Compact Accelerator-based Neutron Sources Research Articles

New technologies for beam spectrometry, quality assurance, real-time monitoring and microdosimetry in BNCT

Boron neutron capture therapy (BNCT) is a next-generation radiotherapy that combines neutron beams with boron compounds that selectively accumulate in cancer cells. Because this therapy requires neutrons for irradiation, compact accelerator-based neutron source devices that can be installed in hospitals are being developed around the world. Clinical trials of several devices have been conducted in Japan, China, and South Korea. The most advanced device was approved by the Japanese regulatory authorities in 2020. As a result, BNCT with the device is being implemented as an insured therapy for recurrent head and neck cancer at two hospitals in Japan. Thus, the development of accelerator-based neutron generators is proceeding in the field of BNCT. However, much remains to be done to establish this therapy as a common cancer treatment and to make it available worldwide. Dosimetry methods in BNCT are one of the issues. In the treatment, the dose given to a patient by neutron irradiation has to be estimated accurately. However, it is difficult to measure neutrons accurately and in real time. Currently, the neutron dose delivered to patients during treatment is not measured. Instead, the current of the charged particles that irradiate the neutron target material is measured to indirectly evaluate the neutron fluence and dose. In addition, accurate dose estimation based on reactions with neutrons and various elements in a human body uses the Monte Carlo method, which is computationally time-consuming. To address these dosimetry issues, several neutron fluence and dose measurement methods are being developed. This review briefly describes the current dosimetry methods and then presents several methods under development that allow real-time neutron measurements applicable to BNCT.

Development of a high current electron beam facility for compact accelerator neutron source target thermal tests

Target thermal capabilities are one of the major key points for CANS (Compact Accelerator-based Neutron Source) developments. Indeed, high energy (few MeV) and high average current (few tens of mA) proton or deuteron beams are required to produce high thermal neutron flux of 101³ n.cm⁻2.s⁻1 or greater. The targets must therefore absorb and dissipate a high thermal power. In order to make progress on their designs without deuteron or proton beams, we developed a compact electron beamline based on an Electron Cyclotron Resonance (ECR) source that permits testing of targets under relevant thermal conditions at power densities up 3 kW. cm⁻2.

Current development status of accelerator-based neutron source for boron neutron capture therapy

Recently, progress in technology for accelerator-based neutron sources has increased attention regarding boron neutron capture therapy (BNCT). BNCT is a type of radiotherapy that combines neutrons and boron drugs and is expected to be used in the treatment of refractory and recurrent cancers. Owing to the need for high-intensity neutrons in treatment, compact accelerator-based neutron sources applicable to BNCT are being developed worldwide. These current projects utilize cyclotrons, linear accelerators, and electrostatic accelerators as accelerators for BNCT devices. Beryllium and lithium are the main target materials for neutron generation. The accelerators for BNCT device are required to accelerate charged particles with an average current ranging from a few milliamperes to a few tens of milliamperes in order to generate neutrons of sufficient intensity for the treatment. Moreover, the target systems require technologies and mechanisms that can withstand the large heat load produced by high-power beam irradiation and prevent blistering. This review outlines and explains the accelerator neutron sources for BNCT and the requirements for the components of each device, such as the accelerator, target material, and beam shaping assembly. In addition, various development projects for accelerator-based BNCT devices worldwide are introduced.

Boron neutron capture therapy in the new age of accelerator-based neutron production and preliminary progress in Canada

Each year more than 3000 Canadians are diagnosed with brain cancers like glioblastoma multiforme or recurrent head and neck cancers, which are difficult to treat with conventional radiotherapy techniques. One of the most clinically promising treatments for these cancers is boron neutron capture therapy (BNCT). This procedure involves selectively introducing a boron delivery agent into tumor cells and irradiating them with a neutron beam, which kills the cancer cells due to the high-linear energy transfer radiation produced by the 10B(n,α)7Li capture reaction. The theory of BNCT has been around for a long time since 1936, but has historically been limited by poor boron delivery agents and non-optimal neutron source facilities. Although significant improvements have been made in both of these domains, it is mainly the advancements of accelerator-based neutron sources that have led to the expansion of over 20 new BNCT facilities worldwide in the past decade. Additionally in this work, particle and heavy ion transport code system simulations, in collaboration with the University of Tsukuba, were performed to examine the effectiveness of the Ibaraki BNCT beam shaping assembly to moderate a neutron beam suitable for BNCT at the proposed prototype Canadian compact accelerator-based neutron source (CANS) site, which uses a similar but slightly higher energy 10 MeV proton accelerator with a 1 mA average current. The advancements of CANSs in recent decades have enabled significant improvements in BNCT technologies, allowing it to become a more viable clinical treatment option.

TOUCANS: A versatile Monte Carlo neutron transport code based on GEANT4

This paper reports the development of TOUCANS, a new Monte Carlo neutron transport code fully written using the GEANT4 toolkit. It aims at modeling complex systems easily and rapidly, thanks to a simple key–value input file. While its main focus is the transport of low energy neutrons – below 20 MeV – using evaluated cross-section libraries, it also takes advantage of the state-of-the-art capabilities offered by GEANT4 regarding the modeled cross-sections for practically all particles at all energies. Hence it gives access to non-specialists to a wide variety of applications involving different particles, such as the simulation of compact accelerator based neutron sources (CANS) which initially motivated its development. It leverages on recent implementations performed within GEANT4 to provide both shielding calculation capabilities (using Adaptive Multilevel Splitting, which is a full y automated variance reduction technique) and criticality calculation capabilities (to estimate the keff of a multiplicative system). It also benefits from a tight coupling with CADMesh to readily import CAD models, with NCrystal to extend the support of thermal neutron transport to crystals, with FIFRELIN to increase compound nucleus de-excitation accuracy, and with FUNZ to provide to the user parametric simulation capabilities (such as multi-objective algorithms and calculation of Pareto sets). Thanks to recent improvements of the neutron physics within the GEANT4 Neutron-HP package, the TOUCANS code can be considered on-par with industrial neutron transport codes such as Tripoli-4® or MCNP in term of neutron physics accuracy. Its sources should be released soon amongst GEANT4 advanced examples.

High-frequency structure design and RF stability analysis of a 4-vane radio frequency quadrupole with pi-mode stabilizer loops

Compact accelerator-based neutron source facilities are garnering attention and play an important and expanding role in material and engineering sciences, as well as in neutron science education and training. Neutrons are produced by bombarding a low-energy proton beam onto a beryllium or lithium target. In such an accelerator-based neutron source, a radio frequency quadrupole (RFQ) is usually utilized to accelerate a high-intensity proton beam to a few MeV. This study mainly covers the high-frequency structure design optimizations of a 4-vane RFQ with pi-mode stabilizer loops (PISLs) and its RF stability analysis. A 176 MHz RFQ accelerator is designed to operate at a 10% duty factor and could accelerate an 80 mA proton beam from 65 keV to 2.5 MeV within a length of 5.3 m. The adoption of PISLs ensures high RF stability, eases the operation of the accelerator, and implies less stringent alignment and machining tolerances.

A prototype compact accelerator-based neutron source (CANS) for Canada

Canada’s access to neutron beams for neutron scattering was significantly curtailed in 2018 with the closure of the National Research Universal (NRU) reactor in Chalk River, Ontario, Canada. New sources are needed for the long-term; otherwise, access will only become harder as the global supply shrinks. Compact Accelerator-based Neutron Sources (CANS) offer the possibility of an intense source of neutrons with a capital cost significantly lower than spallation sources. In this paper, we propose a CANS for Canada. The proposal is staged with the first stage offering a medium neutron flux, linear accelerator-based approach for neutron scattering that is also coupled with a boron neutron capture therapy (BNCT) station and a positron emission tomography (PET) isotope production station. The first stage will serve as a prototype for a second stage: a higher brightness, higher cost facility that could be viewed as a national centre for neutron applications.

Status of development and planning activities on CANS in Korea

This report reviews the overall status of the development and planning activities of compact accelerator-based neutron sources in Korea. For the last decade, the demand for the technology development and application of CANS has significantly increased, and becomes widely accepted by the science, engineering and industry sectors. Since the first technical workshop focused on CANS under the support of the Korea Nuclear Society in fall 2016, there have been numerous efforts to launch projects by several groups. Although unsuccessful, two CANS projects were newly launched in 2020. One is the 30-MeV cyclotron-based neutron source for industrial neutron imaging at the Korea Atomic Energy Research Institute (KAERI), and the other is the BNCT technology development at the Korea Institute of Radiological & Medical Sciences. A project proposal for an expansion of the proton LINAC facility at KAERI to 200 MeV for semiconductor irradiation testing through the produced neutron field is now almost complete and will be submitted to the government funding agency for review. The CANS project for BNCT based on the proton LINAC developed by the Dawonsys consortium is briefly described. The new neutron source based on electron LINAC is prepared by the Pohang Light Source laboratory, and the initial consideration and application targets are also described. A new strategic plan for national R&D on radiation technology and the enforcement of its infrastructure is still under way, and a more systematic approach to the development and application of neutron sources will be implemented through the strategic planning.

The Measurement of the Neutron Yield of the 7Li(p,n)7Be Reaction in Lithium Targets

Simple SummaryA compact neutron source has been proposed and created at the Budker Institute of Nuclear Physics in Novosibirsk, Russia. The source comprises an original design tandem accelerator, solid lithium target, and a neutron beam shaping assembly. The neutron source is capable of producing the high neutron flux for boron neutron capture therapy (BNCT). Currently, the BNCT technique has entered into clinical practice in the world: two clinics began treating patients, and four more BNCT clinics are ready to start operating. The neutron source proposed at the Budker Institute served as a prototype for a facility created for a clinic in Xiamen (China). It is planned to equip the National Medical Research Center of Oncology (Moscow, Russia) and National Oncological Hadron Therapy Center (Pavia, Italy) with the same neutron sources. Due to the impending use of an accelerator neutron source for treating patients, the validation of the neutron yield of the 7Li(p,n)7Be reaction in lithium metal targets is required. The theoretical neutron yield has not been evaluated experimentally so far.A compact accelerator-based neutron source has been proposed and created at the Budker Institute of Nuclear Physics in Novosibirsk, Russia. An original design tandem accelerator is used to provide a proton beam. The neutron flux is generated as a result of the 7Li(p,n)7Be threshold reaction using the solid lithium target. A beam shaping assembly is applied to convert this flux into a beam of epithermal neutrons with characteristics suitable for BNCT. The BNCT technique is being tested in in vitro and in vivo studies, and dosimetry methods are being developed. Currently, the BNCT technique has entered into clinical practice in the world: after successful clinical trials, two clinics in Japan began treating patients, and four more BNCT clinics are ready to start operating. The neutron source proposed at the Budker Institute of Nuclear Physics served as a prototype for a facility created for a clinic in Xiamen (China). It is planned to equip the National Medical Research Center of Oncology (Moscow, Russia) and National Oncological Hadron Therapy Center (Pavia, Italy) with the same neutron sources. Due to the impending use of an accelerator neutron source for treating patients, the validation of the neutron yield of the 7Li(p,n)7Be reaction in lithium metal targets is required. The theoretical neutron yield has not been evaluated experimentally so far.

Monte Carlo simulation of proton- and neutron-induced radiation damage in a tantalum target irradiated by 70 MeV protons

Beams of free neutrons are an important probe to analyze the structure and dynamics of condensed matter and are produced at neutron research reactors, neutron spallation sources or compact accelerator-based neutron sources (CANS). An efficient construction of CANS with a maximized neutron yield and brilliance requires reliable knowledge of the consequences of radiation-induced material damage, the predominating bottleneck of a target’s lifetime. In the framework of the Jülich High-Brilliance neutron Source project, the impact of proton- and neutron-induced material damage of a tantalum target was investigated. The Monte Carlo codes FLUKA and SRIM were utilized to extract the number of displacements per atom resulting from atomic rearrangements. The simulations performed distinctly identify the rear of the neutron target as the most vulnerable area, with the protons as main damage contributors. The minor contribution of neutrons is a material-specific phenomenon due to their high mean free path length in tantalum. Numerical results of the simulations served to calculate average and peak damage rates {R}_{mathrm{d}} (dpa/s), both in turn scaled to annual displacement doses for continuous operation in a full power year (dpa/fpy). Supplemented by the literature, a minimum target lifetime tau _{min } of 2.6 years (33 Ah) is concluded.

Neutron Source Based on Vacuum Insulated Tandem Accelerator and Lithium Target.

Simple SummaryA compact neutron source has been proposed and created at the Budker Institute of Nuclear Physics in Novosibirsk, Russia. The source comprises an original design tandem accelerator, solid lithium target, and a neutron beam shaping assembly. The neutron source is capable of producing the high neutron flux in various energy ranges, from thermal to fast, for boron neutron capture therapy, as well as for other applications. A lot of scientific research has been carried out at the facility, including the study of blistering and its effect on the neutron yield. The Boron Neutron Capture Therapy (BNCT) technique is being tested in in vitro and in vivo studies, and the methods of dosimetry are being developed. It is planned to certify the neutron source next year and conduct clinical trials on it. The neutron source served as a prototype for a facility created for a clinic in Xiamen (China).A compact accelerator-based neutron source has been proposed and created at the Budker Institute of Nuclear Physics in Novosibirsk, Russia. An original design tandem accelerator is used to provide a proton beam. The proton beam energy can be varied within a range of 0.6–2.3 MeV, keeping a high-energy stability of 0.1%. The beam current can also be varied in a wide range (from 0.3 mA to 10 mA) with high current stability (0.4%). In the device, neutron flux is generated as a result of the 7Li(p,n)7Be threshold reaction. A beam-shaping assembly is applied to convert this flux into a beam of epithermal neutrons with characteristics suitable for BNCT. A lot of scientific research has been carried out at the facility, including the study of blistering and its effect on the neutron yield. The BNCT technique is being tested in in vitro and in vivo studies, and the methods of dosimetry are being developed. It is planned to certify the neutron source next year and conduct clinical trials on it. The neutron source served as a prototype for a facility created for a clinic in Xiamen (China).

Depositing a Titanium Coating on the Lithium Neutron Production Target by Magnetron Sputtering Technology.

Lithium (Li) is one of the commonly used target materials for compact accelerator-based neutron source (CANS) to generate neutrons by 7Li(p, n)7 Be reaction. To avoid neutron yield decline caused by lithium target reacting with the air, a titanium (Ti) coating was deposited on the lithium target by magnetron sputtering technology. The color change processes of coated and bare lithium samples in the air were observed and compared to infer the chemical state of lithium qualitatively. The surface topography, thickness, and element distribution of the coating were characterized by SEM, EDS and XPS. The compositions of samples were inferred by their XRD patterns. It was found that a Ti coating with a thickness of about 200 nanometers could effectively isolate lithium from air and stabilize its chemical state in the atmosphere for at least nine hours. The Monte Carlo simulations were performed to estimate the effects of the Ti coating on the incident protons and the neutron yield. It turned out that these effects could be ignored. This research indicates that depositing a thin, titanium coating on the lithium target is feasible and effective to keep it from compounds’ formation when it is exposed to the air in a short period. Such a target can be installed and replaced on an accelerator beam line in the air directly.

Development of compact neutron sources

Many small research reactors, neutron sources built in the 1950s and 1960s are being shut down. The activities that these supported have therefore ended, which motivates their replacements with new facilities. Compact accelerator-based neutron sources under development are able to take up many of those activities. This paper paints the background for these developments, summarizes the replacement technologies, relates recent work that supports them, and alludes to some of the new activities that they enable.

Neutrons production on the IPHI accelerator for the validation of the design of the compact neutron source SONATE

We aim at building a compact accelerator-based neutron source (CANS) which would provide a thermal neutron flux on the order of 4x1012 n.s-1.cm-2.sr-1. Such a brilliance would put compact neutron sources on par with existing medium flux neutron research reactors for neutron scattering experiments. We performed the first neutron production tests on the IPHI proton accelerator at Saclay at a proton energy of 3 MeV. The thermal neutron flux were measured using gold foil activation and 3He detectors. The measured flux were compared with GEANT4 Monte Carlo simulations (10.4) in which the whole experimental setup was modelled. There is a good agreement between the experimental measurements and the Monte-Carlo simulations. The available modelling tools will allow us to optimize the whole Target Moderator Reflector assembly together with the neutron scattering spectrometer geometries for the design of the neutron scattering facility SONATE.

The SONATE project, a French CANS for Materials Sciences Research

We describe the Compact Accelerator-based Neutron Source SONATE which we are aiming for to replace the closed Orphée reactor at Saclay, France. The SONATE source would serve an instrumental suite of about 10 instruments. The instruments would be split into low resolution instruments and higher resolution instruments. Our reference design is based on a proton accelerator operating at an energy in the range 20-30 MeV. The accelerator would serve 2 target stations. The first one operating at 20Hz with 2ms long pulses serving low resolution instruments (SANS, reflectivity, imaging, spin-echo) and the second one operating at 100Hz, 200μs long pulses serving higher resolution instruments (powder diffraction, Direct Time-of-flight spectroscopy, Indirect geometry spectroscopy). The 2 operation modes would be interlaced. The peak current on the target is aimed at 100 mA with an average power on the target on the order of 50-80 kW. Numerical Monte-Carlo simulations show that we may expect instrument performances equivalent to the current instruments around Orphée or ISIS.

UCANS – 8, Paris, July 8-11th 2019 Eighth International Meeting of the Union of Compact Accelerator-based Neutron Sources

UCANS – 8, Paris, July 8-11th 2019 Eighth International Meeting of the Union of Compact Accelerator-based Neutron Sources

Development of a regenerated Beryllium target and a thermal test facility for Compact Accelerator-based Neutron Sources

Recently, the possibility to use compact accelerators coupled to high current ion sources for the production of intense low energy proton or deuteron beams has motivated many research laboratories to develop accelerator based neutrons sources for several purposes, including Neutron Capture Therapy (NCT). The NCT needs a high flux, about 10 9 n.cm-2.s-1, of thermal neutrons (E<10 keV) at the tumour site. Up to now, the NCT required neutron flux was mainly delivered by nuclear reactors. However, the production of such neutron flux is now possible using proton or deuteron beams on specific targets able to stand a high pow er (~15- 30 kW) on a small area (~10 cm2). This specific target design, materials and supports, has to cope with extreme physical constraints . The LPSC team has conceived an original solution formed by a thin (8 μm) rotating beryllium target depos ited on a graphite wheel and coupled with a beryllium sputtering device for periodic 9Be layer restoration. By means of 9Be (d,n) 10B nuclear reaction, this target irradiated by a 10- -20 mA deuteron beam (1.45 MeV) should produce the required neutron flux. In order to validate the target design of the neutron flux production and the beryllium target thermal capabilities, we built a 30 cm diameter rotating Beryllium target prototype and a compact electron beam line able to deliver a power density of 3kW/cm2.

CYTOPATHIC EFFECTS OF ACCELERATOR-BASED BORON NEUTRON CAPTURE THERAPY ON HUMAN GLIOBLASTOMA CELLS

Boron neutron capture therapy (BNCT) is a targeted therapy based on a selective damage to cancer cells due to the interaction between boron-10 isotope and neutron. Reactor-based BNCT has been found to be effective in the treatment of high-grade gliomas. It is believed that compact accelerator-based neutron sources will ensure widespread adoption of the technique in clinical practice. New accelerator-based neutron sources are being actively developed all over the world. At the Institute of Nuclear Physics (Russia), the accelerator-based neutron source was developed for pre-clinical studies of BNCT.Purpose: to determine the cytopathic effects of accelerator-based BNCT on the human U87-glioblastoma cell line and to select a concentration of boron drugs that do not have a toxic effect on the cells before irradiation in vitro.Material and Methods. To assess the cytopathic effects (MTT test and colony-forming assay) of various concentrations of boron-containing drugs, U87 cells were incubated with boronophenylalanine (BPA) and sodium borocaptate (BSH) for 1, 2 and 10 days. The effect of BNCT on the U87 cell line was determined using colony-forming assay.Results. The MTT test showed a decrease in cell survival at a boron-10 isotope concentration of 160 μg/ml after 48 hours and 640 μg/ml after 24 hours of incubation for BPA. The cytopathic effects for sodium BSH appeared at a boron concentration of 80 µg / ml after 48 hours of incubation, and survival fraction of cells was reduced to 89 % compared to the control. According to the colonyforming assay, the cytotoxic effects of BSH and BPA at a boron concentration of 40 µg/ml in the medium were 79.6 and 84 %, respectively. The proportions of surviving cells were 18 ± 2 % and 13 ± 2 % after epithermal neutron irradiation in the presence of boronophenylalanine and in the presence of sodium borocaptate, respectively. Cell death without boron drugs occurred due to the neutron elastic scattering, nuclear reactions of thermal neutron capture by hydrogen and nitrogen, and accompanying gamma radiation.Conclusion. The study clearly showed a decrease in the proportion of surviving U87 cells after accelerator-based BNCT in the presence of 10B-enriched BSH and BPA.

The development of compact neutron sources

Many small research reactors used as neutron sources are being shut down. To replace them, new facilities are being developed. In particular, compact accelerator-based neutron sources can take up many of the activities previously supported by reactor-based facilities.

Development of compact accelerator neutron source

There is a worldwide growing interest for small-scale and reduced-cost neutron sources not based on nuclear fission. High-intensity proton or deuteron beams impinging on light materials could be used to produce such neutron sources with intensities or brightness comparable to nuclear reactor for dedicated experiments. To develop such technologies several key technological issues have to be addressed. Among them the neutron production and the maximization of the neutron extraction and transport to the instrument is a key parameter for the design of high-brightness sources adapted for the required application. This issue have to be addressed with validated and predictive Monte-Carlo simulations. In this paper we present preliminary results on the use of Geant4 in the context of Compact Accelerator based Neutron Source (CANS) developments.