Isotopic Cross Sections Research Articles

Isotopic production cross sections of fragmentation residues produced by 18O ions on a carbon target near 260 MeV/nucleon* *Supported in part by the National Natural Science Foundation of China (11905260, 12005314), the Western Light Project of Chinese Academy of Sciences, the Heavy Ion Research Facility in Lanzhou (HIRFL), and the open research project of CAS large research infrastructures

The isotopic cross sections of residual nuclei produced in fragmentation reactions of 18O projectiles impinging on a carbon target at energies near 260 MeV/nucleon were measured at the HIRFL facility in Lanzhou (China). A full identification of atomic and mass numbers of fragments was achieved from the determination of their magnetic rigidity, energy loss, and time of flight. The production cross sections for a dozen of nitrogen, carbon, and boron isotopes were determined with uncertainties below 30% for most of the cases. The obtained cross sections for N and B isotopes show a rather good agreement with previous experimental data obtained with different projectile energies. The cross sections for some C isotopes seem to exhibit a dependence on the projectile energy. A comparison of the data and several theoretical model calculations are presented.

Prompt gamma rays from fast neutron inelastic scattering on aluminum, titanium and copper

Prompt gamma rays induced by inelastic scattering of fast neutrons on aluminum, titanium and copper were measured at an angle of 90o between fast neutron beam and detector of the instrument FaNGaS, operated by Jülich Centre of Neutron Science at Heinz-Maier-Leibnitz Zentrum in Garching. The fast neutron flux was 1.40 108 cm−2 s−1 with the average energy of 2.30 MeV. Intensities and neutron spectrum averaged isotopic partial cross section for production of 214 gamma lines (22 for aluminum, 72 for titanium and 120 for copper) are presented. The results are consistent with the literature data. However, the new sets of gamma lines are recommended to replace the old datasets from fast neutrons reactors with several new lines also recognizing a few false identifications. Additionally, the detection limits of aluminum, titanium, copper, iron and indium were determined as 1.0, 0.4, 0.9, 0.5 and 1.3 mg, respectively, for a counting time of 12 h.

Measurement of neutron-capture cross sections of Ge70,72 using the DANCE facility

Background: Approximately half of all atomic nuclei heavier than iron are synthesized by the slow neutron-capture process. The weak component of this process is not well understood and the reaction rates of each isotope in the s-process path affect nucleosynthesis abundances downstream.Purpose: To measure the neutron-capture cross sections of two weak s-process nuclei, $^{70,72}\mathrm{Ge}$, using the neutron time-of-flight technique. Measuring the capture cross sections for isotopes in this region of the chart of nuclides has proven challenging due to dominant scattering cross sections.Method: Samples consisted of pellets made of pressed enriched metallic powders. The $^{70,72}\mathrm{Ge}$ neutron-capture cross sections were measured as a function of neutron energy using the Detector for Advanced Neutron Capture Experiments at Los Alamos National Laboratory.Results: Neutron-capture cross sections were measured from 10 eV to 1 MeV. These are the first measurements for $^{70,72}\mathrm{Ge}$ between 300 keV and 1 MeV neutron energy. Maxwellian-averaged cross sections were calculated in the astrophysically relevant neutron energy range (5 keV $\ensuremath{\le}kT\ensuremath{\le}$ 100 keV). Their value at $kT=30$ keV was found to be $89\ifmmode\pm\else\textpm\fi{}11$ mb for $^{70}\mathrm{Ge}$ and $58\ifmmode\pm\else\textpm\fi{}5$ mb for $^{72}\mathrm{Ge}$. Both values are in agreement with recent time-of-flight measurements at n_TOF (neutron Time-Of-Flight facility at the European Organization for Nuclear Research).Conclusions: The average cross section results from this work for $^{70}\mathrm{Ge}$ show minor ($<1\ensuremath{\sigma}$) disagreement with a recent measurement by the n_TOF collaboration at higher neutron energies. This corresponds to the neutron energy region that had previously never been measured ($>300$ keV). Two reaction library databases underestimate the $^{72}\mathrm{Ge}$ average cross section below 30 keV according to n_TOF and DANCE. This is likely due to capture resonances that are missing from the theoretical cross sections in the databases that were identified in both time-of-flight measurements. Additionally, a rudimentary analysis of the impact of both cross section measurements on stellar nucleosynthesis abundances using the NETZ nucleosynthesis tool is presented.

Theoretical study on the production of neutron-rich transuranium nuclei with radioactive beams in multinucleon transfer reactions

The production of neutron-rich transuranium nuclei with $Z=93--98$ in multinucleon transfer reactions induced by radioactive beams $^{92}\mathrm{Kr}, ^{132}\mathrm{Sn}$, and $^{144}\mathrm{Xe}$ with actinide target $^{238}\mathrm{U}$ is investigated within the dinuclear system model with decay code gemini$++$. The isotopic distributions for reactions $^{136}\mathrm{Xe}+^{248}\mathrm{Cm}$ and $^{136}\mathrm{Xe}+^{249}\mathrm{Cf}$ are calculated and compared with the available experimental data. Theoretical calculations can reproduce the experimental results well. Both the $N/Z$ ratio equilibration mechanism and driving potential dominate the transfer process of nucleons. Reaction $^{132}\mathrm{Sn}+^{238}\mathrm{U}$ is an optimal projectile-target combination to obtain large production cross sections of neutron-rich isotopes with $Z=93--98$. The corresponding optimal incident energy is also explored. The production cross sections of 41 unknown neutron-rich transuranium isotopes with cross sections greater than 1 nb are predicted. The reaction $^{132}\mathrm{Sn}+^{238}\mathrm{U}$ at ${E}_{\mathrm{c}.\mathrm{m}.}=521.3$ MeV shows huge advantages in producing neutron-rich transuranium nuclei with $Z=93--98$.

Bayesian evaluation of residual production cross sections in proton-induced nuclear spallation reactions

Residual production cross sections in spallation reactions are key data for nuclear physics and related applications. Spallation reactions are very complex due to the wide range of incident energies and abundant fragments involved. Therefore, it is challenging to obtain accurate and complete energy-dependent residual cross sections. With the guidance of a simplified EPAX formula (sEPAX), the Bayesian neural network (BNN) technique is applied to form a new machine learning model (BNN + sEPAX) for predicting fragment cross sections in proton-induced nuclear spallation reactions. Three types of sample dataset for measured residual production cross sections in proton-induced nuclear spallation reactions are made, i.e. D1 consists of isotopic cross sections in reactions below 1 GeV/u, D2 consists of fragments excitation functions of reactions up to 2.6 GeV/u, and D3 is a hybrid of D1 and D2. With the constructed BNN and BNN + sEPAX models, the isotopic and mass cross section distributions are compared for the 356 MeV/u 40Ca + p and 1 GeV/u 136Xe + p reactions, and fragment excitation functions in 40Ca + p, 56Fe + p, 138Ba + p and 197Au + p reactions. It is found that the BNN model needs sufficient information to achieve good extrapolations, while the BNN + sEPAX model performs better extrapolations based on less information due to the physical guidance of the sEPAX formulas. It is suggested that the BNN + sEPAX model provides a new approach to predict the energy-dependent residual production cross sections produced in proton-induced nuclear spallation reactions of incident energies from tens of MeV/u up to several GeV/u.

Covariance analysis and measurements of photon and neutron induced nuclear reaction cross sections of gallium isotopes

Covariance analysis and measurements of photon and neutron induced nuclear reaction cross sections of gallium isotopes

Target dependence of isotopic cross sections in the spallation reactions 238U + p, d and 9Be at 1 AGeV * *Supported by the National Natural Science Foundation of China (11875328, 12075327)

The spallation of 238U is an important way to produce rare isotopes. This work aims at studying the cross sections of isotopes produced in 238U + p, d and 9Be reactions at 1 A GeV and their target dependence. (1) A physical model dependent (Bayesian neural network) BNN, which includes the details of IQMD-GEMINI++ model and BNN, was developed for a more accurate evaluation of production cross sections. The isospin-dependent quantum molecular dynamics (IQMD) model is used to study the non-equilibrium thermalization of the 238U nuclei and fragmentation of the hot system. The subsequent decay of the pre-fragments is simulated by the GEMINI++ model. The BNN algorithm is used to improve the prediction accuracy after learning the residual error between experimental data and calculations by the IQMD-GEMINI++ model. It is shown that the IQMD-GEMINI++ model can reproduce the available experimental data (3282 points) within 1.5 orders of magnitude. After being fine tuned by the BNN algorithm, the deviation between calculations and experimental data were reduced to within 0.4 order of magnitude. (2) Based on the predictions by the IQMD-GEMINI++-BNN framework, the target dependence of isotopic cross sections was studied. The cross sections to produce the rare isotopes by the 238U + p, d and 9Be reactions at 1 A GeV are compared. For the generation of neutron-rich fission products, the cross sections for the 238U + 9Be are the largest. For the generation of neutron-deficient nuclei in the region of A = 200–220, the cross sections for 238U + p reaction are the largest. Considering the largest cross sections and the atomic density, the beryllium target is recommended to produce the neutron-rich fission products by the 238U beam at 1 A GeV, while the liquid-hydrogen target is suggested to produce the neutron-deficient nuclei in the region of A = 200–220.

Fusion Dynamics of 16O + 72,76Ge →88,92Zr Reactions using Skyrme Energy Density Formalism

In the fusion of 16O+72,76Ge→ 88,92Zr reactions the significance of structural and bulk properties of projectile-target combination is investigated at energies across the Coulomb barrier. For the purpose, the role of distinct Skyrme interactions (SIII, SKM*, SGII, RATP, T6, SkP), in conjunction with different surface diffuseness parameter (a=0.45-0.99) and nuclear charge radii i.e. iso-spin dependent and iso-spin independent are examined for the studied reaction. These geometrical parameters have their straight effect on the interaction barrier and the fusion excitation function. Thus, the sensitivity of fusion barrier and the cross sections in the sub barrier region of 88,92Zr Compound systems is carefully explored. The estimations of fusion cross sections are done in the framework of Wong formula and are compared with the respective experimental data. The observations implies that SKM* Skyrme interaction in which nuclear radius derived from polynomial fit gives relatively better result than the considered iso-spin dependent and independent nuclear charge radii. Further, the behaviour in the cross sections of Zr isotopes is investigated in terms of surface diffuseness parameter, which depicts that surface width is higher for neutron rich nucleus and lower for the neutron deficient one.

Empirical capture cross sections for cosmic neutrino detection with Sm151 and Tm171

The nuclei $^{151}\mathrm{Sm}$ and $^{171}\mathrm{Tm}$ have been identified as attractive candidates for the detection of the cosmic neutrino background. Both isotopes undergo first-forbidden nonunique beta decays, which inhibits a prediction of their spectral shape using symmetries alone, and this has, so far, obstructed a definitive prediction of their neutrino capture cross sections. In this work we point out that for both elements the so-called $\ensuremath{\xi}$ approximation is applicable and this effectively limits the spectral shape to a deviation of at most $1%$ from the one that would arise if beta decays were of the allowed type. Using measured half-lives we extract the relevant nuclear matrix element and predict the neutrino capture cross sections for both isotopes at the $1%$ level, accounting for a number of relevant effects including radiative corrections and the finite size of the nuclei. We obtained $(1.12\ifmmode\pm\else\textpm\fi{}0.01)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}46}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{2}$ for $^{171}\mathrm{Tm}$ and $(4.77\ifmmode\pm\else\textpm\fi{}0.01)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}48}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{2}$ for $^{151}\mathrm{Sm}$. This method is robust as it does not rely on the data points near the endpoint of the beta spectrum, which may be contaminated by atomic physics effects, namely shakeup and shakeoff. Finally, we calculate the target mass which is necessary for cosmic neutrino discovery and discuss several bottlenecks and respective solutions associated to the experimental program. We conclude that the detection of cosmic neutrino background by neutrino capture on $^{151}\mathrm{Sm}$ and $^{171}\mathrm{Tm}$ is achievable and free from theoretical limitations but still subject to technical issues that should be further investigated by the experimentalists in the context of the proposed PTOLEMY project.

Model-independent determination of isotopic cross sections per fission for reactor antineutrinos

Model-independent reactor isotopic cross sections per fission are determined by global fits of the reactor antineutrino data from High-Enriched Uranium (HEU) reactor rates, Low-Enriched Uranium (LEU) reactor rates, and reactor fuel evolution data. Taking account of the implicit quasi-linear relationship between the fission fractions of $^{239}\rm{Pu}$ and $^{241}\rm{Pu}$ in the LEU reactor data, the Inverse-Beta-Decay (IBD) yields and their correlations of the fissionable isotopes $^{235}\rm{U}$, $^{238}\rm{U}$, and Pu's are obtained. The data-driven isotopic IBD yields provide an anomaly-free model for the reactor isotopic cross sections per fission, where better than 1\% accuracy of the expected reactor IBD yields can be achieved for future experiments.

Study of the deformed halo nucleus 31Ne with Glauber model based on microscopic self-consistent structures

The exotic deformed nucleus 31Ne is studied with an approach that combines self-consistent structure and reaction theories. The deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) is utilized to demonstrate that deformation and pairing correlations give rise to a halo structure with a large-amplitude p-wave configuration in 31Ne. Then the valence nucleon wave functions and angle-averaged density distributions of 30Ne from this theory are used as input for the Glauber reaction model to study the observables of neutron-rich neon isotopes to search halo signatures. With NL1 effective interaction, our predictions of the reaction cross sections for these exotic neon isotopes on a carbon target can better reproduce the experimental data than those from the relativistic mean field model for a spherical shape with resonances and pairing correlation contributions, and are roughly 3.3% (∼ 50 mb) larger than those with Gaussian function-fitted densities of the core nuclei. The calculated one-neutron removal cross section at 240 MeV/nucleon, and the inclusive longitudinal momentum distribution of the 30Ne residues from the 31Ne breakup reaction are largely improved over previous theoretical predictions and agree well with data. These reaction evaluations indicate a dilute density distribution in coordinate space and are a canonical signature of a halo structure. Moreover, our predictions with the NL3 and PK1 effective interactions give slightly better descriptions of reaction observables for exotic neon isotopes.

Effect of nuclear potential on the formation cross section of superheavy isotopes of Og, Nh and Cn nuclei

Effect of nuclear potential on the formation cross section of superheavy isotopes of Og, Nh and Cn nuclei

Isotopic cross sections of fragmentation residues produced by light projectiles on carbon near 400A MeV

Isotopic cross sections of fragmentation residues produced by light projectiles on carbon near <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>400</mml:mn><mml:mi>A</mml:mi></mml:mrow></mml:math> MeV

Production of unknown neutron-rich transuranium isotopes 245–249Np, 248–251Pu, 248–254Am, and 252–254Cm in multinucleon transfer reactions

The production cross sections of unknown neutron-rich transuranium isotopes of elements Np, Pu, Am and Cm are investigated in multinucleon transfer (MNT) reactions based on the dinuclear system model with GEMINI code. The influence of the incident energy on the production of neutron-rich transuranium nuclei in actinide–actinide collisions is studied. The calculation results show that the final isotopic production cross sections are larger at 1.06–1.10 V cont than at other energies. Considering the high fissility of transuranium nuclides, 1.06 V cont is chosen as the optimal incident energy. The N/Z ratio equilibration mechanism in the nucleon transfer process is also studied in this work. The larger difference of N/Z ratio between projectile and target corresponds to larger neutron diffusion during the nucleon exchange process. The 238U beam with high N/Z ratio and neutron-rich actinide targets are good selections to produce neutron-rich transuranium nuclides. The production cross sections of unknown neutron-rich transuranium isotopes 245–249Np, 248–251Pu, 248–254Am, and 252–254Cm are predicted in 238U-induced actinide-based (249Bk, 249Cf, and 252Cf) MNT reactions. It is found that a large number of these unknown neutron-rich transuranium nuclei could be generated at the level of nb to μb in the reactions 238U + 249Bk and 238U + 252Cf. Our research indicates that the reaction 238U + 249Bk is a suitable projectile-target combination in the current experimental conditions and the reaction 238U + 252Cf could be a promising candidate to produce unknown neutron-rich transuranium nuclides in case that the 252Cf target were to be achieved in the future.

Self-consistent description of the halo nature of 31Ne with continuum and pairing correlations

Background: A relativistic structure model has previously been used to predict a halo structure for 31Ne (Zhang et al 2014 Phys. Lett. B 730 30), consistent with halo signatures from measured reaction cross sections of Ne isotopes bombarding Carbon targets. However, previous attempts to calculate those cross sections with reaction models were missing contributions from resonances and pairing correlations in their structure input. Purpose: Use a reaction model with our relativistic fully microscopic structure model input to predict these cross sections and momentum distributions and analyze for possible halo signatures. Methods: Structure input for exotic Ne isotopes were obtained via the analytical continuation of the coupling constant (ACCC) method based on the relativistic mean field (RMF) theory with Bardeen–Cooper–Schrieffer (BCS) pairing approximation, the RAB approach. Total reaction cross sections, one-neutron removal cross sections, and momentum distributions of breakup reaction products were calculated with a Glauber model using our relativistic structure input. Results: Our predictions of total reaction and one-neutron removal cross sections of 31Ne on a Carbon target were significantly enhanced compared with those of neighboring Neon isotopes, agreeing with measurements at 240 MeV/nucleon and consistent with a single neutron halo. Furthermore, our calculations of the inclusive longitudinal momentum distribution of the 30Ne and valence neutron residues from the 31Ne breakup reaction indicate a dilute density distribution in coordinate space, another halo signature. Conclusions: We give a full description of the halo nature of 31Ne that includes a self-consistent use of pairing and continuum contributions that makes predictions consistent with reaction cross section measurements. This approach can be utilized to determine the halo structure of other exotic nuclei.

Scientific Motivations for a Reassessment of the Neutron Capture Cross Sections of Erbium Isotopes in the High-Sensitivity Thermal Energy Range for Lwr Systems

Scientific Motivations for a Reassessment of the Neutron Capture Cross Sections of Erbium Isotopes in the High-Sensitivity Thermal Energy Range for Lwr Systems

Isotopic cross section measurement of the nuclear spallation reaction

Isotopic cross section measurement of the nuclear spallation reaction

\u2009Prompt and delayed gamma rays induced by epithermal and fast neutrons with indium

The emission of prompt and delayed gamma rays from (n,γ) and (n,n´γ) reactions induced by irradiation of indium with epithermal and fast neutrons was investigated with the instrument FaNGaS operated at Heinz-Maier-Leibnitz Zentrum (MLZ) in Garching. The average neutron energy of the neutron spectrum was 2.30 MeV. The measurement was done at an angle of 90° between neutron beam and detector. A total of 136 prompt gamma lines from which 42 are related to the capture of epithermal and fast neutrons and 94 to the inelastic scattering of fast neutrons were detected together with the delayed gamma lines of the activation products 113mIn, 114m2In, 115mIn, 116m2In and 116mIn. Intensities and neutron spectrum averaged isotopic partial cross section of the gamma lines are presented. Additionally the neutron spectrum averaged cross sections of the reactions, 113In(n,n´)113mIn, 113In(n,γ)114m2In, 115In(n,n´)15mIn, 115In(n, γ)116m2In and 115In(n, γ)116mIn were determined from the corresponding delayed gamma rays of the formed isotopes as 143 ± 22, 288 ± 13 194 ± 18, 201 ± 10 and 508 ± 24 mb respectively. The various results obtained were found consistent with the literature data. However, our measurement indicate the need to reevaluate the cross section of the 115In(n,γ)116m2In reaction for thermal neutrons.

Quantal diffusion description of isotope production via the multinucleon transfer mechanism inCa48+U238collisions

As an extension of previous work, we calculate the production cross section of heavy neutron-rich isotopes by employing the quantal diffusion description to $^{48}\mathrm{Ca}+^{238}\mathrm{U}$ collisions. The quantal diffusion is deduced from stochastic mean-field approach, and transport properties are determined in terms of time-dependent single-particle wave functions of the time-dependent Hartree-Fock theory. As a result, the approach allows for prediction of production cross sections without any adjustable parameters. The secondary cross sections by particle emission are calculated with the help of the statistical gemini$++$ code.

Unified description of fusion and multinucleon transfer processes within the dinuclear system model

To compare fusion-evaporation (FE) and multinucleon transfer (MNT) approaches and make more reliable predictions for producing superheavy nuclei, the unified description of FE and MNT processes is performed in the reaction $^{48}\mathrm{Ca}+^{238}\mathrm{U}$ within the (DNS) model. We extend the fusion concept in the DNS model based on the deformation degree of freedom. Our calculations support the experimental result [Nishio et al., Phys. Rev. C 77, 064607 (2008)] that compact configuration enhances the fusion probability. The experimental production cross sections of isotopes in FE and MNT processes can be simultaneously reproduced. By comparing the production cross sections in the MNT reaction $^{238}\mathrm{U}+^{248}\mathrm{Cm}$ with the FE reactions $^{48}\mathrm{Ca}+^{238}\mathrm{U}$ and $^{54}\mathrm{Cr}+^{248}\mathrm{Cm}$, we find that the FE process shows great advantages of cross sections for producing Cn isotopes and is the only approach that could produce superheavy elements beyond oganesson.