCL.

Local variations of charge radii for nuclei with even Z from 84 to 120

Pronounced changes of nuclear charge radii provide a stringent benchmark on the theoretical models and play a vital role in recognizing various nuclear phenomena. In this work, the systematic evolutions of nuclear charge radii along even Z = 84–120 isotopic chains are first investigated by the recently developed new ansatz under the covariant density functional. The calculated results show that the shell closure effects of nuclear charge radii appear remarkably at the neutron numbers N = 126 and 184. Interestingly, the arch-like shapes of charge radii between these two strong neutron-closed shells are naturally observed. Across the N = 184 shell closure, the abrupt increase in charge radii is still evidently emerged. In addition, the rapid raise of nuclear charge radii from the neutron numbers N = 138 to N = 144 is disclosed clearly in superheavy regions due to the enhanced shape deformation.

Zr isotopes as a case study for intertwined quantum phase transitions

The scenario of intertwined quantum phase transitions (IQPTs) is identified in the Zr isotopes with neutron numbers 52–70, and shown to involve both a crossing of normal and intruder configurations and a shape-evolution within each configuration. Using the framework of the interacting boson model with configuration mixing, this situation is demonstrated by a quantum analysis of the spectra, E2 transition rates, order parameters, symmetry and configuration content of the wave functions and a classical analysis of energy surfaces.

Half-Space Albedo Problem for Triplet Anlı-Güngör Scattering

Introduction The Anlı-Güngör (AG) scattering function which is written in triplet form is applied to the half-space albedo problem. The aim of the study is to compare the results of albedo between the triplet AG scattering and quadratic AG scattering. Methods The analytical calculations are performed by HN method. Since the HN method is based on the usage of the Case eigenfunctions, they should be derived for the interested in this study. The tabulated results are calculated for varying the secondary neutron number and the scattering parameter. Albedo values for the triplet anisotropic scattering are convergent. A special code is used to get the numerical values in Mathematica with high precision This code holds all numerical values and the results of all algebraic process as a rational number. Thus, the round-off errors in machine language are minimized. A second and completely different numerical process is performed with the Polynomial Regression (PR) and the Artificial Neural Network (ANN). The application of the PR and ANN algorithms are studied with the calculated albedo results in this study. This application is only data mining without performing any analytical calculation. Discussion The expectation is to get bigger albedo values than the quadratic AG scattering. But the results are surprising that the triplet and the quadratic albedo results are close to each other. The result of ANN is more successful than PR results. Moreover, the intermediate values that are not in the data set can also be successfully calculated.

Dineutron decay into sterile antineutrinos in neutron stars and its observable consequences

In some extensions of the Standard Model (SM), two neutrons are allowed to decay into two sterile antineutrinos ($nn\ensuremath{\rightarrow}\overline{\ensuremath{\chi}}\overline{\ensuremath{\chi}}$) via new scalar bosons. This process violates both the baryon number ($\mathcal{B}$) and the lepton number ($\mathcal{L}$) by two units but conserves their difference $(\mathcal{B}\ensuremath{-}\mathcal{L})$. Neutron stars contain a large number of neutrons, and thus the $nn\ensuremath{\rightarrow}\overline{\ensuremath{\chi}}\overline{\ensuremath{\chi}}$ process can be greatly enhanced inside a neutron star. This process could result in nontrivial effects that are different from the SM predictions and can be explored through astrophysical and laboratory observations. Furthermore, a large number of sterile antineutrinos, which may be dark matter candidates, can be emitted from the interior of the neutron star. The properties of the emitted particles show a particular pattern that can be uniquely determined by the mass and radius of the neutron star. In addition, the dineutron decay may contribute to the orbital-period change of the binary systems containing neutron stars. We analyze the possibility of constraining the mass of the new scalar bosons using the observations of the binary's orbital-period changes. It is found that the mass of the new scalar bosons is roughly restricted in the range from 1 TeV to several TeV, which is possibly within the reach of direct searches at the LHC or future high-energy experiments. The joint analysis which combines the astrophysics and particle phenomenology could provide an excellent opportunity for the study of the new physical effects beyond the SM.

α and 2α decay of nuclei in the region 94≤Z≤101 using the modified generalized liquid drop model

The \ensuremath{\alpha} decay and $2\ensuremath{\alpha}$ decay of various isotopes of Pu, Am, Cm, Bk, Cf, Es, Fm, and Md in the mass region $A=218$ to 273 are investigated using the modified generalized liquid drop model (MGLDM) and universal decay law. The comparison of experimental alpha decay half-lives with the predicted half-lives proves the consistency of our calculations. As a result we broadened our investigation to also include a study of double alpha decay of these isotopes. There is a considerable interest in performing research on double alpha decay, as seen by the proposal submitted at CERN to investigate the double alpha radioactivity of $^{224}\mathrm{Ra}$. In view of this, the decay half-lives of most probable $2\ensuremath{\alpha}$ emitters, calculated using MGLDM by employing different preformation factors, are presented which can be beneficial for upcoming experimental investigations on this topic. A peak or dip in \ensuremath{\alpha} and $2\ensuremath{\alpha}$ decay half-life is witnessed which indicates the stability of parent or daughter isotopes correspondingly. Minimum and maximum half-lives for decay are observed when the daughter and parent nuclei, respectively, contain a magic number of neutrons. From our study, 126 and 162 are found as magic/semimagic numbers. A linear plot is obtained while plotting ${\mathrm{log}}_{10}{T}_{1/2}$ of all the isotopes against $Z{Q}^{\ensuremath{-}1/2}$, which emphasizes that our estimations are reliable.

Neutron dose from a 6-MV X-ray beam in radiotherapy.

Although a 6-MV X-ray beam is employed clinically as a non-neutron-producing beam, no studies have reported how few neutrons are produced from a 6-MV beam. This study aimed to theoretically deduce the neutron dose from a 6-MV beam using Monte Carlo simulations for the notification of safety and risk in radiotherapy. Nuclei from a nuclear database with neutron separation energies below 6MeV were surveyed, suggesting that the certain content of 2H in the human body may result in some contribution. Thus, Monte Carlo calculation considering 2H in a phantom was performed. The calculation suggested that the distribution of the neutron dose from a 6-MV beam consisted of two components: one had neutrons from 2H concentrated within an irradiation field, and the other had those due to other elements such as 183W spreading from a gantry head to a treatment room. Although uncertainty owing to the normalization factor of the Monte Carlo calculations was a factor of three, the neutron doses at distances of 0 and 50cm from an irradiation field were calculated as 27 and 1.5 nSv/MU, respectively, under intensity-modulated radiotherapy (IMRT) or volumetric modulated arc therapy (VMAT). The calculations suggest that neutrons produced by a 6-MV beam are approximately 70 and 20 times safer than those by a 10-MV beam in the case of IMRT/VMAT and total body irradiation, respectively. Thus, this study theoretically reported the approximate number of neutrons delivered by a 6-MV beam for the first time.

Dual-panel polyvinyl toluene scintillator application as a radiation portal monitor device for gamma and neutron detection

Detection techniques for radiation portal monitors (RPMs) are being developed at Canadian Nuclear Laboratories. One of the purposes of RPM systems at the border ports of entry is to detect illegal transportation of special nuclear material (SNM), which can be used for radiation dispersal devices or nuclear weapons production.One of the most widely used detection technologies considered for RPMs is the polyvinyl toluene (PVT) scintillator. PVT is the most widely used material due to its low cost and its capability to be formed into different shapes and sizes. However, the primary limitation of PVT scintillators is their poor energy spectrum resolution, which limits the discrimination between neutron and gamma radiation.In the present work, a method that allows for the discrimination of fast neutron events from gamma events in a PVT-based RPM was investigated. This method uses two sets of plastic scintillators separated by an air gap. The gap increases the travel distances between scattering events to more easily distinguish pulses produced by neutron interactions in the scintillator from those produced by gamma rays. The time-of-flight (TOF) values between the coincident events in these two sets of scintillators were measured. The TOF for neutrons is significantly longer than the TOF for gamma rays. Another distinguishing characteristic of neutrons is that the flight time between these two scintillator panels will vary according to their energy.The results show that TOF measurements can distinguish neutron sources with sufficiently different energies. Therefore, this method is capable of identifying radioactive material based on neutron energy.In addition to the experimental work, Monte Carlo simulations were carried out using MCNP6.2. The simulation showed that the detector setup had an efficiency (which is the ratio of the number of counts recorded by the detector to the number of neutrons that are incident on the detector) of approximately 12%. Also, the MCNP results showed that the thickness of the second panel had a minimal effect on the signal and no effect on the gamma/neutron peak separation, and therefore could be any conveniently available thickness. However, increasing the air gap between panels increased the peak separation distance but reduced the signal, with a gap distance between 50 cm and 100 cm producing acceptable results.

Excitation-energy dependence of the fission-fragment neutron-excess ratio

Within the improved scission-point fission model, it is shown that the average neutron number per proton is not the same in fission fragments and is not equal to that in a fissioning nucleus. For the induced fission of $^{238}\mathrm{U}$, $^{240}\mathrm{Pu}$, $^{244}\mathrm{Cm}$, and $^{250}\mathrm{Cf}$, the dependencies of the fission-fragment neutron-excess ratio on the shell structure and excitation energy of fragment are studied.