Neutron Generator Target Research Articles

Non-destructive measurement of the beryllium thickness of the iBNCT neutron-generation target using negative muons

Accelerator-based boron neutron capture therapy (BNCT) has recently been studied by several researchers. In BNCT, a neutron-generation target is an important component because an intense neutron flux of more than 109n/cm2/s is required to complete medical treatments within an acceptable treatment time. In the Ibaraki BNCT (iBNCT) project, a proton linear accelerator (linac) consisting of a 3-MeV radio-frequency quadrupole and an 8-MeV drift-tube linac based on J-PARC linac techniques was used. As for the neutron-generation target, beryllium was adopted with an incident proton energy of 8 MeV. The target has a three-layer structure fabricated using hot-isostatic pressing (HIP). The first layer consists of 0.5 mm-thick beryllium, which is slightly shorter than the 8-MeV proton range in beryllium for neutron generation. The second is a 0.5 mm-thick palladium, which was selected owing to its durability against blistering, and the third is a 10 mm-thick copper for heat removal purposes with cooling water circulation. The thickness of the beryllium is very important because a shortage of thickness reduces the yield of neutrons, while an excess of thickness results in damage by stopped protons owing to a blistering effect. Despite its importance, this thickness has not yet been confirmed because it is not realistic to measure it destructively in terms of the construction cost of the iBNCT target; thus, a non-destructive measurement is desirable. This paper describes a method for measuring the thickness of the beryllium layer of a mockup of an iBNCT neutron target, which was constructed in the same way as the actual iBNCT, in a non-destructive manner using negative muon X-rays. The experiment was performed in the J-PARC MLF muon facility, and the obtained thickness was 0.48 ± 0.02 mm, which corresponds to the designed value of 0.50 ± 0.05 mm.

Research of Interaction Processes of Fast and Thermal Neutrons with Solution of Organic Dye Methyl Orange

The emergence of powerful sources of ionizing radiation, the needs of nuclear energy, technology and medicine, as well as the need to develop reliable methods of protection against the harmful effects of penetrating radiation stimulated the development of such branches of science as radiation chemistry, radiation biology, radiation medicine. When an organic dye solution is exposed to ionizing radiation, it irreversibly changes color. As a result, the absorbed dose can be determined. The processes of interaction of neutron fluxes with an aqueous solution of an organic dye methyl orange (МО) – C14H14N3О3SNa, containing and not containing 4% boric acid, have been investigated. The work was carried out on a LINAC LUE-300 at NSC KIPT. A set of tungsten plates was used as a neutron-generating target. The electron energy was 15 MeV, the average current was 20 μA. The samples were located behind the lead shield and without it, with and without a moderator. Using the GEANT4 toolkit code for this experiment, neutron fluxes and their energy spectra were calculated at the location of experimental samples without a moderator and with a moderator of different thickness (1-5 cm). An analysis of the experimental results showed that when objects without lead shielding and without a moderator are irradiated, the dye molecules are completely destroyed. In the presence of lead protection, 10% destruction of the dye molecules was observed. When a five-centimeter polyethylene moderator was installed behind the lead shield, the destruction of dye molecules without boric acid on thermal neutrons was practically not observed. When the fluxes of thermal and epithermal neutrons interacted with a dye solution containing 4% boric acid, 30% destruction of dye molecules was observed due to the exothermic reaction 10B (n, α). The research has shown that solutions of organic dyes are a good material for creating detectors for recording fluxes of thermal and epithermal neutrons. Such detectors can be used for radioecological monitoring of the environment, in nuclear power engineering and nuclear medicine, and in the field of neutron capture therapy research in particular.

High heat removal technique for a lithium neutron generation target used for an accelerator-driven BNCT system

Accelerator-driven neutron sources have been developed worldwide for boron neutron capture therapy (BNCT) instead of nuclear reactors. Nagoya University is currently developing a compact DC accelerator driven BNCT system using a sealed lithium (Li) target. The target receives a high heat load by a proton beam, and the heat then requires efficient removal. This study developed a high-efficiency heat removal technique that uses V-shaped staggered ribs on the heat removal side of the flow channels. We performed experiments using an electron beam to confirm the technique performance. The results showed double the heat removal performance compared to the smooth surface channel. The value expected to sufficiently remove 6.6 MW/m2 of heat load provided by the proton beam at the Nagoya University neutron source for BNCT.

On the Issue of Stability and Safety of the Superbooster, a Pulsed Neutron Source

A high-intensity pulsed neutron source can be constructed according to the principle of a superbooster, i.e., a neutron multiplying system of the neutron-generating target of the proton accelerator with proton energy of about 1 GeV in the subcritical reactivity modulation system. Usually, superboosters are considered to be safe and reliable nuclear facilities. However, as indicated in this paper, a powerful superbooster may prove to be less stable in operation than a pulsed reactor. Therefore, the problems of its safety call for close study.

Experimental determination of the induced activity in activation detectors of a complex geometric shape

The paper presents the results of experimental determination of the induced activity in copper-/aluminum-based activation detectors when irradiated with neutrons with energies of about 14 MeV. The activation detectors were square-shaped metal plates with a thickness from 1.0 to 1.5 mm and a side size about 5.0 cm. These dimensions significantly exceed those of the detectors that are used in the research of high-intensity neutron fluxes. The detectors described in this work can be used for studying low-intensity neutron fluxes (with a flux density of up to 106n/cm2∙s). It is shown that, when working with such detectors, it is possible to apply the usual methods for calculating the induced activity in thin activation detectors, with corrections that take into account the emerging features of the ‘neutron source - activation detector’ and ‘activation detector - secondary radiation detector’ geometries. The effects of absorption of primary and secondary radiation by the detector substance are also revealed.The Geant4 tools were used for calculating the geometric factors and theoretical induced activity. The study confirms the applicability of such activation detectors for solving the problem of determining the yield of neutrons with energies of about 14 MeV from a neutron generator target. The results of the experiments coincide, within the margin of error, with the results of simulations performed using the Geant4 tools.

Upgrade Plan of the KOMAC Proton Linac for the Atmospheric Radiation Test on Semiconductor Devices

At the Korea Multi-purpose Accelerator Complex (KOMAC), a 100-MeV high-power proton linac has been used for proton-beam irradiation services for various applications and research programs, including material science, bio-medical science, semiconductor applications, as well as nuclear physics and basic science, since commissioning of the machine in 2013. Recently, demands for fast neutrons from users in the semiconductor industries are increasing to test the semiconductor device SER (soft error rate) or SEE (single event effect). At present, we provide pilot services to users with pulsed white-spectrum neutrons (max. neutron energy ∼100 MeV) generated at the beam dump, which is made of copper. However, the neutron energy should be increased at least to 200 MeV to meet international standards such as ISO26262 or JEDEC89A. For the upgrade of the linac energy to 200 MeV, we conducted a preliminary design study, including superconducting radio-frequency (SRF) based linac structure, a neutron generation target and a neutron utilization facility. The upgrade plan for the KOMAC linac, along with the preliminary results of the design study on the superconducting linac and neutron generation facility, will be given in this paper.

Calculation of neutron spectra produced in neutron generator target: Code testing

DT-neutron spectra calculated using the SRIANG code was benchmarked against the results obtained by widely used Monte Carlo codes: PROFIL, SHORIN, TARGET, ENEA-JSI, MCUNED, DDT and NEUSDESC. The comparison of the spectra obtained by different codes confirmed the correctness of SRIANG calculations. The cross-checking of the compared spectra revealed some systematic features and possible errors of analysed codes.

An evaluation of activation and radiation damage effects for the European Spallation Source Target

ABSTRACT The details concerning the generation and accumulation of radionuclides produced by spallation reactions within the neutron generation target to be installed at the European Spallation Source are described. The resulting radiation damage for the target tungsten blocks constituents as well as the target encasing is evaluated and explicit results are given for the effects of knock-on atoms as well as those resulting from the accumulation of light and volatile hydrogen and helium isotopes resulting from spallation reactions. Their effects on the mechanical properties are discussed on the light of available experimental data and, on this basis, an estimation of the target lifetime is given.

14 MeV calibration of JET neutron detectors—phase 1: calibration and characterization of the neutron source

In view of the planned DT operations at JET, a calibration of the JET neutron monitors at 14 MeV neutron energy is needed using a 14 MeV neutron generator deployed inside the vacuum vessel by the JET remote handling system. The target accuracy of this calibration is ±10% as also required by ITER, where a precise neutron yield measurement is important, e.g. for tritium accountancy. To achieve this accuracy, the 14 MeV neutron generator selected as the calibration source has been fully characterised and calibrated prior to the in-vessel calibration of the JET monitors. This paper describes the measurements performed using different types of neutron detectors, spectrometers, calibrated long counters and activation foils which allowed us to obtain the neutron emission rate and the anisotropy of the neutron generator, i.e. the neutron flux and energy spectrum dependence on emission angle, and to derive the absolute emission rate in 4π sr. The use of high resolution diamond spectrometers made it possible to resolve the complex features of the neutron energy spectra resulting from the mixed D/T beam ions reacting with the D/T nuclei present in the neutron generator target. As the neutron generator is not a stable neutron source, several monitoring detectors were attached to it by means of an ad hoc mechanical structure to continuously monitor the neutron emission rate during the in-vessel calibration. These monitoring detectors, two diamond diodes and activation foils, have been calibrated in terms of neutrons/counts within ±5% total uncertainty. A neutron source routine has been developed, able to produce the neutron spectra resulting from all possible reactions occurring with the D/T ions in the beam impinging on the Ti D/T target. The neutron energy spectra calculated by combining the source routine with a MCNP model of the neutron generator have been validated by the measurements. These numerical tools will be key in analysing the results from the in-vessel calibration and to derive the response of the JET neutron detectors to DT plasma neutrons starting from the response to the generator neutrons, and taking into account all the calibration circumstances.

Design specification for the European Spallation Source neutron generating target element

The paper addresses some of the most relevant issues concerning the thermal hydraulics and radiation damage of the neutron generation target to be built at the European Spallation Source as recently approved after a critical design review. The target unit consists of a set of Tungsten blocks placed inside a wheel of 2.5m diameter which rotates at some 0.5Hz in order to distribute the heat generated from incoming protons which reach the target in the radial direction. The spallation material elements are composed of an array of Tungsten pieces which rest on a rotating steel support (the cassette) and are distributed in a cross-flow configuration. The thermal, mechanical and radiation effects resulting from the impact of a 2GeV proton pulse are analysed in detail as well as an evaluation of the inventory of spallation products. The current design is found to conform to specifications and found to be robust enough to deal with several accident scenarios.

The spatial dose rate and energy characterization of a P 385 D-D Neutron Generator using a nested neutron spectrometer and a tissue equivalent proportional counter

A nested neutron spectrometer (NNS) and a tissue equivalent proportional counter (TEPC) were used to measure the spatial dose equivalent and energy neutron fluence distribution of a P 385 D-D Thermo Fisher Scientific Neutron Generator located in the mixed field dosimetry facility at the University of Ontario Institute of Technology. The P 385 Neutron Generator uses the D-D nuclear reaction to generate neutrons with an expected average energy of 2.5 MeV. The NNS uses a He-3 proportional counter to measure the neutron capture count rate as a function of nested cylindrical moderator thickness. Using the NNS and associated unfolding software, the energy neutron fluence distribution at various locations from the P 385 neutron generator were determined along with other radiation protection quantities of interest. Measurements of the dose equivalent rate were also conducted at the same locations using a 5-inch spherical TEPC and compared to the NNS results. The TEPC was further used to measure the dose equivalent as a function of radial distance from the neutron generator target and also for different P 385 operating conditions.

A study of gamma-ray and neutron radiation in the interaction of a 2 MeV proton beam with various materials

Epithermal neutron source based on a tandem accelerator with vacuum insulation and lithium target has been proposed, developed and operated in Budker Institute of Nuclear Physics. The source is regarded as a prototype of a future compact device suitable for carrying out BNCT in oncology centers. In this work the measurements of gamma-ray and neutron radiation are presented for the interaction of a 2MeV proton beam with various materials (Li, C, F, Al, V, Ti, Cu, Mo, stainless steel, and Ta). The obtained results enabled the optimization of the neutron-generating target and the high energy beam transportation path.

Sputtering of Neutron-Generator Targets

Sputtering of Neutron-Generator Targets

Neutron target research and development for BNCT: direct observation of proton induced blistering using light-polarization and reflectivity changes

The blistering problem due to high power proton irradiation is a crucial issue for any neutron generation target. When a proton beam irradiates a metal, the protons stopped inside capture free electrons in the metal to form a hydrogen gas. Eventually, blisters and/or flakes appear on the surface as the pressure of the hydrogen gas rises enough to cause ruptures. An experimental setup for observation of the metal surface that would have high sensitivity and high spatial resolution was proposed, designed and implemented. The system observes light-polarization and reflectivity and has successfully detected blistering surface dynamics.

On the possibility of increasing lifetime of a neutron generator target through laser-induced nanorelief generation at the film – substrate interface

The evolution of an ensemble of point defects (vacancies and interstitials) produced by irradiating a tritium-saturated titanium target (sorbent film on substrate) with deuterium is considered. It is shown that when the concentration of defects exceeds a certain critical value, the film undergoes transition into a quasi-periodic bent state with simultaneous clustering of defect aggregates at the relief extrema, spontaneously created at the film – substrate interface and at the film free surface. The aggregation of vacancies leads to the formation of pores. The subsequent deadherence or rapture of the film in the regions of large pores at the film – substrate interface leads to irreversible degradation of the target. We discuss the possibility of suppressing this effect by nanostructuring a laser-induced nanorelief at the substrate surface before the sorbent film deposition. Different types of such a relief are experimentally demonstrated.

Development of liquid-lithium film jet-flow for the target of 7Li(p,n)7Be reactions for BNCT

A feasibility study on liquid lithium target in the form of a flowing film was performed to evaluate its potential use as a neutron generation target of 7Li(p,n)7Be reaction in BNCT. The target is a windowless-type flowing film on a concave wall. Its configuration was adapted for a proton beam which is 30mm in diameter and with energy and current of up to 3MeV and 20mA, respectively. The flowing film of liquid lithium was 0.6mm in thickness, 50mm in width and 50mm in length. The shapes of the nozzle and concave back wall, which create a stable flowing film jet, were decided based on water experiments. A lithium hydrodynamic experiment was performed to observe the stability of liquid lithium flow behavior. The flowing film of liquid lithium was found to be feasible at temperatures below the liquid lithium boiling saturation of 342°C at the surface pressure of 1×10−3Pa. Using a proto-type liquid lithium-circulating loop for BNCT, the stability of the film flow was confirmed for velocities up to 30m/s at 220°C and 250°C in vacuum at a pressure lower than 10−3 Pa. It is expected that for practical use, a flowing liquid lithium target of a windowless type can solve the problem of radiation damage and target cooling.

Protective overcoatings on thin-film titanium targets for neutron generators

We have developed a thin-film coating for neutron generator targets that can be loaded with deuterium or tritium at low temperatures (100°C), and at gas/Ti ratios greater than 1.7. The key to this improvement is the addition of a thin palladium overcoat at the end of the titanium deposition. This overcoat prevents the oxidation of the titanium film, yet still allows loading to take place at low temperatures. A palladium overcoat of just 50–100Å is sufficient to protect the titanium, while presenting a minimal energy loss to incident ions. We have just begun producing targets using this method, and see the possibility of substantial improvement in neutron generator efficiencies.

Gamma dose measurements and spectroscopy analysis for spallation products in JSNS mercury circulation system

Mercury used as a spallation neutron target at JSNS (J-PARC Spallation Neutron Source)� is highly activated by proton beam operation. In order to evaluate the feasibility of hands-on maintenance after nominal beam operation with 1 MW in the where a mercury circulation system was installed, gamma dose measurements and gamma spectroscopy analysis were carried out after low power operation during the commissioning period. By analyzing the data, it was found that radioactive spallation products adhered to the inner surface of piping wall of the circulation systemand those significantly raised the dose rates in the cell. In order to discuss about measures for future hot-cell entry, the gamma dose rates after the nominal operation were evaluated based on the measured data obtained in this work. 1) is a multipurpose research facility with muon and neutron generation target. The operation of the J-PARC spallation neutron source (JSNS) in MLF started in May 2008, and an effort is being made now to increase the proton beam intensity up to 1 MW together with many kinds of researches on materials and life science. 2. Mercury Target and Circulation System. In JSNS, mercury was selected as a material of neutron generation target in consideration of the neutron generation efficiency and the cooling. A drawing of the mercury target vessel and a mercury circulation system on a trolley is shown in Fig 1. Neutrons are generated by bombarding mercury in the target vessel with a proton beam, and the mercury heated by incident protons and accompanying nuclear reactions is circulated in the loop between the target vessel and the mercury circulation system for cooling. The target vessel is inserted to the core of the neutron station consisted of moderators, reflector, neutron beam shutters and shields. For the maintenance, the trolley is moved to the hot cell prepared for handling of activated devices. Mercury in the circulation system is highly activated due to radioactive isotopes produced via spallation reactions. Therefore most of the maintenance works for the mercury target and the circulation system were designed to be done by using remote handling system equipped in the cell. However a few works, which is expected to happen once or twice during the facility lifetime of about 30 years, will need to be done by hands-on; this will necessitate entrance of workers to the cell. Mercury in the circulation system can be transferred to the drain tanks under the circulation system on the bottom of the

New technical solution for using the time-of-flight technique to measure neutron spectra

New technical solution is proposed for using the time-of-flight technique to measure neutron spectra on VITA-facility. During 200 ns the energy of protons increases from 1.865 up to 1.915 MeV by supplying the square pulse of 50 kV on the neutron-generating target, which is isolated from facility body. During these 200 ns the generation of neutrons is performed. The spectrum can be obtained measuring the time of flight by a remote neutron detector.

Effect of the residual gas on the lithium layer of a neutron-generating target

An epithermal neutron source based on a tandem accelerator is being constructed at the Budker Institute of Nuclear Physics for use in neutron capture therapy at a cancer clinic. A lithium neutron-generating target obtained by deposition of lithium onto the target substrate is one of the key elements of the facility. The effect of residual gas on the lithium layer composition has been investigated using a secondary-ion mass spectrometer.