Isotopic Cross Sections Research Articles

Measurement of the Production Cross Sections for Isotopes of Transfermium Elements in Complete Fusion Reactions with the Subsequent Evaporation of a Proton and Neutrons

Experiments aimed at synthesizing and investigating the features of radioactive decay of isotopes of superheavy elements (Z ≥ 110) have been conducted in the Flerov Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research. Complete fusion reactions of an accelerated beam of 48Ca ions with transactinide targets with the subsequent evaporation of several neutrons from excited compound nucleus are typically used in these experiments. “Exotic” reaction channels with the evaporation of protons and several neutrons may be used to produce more neutron-rich isotopes of superheavy elements. The production cross sections were measured in experiments at the SHELS separator for Db and Rf isotopes produced in xn and pxn channels of the 50Ti + 209Bi → 259Db* reaction. The ratio of cross sections σ(xn)/σ(pxn) was on the order of 100.

Neutron capture cross sections of stable Cd isotopes

Cross sections for radiative neutron capture have been measured by activation for the stable isotopes of Cd with mass numbers 106, 108, 110, 112, 114, and 116 by observing the decays of the 8 radioisotopes produced by captures in samples of both natural and enriched abundances. Determination of the thermal cross sections requires correction for captures by epithermal neutrons, so careful attention has been paid to the measurement of the resonance integrals, which were found to vary for irradiations at different sites in the reactor.

Production of light neutron-rich nuclei in multinucleon transfer reactions

In order to produce more unknown light neutron-rich nuclei, multinucleon transfer processes at energies slightly above the Coulomb barrier are investigated within the inclusion of the deformations of interacting nuclei as independent variables of the dinuclear system (DNS) model (improved DNS model). Transfer cross sections 58,64Ni+208Pb and 40Ca+208Pb are calculated and compared with the experimental data, we find the improved dinuclear system model describes the transfer cross sections reasonably. The calculated results showed that protons and neutrons are transferred to be strongly influenced by the potential energy surface, the injection point position of the projectile on the potential energy surface and the dynamical properties of the DNS. The cross sections of new neutron-rich isotopes through the transfer reactions 70Ni+208Pb and 32,36S+238U are estimated by the multinucleon transfer reactions.

A scaling phenomenon for the cross section of fragment produced in projectile fragmentation reactions

A scaling phenomenon has been found for the cross section of a fragment, which is defined as a “square” cross section (SCS). This phenomenon can unify the cross sections of fragments in projectile fragmentation (PF) reactions. An empirical formula is proposed to calculate SCS for a fragment with parameters determined by an extensive investigation of measured reactions ranging from Fermi energies to relativistic energies. The scaling phenomenon of SCS has been verified using different techniques, showing that the scaling of SCS generally exists in PF reactions. The concept of SCS, which can be assumed as a standard value for a fragment, is shown to accurately predict the cross sections of isotopes in PF reactions with incident energies ranging from tens of A MeV to approximately 1000A MeV.

Cross sections of (n,x) reactions on cerium isotopes induced by D-T neutrons

Neutron induced reaction cross sections of Cerium isotopes (136Ce, 138Ce, 140Ce, 142Ce) were investigated for the (n, 2n), (n, α), (n, p) and (n, γ) reactions in the neutron energy around 14 MeV. Experimental cross sections have been obtained for 136Ce(n, 2n)135m+gCe, 138Ce(n, 2n)137mCe, 140Ce(n, 2n)139m+gCe, 142Ce(n, 2n)141gCe, 140Ce(n, p)140gLa, 142Ce(n, p)142gLa, 140Ce(n, α)137mBa, 142Ce(n, α)139Ba and 142Ce(n, γ)143Ce reactions. The measured values were compared with the literature data as well as the evaluated nuclear data from ENDF/B-VII.1, CENDL-3.1, JENDL-4.0 and the calculated results by Talys-1.8 code.

Neutron capture data for unstable nuclei – Astrophysical quests and experimental challenges

The abundances of the chemical elements heavier than iron can be attributed in about equal parts to the r and s processes, which are taking place in supernova explosions and during the He and C burning phases of stellar evolution, respectively. So far, quantitative studies of the r-process are out of reach, because it involves reactions on extremely short-lived neutron-rich nuclei. On the contrary, the situation for the s-process is far advanced, thanks to a comprehensive database of experimental (n,γ) cross sections for most isotopes along the reaction path from 12C to the Pb/Bi region. For the stable isotopes last gaps in the data are presently closed, but further studies are clearly needed to reach the required accuracy and to resolve remaining discrepancies. The quest for cross sections of unstable isotopes remains a persisting challenge though. In particular, nuclei which act as branching points are of prime interest, because they provide key information on the deep stellar interior. While the activation method is limited to a few exceptional branch-point nuclei, successful measurements via the time-of- flight technique are depending on intense pulsed neutron sources and elaborate methods for sample production. Current developments in Europe are providing promising perspectives in both areas.

Evaporation and fission of the primary fragments produced by multinucleon transfer reactions

The multinucleon transfer (MNT) reaction has aroused wide interest in recent years largely due to its ability to produce neutron-rich heavy nuclei. The semiclassical model GRAZING can describe well the experimental MNT data for many medium-heavy systems, but only simply considers neutron evaporation in the deexcitation of primary fragments. In order to describe the final MNT products for heavy and even superheavy systems, we try to consider both the transfer and subsequent deexcitation processes by combining, for the first time, the GRAZING model and the statistical-decay model GEMINI as well as the improved version GEMINI++. Considering fission in the deexcitation of primary fragments by GEMINI++ model, the isotope distributions of final fragments are much wider than those only by GRAZING model, indicating an important role of fission in the deexcitation process for heavy and superheavy fragments. However, our results have large deviations from the GRAZING-F results, which may result from the different technique adopted in the deexcitation process. Moreover, it is shown that the GEMINI++ model is more reasonable than the GEMINI model, because the latter overpredicts the fission probability and the width of fission isotope distributions to a large extent. With GEMINI++ model, the predictions of cross sections for final isotopes can be improved by taking into account charged-particle evaporations, especially the $\ensuremath{\alpha}$ evaporation.

Second-order sensitivity analysis of uncollided particle contributions to radiation detector responses using ray-tracing

The Second-Level Adjoint Sensitivity System (2nd-LASS) that yields the second-order sensitivities of a response of uncollided particles with respect to isotope densities, cross sections, and source emission rates has previously been derived and solved using the off-the-shelf discrete ordinates code PARTISN. In this paper, the 2nd-LASS equations are solved using ray-tracing for the case when the response is evaluated at a point on the boundary (the partial current density or scalar flux). The resulting second derivatives, including all mixed partial derivatives as well as derivatives involving material mass densities, are compared with analytic and PARTISN results for a homogeneous sphere and PARTISN results for a two-region sphere. Second derivatives computed using ray-tracing are within 0.003% of those computed using PARTISN and are over 100 times faster to compute for the spherical test problems.

Physical characteristics of a PWR core loaded with micro-cell UO2 pellet fuels

In this work, the physical characteristics of PWR cores are evaluated for several micro-cell UO2 pellets with Cr-coated Zircaloy-4 cladding through consistent fuel assembly (FA) and core-level analyses. The micro-cell UO2 pellets that are currently researched as accident tolerant fuel (ATF) candidates in the Korea Atomic Energy Research Institute (KAERI) are UO2-Cr, UO2-Mo, and UO2-SiO2-TiO2. In particular, a calculational matrix is used to consider not only the micro-cell UO2 pellets and the cladding coating, but also to estimate the achievable cycles within the usual 5.0 wt% uranium enrichment limit and the uranium enrichment required to achieve a reference cycle length of 480 effective full power days (EFPDs). The core analyses using the 3D nodal diffusion code MASTER showed that the cores loaded with micro-cell UO2 pellets (i.e., UO2-Cr and UO2-Mo) with Cr-alloy coating on Zircaloy-4 cladding have considerably shorter cycle lengths, lower discharge burnups, and more negative fuel temperature coefficients than the conventional UO2 fuel. The more negative fuel temperature coefficients lead to a more rapid stabilization under rod ejection accident with a substantially lower fuel temperature. In particular, the Mo-based micro-cell UO2 fueled cores have a much shorter cycle length and more negative moderator temperature coefficient than Cr-based one due to the large thermal and resonance capture cross sections of Mo isotopes and due to its lower critical boron concentration (CBC). However, the effect of Cr-alloy coating on core performance is not significant in comparison with the effects of the micro-cell UO2 pellets.

Monte Carlo nuclear data adjustment via integral information

In this paper, we present three Monte Carlo methods to include integral benchmark information into the nuclear data evaluation procedure: BMC, BFMC and Mocaba. They allow to provide posterior nuclear data and their covariance information in a Bayesian sense. Different examples will be presented, based on 14 integral quantities with fast neutron spectra (keff and spectral indices). Updated nuclear data for 235U, 238U and 239Pu are considered and the posterior nuclear data are tested with MCNP simulations. One of the noticeable outcomes is the reduction of uncertainties for integral quantities, obtained from the reduction of the nuclear data uncertainties and from the rise of correlations between cross sections of different isotopes. Finally, the posterior nuclear data are tested on an independent set of benchmarks, showing the limit of the adjustment methods and the necessity for selecting well representative systems.

Photoneutron cross sections for Ni isotopes: Toward understanding (n,γ) cross sections relevant to weak s -process nucleosynthesis

Photoneutron cross sections were measured for $^{58}$Ni, $^{60}$Ni, $^{61}$Ni, and $^{64}$Ni at energies between the one-neutron and two-neutron thresholds using quasi-monochromatic $\gamma$-ray beams produced in laser Compton-scattering at the NewSUBARU synchrotron radiation facility. The new photoneutron data are used to extract the $\gamma$-ray strength function above the neutron threshold complementing the information obtained by the Oslo method below the threshold. We discuss radiative neutron capture cross sections and the Maxwellian-averaged cross sections for Ni isotopes including $^{63}$Ni, a branching point nucleus along the weak s-process path. The cross sections are calculated with the experimentally constrained $\gamma$-ray strength functions from the Hartree-Fock-Bogolyubov plus quasi-particle-random phase approximation based on the Gogny D1M interaction for both $E1$ and $M1$ components and supplemented with the $M1$ upbend.

Multi-group effective cross section calculation method for Fully Ceramic Micro-encapsulated fuel

A multi-group effective cross section calculation method for Fully Ceramic Micro-encapsulated (FCM) fuels containing stochastically dispersed tri-structural isotropic (TRISO) coated fuel particles is proposed to solve the double heterogeneity (DH). In resonance-energy range, the disadvantage factors are obtained by solving a one-dimensional model containing a TRISO particle with hyperfine group method. The matrix and TRISO particles will be homogenized by correcting the hyperfine-group cross sections with disadvantage factors. Due to the large absorption cross section of heavy isotopes in thermal-energy range, the spatial self-shielding effect in the TRISO particles should also be taken account. In the thermal-energy range, the multi-group disadvantage factors are obtained by the neutron’s first-collision probabilities and penetrating probability equivalent. Based on the methods described above, the materials in the fuel rod are merged into a homogeneous material. The FCM fuel can be treated as traditional PWR lattice. In the present paper, the Dancoff correction factor of every rod is firstly obtained with neutron current method. Then a one-dimensional model for every fuel rod will be established by Dancoff factor equivalent. Finally, the hyperfine group calculation is carried out based on the one-dimensional rod model to get the effective cross sections of each fuel rod. Numerical results show that the proposed method is proved effective to treat DH for FCM fuel and capable of providing accurate effective cross sections.

Measuring neutron leakage spectra using spherical benchmarks with 252Cf source in its centers

The presented paper summarizes the methodology of fast neutron leakage fluxes measurement using a stilbene scintillation detector on spherical benchmark assemblies. The experiments are realized in a spherically simple geometry, which does not need validation of the neutron transport model. Hence, this type of experiment is suitable for validation of the nuclear cross sections of various isotopes. The 252Cf neutron source is always placed in the center of a sphere of different pure materials. The selection is focused on structural materials used in the nuclear industry. In the presented set, the materials include light water, heavy water and nickel. For example, the light and heavy water spheres can be used to eliminate the effect of hydrogen and estimate the effect of oxygen. The neutron spectra in the region of 1–10 MeV are measured in a room where the background could substantially influence the final result. For this reason, the estimation of the scattered neutrons is crucial for the correct evaluation of the experiment. The comparison of the calculated and measured neutron fluxes and background signal share are presented. Calculations were performed using the MCNP6 program with the ENDF/B-VII.1 nuclear data library.

The discovery of chemically produced mass independent isotope effects: The physical chemistry basis and applications to the early solar system, planetary atmospheres, and the origin of life

The discovery of chemically produced mass independent isotope effects: The physical chemistry basis and applications to the early solar system, planetary atmospheres, and the origin of life

Current status and desired precision of the isotopic production cross sections relevant to astrophysics of cosmic rays: Li, Be, B, C, and N.

The precision of the current generation of cosmic-ray (CR) experiments, such as AMS-02, PAMELA, CALET, and ISS-CREAM, is now reaching ≈1-3% in a wide range in energy per nucleon from GeV/nucleon to multi-TeV/nucleon. Their correct interpretation could potentially lead to discoveries of new physics and subtle effects that were unthinkable just a decade ago. However, a major obstacle in doing so is the current uncertainty in the isotopic production cross sections that can be as high as 20-50% or even larger in some cases. While there is a recently reached consensus in the astrophysics community that new measurements of cross sections are desirable, no attempt to evaluate the importance of particular reaction channels and their required precision has been made yet. It is, however, clear that it is a huge work that requires an incremental approach. The goal of this study is to provide the ranking of the isotopic cross sections contributing to the production of the most astrophysically important CR Li, Be, B, C, and N species. In this paper, we (i) rank the reaction channels by their importance for a production of a particular isotope, (ii) provide comparisons plots between the models and data used, and (iii) evaluate a generic beam time necessary to reach a 3% precision in the production cross sections pertinent to the AMS-02 experiment. This first road map may become a starting point in the planning of new measurement campaigns that could be carried out in several nuclear and/or particle physics facilities around the world. A comprehensive evaluation of other isotopes Z ⩽ 30 will be a subject of follow-up studies.

Binding energies of near proton-drip line Z = 22–28 isotopes determined from measured isotopic cross section distributions

A new method is proposed to determine the binding energy (B) of near proton-drip line isotopes from isotopic cross section distribution. To determine B of Z = 22–28 isotopes (with Tz = −2 and −5/2), the lack of cross sections for proton-rich isotopes in the 345A MeV 78Kr + 9Be is overcome by predicting the proton-rich isotopes from a newly discovered scaling phenomenon found in the proton-rich isotopes measured in the 140A MeV 40;48Ca(58;64Ni) + 9Be reactions. The cross sections for proton-rich isotopes are verified to exponentially depend on the average binding energy per nucleon, based on which B of the Z=22–28 isotopes with Tz = −2 and −5/2 are determined from cross sections. The determined B of the isotopes are justified from obeying the scaling phenomenon of the difference between the mass of mirror nuclei. The cross sections for the Z = 22–28 isotopes with Tz = −1 and −3/2, which in potential can be experimentally studied in mass storage ring, are also predicted.

Fragmentation binding energies and cross sections of isotopes near the proton dripline

Fragmentation binding energies and cross sections of isotopes near the proton dripline

A temperature effect analysis of the KRITZ-1 benchmark based on keff decomposition and using the JENDL-4.0 and ENDF/B-VII.1 libraries

This paper provides a comparison between multiplication factors within the UO2 fuelled cores that were measured during the original KRITZ-1 experiments performed in the early 1970s. Results were calculated using the MCNP6.1 code and the most recent cross section libraries, ENDF/B-VII.1 and JENDL-4.0. The results of this study reveal a good level of agreement between calculated and measured outcomes; indeed, the maximum relative error of calculated keff from experimental data does not exceed 0.5% (absolute value) for all cores and for both evaluations. The reactivity temperature coefficient, expressed as the temperature dependence of the reactivity, was examined into details using the seven factors that incorporate the keff parameter rather than just the five that exist in the literature. In order to better investigate the influence of differences in neutron cross sections we also quantified the temperature effect on the five factors of the infinite multiplication factor on each one separately by admitting a pin cell model.Calculated thermal and fast non-leakage probabilities using JENDL-4.0 are found to overestimate the ones calculated using ENDF/B-VII.1 for all temperatures, possibly because the JENDL-4.0 library overestimates some absorptions, especially in the resonance region of fissionable nuclides. This discrepancy between the libraries decreases with increasing temperature, however, while the inverse tends to occur in the case of standard deviations. Our assessment has shown that the temperature coefficient in the thermal temperature range is linked to thermal spectrum and water density effects, while within the epithermal temperature range this is strongly dependent on the thermal shapes of the cross sections of the uranium isotopes; the resonance escape probability highlights that the error is mainly due to the Doppler broadening effect.

Theoretical study on production of unknown neutron-deficient Fl280–283 and neutron-rich Fl290–292 isotopes by fusion reactions

We attempt to calculate the production cross sections of unknown $^{280--283}\mathrm{Fl}$ and $^{290--292}\mathrm{Fl}$ isotopes by using hot fusion reaction mechanism within the dinuclear system model. The production of unknown neutron-deficient Fl isotopes ($^{280--283}\mathrm{Fl}$) is studied in the reactions $^{44}\mathrm{Ca}+^{242}\mathrm{Pu}$ and $^{36}\mathrm{S}+^{249}\mathrm{Cf}$ with the maximum evaporation residue cross sections values 0.91 pb, 6.17 pb, 36.16 pb, and 2.02 pb, respectively. The use of neutron-rich radioactive beams $^{44}\mathrm{Ar}$ and $^{46}\mathrm{Ar}$ may help us produce new neutron-rich Fl isotopes via fusion reaction mechanism only if an extremely high beam intensity were to be achieved in the future. The maximum production cross sections of unknown neutron-rich isotopes ($^{290--292}\mathrm{Fl}$) in the reactions $^{46}\mathrm{Ar}+^{248}\mathrm{Cm}$ and $^{46}\mathrm{Ar}+^{250}\mathrm{Cm}$ are predicted to be 4.06 pb, 8.55 pb, and 3.35 pb, respectively. At present, reaction with radioactive ion beams is not a promising method to produce neutron-rich superheavy nuclei and other reaction mechanisms such as transfer reaction need to be developed.

Production of neutron-rich Pt209–212 isotopes based on a dinuclear system model

The production cross sections of new neutron-rich nuclei $^{209\text{--}212}\mathrm{Pt}$ are investigated with multinucleon transfer reactions by the dinuclear system model. It is found that the $^{133}\mathrm{Sn}+^{204}\mathrm{Hg}$ and $^{145}\mathrm{Xe}+^{208}\mathrm{Pb}$ systems are advantageous to produce the neutron-rich nuclei, in which the production cross sections are much higher than those produced in projectile fragmentation reactions. The optimal incident energies for these two systems are about 1.18 and 1.40 times the Coulomb barrier, respectively. The highest cross sections of unknown isotopes $^{209\text{--}212}\mathrm{Pt}$ in the $^{145}\mathrm{Xe}+^{208}\mathrm{Pb}$ reaction are 2.7 nb, 0.4 nb, 8.2 pb, and 2.7 pb, respectively, and those for the $^{133}\mathrm{Sn}+^{204}\mathrm{Hg}$ reaction are 1.7 nb, 0.4 nb, 23.3 pb, and 4.8 pb, respectively.