Neutron Energy Dependence Research Articles

Opportunities for high-energy neutron- and deuteron-induced measurements for fusion technology at the Soreq applied research accelerator facility (SARAF)

The Soreq Applied Research Accelerator Facility (SARAF) will be based on a 40 MeV, 5 mA CW (continuous wave) proton/deuteron superconducting linear accelerator, currently under construction at Soreq Nuclear Research Center in Yavne, Israel. It is planned to commence operation during 2025. Experiments at SARAF could provide data on high-energy deuteron- and neutron-induced cross-sections, yields and radiation damage, which are invaluable for the design and operation of the International Fusion Materials Irradiation Facility-DEMO-Oriented NEutron Source (IFMIF-DONES), and fusion technology in general. Pulsed beams (∼1 nsec) of variable energy deuterons will irradiate a lithium target and generate pulsed neutron beams with energy up to ∼55 MeV, which will be used to measure energy-dependent neutron-induced differential cross-sections, utilizing time of flight techniques. Impinging continuous wave (CW) 40 MeV deuteron beams on a unique gallium-indium (GaIn) liquid-jet target, will generate a neutron rate of more than 1 × 1015 n/sec, with energies up to ∼45 MeV. We plan to use this high rate to measure integral neutron-induced reaction yields of all channels simultaneously, employing an original novel method that will identify the reaction-produced nuclei via accurate mass measurement. The neutron-energy dependence of the yields could be deduced by combining measurements at various deuteron energies. The measured cross-sections and yields at SARAF may predict the activation characteristics of construction materials of IFMIF-DONES and future fusion reactors. The deuteron beams will also be used directly to measure cross-sections via in-beam and offline methods. The high neutron and deuteron rates will extend SARAF’s reach to rare materials. The deuteron beam power density on the liquid GaIn target will be 100 kW/cm2(similar to IFMIF-DONES) on a 2 cm2spot. The resulting neutron flux on small secondary samples will be in the 1013 n/cm2/s level, only an order of magnitude less than IFMIF-DONES. Therefore, SARAF may serve as a pilot facility for fusion-related radiation damage studies, providing important information towards the design of IFMIF-DONES.

Towards the characterization of neutron carcinogenesis through direct action simulations of clustered DNA damage

Neutron exposure poses a unique radiation protection concern because neutrons have a large, energy-dependent relative biological effectiveness (RBE) for stochastic effects. Recent computational studies on the microdosimetric properties of neutron dose deposition have implicated clustered DNA damage as a likely contributor to this marked energy dependence. So far, publications have focused solely on neutron RBE for inducing clusters of DNA damage containing two or more DNA double strand breaks (DSBs). In this study, we have conducted a novel assessment of neutron RBE for inducing all types of clustered DNA damage that contain two or more lesions, stratified by whether the clusters contain DSBs (complex DSB clusters) or not (non-DSB clusters). This assessment was conducted for eighteen initial neutron energies between 1 eV and 10 MeV as well as a reference radiation of 250 keV x-rays. We also examined the energy dependence of cluster length and cluster complexity because these factors are believed to impact the DNA repair process. To carry out our investigation, we developed a user-friendly TOPAS-nBio application that includes a custom nuclear DNA model and a novel algorithm for recording clustered DNA damage. We found that neutron RBE for inducing complex DSB clusters exhibited similar energy dependence to the canonical neutron RBE for stochastic radiobiological effects, at multiple depths in human tissue. Qualitatively similar results were obtained for non-DSB clusters, although the quantitative agreement was lower. Additionally we identified a significant neutron energy dependence in the average length and complexity of clustered lesions. These results support the idea that many types of clustered DNA damage contribute to the energy dependence of neutron RBE for stochastic radiobiological effects and imply that the size and constituent lesions of individual clusters should be taken into account when modeling DNA repair. Our results were qualitatively consistent for (i) multiple radiation doses (including a low-dose 0.1 Gy irradiation), (ii) variations in the maximal lesion separation distance used to define a cluster, and (iii) two distinct collections of physics models used to govern particle transport. Our complete TOPAS-nBio application has been released under an open-source license to enable others to independently validate our work and to expand upon it.

Energy-dependent angular distribution of individual γ rays in the La139(n,γ)La140* reaction

Neutron energy-dependent angular distributions were observed for individual $\gamma$-rays from the 0.74 eV p-wave resonance of $^{139}$La+$n$ to several lower excited states of $^{140}$La. The $\gamma$-ray signals were analyzed in a two dimensional histogram of the $\gamma$-ray energy, measured with distributed germanium detectors, and neutron energy, determined with the time-of-flight of pulsed neutrons, to identify the neutron energy dependence of the angular distribution for each individual $\gamma$-rays. The angular distribution was also found for a photopeak accompanied with a faint p-wave resonance component in the neutron energy spectrum. Our results can be interpreted as interference between s- and p-wave amplitudes which may be used to study discrete symmetries of fundamental interactions.

Modeling long-term distribution of fast and thermal neutron fluence in degraded concrete biological shielding walls

Since neutron radiation can deteriorate mechanical properties of the concrete materials, it’s critical to obtain accurate neutron radiation levels in concrete structures during their service live. A two-group neutron diffusion model for fast and thermal neutron transport is developed in this study which considers the kinetic energy of the neutron more realistically. Based on the cross-property correlation theory, the variation of transport properties of concrete can be estimated using the degradation of mechanical properties of concrete, then, the thermal and fast neutron radiation fields with two representative energy levels as well as the thermal field in a concrete bioshield can be calculated. Coupled radio-thermo analysis of a section of simplified concrete bioshield was performed to 80 years as a case study, and the results were discussed and compared with the results from the one-speed model. The degradation of concrete induced by neutron radiation and elevated temperature can lead to considerable increases of thermal and fast neutron flux/fluence in the concrete. The profiles of thermal neutron flux/fluence are very different from the profiles of fast neutron flux/fluence. A proper treatment of the neutron energy dependence is needed to predict long-term neutron radiation levels in concrete biological shields accurately.

First Successful Measurement of Neutron Energy Dependence of Semiconductor Soft Errors

First Successful Measurement of Neutron Energy Dependence of Semiconductor Soft Errors

Nuclear explosions: a study

The incident neutron energy dependence of the neutron multiplication rate constant α is studied for 235U- and 239Pu-based nuclear explosions. At high neutron energy, α comes out to be about 10 generations/shake for both 235U and 239Pu. In addition, the photon gas model seems to hold well for the very early stage of a nuclear explosion as one is able to reproduce the yield (20.4 ± 2.4) kiloton for the Trinity test.

Development of Reference Layer Method in Resonant Neutron Reflectometry

A new method of phase recovery in neutron reflectometry is proposed based on the use of the Gd reference layer deposited on the top of an “unknown” layered structure. The idea of the method is to apply the energy dependence of neutron scattering length density to change the reference layer properties. Using three reflectivity curves at different neutron energies, the modulus and phase of the coefficient of reflection from the “unknown” structure can be reconstructed. We discuss the mathematics of phase recovery and present the first experimental results for a multilayered system.

Calculated neutron energy dependence of the dose-response of large recombination chamber

Abstract A model of REM-2-type chamber was modeled with MCNPX code to study the dose-response to monoenergetic neutrons in wide energy range from thermal to 20 MeV for various compositions of gas in the chamber. The energy dependence of the total dose absorbed in the filling gas was compared with the energy dependence of ambient absorbed dose D*(10) and with experimental data. The results of the studies will be useful for designing new, improved generation of recombination chambers.

Simulation study of alpha-neutron reactions from AmBe directional source using MCNP 6.1.1 with TENDL 2012, 2014, and 2017 libraries

Angular dependence of 9Be(α, n)12C was simulated in Monte-Carlo N-Particle transport 6.1.1 (MCNP) with TALYS Evaluated Nuclear Data Library (TENDL) 2012, 2014, and 2017 data to determine secondary neutron direction and energy for neutron imaging. The simulations consisted of a 90 μCi 241Am source and a 25 μm thick 9Be target. Neutrons emitted from the 9Be(α, n)12C were collected at different angles of emission within the MCNP simulation, which will be compared to experimental data in the future. The MCNP simulation used alpha induced data obtained through TALYS and processed through NJOY2016 into RECONR and ACER formats. Cross section tables were mapped appropriately in MCNP for the cross-section data to be read. Appropriate source particle weighting was determined for the alpha particles and neutrons, and the results were displayed in the F4 tallies. The total neutron production and neutron spectrum was compared to previous work. Discrepancies between the obtained results and previous work are discussed. Angular and energy dependence of secondary neutrons from TENDL 2012, 2014, and 2017 libraries were found, and will later be compared to experimental results. This work was done to support Patent No: 62/529,583.

Optimum neutron energy simulation in treatment of head and neck cancer at different depths in the BNCT method

Introduction: Recently head and neck cancer has pay attention to many researchers. Its therapeutic methods include surgery, chemotherapy, radiotherapy and Boron neutron capture therapy (BNCT). BNCT is better than conventional radiotherapy because it targets the tumor cell. This method involves two steps of infusion of stable 10B and then neutron radiation with a suitable intensity and energy. The BNCT in combination with boronphenylalanine (BPA) and borocaptate sodium (BSH) that was make using the epithermal neutron. BSH and PBA are used as 10B carriers. Epithermal neutrons reach to thermal transiting through tissues of the body. When 10B absorbed thermal neutrons, the α and 7Li particles produced in the 10B (n, α) 7Li reaction are of high linear energy. Transfer radiation have a short range of one cell diameter. Materials and Methods: Monte Carlo simulations were performed with MCNPX2.6 and RO31 MIRD phantom. The neutron source was employed the surface disk with 10 diameters and the range of energy was considered from 1ev-10Kev. The results of neutron and gamma dose at various depths was calculated using tally F4 and F6 in MCNPX2.6 code. Results: Relative Dose was obtained at various depths based on energy changes for gamma, fast and thermal neutron. The results of this study have shown increases of optimum energy as the tumor get deeper respect to the skin. In addition, an analytical relation was proposed for energy optimization with the position of the tumor. Conclusion: The optimum neutron energy dependence was investigated for neck tumor in different depths. These results provide useful information to the physicians to choice best optimum energy neutron beam in BNCT method.

Neutron energy dependence of delayed neutron yields and its assessments

ABSTRACT Incident neutron energy dependence of delayed neutron yields of uranium and plutonium isotopes is investigated. A summation calculation of decay and fission yield data is employed, and the energy dependence of the latter part is considered in a phenomenological way. Our calculation systematically reproduces the energy dependence of delayed neutron yields by introducing an energy dependence of the most probable charge and the odd–even effect. The calculated fission yields are assessed by comparison with JENDL/FPY-2011, delayed neutron activities, and decay heats. Although the fission yields in this work are optimized to delayed neutron yields, the calculated decay heats are in good agreement with the experimental data. Comparison of the fission yields calculated in this work and JENDL/FPY-2011 gave an important insight for the evaluation of the next Japanese evaluated nuclear data library (JENDL) .

ENERGY RESPONSE OF FLUORESCENT NUCLEAR TRACK DETECTORS OF VARIOUS COLORATIONS TO MONOENERGETIC NEUTRONS.

The neutron-energy dependence of the track-counting sensitivity of fluorescent nuclear track detectors (FNTDs) at two ranges of Mg doping, resulting in different crystal colorations, was investigated. The performance of FNTDs was studied with the following converters: Li-glass for thermal to intermediate-energy neutrons, polyethylene for fast neutrons, and polytetrafluoroethylene (Teflon™) for photon- and radon-background subtraction. The irradiations with monoenergetic neutrons were performed at the National Physics Laboratory (NPL), UK. The energy range was varied from 144 keV to 16.5 MeV in the personal dose equivalent range from 1 to 3 mSv. Monte Carlo simulations were performed to model the response of FNTDs to monoenergetic neutrons. A good agreement with the experimental data was observed suggesting the development of a basic model for future MC studies. Further work will focus on increasing FNTD sensitivity to low-energy neutrons and developing a faster imaging technique for scanning larger areas to improve counting statistics.

Енергетична залежність перерізів розсіяння швидких нейтронів ядрами 54Fe

Енергетична залежність перерізів розсіяння швидких нейтронів ядрами 54Fe

A new UK fission yield evaluation UKFY3.7

The JEFF neutron induced and spontaneous fission product yield evaluation is currently unchanged from JEFF-3.1.1, also known by its UK designation UKFY3.6A. It is based upon experimental data combined with empirically fitted mass, charge and isomeric state models which are then adjusted within the experimental and model uncertainties to conform to the physical constraints of the fission process. A new evaluation has been prepared for JEFF, called UKFY3.7, that incorporates new experimental data and replaces the current empirical models (multi-Gaussian fits of mass distribution and Wahl Zp model for charge distribution combined with parameter extrapolation), with predictions from GEF. The GEF model has the advantage that one set of parameters allows the prediction of many different fissioning nuclides at different excitation energies unlike previous models where each fissioning nuclide at a specific excitation energy had to be fitted individually to the relevant experimental data. The new UKFY3.7 evaluation, submitted for testing as part of JEFF-3.3, is described alongside initial results of testing. In addition, initial ideas for future developments allowing inclusion of new measurements types and changing from any neutron spectrum type to true neutron energy dependence are discussed. Also, a method is proposed to propagate uncertainties of fission product yields based upon the experimental data that underlies the fission yield evaluation. The covariance terms being determined from the evaluated cumulative and independent yields combined with the experimental uncertainties on the cumulative yield measurements.

Spectroscopic neutron radiography for a cargo scanning system

Detection of cross-border smuggling of illicit materials and contraband is a challenge that requires rapid, low-dose, and efficient radiographic technology. The work we describe here is derived from a technique which uses monoenergetic gamma rays from low energy nuclear reactions, such as 11B(d,nγ)12C, to perform radiographic analysis of shipping containers. Transmission ratios of multiple monoenergetic gamma lines resulting from several gamma producing nuclear reactions can be employed to detect materials of high atomic number (Z), the details of which will be described in a separate paper. Inherent in this particular nuclear reaction is the production of fast neutrons which could enable neutron radiography and further characterization of the effective-Z of the cargo, especially within the range of lower Z. Previous research efforts focused on the use of total neutron counts in combination with X-ray radiography to characterize the hydrogenous content of the cargo. We present a technique of performing transmitted neutron spectral analysis to reconstruct the effective Z and potentially the density of the cargo. This is made possible by the large differences in the energy dependence of neutron scattering cross-sections between hydrogenous materials and those of higher Z. These dependencies result in harder transmission spectra for hydrogenous cargoes than those of non-hydrogenous cargoes. Such observed differences can then be used to classify the cargo based on its hydrogenous content. The studies presented in this paper demonstrate that such techniques are feasible and can provide a contribution to cargo security, especially when used in concert with gamma radiography.

The energy dependent Pál–Bell equation and the influence of the neutron energy on the survival probability in a supercritical medium

The survival probability of a neutron injected into a supercritical fissile medium is studied with respect to the energy dependence of the incoming neutron. We assume a point model but allow the energy dependence to be included through a general energy exchange model. We have studied the effect of slowing down on the survival probability by means of the Pál–Bell equation and the Goertzel-Greuling kernel, the separable kernel, the Hansen–Roach dataset and a WIMS generated dataset for a homogenised reactor to approximate the slowing down process. The Goertzel-Greuling model is known to be exact for A=1 and reverts to age theory for large mass ratios. It is also accurate for all intermediate mass numbers, except possibly when strong resonances are present. The separable kernel is a simple model of energy exchange, corresponding to the thermalisation of neutrons in a single collision, which ignores the slowing down process but provides a simple result allowing both ends of the reactor spectrum to be included. The Hansen–Roach data set is obtained from a realistic slowing down model in a fast system and the thermal system is modelled by homogenised reactor data, generated using WIMS, and is typical of the material found in a PWR. Using a scattering cross section which is an arbitrary function of energy, and capture and fission cross sections which are proportional to 1/v, we find that the survival probability is energy independent insofar as it depends only on the values of the ratio of the fission and capture cross sections. For non-1/v cross sections there is an energy dependence which we discuss below. The formalism developed is robust enough for studies to be made of the influence of resonance cross sections and inelastic scattering on survival probability.

Development of One-dimensional Fractional-order Two-Group Models for Nuclear Reactor

Abstract This paper deals with fractional-order modeling of neutron transport in a nuclear reactor considering the energy-dependence of neutrons. The paper reports, using two energy group framework, the development of two novel fractional-order models: Fractional-order Two-Group Telegraph-Subdiffusion Model and Fractional-order Two-Group Subdiffusion Model. The models are developed with one-dimensional space consideration. These models are in the form of coupled, linear partial differential equations representing the movement of fast and thermal neutrons. The proposed models can be thought as more faithful and realistic representations of movement of neutrons in a heterogeneous core of nuclear reactor.

Energy Dependence of Fission Product Yields from 235U, 238U and 239Pu for Incident Neutron Energies Between 0.5 and 14.8 MeV

Fission Product Yields (FPY) have historically been one of the most observable features of the fission process. They are known to have strong variations that are dependent on the fissioning species, the excitation energy, and the angular momentum of the compound system. However, consistent and systematic studies of the variation of these FPY with energy have proved challenging. This is caused primarily by the nature of the experiments that have traditionally relied on radiochemical procedures to isolate specific fission products. Although radiochemical procedures exist that can isolate all products, each element presents specific challenges and introduces varying degrees of systematic errors that can make inter-comparison of FPY uncertain. Although of high importance in fields such as nuclear forensics and Stockpile Stewardship, accurate information about the energy dependence of neutron induced FPY are sparse, due primarily to the lack of suitable monoenergetic neutron sources. There is a clear need for improved data, and to address this issue, a collaboration was formed between Los Alamos National Laboratory (LANL), Lawrence Livermore National Laboratory (LLNL) and the Triangle Universities Nuclear Laboratory (TUNL) to measure the energy dependence of FPY for 235U, 238U and 239Pu. The measurements have been performed at TUNL, using a 10 MV Tandem Van de Graaff accelerator to produce monoenergetic neutrons at energies between 0.6 MeV to 14.8 MeV through a variety of reactions. The measurements have utilized a dual-fission chamber, with thin (10-100 μg/cm2) reference foils of similar material to a thick (100-400 mg) activation target held in the center between the chambers. This method allows for the accurate determination of the number of fissions that occurred in the thick target without requiring knowledge of the fission cross section or neutron fluence on target. Following activation, the thick target was removed from the dual-fission chamber and gamma-ray counted using shielded HPGe detectors for a period of 1-2 months to determine the yield of various fission products. To the extent possible all irradiation and counting procedures were kept the same to minimize sources of systematic errors. FPY have been determined at incident neutron energies of 0.6, 1.4, 2.4, 3.5, 4.6, 5.5, 8.9 and 14.8 MeV.

Pre-neutron-emission mass distributions for reaction 238U(n, f) up to 60 MeV

The pre-neutron-emission mass distributions for reaction 238U(n, f) up to 60 MeV are systematically studied with an empirical fission potential model. The energy dependence of the peaks and valleys of the pre-neutron-emission mass distributions is described by an exponential form based on the newly measured data. The energy dependence of evaporation neutrons before scission is also considered, which plays a crucial role in the reasonable description of the mass distributions. The measured data of the pre-neutron-emission mass distributions for reaction 238U(n, f) are reasonably well reproduced up to 60 MeV. The mass distributions at unmeasured energies are also predicted using this approach.

Pre-neutron-emission Mass Distributions for Reaction 232Th(n, f) up to 60 MeV

The pre-neutron-emission mass distributions for reaction 232Th(n, f) up to 60 MeV are systematically studied with an empirical fission potential model. The energy dependences of the peaks and valleys of the pre-neutron-emission mass distributions are described by the exponential expressions based on the newly measured data. The energy dependence of evaporation neutrons before scission, which plays a crucial role for the reasonable description of the mass distribution, is also considered. Both the double-humped and triple-humped shape of the measured pre-neutron-emission mass distributions for reaction 232Th(n, f) are reasonably well reproduced at incident energies up to 60 MeV. The mass distributions at unmeasured energies and the critical energies at which the humped pre-neutron-emission mass distributions are transformed into each other are also predicted.