Accelerator-based Neutron Source Research Articles

Evaluation of the neutron energy spectrum, angular distribution, and yield of the9Be(d,n) reaction with a thick beryllium target

A mathematical model and a computer program are developed to calculate the neutron energy spectrum, angular distribution, and integrated yield of the ${}^{9}$Be($d$,$n$) reaction on a thick beryllium target as an accelerator-based neutron source in the incident-deuteron-energy range from 0.5 to 20.0 MeV. The double-differential cross section computed by the talys code and the stopping power derived from the SRIM-2010 code are adopted in the program. Typical computational results are presented, and are compared with the previous experimental data to evaluate the computing model as well as the characteristics of the ${}^{9}$Be($d$,$n$) reaction with a thick Be target. Moreover, the developed theory and calculation methods can also provide a reasonable evaluation for calculating data of double-differential cross sections and stopping power. This model and the program can predict the above characteristics parameters of the ${}^{9}$Be($d$,$n$) reaction for a thick beryllium target as a neutron source in the incident-deuteron-energy range from 0.5 to 20.0 MeV.

Boron neutron capture therapy for brain tumors

Boron neutron capture therapy (BNCT) is a unique method that can provide the delivery of tumor cell-selective high-linear energy transfer (LET) particle radiotherapy to tumor mass and the microscopic invasion while avoiding radiation damage to the surrounding normal brain tissue. The rationale of BNCT is based on the nuclear interaction of 10 B with thermal neutrons with the release of high LET α and 7 Li particles through the boron neutron capture reaction, 10 B(n, α) 7Li. The very short path length (<9 μμm) of α-particles and 7 Li enables high-LET irradiation of tumor cells without undesirable damage to 10 B-unloaded normal cells. Eight non-randomized prospective external beam BNCT trials for glioblastoma (GBM) have been performed over the past 15 years using two available boron drugs and neutron beams at the nuclear reactor. The reported median time to progression and the median survival time (MST) are 6-12 and 12-27 mos, respectively. Optimization of dosage and boron delivery agents, the combined use of different boron agents, the combination of BNCT with other therapeutic modalities, and the development of in-hospital accelerator-based neutron sources are underway for the improvement of BNCT. In light of the existing clinical reports, there is a clear need for more evidence-based data.

Measurement of cross section of (n, γ) reaction for, iodine, sodium and vanadium in the energy range 1 keV to 4 MeV using accelerator based neutron source

The cross sections of 127I(n, γ)128I, 23Na(n, γ)24Na and 51V(n, γ)52V reactions for Iodine, sodium and vanadium were measured at continuous energy spectrum using a Microtron accelerator based neutron source. In this case, the bremsstrahlung radiation emitted by impinging 6MeV electrons on the e–γ primary target (tungsten) was allowed to fall on the γ–n secondary target (beryllium) to produce continuous neutrons. The optimization of bremsstrahlung and neutron producing targets along with their spectra were estimated using FLUKA code. The cross sections of 127I(n, γ)128I, 23Na(n, γ)24Na and 51V(n, γ)52V reactions over the neutron energy from 1keV to 4MeV have been also calculated using the TALYS-1.2 and EMPIRE nuclear model codes. The variations of the cross sections with the level densities and effective imaginary potentials were studied to obtain the best fit of the excitation function. It is observed that the experimental cross sections for iodine, sodium and vanadium are in good agreement with the TALYS-1.2 and EMPIRE codes.

Evaluation of performance of an accelerator-based BNCT facility for the treatment of different tumor targets

PurposeEncouraging Boron Neutron Capture Therapy (BNCT) clinical results obtained in recent years have stimulated intense research to develop accelerator-based neutron sources to be installed in clinical facilities. In this work an assessment of an accelerator-based BNCT facility for the treatment of different tumor targets was performed, comparing the accelerator-derived results with reported reactor-based trials under similar conditions and subjected to the same clinical protocols. Materials and methodsA set of real image studies was used to cover clinical-like cases of brain and head-and-neck tumors. In addition, two clinical cases of malignant nodular melanoma treated at the RA-6 BNCT facility in Argentina were used to thoroughly compare the clinical dosimetry with the accelerator-derived results. ResultsThe minimum weighted dose delivered to the clinical target volume was higher than 30 Gy and 14 Gy for the brain tumor and head-and-neck cases, respectively, in agreement with those achieved in clinical applications. For the melanoma cases, the minimum tumor doses were equal or higher than those achieved with the RA-6 reactor for identical field orientation and protocol. The whole-body dose assessment showed that the maximum photon-equivalent doses for those normal organs close to the beam direction were below the upper limits considered in the protocols used in the present work. ConclusionsThe obtained results indicate not only the good performance of the proposed beam shaping assembly design associated to the facility but also the potential applicability of accelerator-based BNCT in the treatment of both superficial and deep-seated tumors.

The replacement of research reactors with a compact proton linac for neutron radiography

The work presented here examines a neutron radiography facility, based on accelerator-driven compact neutron source, in order to find a suitable replacement for the facilities, which is based on research nuclear reactors. High-quality neutrons beam can be produced via the 9Be(p,n)9B reaction at proton energies of about 4MeV. Except for the Be target the materials considered were compatible with the European Union Directive on ‘Restriction of Hazardous Substances’ (RoHS) 2002/95/EC. According to this directive some common materials in radiography units such as lead and cadmium have been excluded. The suggested facility has been simulated with an extensive range of parameters, which characterizes the neutron radiography, and the results specify that an accelerator-based neutron source is an attractive alternative to research nuclear reactors.

Study of coded source neutron imaging based on a compact accelerator

Compact accelerator based neutron source has lower cost and better flexibility than nuclear reactor. Neutron imaging using such a neutron source has attracted more and more attention in recent years, in spite of its relatively low neutron fluence. In order to keep a definite neutron flux above a reasonable level on a compact accelerator based neutron imaging system, one could not set the collimation ratio to be as high as the reactor neutron source to obtain a high resolution. Coded source could increase the collimation ratio without reducing the neutron flux much. It may benefit neutron imaging system in the case of low yield neutron source. Since 2005, several laboratories in Germany and USA have carried out simulation and experiments of coded source neutron imaging. Those experiments are based on the reactor neutron sources, which have high neutron yield and low scattered neutron background. Recently, a preliminary coded source neutron imaging experiment was carried out on PKUNIFTY (Peking University Neutron Imaging Facility), which is based on a 2 MeV deuteron RFQ accelerator. It is the first time that coded source neutron imaging has been applied to an accelerator-based neutron source. Projections of coded neutron source are taken with a neutron yield of 2.6×1011 s-1. With Wiener filter deconvolution and Lucy-Richardson maximum likelihood iteration algorithm, the experimental projections are reconstructed successfully. Because the accumulated neutron fluence is low and the neutron background is high, the signal-to-noise ratio of reconstructed images is not good enough, which will be improved by reducing the neutron background.

Measurements of the neutron spectra from the 7Li(p,n) accelerator based neutron source: Position and angular dependences

Thick target 7Li(p,n) neutron spectra were measured using a 3He ion chamber in the proton energy range of 1.95 to 2.30MeV. The fast neutron spectra were collected for various distances from the lithium target as well as for various neutron emission angles. By unfolding the 3He raw data with the iterative van Cittert algorithm, the neutron fluence spectra were obtained. The 3He measured neutron spectra were compared with both analytically computed and Monte Carlo simulated spectra to account for neutron scatterings in the lithium target assembly and in the experimental area. To verify the accuracy of the neutron dose computation, the fast neutron kerma was obtained for each neutron spectrum using the fluence to kerma conversion coefficients and was compared with the measured neutron dose using tissue-equivalent proportional counters. In the position dependence investigation at the 0° emission angle, the analytically computed neutron kerma overestimates the experimental kerma by a factor of two mainly due to neutron moderation. The corresponding neutron kerma from the 3He measured spectra were in agreement with the neutron doses measured using tissue-equivalent proportional counters within 20% for lower proton energies, but the discrepancy increased to ∼50% for higher proton energies. In the angular distribution investigation, a notable discrepancy between measured and computed neutron spectra were observed due to the neutron scattering effects in the target assembly and experimental room.

Development of epithermal neutron camera based on resonance-energy-filtered imaging with GEM

An epithermal neutron camera based on energy-filtered imaging with gas electron multipliers was developed. Epithermal neutron imaging is achievable without time-of-flight detection of neutrons by using a resonance filter and a thermal neutron absorber. This technique is applicable to compact accelerator-based neutron sources. Blurring of epithermal neutron images caused by neutron scattering in the Ag resonance filter and the B4C sheet (used as a thermal neutron absorber) was investigated experimentally. The spatial resolution for epithermal neutrons with energies in the range 4.2 to 6.3 eV (corresponding to the resonance peak of 109Ag) was estimated to be 1.9±0.5 mm in a prototype detector.

Neutron transmission: A powerful technique for small accelerator-based neutron sources

Abstract The determination of total cross section of a material as a function of neutron energy by means of transmission experiments is rather easy on a pulsed neutron source. The spectrometer and associated instrumentation required may be described as relatively simple, and sound statistical data are achieved even using a small, pulsed, accelerator based neutron source. Despite its simplicity, detailed scientific and technological information can be extracted from such measurements, at the cost of fairly elaborate data analysis techniques. These features make this an attractive tool for neutron-based materials research within small research groups. Different physical properties of a material manifest over the different neutron energy ranges. At our group we have focused on the determination and analysis of the total cross section for thermal and sub-thermal neutrons, which is very sensitive to the geometric arrangement and movement of the atoms, over distances ranging from the’ first-neighbour scale’ up to the microstructural level or’ grain scale’.

Neutronic studies on a pulsed thermal neutron source based on the Be(p,n) reaction by using a compact proton accelerator

A neutron source based on a compact proton accelerator can be used for neutron scattering and imaging experiments. To promote the neutron utilization in various fields of sciences and technologies, it is necessary to develop a high-performance compact accelerator based neutron source for efficient neutron beam experiments. For this purpose, we have performed design studies for an optimal moderator system for thermal neutrons aiming at the imaging. Therefore, we have carried out the neutronic studies by using the MCNPX code. The Be(p,n) reaction was assumed (proton energy 11 MeV), which gives a neutron yield of 2.15x1013 n/sec at 1 mA. Firstly, we studied neutronic characteristics of the intensity, the brightness and the pulse width to choose a moderator material for imaging between light water and heavy water. Secondly, we optimized moderator size and reflector thickness. It was indicated that a thermal neutron flux at 10 m from the moderator was 9.43x105 n/cm2/sec (L/D is 70.7) in case of a slab type. Finally, we investigated the effect of a target cooling system, a moderator vessel and a gap between the Be target and the moderator on a neutron flux. In such a practical model, the thermal neutron flux reduced to about 76% of a simple model.

Act for Establishment of BNCT with Research and Development for Accelerator Based Neutron Source

Act for Establishment of BNCT with Research and Development for Accelerator Based Neutron Source

Gallium-Cooled Target for Compact Accelerator-Based Neutron Sources

This paper discusses the motivation for gallium cooling of targets of compact accelerator-based neutron sources (CANS); summarizes features of the low-power alternative, i.e., water cooling, and the limitations of boiling water heat transfer; lists the properties of liquid gallium; and cites its low hazards potential. I set out working equations for heat transport and fluid flow in liquid gallium and present a concept for a gallium-cooled system, including a scoping calculation of temperatures and pressure drops, and present conclusions and a recommendation.

An overview of design for CSNS/RCS and beam transport

The China Spallation Neutron Source(CSNS) is the first accelerator-based pulsed neutron source in China.Its accelerators are made up of an 80 MeV H~- linac,a Rapid Cycling Synchrotron(RCS) and two beam transport lines.RCS accumulates and accelerates protons to the design energy of 1.6 GeV,and ext...

High-power liquid-lithium target prototype for accelerator-based boron neutron capture therapy

A prototype of a compact Liquid-Lithium Target (LiLiT), which will possibly constitute an accelerator-based intense neutron source for Boron Neutron Capture Therapy (BNCT) in hospitals, was built. The LiLiT setup is presently being commissioned at Soreq Nuclear Research Center (SNRC). The liquid-lithium target will produce neutrons through the (7)Li(p,n)(7)Be reaction and it will overcome the major problem of removing the thermal power generated using a high-intensity proton beam (>10 kW), necessary for sufficient neutron flux. In off-line circulation tests, the liquid-lithium loop generated a stable lithium jet at high velocity, on a concave supporting wall; the concept will first be tested using a high-power electron beam impinging on the lithium jet. High intensity proton beam irradiation (1.91-2.5 MeV, 2-4 mA) will take place at Soreq Applied Research Accelerator Facility (SARAF) superconducting linear accelerator currently in construction at SNRC. Radiological risks due to the (7)Be produced in the reaction were studied and will be handled through a proper design, including a cold trap and appropriate shielding. A moderator/reflector assembly is planned according to a Monte Carlo simulation, to create a neutron spectrum and intensity maximally effective to the treatment and to reduce prompt gamma radiation dose risks.

Accelerator-based neutron tomography cooperating with X-ray radiography

Abstract Neutron resonance absorption spectroscopy (N-RAS) using a pulsed neutron source can be applied to time-of-flight (TOF) radiography, and the obtained parameters from the peak shape analysis can be reconstructed as the tomograms of nuclide distributions using computed tomography (CT). The problem is that the available spatial resolution is not sufficient for radiography imaging. In this study, we combined neutron and X-ray radiographies to improve the quantitative reconstruction of the neutron tomogram. The accelerator-based neutron source emits X-rays (or gamma-rays) at the same time the neutron pulse is emitted. We utilized the X-ray beam from the neutron source to obtain X-ray radiogram on the same beam line with neutron radiography and then reconstructed the neutron tomogram quantitatively with the help of a detailed sample internal structure obtained from the X-ray radiogram. We calculated the nuclide number density distribution tomogram using a statistical reconstruction procedure, which was easy to include in the structure model during the reconstruction. The obtained result of nuclide number density distribution showed good coincidence with the original object number density.

Thermo-structural analysis of target assembly and back plate in the IFMIF/EVEDA lithium test loop

IFMIF is an accelerator-based intense neutron source for testing candidate materials for fusion reactors. The Engineering Validation and Engineering Design Activities (EVEDA) of IFMIF are in progress under the Broader Approach Agreement. In the EVEDA Li test loop, two types of target assemblies, “an integrated type target assembly without a back plate”, made of SUS316L, and “a target assembly with replaceable bayonet back plate”, made of F82H steel, will be evaluated. For these target assemblies, thermal stresses were evaluated using the ABAQUS code. As the permitted stress, the values of yield strengths at 300°C were used. In the case of the integrated target assembly, the maximum thermal stress was below the allowed stress (164MPa). However, in the case of the target assembly with the bayonet back plate, thermal insulation around the back plate should be necessary to reduce the thermal stress below the allowed value (455MPa).

Accelerators for Neutron Generation and Their Applications

This article briefly reviews the most important points of neutron generation using accelerators in the small and medium energy ranges. The interest in neutron research is still growing, due to improvement of detectors and analyzing tools. Smaller accelerator-based neutron sources can serve for proof-of-principle experiments and for data generation. In developing and emerging economies they may replace underutilized research reactors, if there is a need for neutron research. The complementarity of neutron research to synchrotron and X-ray analysis will always keep some focus on effective and lower cost options for neutron production.

Gallium-cooled target for compact accelerator-based neutron sources

This paper discusses the motivation for gallium-cooling of targets of compact accelerator-based neutron sources (CANS); summarizes features of the low-power alternative, i.e., water cooling, and the limitations of boiling water heat transfer; lists the properties of liquid gallium; and cites its low hazards potential. I set out working equations for heat transport and fluid flow in liquid gallium and present a concept for a gallium-cooled system, including a scoping calculation of temperatures and pressure drops, and present conclusions and a recommendation.

ChemInform Abstract: Pulsed Neutrons in Chemistry

Neutrons, like X-rays, have been recognised for many years as a very powerful weapon in the chemist's armoury. However, the way in which the neutron interacts with atoms-largely with the nucleus-not only gives it some major advantages over X-rays in structural studies over a wide range of length scales, but also make it an extremely versatile probe of the dynamic of molecules. The recent advent of accelerator-based pulsed neutron sources has greatly widened the range of chemical problems that can be tackled by using neutrons, in areas including the structures and dynamics of molecular crystals, adsorption at interfaces, solution structures, and the organisation of complex macromolecular and biomolecular assemblies.

Simulation of e– γ– n targets by FLUKA and measurement of neutron flux at various angles for accelerator based neutron source

A 6 MeV Race track Microtron (an electron accelerator) based pulsed neutron source has been designed specifically for the elemental analysis of short lived activation products where the low neutron flux requirement is desirable. The bremsstrahlung radiation emitted by impinging 6 MeV electron on the e– γ primary target, was made to fall on the γ– n secondary target to produce neutrons. The optimisation of bremsstrahlung and neutron producing target along with their spectra were estimated using FLUKA code. The measurement of neutron flux was carried out by activation of vanadium and the measured fluxes were 1.1878 × 10 5, 0.9403 × 10 5, 0.7428 × 10 5, 0.6274 × 10 5, 0.5659 × 10 5, 0.5210 × 10 5 n/cm 2/s at 0°, 30°, 60°, 90°, 115°, 140° respectively. The results indicate that the neutron flux was found to be decreased as increase in the angle and in good agreement with the FLUKA simulation.