Neutron Angular Distributions Research Articles

Study of Neutrons Produced in the Interaction of Muon Antineutrinos in the ND280 near Neutrino Detector of the T2K Experiment

Neutrons produced during scattering of muon antineutrinos through charged currents in the ND280 near neutrino detector of the T2K experiment are studied. Based on Monte-Carlo simulations of the beam of accelerator antineutrinos with an energy of ~0.6 GeV, the kinematics of the quasi-elastic interaction is reconstructed. Energy and angular distributions of neutrons are obtained, their detection efficiency is calculated using a method accounting for the particle time of flight.

Constraining the destruction rate of K40 in stellar nucleosynthesis through the study of the Ar40(p,n)K40 reaction

Background: $^{40}\mathrm{K}$ plays a significant role in the radiogenic heating of Earth-like exoplanets, which can affect the development of a habitable environment on their surfaces. The initial amount of $^{40}\mathrm{K}$ in the interior of these planets depends on the composition of the interstellar clouds from which they formed. Within this context, nuclear reactions that regulate the production of $^{40}\mathrm{K}$ during stellar evolution can play a critical role.Purpose: In this study, we constrain for the first time the astrophysical reaction rate of $^{40}\mathrm{K}(n,p)^{40}\mathrm{Ar}$, which is responsible for the destruction of $^{40}\mathrm{K}$ during stellar nucleosynthesis. We provide to the nuclear physics community high-resolution data on the cross section and angular distribution of the $^{40}\mathrm{Ar}(p,n)^{40}\mathrm{K}$ reaction. These are important to various applications involving $^{40}\mathrm{Ar}$. The associated reaction rate of the $^{40}\mathrm{Ar}(p,n)^{40}\mathrm{K}$ process addresses a reaction rate gap in the Joint Institute for Nuclear Astrophysics REACLIB database in the region of intermediate-mass isotopes.Methods: We performed differential cross-section measurements on the $^{40}\mathrm{Ar}(p,n)^{40}\mathrm{K}$ reaction, for six energies in the center-of-mass system between 3.2 and 4.0 MeV and various angles between ${0}^{\ensuremath{\circ}}$ and ${135}^{\ensuremath{\circ}}$. The experiment took place at the Edwards Accelerator Laboratory at Ohio University using the beam swinger target location and a standard neutron time-of-flight technique. We extracted total and partial cross sections by integrating the double differential cross sections we measured.Results: The total and partial cross sections varied with energy due to the contribution from isobaric analog states and Ericson type fluctuations. The energy-averaged neutron angular distributions were symmetrical relative to ${90}^{\ensuremath{\circ}}$. Based on the experimental data, local transmission coefficients were extracted and were used to calculate the astrophysical reaction rates of $^{40}\mathrm{Ar}(p,n)^{40}\mathrm{K}$ and $^{40}\mathrm{K}(n,p)^{40}\mathrm{Ar}$ reactions. The new rates were found to vary significantly from the theoretical rates in the REACLIB library. We implemented the new rates in network calculations to study nucleosynthesis via the slow neutron capture process, and we found that the produced abundance of $^{40}\mathrm{K}$ is reduced by up to 10% compared to calculations with the library rates. At the same time, the above result removes a significant portion of the previous theoretical uncertainty on the $^{40}\mathrm{K}$ yields from stellar evolution calculations.Conclusions: Our results support a destruction rate of $^{40}\mathrm{K}$ in massive stars via the $^{40}\mathrm{K}(n,p)^{40}\mathrm{Ar}$ reaction that is larger compared to previous estimates. The rate of $^{40}\mathrm{K}$ destruction via the $^{40}\mathrm{K}(n,p)^{40}\mathrm{Ar}$ reaction now has a dramatically reduced uncertainty based on our measurement. This result directly affects the predicted stellar yields of $^{40}\mathrm{K}$ from nucleosynthesis, which is a critical input parameter for the galactic chemical evolution models that are currently employed for the study of significant properties of exoplanets.

Angular Distribution of Neutrons Around Thick Beryllium Target of Accelerator-Based 9Be(d, n) Neutron Source

Abstract An experimental work and simulations were carried out to determine the angular distributions of neutrons and yields of the 9Be(d, n) reaction over all angular range (360 deg) on a thick beryllium target as an accelerator-based neutron source at incident-deuteron energy 13.6 MeV. The neutron activation method was used in the experimental part using aluminum and iron foils as detectors to calculate the neutron flux. The Monte Carlo neutral-particles code (MCNP5) was used to demonstrate and simulate the neutron distribution, also to understand and compare with the experimental results. The neutron energy spectrum was computed using the projection angular-momentum coupled evaporation code PACE4 (LISE++) and the spectrum was adopted in MCNP5 code. Two experimental ways were used, one with beryllium target and another one without the beryllium target, to evaluate the neutron flux emitted only by the beryllium target. Typical computational results were presented and are compared with the previous experimental data to evaluate the computing model as well as the characteristics of emitted neutrons produced by the 9Be(d, n) reaction with a thick Be-target. Moreover, the results can be used to optimize the shielding and collimating system for neutron therapy.

Experiments with neutron induced neutron emission from U-235, Pu-239, and graphite

A neutron induced neutron emission experiment was conducted as the Los Alamos Neutron Science Center (LANSCE) facility at Los Alamos National Laboratory (LANL). In this experiment, a sample was placed in a well collimated neutron beam and was surrounded by an array of 28 fast neutron detectors (EJ-309). The experiment was performed with a neutron flight path of 21.5 m from the source to the sample, and 1 m from the sample to the detectors. The neutron emission from the sample was measured as a function of neutron time of flight covering an incident energy range from 0.7- 20 MeV. The samples included U-235, Pu-239, carbon (graphite), and blanks that matched the encapsulation of the sample. The measured samples were constantly cycled in and out of the neutron beam. This type of experiment measures neutron emission from all reactions occurring in the sample such as fission and elastic and inelastic scattering. Similar to the methodology previously developed at RPI [1], the measurements were compared with detailed simulations of the experiment using different cross section evaluations for the sample. The observed differences can be attributed to the evaluated neutron cross section and angular distributions. The carbon sample was used as a reference to validate both the experiment and simulation methodology and showed good agreement between experiments and simulations. A review of the experimental setup, analysis methods, and some of the results will be presented.

Measurement of the angular distribution of neutrons scattered from deuterium below 3 MeV

The differential cross section of neutron scattering on deuterium was investigated in the energy range from 400 keV to 2.5 MeV using the recoil detection method, irradiating with monoenergetic neutrons a proportional counter filled with deuterated gases. Comparing simulations of the transport of neutrons and recoil nuclei in the detector to the experimental pulse-height distribution, it was possible to establish a procedure for the determination of the coefficients of the Legendre expansion of the n-d angular distribution.

Measurement of neutron yield and angular distribution for D-T neutron generator by neutron activation analysis method

To measure the neutron yield of D-T neutron generator, the activation foils of iron, copper and aluminum were used to be irradiated in the neutron field. The 14.1 MeV neutron yield was deduced by counting the characteristic γ-rays of radioisotopes produced by five nuclear reactions [56Fe(n,p)56Mn, 65Cu(n,2n)64Cu, 63Cu(n,2n)62Cu, 27Al(n,α)24Na, 27Al(n,p)27Mg]. The relationship between the neutron yield and the deuteron beam energy, beam current of the D-T neutron generator was measured by the BF3 proportional counter and the fluctuation of neutron yield under specified parameters was evaluated. Eleven activated iron foils were used to measure 14.1 MeV neutron yield at different angles of D-T neutron generator. The direction with the highest neutron flux is 30∘-45∘ along the beam direction and the neutron flux decreases gradually with the increase of angle. The measurements of neutron yield, stability and angular distribution of D-T neutron generator are significant for improving the accuracy of neutron activation analysis and neutron irradiation efficiency, as well as optimizing the neutron shielding design.

Physical design and evaluation of a high-intensity accelerator-based D-D/D-T fusion neutron source

A high-intensity accelerator-based D-D/D-T fusion neutron source (ZF-400) with a thick adsorption target is designed with an intensity of $ 10^{13}$ n/s. A high-current microwave ion source is used to produce a large current deuteron beam, and neutrons are generated by irradiating the deuteron beam on a deuterium-adsorption target or tritium-adsorption target. According to the particle-in-cell (PIC) code, the length of the whole high-current D+ beam transport line is 500cm, the D+ beam transfer efficiency is up to 96%, and various components can match each other. On the rotating target, the D+ beam spot size is about 20.0 mm with energy of 450 keV. Based on the heat conduction theory, the thick adsorption rotating target with water-cooling can withstand the D+ ions beam with 450 kV/50 mA and ensure that the temperature is less than 200 °C. According to the multi-layer computing model, neutron energy spectra, angular distributions and yields for the thick target can be calculated with remarkable precision. The neutron energy spectra are non-mono-energetic neutrons for the ZF-400 neutron generator, the neutron angular distributions are anisotropic distributions, and they can provide neutrons with an intensity of $ 2.8\times 10^{11}$ n/s (D-D) and $ 1.4\times 10^{13}$ n/s (D-T), respectively, with the deuteron of 450 keV/50 mA.

Experimental and Theoretical Research on the Angular Distribution of Neutrons Produced in 7Li(p, n)7Be Reactions during the Interaction of Intense Laser Pulses with Solid Targets

Experimental and Theoretical Research on the Angular Distribution of Neutrons Produced in 7Li(p, n)7Be Reactions during the Interaction of Intense Laser Pulses with Solid Targets

Neutron-neutron angular and energy-angle correlations of plutonium samples with varying α-ratio

Abstract Accurate and timely characterization of physical properties pertinent to plutonium bearing materials is important for fulfilling nuclear nonproliferation and safeguards goals. Physical properties include the fissile mass, leakage multiplication, and the α -ratio, defined as the ratio of ( α ,n) neutrons to spontaneous fission neutrons. Traditionally, these properties can be inferred by relating the measured neutron multiplicity count rates to the well-established point kinetics moments equations; the current state-of-the-art utilizes 3 He-based detection systems. Organic scintillators have been used extensively to study and measure characteristic signatures in the neutron angular and energy distributions. Previous work has proposed techniques that independently leverage the energy and angle sensitivity of organic scintillators to estimate the α -ratio of plutonium bearing material; however, it is expected that the energy and angular distributions are correlated to one another due to the underlying physics of fission and ( α ,n) neutron emissions. This work presents experimental results that characterize neutron-neutron angular distribution and subsequently the neutron-neutron energy-angle correlations for plutonium samples of similar mass and multiplication, but varying α -ratio due to the type of low-Z impurity. Full neutron-neutron angular distributions are presented using a low-energy detection threshold of 0.10, 0.15, and 0.20 MeVee (0.73, 0.96, 1.16 MeV neutron-equivalent energy). Neutron anisotropy was quantified by taking the ratio of neutron-neutron coincidences at 180°to those at 90°, where a value of unity indicates a purely isotropic source. The results show that the observed neutron-neutron correlations transition away from fission-induced signal to the cross-talk signal associated with single ( α ,n) neutrons with increasing α -ratio. Energy-angle correlations are characterized by calculating the neutron anisotropy at various detection thresholds and show positive correlation between the observed anisotropy and the energy of the neutrons.

Thick target neutron yields from 100- and 230-MeV/nucleon helium ions bombarding water, PMMA, and iron

The secondary neutrons produced from 100- and 230-MeV/nucleon 4He ions, respectively, stopping in the thick natFe, PMMA and water targets are measured by the time of flight method combined with the pulse shape discrimination of liquid scintillation detectors. The experimental data show that the secondary neutrons were contributed from breakup of projectiles, emission from overlap regions of projectile nuclei and target nuclei, and evaporation of projectiles and target nuclei.The measured quantities, including the double-differential thick target neutron yields, angular distributions, and total neutron yields per ion, were benchmarked against model calculations with the PHITS, FLUKA, and MCNP Monte Carlo simulation codes. The default models implemented in these codes agree the experimental data well at intermediate-to-large angles in the low-to-intermediate energy range. However, the physics models implemented in the FLUKA and the PHITS codes under-predict secondary neutrons at energies higher than the specific beam energies by more than one order. The energy-integrated simulation yields at 0° differ from the measured values by −75% to 240%. The underestimation of low-energy neutron yields by the models at small angles for 230-MeV/nucleon 4He projectiles on the light targets are as much as five times lower. Our results indicate that improvements are needed in the physics models used to describe 4He-induced nuclear reactions for predictions of neutron production.

Calculation of the wide-angle neutron spectra from the 9Be(d, xn) reaction in a thick beryllium target * * Supported by the National Magnetic Confinement Fusion Science Program of China (2014GB104002), the National Natural Science Foundation of China (11705071, 11875155, 11675069, 21327801), NSAF (U1830102), the National Key Scientific Instrument and Equipment Development Project (2013YQ40861), and the Fundamental Research Funds for the

The multi-layer computing model is developed to calculate wide-angle neutron spectra, in the range from 0° to 180° with a 5° step, produced by bombarding a thick beryllium target with deuterons. The double-differential cross-sections (DDCSs) for the 9Be(d, xn) reaction are calculated using the TALYS-1.8 code. They are in agreement with the experimental data, and are much better than the PHITS-JQMD/GEM results at 15° , 30° , 45° and 60° neutron emission angles for deuteron energy of 10.0 MeV. In the TALYS-1.8 code, neutron contributions from direct reactions (break-up, stripping and knock-out reactions) are controlled by adjustable parameters, which describe the basic characteristics of typical direct reactions and control the relative intensity and the position of the ridgy hillock at the tail of DDCSs. It is found that the typical calculated wide-angle neutron spectra for different neutron emission angles and neutron angular distributions agree quite well with the experimental data for 13.5 MeV deuterons. The multi-layer computing model can reproduce the experimental data reasonably well by optimizing the adjustable parameters in the TALYS-1.8 code. Given the good agreement with the experimental data, the multi-layer computing model could provide better predictions of wide-angle neutron energy spectra, neutron angular distributions and neutron yields for the 9Be(d, xn) reaction neutron source.

Numerical Simulation of Radiation Anisotropy of the Pyroelectric Neutron Generator

The pyroelectric neutron generator is a compact source of fast neutrons with an energy of 2.45 MeV and a yield up to ∼104 neutrons/s. The device is designed for calibration of low-background neutrino and dark matter detectors and may also serve as an alternative to traditional radioactive sources of fast neutrons in physical research and practical work. Numerical simulation of the angular distribution of neutrons emitted by the pyroelectric generator with the D(d, n)3He reaction proceeding within it was performed in order to calculate the neutron yield in the full solid angle and in a given direction correctly. The angular distribution was found to be anisotropic: the neutron yield increased in the direction of motion of incident deuterium ions. This anisotropy was as large as ∼25% at a maximum energy of 28 keV of incident particles. The anisotropy increased nonlinearly with the ion energy: it reached ∼70% at 50 keV and a monoenergetic flux, but was virtually zero below 10 keV. The obtained angular distribution is similar to that of neutrons in the case of a 15-keV monoenergetic flux of deuterium ions.

Analysis of the Angular Distribution of Emission of Neutrons Generated with the Ponderomotive Mechanism of Ion Heating by High-Power Short Laser Pulse Acting on a (CD2)n Target

Experiments on the angular distribution of DD neutrons generated in nuclear reactions upon irradiation of a (CD2)n target have been performed in the “Neodymium” laser facility. Apart from the main pulse, prepulses were observed in the experiment. Measurements have shown that neutrons have an isotropic angular distribution. Experimental results have been analyzed using hydrodynamic calculations accounting for the ponderomotive force. The ion heating mechanism in a shock wave emerging under the action of the ponderomotive pressure of the main pulse in the supercritical region of the plasma has been considered. It is shown that neutrons are generated mainly in the supercritical plasma heated by the ion heat wave. The time of plasma cooling due to hydrodynamic spreading turns out to be much longer than the isotropization time of the ion velocity distribution function due to Coulomb collisions. In these conditions, the neutron angular distribution must be isotropic.

Cross section and neutron angular distribution measurements of neutron scattering on natural iron

New measurements of the neutron scattering double differential cross section of iron were carried out at the neutron time-of-flight facilities GELINA and nELBE. A neutron spectrometer consisting of an array of up to 32 liquid organic scintillators was employed, which was designed to measure the scattering differential cross section at eight scattering angles and to simultaneously determine the integral cross section via numerical quadrature. The separation of elastic from inelastic scattering was achieved by analyzing the time-of-flight-dependent light-output distributions to determine the scattered neutron energy. The method was validated by studying elastic scattering on carbon and it was proved to work well for the determination of the elastic cross section. Here, the possibility to extend it to inelastic scattering was investigated too. For these experiments a sample of natural iron was used and the results cover the incident neutron energy range from 2 to 6 MeV. Both the differential and the integral elastic cross sections were produced for $^{\mathrm{nat}}\mathrm{Fe}$, while for inelastic scattering, partial angular distributions for scattering from the first excited level of $^{56}\mathrm{Fe}$ could be determined.

Rejection-based sampling of inelastic neutron scattering

Distributions of inelastically scattered neutrons can be quantum dynamically described by a scattering kernel. We present an accurate and computationally efficient rejection method for sampling a given scattering kernel of any isotropic material. The proposed method produces continuous neutron energy and angular distributions, typically using just a single interpolation per sampling. We benchmark the results of this method against those from accurate analytical models and one of the major neutron transport codes. We also show the results of applying this method to the conventional discrete double differential cross sections.

Prompt fission neutron anisotropy in low-multiplying subcritical plutonium metal assemblies

Fission neutron anisotropy, due to the kinematics of the fission process, has been studied for non-multiplying sources and highly multiplying subcritical plutonium metal assemblies (i.e. relatively long fission chains). The studies on highly multiplying assemblies show that the observed neutron–neutron angular distribution appear isotropic, while the studies on non-multiplying sources show that the neutron–neutronangular distribution appear anisotropic. No measured data exists, however, that investigates the dependence of neutron anisotropy on multiplication for low-multiplying assemblies. We have experimentally characterized the dependence of fission neutron anisotropy on multiplication for low-multiplying plutonium metal assemblies. Here, an array of 16 organic scintillators was used to measure plutonium metal assemblies (95% 239Pu, by mass) exhibiting a leakage multiplication of 1.0722(3) to 1.6006(4). Full neutron–neutron angular distributions were measured, and the fission neutron anisotropy was quantified with the ratio of neutron–neutron coincidences observed at 180°and 90°. The results show that the neutron–neutron angular distribution becomes more isotropic as the multiplication increases. Additionally, energy–angle correlations were also characterized showing that the angular distributions are more anisotropic when observing neutrons of higher energy.

Angular correlations in the prompt neutron emission of spontaneous fission of 252Cf

Neutron angular distributions in spontaneous fission of 252Cf are investigated. The CORA experiment, performed at IPHC Strasbourg, aims at elucidating neutron emission mechanisms in the fission process. The experimental setup is composed of the angle-sensitive twin ionisation chamber CODIS for the detection of fission fragments and the DEMON neutron detector assembly. The development of a simulation toolkit based on GEANT4 and MENATE_R is described, adapted as a strategy to investigate the influence of experimental conditions on the observed properties of neutrons emitted. Besides the kinematic neutron anisotropy in the laboratory system due to neutron evaporation from moving fragments, two additional effects are discussed which may have an influence on the angular distributions of neutrons: scission neutrons and dynamic neutron emission anisotropy in the CM system of fragments due to the spin carried by fragments. A new analysis method is presented to disentangle the dynamic anisotropy from the other effects in an independent way. For the dynamic anisotropy only an upper limit could be found. Results for the angular correlation $ (\mathrm{n},\mathrm{n})$ between two evaporated neutrons and the correlation $ (\mathrm{n},\mathrm{LF})$ between an evaporated neutron and the Light Fragment direction of flight are reported.

Measurement of the neutron angular distribution from a beryllium target bombarded with a 345-MeV/u 238U beam at the RIKEN RI beam factory

Abstract The angular distribution of neutrons produced from a 4-mm-thick beryllium target bombarded with a 345-MeV/u 238U beam was measured outside the target chamber using bismuth and aluminum activation detectors at angles of 4.5°, 10°, 30°, 60°, 70° and 90° from the beam axis. Following two hours of irradiation and photo-peak analyses, the production rates of the radionuclides were obtained for the 209Bi(n,xn)210-xBi(x = 4–12) and 27Al(n,α)24Na reactions. Using the Particle and Heavy Ion Transport code System (PHITS), a Monte Carlo simulation of the production rates was performed and the ratios of the calculated to the experimental results (C/E) ranged from 0.6 to 1.0 generally and 0.4 to 1.3 in worst cases.

A function to provide neutron spectrum produced from the 9Be + p reaction with protons of energy below 12 MeV

ABSTRACTA function to give the total neutron production cross section, angular distribution, and energy spectrum via the 9Be + p reaction has been created by fitting experimental data to characterize compact neutron sources with thick Be targets bombarded by protons with energy below 12 MeV. To examine the suitability of the function, calculations of the angle-dependent neutron energy spectra produced in thick Be targets with 4- and 12-MeV protons using the function were compared with corresponding experiments and calculations using the nuclear data libraries of ENDF/B-VII.0 and JENDL4.0/HE. The function was in better agreement with the experiments than the calculations using the libraries except for at backward angles. The 115In(n,n’)115mIn reaction rates calculated using GEANT4 with source neutrons given by both the function and ENDF/B-VII.0 were compared with that measured at the RIKEN Accelerator-Driven Compact Neutron Source to evaluate the neutron spectrum above 1 MeV. The function slightly overestimated the measurement by 14% and the calculation with ENDF/B-VII.0 underestimated by 35%. It was concluded that the function can be applied in compact neutron source designs.

Nuclear Astrophysics at LNL: the 25Mg(α,n)28Si and 10B(p,α)7Be cases

The National Laboratory of Legnaro (LNL) has a long experience in Nuclear Physics measurements. Recently a new effort to perform Nuclear Astrophysics studies has been initiated. This effort started with the collaboration of LNL with the LUNA (Laboratory for Underground Nuclear Astrophysics) collaboration for the study of targets. After that in 2012, thank to a fruitful collaboration between nuclear astrophysicist and nuclear physics groups involved in neutron detection, the study of the 25Mg(α,n)28Si reaction was developed in order to help solving the 26Al puzzle. For the first time the angular distributions of neutrons emitted by this reaction were studied deeply founding discrepancies between the previous studies in literature. In 2014 the study of 10B(p,α)7Be was performed in order to give a precise normalization to the indirect measurements. This study was done by measuring the activated samples and it is still under analysis. A report of the status of the two experiments will be given in this contribution.