Accelerator-driven Neutron Source Research Articles

Operation of a 250μm-thick SiC detector with DT neutrons at high temperatures

The Silicon Carbide detector (SiC) is an object of research as an alternative to diamond detectors for fast neutron detection and spectrometry where harsh environments are an issue, like in Tokamaks. Since future breeding blankets mock-ups will feature temperatures up to 550 °C, diamond detectors were characterized in the past, finding limitations in their functionality at high temperatures. This paper expands on the previous work by proving the detection of fast neutrons with good detection parameters of a 250 μm-thick 4 H-SiC detector prototype at temperatures up to 250 °C, highlighting the detector's excellent resilience to temperature. The experiment is conducted with instrumentation similar to the one used in the past with diamond detectors, using as source of irradiation the Frascati Neutron Generator (FNG) in ENEA, which is accelerator driven neutron source based on deuterium-tritium (DT) fusion reaction.

Design and beam dynamics simulation of an 8 MeV compact accelerator-driven neutron source

A compact accelerator-driven neutron source is proposed at Sino-French Institute of Nuclear Engineering and Technology, Sun Yat-Sen University, called Sun Yat-Sen University Proton Accelerator Facility (SYSU-PAFA). The proton accelerator is composed of a proton electron cyclotron resonance source, a four-vane radio frequency quadrupole (RFQ), and an alternative phase focusing drift tube linac (APF-DTL). It can accelerate 10 mA proton beam to 8 MeV. Due to the high current, beam matching is particularly important. In order to achieve beam matching between various components, beam transport sections are needed. The beam transport line is divided into three segments. The Low Energy Beam Transport (LEBT) ensures that the beam parameters are matched before entering the RFQ. The Medium Energy Beam Transport (MEBT) segment efficiently transfers the beam between the RFQ and DTL. The High Energy Beam Transport (HEBT) focuses on transporting the beam to the targets. The design goal of beam transport line is as short as possible while ensuring high efficiency of beam transportation. SYSU-PAFA has an overall transmission efficiency of 99%, with optimal transverse matching conditions between beam transport and RFQ or DTL accelerators. The efficient use of solenoids and magnets allows for a compact transmission section, resulting in a total length of 13.6 meters, shorter than most accelerators at the same beam energy. This paper will provide the detailed beam dynamics of the compact accelerator.

Calibration of the 2-Phase Bubble Tracking Model for Liquid Mercury Target Simulation with Machine Learning Surrogate Models

The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory is one of the most powerful accelerator-driven neutron sources in the world. The intense protons strike on SNS’s mercury target to provide bright neutron beams, which also leads to severe fluid-structure interactions inside the target. Prediction of resultant loading on the target is difficult particularly when helium gas is injected into mercury to reduce the loading and mitigate the pitting damage on vessel walls. A 2-phase material model that incorporates the Rayleigh-Plesset (R-P) model is expected to address this multi-physics problem. However, several uncertain parameters in the R-P model require intensive simulations to determine their optimal values. With the help of machine learning and the measured target strain, we have studied the major uncertain parameters in this R-P model and developed a framework to identify optimal parameters that significantly reduce the discrepancy between simulations and experimental strains. The preliminary results show the possibility of using this mercury/helium mixture and surrogate models to predict a better match of target strain response when the helium gas is injected.

Study and design of the coupled cavity with ladder RFQ and IH DTL structure for transportable neutron source

A transportable accelerator-driven neutron source is under development in Xi'an Jiaotong University (X-TANS), aiming at realizing various outdoor applications, such as on-site degradation diagnosis of concrete infrastructures and analysis of raw materials. To downsize the accelerator cavity for X-TANS, we coupled the Ladder RFQ and an Interdigital H-type Drift tube linac (IH-DTL) into a single cavity to combine the strength of the RFQ's efficient bunching efficiency and DTL's high accelerating gradient and to distantly reduce the weight and size of the linac. To achieve electromagnetic resonance between two structures and a high coupling factor, a novel coupled structure was adopted by adjusting the last supporting plate at the exit of RFQ. The mode separation between 0-mode and π-mode was expanded to 7.96 MHz. Consequently, the 15 mA proton beam can be accelerated to 2.5 MeV with a length of 1.73 m and the effective transmission of above 90%. The dissipated cavity power was 96.87 kW with an operation frequency of 200 MHz and a duty factor of 3%. The design concept of the coupled structure and the results of the beam dynamics design, electromagnetic simulation and multi-physics will be comprehensively presented in this paper.

A compact accelerator driven neutron source at the Applied Nuclear Physics Laboratory, Lund University

The Applied Nuclear Physics Group at Lund University has constructed a CANS (Compact Accelerator-driven Neutron Source). The CANS is based around a 3 MV, single-ended, Pelletron accelerator, which is used to impinge a 2.8 MeV deuterium beam into a beryllium target. The anticipated neutron production will be on the order of 1010 n/s in 4π sr, with future upgrades expected to increase neutron production to 1011 n/s. Neutron energy will be up to 9 MeV with peak emission at ∼5 MeV. Shielding and moderation will be provided by a large water tank surrounding the target, with exit ports to allow moderated neutrons to be directed to experiments. The thermal-neutron flux at the exit of the extraction ports is anticipated to be up to 106 n/cm2/s. The CANS will be used to forward the activities of the group in the area of neutron-activation analysis, in addition to a broader range of neutron related applications.

Simulations on the thermal and mechanical performance of the rotating target system of accelerator-driven neutron source for Boron Neutron Capture Therapy(BNCT)

The development of an accelerator-based BNCT facility, X-BNCT, at Xi’an Jiaotong University was introduced. The 30 mA protons were accelerated to 2.8 MeV by a linear RFQ accelerator, then the lithium target was bombarded to produce neutrons required for treatment through 7Li(p, n)7Be reaction, and a large amount of energy was deposited on the target. To remove the heat on the target, the design and analysis of the rotating target system was discussed in this paper. The channels with a small size in the target flap were studied and an interlayer was added to avoid the problem of hydrogen embrittlement. The heat transfer simulation was carried out with Gaussian beam or uniform beam in the rotating target system by the CFD method. The maximum temperatures of lithium were lower than the melting point, indicating the advancement of the rotating target structure in cooling. And it was concluded that the uniform scheme should be considered even for the rotating target system. Finally, the stress analysis of each component of the rotating target in the process of rotation was simulated, and the results showed that the design met the material requirements.

Pseudo-random time modulation technique for neutron diffraction instruments on compact accelerator-driven neutron sources

Time modulation methods are routinely used on neutron scattering time-of-flight instruments, which exploit the time structure of neutron pulses for energy determination. In the past, complex time modulation methods were proposed, either to maximize the neutron flux which can be used, or to increase the energy resolution of the measurements. In this article, we explore the possibilities offered by such methods and in particular random modulation using statistical choppers to improve the performances of the DIoGENE scattering instrument installed around the IPHI-neutron CANS source at Saclay. We conclude that when the source is operated in continuous mode, the implementation of a statistical chopper is very efficient to perform either metallurgical studies such as strain scanning or phase transition studies. Random modulation techniques may be easily and efficiently implemented because the high capacity of modern computers enables high-speed data processing from large surface pixelated detectors.

Experimental validation of cold neutron source performance with mesitylene moderator installed at RANS

The RANS (RIKEN Accelerator driven Neutron Source), one of compact accelerator neutron sources (CANS), tries to expand its performance by installing a cold neutron which may provide new opportunities in many applications. RANS is a low power CANS with a proton beam of 7 MeV and 100 µA at maximum. A moderator system was constructed based on results of optimization design study with mesitylene. Recently, we have done performance tests aiming at showing characteristics as cold neutron source. Cryogenic mesitylene moderator was installed on a plug with a new target moderator reflector configuration of RANS. Experiment using a gas electron multiplier (GEM) detector was carried out to measure neutron spectra of the cold moderator. This paper describes performance of the cold moderator in terms of 1) Cold neutron gain of optimization design with respect to a polyethylene moderator, 2) Temperature dependency of cold neutron spectrum flux regarding scattering kernel (SK), and 3) comparison between experiment and calculation. A note is given for comparison between calculations with different SKs available. Also, two-dimensional imaging of cold and thermal neutron spectrum flux on the viewed surface is shown with a pinhole slit configuration.

Simulation and design of an IPHI-based neutron source, first steps toward SONATE

Facilities providing bright thermal neutron beams are of primary importance for various research topics. At CEA-Saclay, a compact accelerator driven neutron source, SONATE, is investigated in taking advantage of the IPHI accelerator able to deliver a 3 MeV proton beam with an intensity up to 100 mA. To optimize the performances of such a neutron source, it is necessary to maximize the thermal neutron flux while minimizing the contribution of other particles. In this work, optimization has been performed using the Monte Carlo code TOUCANS, a neutron transport code based on Geant4 developed at CEA-Saclay. This latter has been coupled to PROMETHEE, a software allowing multi-objective optimization for many simulation software. In this work the Kriging metamodel based approach is used to optimize a neutron beamdump. To take into account the various constraints, noise on the detection system and radiation protection issues, several beamdump configurations are evaluated. The variation of beamdump parameters makes it possible to identify the set of optimal solutions, the Pareto front. It allows to focus on the set of best choices and to choose wisely the best configurations. After describing the validation of TOUCANS on experimental tests performed from 2016 to 2022, the capability of such an approach will be presented.

Development of a Pelletron-based compact neutron source

The Applied Nuclear Physics Group at Lund University is constructing a prototype CANS (Compact Accelerator-driven Neutron Source). The CANS is based around a 3 MV, single-ended, Pelletron accelerator, which is used to impinge a 2.8 MeV deuterium beam into a beryllium target. The anticipated neutron production will be on the order of 1010 n/s in 4π sr. A further upgrade to the ion source of the Pelletron is expected to increase neutron production to 1011 n/s. Neutron energies will be up to 9 MeV with peak emission at ∼5 MeV. Shielding and moderation will be provided by a large water tank surrounding the target, with three exit ports to allow neutrons of different energies to be directed to experiments. The design is supported by simulation results which predict fast-neutron fluxes of 9×104 to 5×106 n/cm2/s, and thermal-neutron fluxes of 1×104 to 5×104 n/cm2/s to be readily obtainable with a 10 µA deuteron beam.

The HERMES reflectometer at the JULIC Neutron Platform

HERMES is a time-of-flight reflectometer that operated at the Orphée reactor until 2019. In 2022, HERMES was installed at the JULIC (Jülich Light Ion Cyclotron) Neutron Platform as part of a collaboration between the Laboratoire Léon Brillouin and the Jülich Centre for Neutron Science. The main goal of the current setup is to probe the viability of neutron instrumentation at a High Current Compact Accelerator-driven Neutron Source (HiCANS). As the flux at the JULIC neutron platform is several orders of magnitude lower than the original Orphée flux or the expected flux for a HiCANS, our current objective is to perform reflectivity experiments with supermirrors as a proof of concept. Nevertheless, Monte-Carlo simulations showed that the HERMES instrument’s performance at a HiCANS such as HBS or ICONE could match that of reflectometry instruments operating at research reactors or spallation sources. An experiment with a supermirror carried out in December 2022 allowed us to preliminary prove the feasibility of this kind of experiments at an accelerator-driven neutron source.

Thermal moderator-reflector design of the 24 Hz target station for the High Brilliance Neutron Source

The High Brilliance Neutron Source (HBS) project develops a high current accelerator driven neutron source (HiCANS), aiming to substitute existing neutron research reactors, that reach the end of life. This study focuses on the thermal neutron moderator design for a low frequency, long pulse target station of HBS. We investigate the neutronic characteristics of the D2O+H2O mixture moderator material using the Monte Carlo particle transport code PHITS. Our findings show that, compared to D2O with lower neutron absorption, confinement of H2O is the dominant factor in achieving a high neutron flux within the moderator and thus a high neutron brightness. We find that surrounding the central thermal water moderator with a D2O+H2O mixture can achieve a better balance between confinement and absorption. However, because of multiple angles of reflecting neutron, this design will also increase the divergence of the neutron beam.

The High Brilliance Neutron Source Target Stations

High Current Accelerator driven Neutron Sources (HiCANS) are a cost-efficient alternative for future large scale neutron facilities. They excel in transforming neutrons released by the primary nuclear reaction into a spectral range usable for applications. In particular, the cost of a target station represents only a minor fraction of the overall construction cost due to the lower energy of the primary neutrons, which requires less shielding. They can be designed to provide optimized pulse and spectral properties for applications in neutron scattering, analytics and imaging experiments. For the High Brilliance neutron Source (HBS) project at Forschungszentrum Jülich, we have developed a modular design that meets the radiation protection requirements while providing sufficient space in its core to adapt the target-moderator-reflector assembly to the different applications. In the following, we present the basic target station design which will be used at HBS for three different realizations with their own instrument suite. All relevant components have been designed, built and tested at the JULIC Neutron Platform which has produced neutrons since December 12th 2022. The simulated performance of a target station shows that the brightnesses of the moderators are in the range of modern research reactors and sub-MW power spallation sources.

Towards a conceptual design for the moderators of ARGITU: A preliminary neutronics study

This work reports on preliminary calculations of potential low-dimensional moderators for the high-current accelerator-driven neutron source (HiCANS) ARGITU. Simulations start with the selection of materials, depending on the neutron energy range to be used for each instrument. Results evaluate the performance of water for thermal moderators to deliver neutrons for thermal instruments, whereas para-H2 and solid methane have been analyzed to deliver cold neutrons. Additionally, alternative concepts like using hybrid moderators (water/liquid methane) or reduced-size cold moderators (reduced-size para-H2) have been scrutinized for their use in bispectral instruments that require a wide range of intermediate neutron energies. The dimensions of the moderators have been refined to improve the neutron yield for the neutron wavelength range selected in each case. After that, a space-efficient layout has been proposed to implement four moderators next to the Be target, linked to a preliminary suite of instruments that these moderators would serve. Although the eventual selection shall consider both the final instrument suite and the phase space volume required for such neutron instruments (that defines their neutron optics features), the results presented here represent a qualitative step towards the conceptual development of the ARGITU neutron source.

A Design for the High Yield Photoneutron Source Target Station.

Low energy accelerator driven neutron sources are promising candidates to obtain a neutron yield as high as 1014 n/s, which is required for a variety of applications, such as boron neutron capture therapy, neutron imaging, and neutron scattering. The methods to generate neutrons can be divided into two categories: hadron-based and photon-based methods. In order to better understand which kind of source would be the better choice for delivering a brilliant neutron beam robustly, in this paper, the underlying principles of neutron production, as well as the simulation results of neutron yield, target heat dissipation, thermal stress, and reaction byproducts concentration of these two types of neutron sources, will be elaborated on. A preliminary photoneutron target station design based on a 50 MeV/50 kW electron linear accelerator, including the optimized neutron yield, thermal hydraulic analysis, and shielding calculation, is presented as well to demonstrate the method to deliver brilliant thermal neutron beam of 1.03 × 1010 cm-2 s-1 sr-1.

An optimized microchannel Ta target for high-current accelerator-driven neutron sources

An optimized neutron producing tantalum target with an optimized internal microchannel cooling was developed for a 70 MeV proton beam with a peak current of 100 mA, a duty cycle of 1.43% and an average power of 100 kW on a target surface area of 100 cm 2. In this work a target with microchannel cooling structure is described which matches with the proton’s energy to minimize hydrogen implantation and to produce energy deposition with optimum homogeneity inside the target to minimize the thermal stresses. For the purpose of getting an optimal target design, the investigations of energy deposition, proton fluence, the spatial distribution of (p, n) reactions and the spatial distribution of stopping protons of the target with different microchannel geometries were performed with the particle transport code FLUKA. The resulting design produces a homogeneous proton fluence and energy deposition without hot spots. Furthermore, only 4.4% of the impinging protons accumulate in the metal target, which significantly decreases the risk of hydrogen embrittlement and blistering.

The prototyping of a high-resolution neutron activation analysis system – based on a Pelletron accelerator and fast pneumatic sample-transport

A new neutron activation analysis system is currently being designed at Lund University. The design incorporates a compact accelerator driven neutron source, based on a 3 MV Pelletron accelerator and a pneumatic sample conveyor to transport samples from the neutron source to a measurement station consisting of an array of high-purity Ge γ-ray detectors. A prototype for this new station is currently in operation, with a Genie 16 SODERN neutron generator used in place of the compact accelerator driven neutron source. Preliminary results from the prototype system are presented, alongside qualitative analysis supported by simulations performed in FISPACT-II. The system has been tested with the measurements of Al and In foils, using a PLA sample holder. The results demonstrate that activation products with half-lives of as little as 2 s can be measured. γ-rays from the 2 s isomer, 116n In are clearly observed providing the irradiation and measurement times are appropriately chosen.

Position sensitive detector applications in nuclear physics and nuclear industry

The Birmingham Cyclotron and associated facilities have an active programme of detector use and irradiation, ranging from nuclear physics and related applications to positron imaging and radiation damage studies. In 2022 a new high flux neutron source (HF-ADNeF) will be installed and commissioned, extending the present charged-particle studies to neutron physics and neutron damage. An overview of the Birmingham Cyclotron Facility is given along with details of the accelerator-driven neutron source. Several examples around detector testing, nuclear physics and positron imaging are outlined.

Evaluation of heat removal performance of a sealed Li target for an accelerator-driven neutron source of Boron Neutron Capture Therapy at Nagoya University

An accelerator-driven neutron source has been developed in Nagoya University for boron neutron capture therapy using a new concept of thick lithium (Li) target in which protons are stopped in a Li layer. A sealed Li target developed consists of a Li sheet placed on a copper (Cu) base plate equipped with water-cooled channels and a titanium (Ti) foil seal to cover Li surface. The proton beam injected into the target is produced through the proton–Dynamitron accelerator (IBA) with a maximum energy of 2.8 MeV and a current of 15 mA. The results of our previous study confirmed that the target was not damaged when irradiated with an acceleration energy of 1.8 MeV and a current of 0.5 mA (heat input of 4.6 MW/m2). To keep the soundness of the target up to 6–7 MW/m2, it is considered to be essential to improve the bonding between the Ti foil and Li interface, which will contribute the heat removal. It was suggested from our previous experiences that the bonding property may be improved by forming a Cu–Li alloy at the Ti–Li interface. In this paper, we evaluate the heat removal performance of a sealed Li target with Cu–Li alloy formation to improve the target durability. The sealed Li target was produced using a “Cu-coated pure Ti foil”, in which Cu was deposited on the surface of a Ti foil with a thickness of 0.2μm. The use of Cu-coated pure Ti foil actively forms Cu–Li alloys at the Ti–Li interface. For comparison, sealed Li targets were produced with pure Ti foil, and irradiation tests were conducted on each target. The heat removal performance was evaluated by electron beam irradiation using the active cooling teststand 2 (ACT2), a high heat flux test facility, and proton beam irradiation using the Dynamitron accelerator. We obtain a result that the Cu-coated pure Ti foil-sealed Li target has a heat removal capacity of 11 MW/m2, about five times higher than that of the pure Ti foil-sealed Li target. This confirmed that the Cu–Li alloy contributed to the improvement of the heat removal performance. For the proton beam irradiation test, a Cu-coated pure Ti foil target was produced and irradiated for 26 h at an acceleration energy of 1.8 MeV and an average current of 3.5 mA, where no neutrons were generated. The tests confirmed that the Cu-coated pure Ti foil target could withstand 26 h of irradiation at a heat input of 9.0 MW/m2. About anticipated degradation of the heat removal performance due to stopping the protons in the Li layer, no change was observed during this long irradiation test, in which 2.15 × 1024 protons were injected into the Li layer. Although further long-time irradiation test will be needed in the future, at present we have confirmed that there is no problem with stopping protons in the Li layer.

Design of a compact RFQ linac for the transportable neutron source

A transportable accelerator-driven neutron source based on the Radio Frequency Quadrupole (RFQ) linac is developing at Xi’an Jiaotong University (X-TANS). It will be a promising tool for the non-destructive inspection of immovable objects. The neutron yield above 10 11n/s can be obtained via 7Li(p,n)7Be reaction with a proton beam energy of 2.5 MeV. To exactly guarantee the transportability of the neutron source, it is essential to achieve the light, compact and low-power consumption of RFQ linac. The operation frequency of 325 MHz is chosen considering the balance among cavity size, cavity consumption, and electrode aperture. In addition, compact dynamics scheme is adopted to achieve short RFQ by sacrificing a beam bunching efficiency. The beam dynamics design and optimization have been performed based on Parmteqm. Beam tracking results show that RFQ can accelerate the proton beam to 2.5 MeV with an electrode length of 2.6 m and an effective transmission efficiency of 93.8%. To enlarge the redundancy of the input beam mismatch and make the beam match easier from LEBT to RFQ, the electrode aperture is designed to shrink gradually in the RFQ entrance. In addition, we also performed the RF electromagnetic design and optimization based on the full-length 3D RFQ model. Multiphysics simulations of the cavity in different working conditions are investigated at last.