MeV Incident Neutron Energy Research Articles

Fixed-energy inverse scattering with radial basis function neural networks and its application to neutron–α interactions

Abstract This paper proposes a data-driven method to solve the fixed-energy inverse scattering problem for radially symmetric potentials using radial basis function (RBF) neural networks in an open-loop control system. The method estimates the scattering potentials in the Fourier domain by training an appropriate number of RBF networks, while the control step is carried out in the coordinate space by using the measured phase shifts as control parameters. The system is trained by both finite and singular input potentials, and is capable of modeling a great variety of scattering events. The method is applied to neutron–α scattering at 10 MeV incident neutron energy, where the underlying central part of the potential is estimated by using the measured l = 0, 1, 2 phase shifts as inputs. The obtained potential is physically sensible and the recalculated phase shifts are within a few percent relative error.

Neural network predictions of (n,2n) reaction cross-sections at 14.6 MeV incident neutron energy

In this study, we have estimated the (n,2n) reaction cross-section for 14.6 MeV incident neutron energy by using the artificial neural network (ANN) method. We have also predicted the reaction cross-sections whose experimental data are not available in the literature. For the construction of the present ANN, available experimental data in the literature has been borrowed. The ANN estimations have been compared with the available experimental data and the results from a theoretical calculation and the two commonly used computer codes. According to the results that the ANN results are in good agreement with the experimental data than the codes and this shows that the method can be a powerful tool for the estimation of cross-section data for the neutron-induced reactions. Considering the predictions of the ANN of the cross-sections whose experimental data are not available in the literature, it is seen that they are in line with the trend of the experimental data, but far from the results given by the theoretical calculations and two computer codes.

Measurement of the U235(n,f) prompt fission neutron spectrum from 10 keV to 10 MeV induced by neutrons of energy from 1 MeV to 20 MeV

The characterization of fission-driven nuclear systems primarily relies on calculations of neutron-induced chain reactions, and these calculations require evaluated nuclear data as input. Calculation accuracy heavily depends on input nuclear data evaluation accuracy, and thus high precision on the experimental input to the nuclear data evaluation is essential for fundamental quantities like the energy spectrum of neutrons emitted from neutron-induced fission (i.e., the prompt fission neutron spectrum, PFNS). Despite decades of measurement efforts, prior to the measurements described in this work there were only three literature data sets for the $^{235}\mathrm{U}(n,f)$ PFNS at incident neutron energies above 1.0 MeV considered reliable for inclusion in nuclear data evaluations and no reliable data sets above 3.0 MeV incident neutron energy. In this work we report on new measurements of the $^{235}\mathrm{U}(n,f)$ PFNS spanning a grid of 1.0--20.0 MeV in incident neutron energy and 0.01--10.0 MeV in outgoing (PFNS) neutron energy. These measurements were carried out at the Weapons Neutron Research facility at the Los Alamos Neutron Science Center and used a multifoil parallel-plate avalanche counter target with both a Li-glass and a liquid scintillator detector array in separate experiments to span the quoted outgoing neutron energy ranges. The PFNS results are shown in terms of the energy spectra themselves as well as the average PFNS energy ($\ensuremath{\langle}E\ensuremath{\rangle}$) and ratios of $\ensuremath{\langle}E\ensuremath{\rangle}$ at forward and backward angles. The results are compared with literature data and selected nuclear data evaluations. Generally, the data agree with the ENDF/B-VIII.0 evaluation below 5.0-MeV incident neutron energy and more closely with the JEFF-3.3 evaluation above 5.0 MeV, though no evaluations considered for comparison in this work agree with the data across all of the incident and outgoing neutron energies shown, especially in regions where the third-chance fission process becomes available. Additionally, we show a ratio of the present PFNS results for $^{235}\mathrm{U}(n,f)$ with a recent and highly correlated experiment to measure the $^{239}\mathrm{Pu}(n,f)$ PFNS at the same experimental facility and with nearly identical equipment and analysis procedures. Many observations reported in this work are the first of their kind and represent significant advancements for knowledge of the $^{235}\mathrm{U}(n,f)$ PFNS.

Recommendation for computing neutron irradiation damage from evaluated nuclear data

Accurate evaluation of displacement damage is important for studying the nuclear materials after irradiation. The present work investigates neutron-induced displacement damage evaluation via damage cross sections. There are potential discrepancies between different evaluations on the damage cross sections induced by the (n,γ) reaction and potential discontinuity at 20 MeV incident neutron energy. These two issues are however not important for evaluating neutron irradiation damage in fission and fusion reactors. Due to some issues associated with the recoil distributions in evaluated nuclear data files, the corresponding damage cross sections are questionable, such as those of 52Cr in JEFF-3.3, 55Mn in JEFF-3.3 and ENDF/B-VIII.0, and 180,182,183,184,186W in ENDF/B-VIII.0. Therefore, the present work recommends using two-body kinematic considerations and the differential cross sections of light particles for evaluating neutron irradiation damage (via either displacement cross sections or PKA spectra), unless the recoil distributions have been pre-validated/verified. The recommended method reduces the 70% discrepancy between different nuclear data evaluations to 13% for evaluated displacement damage of tungsten in ITER tokamak.

Theoretical Calculations of the Cross-sections for (n,α) and (n,xα) reactions on the Structural Material for Fusion Reactor 46-50Ti

The biggest problem of structural materials for fusion reactor is the damage caused by the fusion product neutrons to the structural material. If this problem is overcomed, an important milestone will be left behind in fusion energy. One of the important problems of the structural material is that nuclei forming the structural material interacting with fusion neutrons are transmuted to stable or radioactive nuclei via (n, x) (x; alpha, proton, gamma etc.) reactions. In particular, the concentration of helium gas in the structural material increases through deuteron- tritium (D-T) and (n, α) reactions, and this increase significantly changes the microstructure and the properties of the structural materials. Therefore, in this study, the effects of the different nuclear level density models on the excitation functions of the (n, α) reactions on 46-50Ti isotopes, an attractive candidate for the structural material for fusion reactors, have been investigated for the first time. Also, the differential cross-sections with respect to alpha energy for the emission of alpha particles of the 46-50Ti (n, xα) reactions have been investigated at 14.1 MeV incident neutron energy. The calculations are performed using the two-component exciton model in the TALYS 1.9 code, and the results are compared with available experimental data. The results of this study will contribute to nuclear database as required for improving, design and operations of the important facilities as ITER (International Thermonuclear Experimental Reactor), DEMO (The demonstration power plant) and ENS (European Nuclear Society).

Semi-empirical systematics formulas for the (n, p), (n, α), and (n, 2n) reaction cross-sections at 14.5 MeV

New Semi-empirical mass formulas were developed for the (n, p), (n, α), and (n, 2n) reaction cross-sections at 14.5 MeV neutron energy by using the literature data available on EXFOR library. The new formulas were derived on the basis of the statistical model considering Q − value dependence. The results obtained from the present exercise were compared with other systematic formulas developed in past years as well as with the experimental literature data reported on EXFOR library. The comparison has been done on the basis of statistical model as well as on the asymmetry parameter dependence. The present work offers an alternative to reproduce nuclear data at 14.5 MeV incident neutron energies.

C13(n,2nγ)C12 γ -ray production in the 14–16 MeV incident neutron energy range

$\ensuremath{\gamma}$-ray emission from $^{12}\mathrm{C}$ and $^{13}\mathrm{C}$ samples irradiated with deuterium-tritium fusion neutrons was experimentally measured at the Omega Laser Facility and at the Ohio University Edwards Accelerator Laboratory. The intent of these measurements was to determine the feasibility of using $^{13}\mathrm{C}$-based plastic ablators with embedded $^{12}\mathrm{C}$ layers for ``dark mix'' diagnosis of inertial confinement fusion implosions. Spectrally resolved measurements at Ohio University identified significant 4.44-MeV $\ensuremath{\gamma}$-ray emission from the $^{13}\mathrm{C}(n,2n\ensuremath{\gamma})^{12}\mathrm{C}$-L1 reaction channel. The recorded 4.44-MeV $^{13}\mathrm{C}$ signal was compared against emission from an identically irradiated $^{12}\mathrm{C}$ target with known $^{12}\mathrm{C}$($n,{n}^{\ensuremath{'}}\ensuremath{\gamma})^{12}\mathrm{C}$-L1 cross section, which resulted in an average $^{13}\mathrm{C}(n,2n\ensuremath{\gamma})^{12}\mathrm{C}$-L1 cross section of 117 $\ifmmode\pm\else\textpm\fi{}$ 17 mb over the incident neutron energy distribution range from 14.4 to 15.8 MeV. Integrated $^{13}\mathrm{C}$ $\ensuremath{\gamma}$-ray signals above 2.9 MeV recorded with the Gas Cherenkov Detector at Omega exceeded MCNP6.1 predictions by a factor of 3. The additional signal was attributed to 4.44-MeV $\ensuremath{\gamma}\mathrm{s}$ resulting in an inferred $^{13}\mathrm{C}(n,2n\ensuremath{\gamma})^{12}\mathrm{C}$-L1 cross section of $95\ifmmode\pm\else\textpm\fi{}11$ mb at 14.1-MeV average incident neutron energy. As a result, the $^{13}\mathrm{C}$-based ``dark mix'' diagnostic concept was deemed infeasible.

Estimations of (n, p) reaction cross-sections at 14.5 MeV incident neutron energy by artificial neural networks

The cross-sections for (n, p) reactions around 14 MeV are important for nuclear research field and applications of nuclear energy. Also these neutron-induced reactions have been extensively studied in the literature. In this study, we have theoretically estimated the (n, p) reaction cross-section of different elements for 14.5 MeV incident neutron energy by using artificial neural network (ANN) methods whose experimental data are not available in the literature. For the construction of the ANN, available experimental data have been used. The results from the constructed ANN have been compared with the experimental data and those obtained from the theoretical formula. Furthermore, by using the constructed ANN through the limited experimental data, the new cross-section data for some (n, p) reactions have been generated and the results have been compared with a common database. The results give a good agreement with the literature and indicate that the method can be a powerful tool for the estimation of neutron cross-section data for the neutron-induced reaction.

Total kinetic energy and mass yields from the fast neutron-induced fission of $$^{239}\hbox {Pu}$$

The total kinetic energy (TKE) release in fission is an important observable, constituting over 80% of the energy released in fission (E$_{f}$ $\approx$ 200 MeV). While the TKE release in the $^{239}$Pu(n,f) reaction was previously measured up to 50 MeV incident neutron energy (E$_{n}$), there were features in TKE release at the highest values of E$_{n}$ that were puzzling. There was a marked flattening of TKE release from E$_{n}$ = 30 to 50 MeV, in disagreement with the clearly decreasing TKE observed from E$_{n}$ = 0.5 to 30 MeV. To verify and clarify this trend, TKE measurements at higher values of E$_n$ were made. We present absolute measurements of TKE release in $^{239}$Pu(n,f) from E$_{n}$ = 2.4 to 100 MeV. We used silicon PIN detectors to measure the fragment energies and deduce mass-yield curves using the 2E-method. We also discuss fission asymmetry and the relationships between approximate fission fragment mass and distortion.

Theoretical cross-sectional calculation of some structural fusion material on (n, α)-induced reactions

27Al, 51V, 52Cr, 55Mn, 56Fe and 58Ni nuclei are some structural fusion substances. The neutron incident energy around 14–15 MeV is adequate to excite the nucleus for the reactions such as (n, p), (n, d), (n, 2n), (n, t), and (n, α). For fusion reactor technology, the reaction cross-sectional data have a critical importance in fusion reactors and development. Neutron irradiation produces considerable modifications in the mechanical and physical properties of each of the structural fusion material systems raising feasibility questions and design limitations. In this paper, for some structural fusion materials (n, α) reactions such as 52Cr(n, α)49Ti, 51V(n, α)48Si, 27Al(n, α)24Na, 58Ni(n, α)55Fe, 56Fe(n, α)53Cr and 55Mn(n, α)52V were done up to 40 MeV incident neutron energy. In the calculations, the equilibrium and pre-equilibrium impacts have been used. Calculations have been carried out with TALYS 1.9 and EMPIRE 3.2 (Malta) nuclear model codes. Results from performed calculations have been compared with the experimental nuclear reaction data, ENDF/B-VII.b4, JENDL-4.0 and JEFF-3.2 evaluated data.

First Results on 238U(n,f) Prompt Fission Neutron Spectra from 1 to 200 MeV incident neutron energy

A new 238U(n,f) prompt fission neutron spectra (PFNS) measurement has been recently performed at the WNR facility of the Los Alamos National Laboratory. The measurement allows one to explore the dependence of the prompt fission neutron energy spectra on the incident neutron energy. The experimental setup couples the Chi-Nu scintillator array to a newly developed fission chamber, characterized by an improved alphafission discrimination and time resolution, a reduced amount of matter in the neutron beam and a higher actinide mass. The dedicated setup and the high statistics collected allow us to obtain a good precision on the measured fission neutron energy, as well as to explore the low energy region, down to 650keV, and the high energy region, above 5 MeV, of the emitted neutron spectrum. These are indeed the regions where discrepancies in the evaluated PFNS data are found. We present here the first preliminary results of the experiment.

Estimation of (n, p) and (n, α) Cross Section of Radionuclide 60Co for Fusion Technology Applications

For fusion application, there is a high demand for nuclear data for long-lived radionuclides produced in a neutron environment. Cobolt-60 (t1/2 = 5.3 years) is one of the radionuclides produced in a large amount inside the fusion reactor via different pathways. In this context, the excitation function of 60Co(n, p) and 60Co(n, α) reaction from threshold to 20 MeV has been calculated using TALYS-1.6 in the framework of the Hauser Feshbach statistical model along with preequilibrium effects. Outgoing (proton and alpha) particle energy spectra (dσ/dEp, dσ/dEα) and double-differential cross section (d2σ/dE dΩ) has also been estimated at 14 MeV incident neutron energy. Optimized input parameters used during the model calculation were determined by fitting the (n, p) and (n, α) cross sections to the experimental data for the adjacent stable nuclide 59Co. The activation analysis has also been carried out for 1 kg of stainless steel (SS316) using FISPACT-2007.

(n, p) Reaction Cross Sections Calculations of Some Stellar Iron Group Fusion Materials

The excitation functions for (n, p) reactions from reaction threshold to 24 MeV on some important iron (Fe) group target elements (20 ≤ Z ≤ 28) for astrophysical (n, p) reactions such as Si, Ca, Sc, Ti, Cr, Fe, Co and Ni were calculated using TALYS-1.0 nuclear model code. The new calculations on the excitation functions of 28Si(n, p)28Al, 29Si(n, p)29Al, 42Ca(n, p)42K, 45Sc(n, p)45Ca, 46Ti(n, p)46Sc, 53Cr(n, p)53V, 54Fe(n, p)54Mn, 57Fe(n, p)57Mn, 59Co(n, p)59Fe, 58Ni(n, p)58Co and 60Ni(n, p)60Co reactions have been carried out up to 24 MeV incident neutron energy. In these calculations, the compound nucleus and pre-equilibrium reaction mechanism studied extensively. According to these calculations, we assume that these model calculations can be applied to some heavy elements, ejected into interstellar medium by dramatic supernova events.

Cross-section measurement for the 206Pb(n, α)203Hg reaction induced by neutrons around 14 MeV

The cross section for the 206Pb(n, α)203Hg reaction has been measured in the neutron energy range of 13.5–14.7MeV using the activation technique and a coaxial HPGe γ-ray detector. The cross-section data of the 206Pb(n, α)203Hg reaction which are scaled to the evaluated values of the 93Nb(n, 2n) 92mNb reaction are reported to be 0.99±0.07, 1.23±0.11, and 1.39±0.12mb at 13.5±0.2, 14.4±0.2, and 14.7±0.2MeV incident neutron energies, respectively. The results are discussed and compared with experimental data found in the literatures, with the results of published empirical formulae and the evaluated values of the databases. The comparison shows that the value of our excitation curve at 14.5MeV is close to the estimation obtained from the published empirical formula based on the statistical model with dependence on the Q-value and odd–even effect taken into consideration.

Double Differential Cross Section and Stopping Power Calculations of Light Charged Particle Emission for the Structural Fusion Materials 50,52Cr

Double differential cross section is a fundamental value to determine nuclear heating and material damages in structural fusion material research. In this study, double differential light charged particle emission cross sections for 50,52Cr target nuclei have been calculated by the TALYS 1.6 code at 14.8 MeV incident neutron energy. Penetrating distance and stopping powers have been calculated for the alpha, deuteron and proton particles, taking into consideration all possible reactions in 50,52Cr for incident energies of 0.5–22.2 MeV using GEANT4 calculation code. The compound nucleus formation process dominates the emission of proton and alpha particles. Direct reaction contribution becomes dominant in higher particle emission energies. The calculated double differential cross sections have been compared with the available experimental data taken from the literature.

Study of Some Structural Fusion Materials for (n,2n) Reactions

Studies of (n,2n) reaction are especially important for neutron multiplication. The (n,2n) cross section is neutron multiplier reaction in fusion reactor design. 27Al, 51V, 52Cr, 55Mn, 56Fe and 58Ni nuclei are the some structural fusion materials. Therefore, (n,2n) reactions of the selected blanket materials can play a key role for multiplying neutrons in reactor environment. In this study, for some structural fusion materials (n,2n) reactions such as 27Al(n,2n)26Al, 51V(n,2n)50V, 52Cr(n,2n)51Cr, 55Mn(n,2n)54Mn, 56Fe(n,2n)55Fe and 58Ni(n,2n)57Ni have been carried out up to 30 MeV incident neutron energy. In the calculations, the pre-equilibrium and equilibrium effects have been used. The calculated results have been compared with the experimental data as well as with evaluated data files.

Double Differential Alpha, Proton and Deuteron Emission Cross Section Calculations for the Structural Fusion Materials 46,48Ti

Double differential light charged particle emission cross section is a fundamental value to determine nuclear heating and material damages in structural fusion material development. In this study, double differential alpha, proton and deuteron emission cross sections for 46Ti and 48Ti target nuclei have been calculated by the TALYS 1.6 code at 15 MeV incident neutron energy. The light charged particles are emitted due to mainly three different processes—compound, direct and pre-equilibrium. The compound nucleus formation process dominates the emission of light charged particle up to 8 MeV emission energy. Pre-equilibrium and direct reaction contribution become dominant in higher particle emission energies. The calculated double differential cross sections have been compared with the available experimental data taken from the literature.

169Tm(n,2n)168Tm Cross Sections from the Threshold to 20 MeV

The cross sections of the 169Tm(n,2n)168Tm reaction induced by neutrons with energies of ∼14 MeV were determined combining the activation technique with the latest decay data. Fast neutrons were produced by using a neutron generator at the China Academy of Engineering Physics, through the 3H(d,n)4He reaction. Induced gamma activities were measured by means of high-resolution gamma-ray spectrometry. Data for 169Tm(n,2n)168Tm reaction cross sections are reported to be 1827 ± 95 and 1926 ± 82 mb at 13.5 ± 0.2 and 14.8 ± 0.2 MeV incident neutron energies, respectively. The cross sections were also estimated with the TALYS-1.4 nuclear model code using different level density models, at neutron energies varying from the reaction threshold to 20 MeV. Results are also discussed and compared with some corresponding values found in the literature.

Measurement of 167Er(n,p)167Ho reaction at 13.5 and 14.8 MeV

We have measured the 167Er(n,p)167Ho cross-sections at two different neutron energies 13.5 and 14.8MeV. Measurements were performed at Pd-300 neutron generator of Chinese Academy of Engineering Physics (CAEP) with monoenergetic neutrons produced via the 3H(d,n)4He reaction using a tritium–titanium (T–Ti) target. Induced gamma activities were measured by a high-resolution gamma-ray spectrometer with high-purity germanium (HPGe) detector. The data for 167Er(n,p)167Ho reaction cross-sections are reported to be 2.2±0.6 and 2.8±1.4mb at 13.5±0.2 and 14.8±0.2MeV incident neutron energies, respectively. The cross sections were also estimated with the TALYS-1.4 nuclear model code and compared with experimental data found in the literature, and with the comprehensive evaluation data in ENDF/B-VII.1 and JEFF-3.1/A libraries.

Pre-equilibrium neutron-emission spectra of 238U with an effective nucleon–nucleon interactions

In this study, the initial exciton numbers for the target nucleus 238U were calculated through a new method offered by Tel et al. (Ann. Nucl. Energy, 35, 220, 2008). Neutron-emission spectra produced by (n,xn) reactions on 238U nuclei have been calculated by using Hartree–Fock method with effective nucleon–nucleon Skyrme interactions with SKM∗ parameters. Pre-equilibrium nuclear reactions have been used to investigate the effect of initial exciton numbers on the nucleon emission spectra. Calculations have been made in the framework of the hybrid, equilibrium and GDH models using ALICE/ASH computer code. The initial exciton numbers calculated with the theoretical neutron and proton densities have been obtained with SKM∗ for the 238U(n,xn) reaction at 14.0 and 18.0MeV incident neutron energies. We also compared the geometry-dependent hybrid model (GDH), newly evaluated with the initial exciton number calculations of the neutron emission spectra of the 238U(n,xn) reaction. The obtained results are discussed and compared with the available experimental data and are shown to be in agreement with each other. All calculated results have been compared with experimental data from Experimental Nuclear Reaction Data (EXFOR).