Neutron Production Target Research Articles

Optimization Calculations for Neutron Production Target at Variable Energy Cyclotron Centre, Kolkata with 50 MeV Electron Linear Accelerator

Optimization Calculations for Neutron Production Target at Variable Energy Cyclotron Centre, Kolkata with 50 MeV Electron Linear Accelerator

Effects of Monovacancy and Divacancies on Hydrogen Solubility, Trapping and Diffusion Behaviors in fcc-Pd by First Principles.

The hydrogen blistering phenomenon is one of the key issues for the target station of the accelerator-based neutron source. In the present study, the effect of monovacancies and divacancies defects on the solution, clustering and diffusion behaviors of H impurity in fcc-Pd were studied through first principles calculations. Our calculations prove that vacancies behave as an effective sink for H impurities. We found that, although the H-trap efficiency of the larger vacancy defect was reduced, its H-trap ability strengthened. There is a short-ranged area around the vacancy defects in which H impurities tend to diffuse to vacancy defects, gather and form hydrogen bubbles. Therefore, the characteristic of large vacancy defects formation in materials should be considered when screening anti-blistering materials for neutron-producing targets or when designing radiation resistant composite materials.

Fast neutrons at LNL Legnaro

In this contribution we describe NEPIR, the fast-neutron irradiation facility under construction at the 70 MeV cyclotron SPES facility of the INFN laboratory of Legnaro (LNL). NEPIR will be constructed in stages, according to the available funds. The initial configuration, based on a thick Be neutron production target, will be operational in 2022; it will be used for shielding studies against fast neutrons for space applications and to investigate neutron-induced Single Event Effects (SEE) in microelectronic devices and systems. In its final configuration NEPIR will have two target systems: one will deliver a Quasi Mono-energetic Neutron (QMN) beam, of general interest, with an adjustable energy peak in the 20–70 MeV range; the second target will deliver a specialized continuous energy neutron beam for studying the effects of fast neutrons produced in cosmic ray air-showers in electronic devices and systems. We review the use of NEPIR to characterize the sensitivity of electronics, describe the neutron production targets and the facility layout. In closing we describe ways, presently under investigation, to use the 15 MV XTU Tandem of LNL to produce nearly monochromatic fast neutrons that would complement the QMN system by allowing one to probe for SEE below 20 MeV.

Status of low-energy accelerator-based BNCT worldwide and in Argentina

Existing and active low-energy Accelerator-Based BNCT programs worldwide will be reviewed and compared. In particular, the program in Argentina will be discussed which consists of the development of an Electro-Static-Quadrupole (ESQ) Accelerator-Based treatment facility. The facility is conceived to operate with the deuteron-induced reactions 9Be(d,n)10B and 13C(d,n)14N at 1.45 MeV deuteron energy, as neutron sources. Neutron production target development status is specified. The present status of the construction of the new accelerator development laboratory and future BNCT centre is shown.

Neutron-Physical Calculation of Targets for a Subcritical Assembly Controlled by a Proton Accelerator

A neutron-physical calculation is performed for neutron-producing lead, tungsten, and natural uranium targets for a subcritical assembly controlled by a proton accelerator at 0.6, 1, and 2.5 GeV. At these high proton energies, the interaction of protons with target atoms is accompanied by a splitting reaction. In terms of the neutron yield per primary proton, this reaction is more advantageous than the fission reaction. The calculation results are used to estimate the neutron-flux densities in a subcritical multiplying assembly.

Monte Carlo study toward the development of a radiation field to simulate secondary neutrons produced in carbon-ion radiotherapy

This study investigates the feasibility of developing a neutron field to simulate secondary neutrons produced in carbon ion radiotherapy (CIRT) with a passive beam using a monoenergetic carbon beam, a neutron-producing target, and neutron-shaping filters via Monte Carlo calculations. The general-purpose particle and heavy-ion transport code system (PHITS) was employed throughout this investigation. After characterizing the targeted neutron field, a neutron-producing target and neutron-shaping filters were selected. A dataset of the neutron energy spectra was compiled using the selected target and filters. Then, we determined the best combination of target and filters and the best angle to the beam axis to reproduce the neutron energy spectrum in the targeted neutron field. The root mean square percentage error and the mean absolute percentage error were used as figures of merit to quantify the agreement with neutron energy spectra in the CIRT treatment room. We found that a monoenergetic carbon beam can sufficiently reproduce the neutron energy spectra in a CIRT treatment room with a passive beam using an iron neutron-producing target doubling as a sharping filter and/or a polyethylene filter and selecting the angle to the beam axis. Therefore, the development of a neutron field to simulate secondary neutrons produced in CIRT with a passive beam is feasible in a non-clinical facility. This simulated neutron field can be useful for not only biological experiments but also physics experiments such as the development and calibration of neutron dosimeters.

Monte Carlo simulations and n-p differential scattering data measured with Proton Recoil Telescopes

The neutron-induced fission cross section of 235U, a standard at thermal energy and between 0.15 MeV and 200 MeV, plays a crucial role in nuclear technology applications. The long-standing need of improving cross section data above 20 MeV and the lack of experimental data above 200 MeV motivated a new experimental campaign at the n_TOF facility at CERN. The measurement has been performed in 2018 at the experimental area 1 (EAR1), located at 185 m from the neutron-producing target (the experiment is presented by A. Manna et al. in a contribution to this conference). The 235U(n,f) cross section from 20 MeV up to about 1 GeV has been measured relative to the 1H(n,n)1H reaction, which is considered the primary reference in this energy region. The neutron flux impinging on the 235U sample (a key quantity for determining the fission events) has been obtained by detecting recoil protons originating from n-p scattering in a C2H4 sample. Two Proton Recoil Telescopes (PRT), consisting of several layers of solid-state detectors and fast plastic scintillators, have been located at proton scattering angles of 25.07° and 20.32°, out of the neutron beam. The PRTs exploit the ΔE-E technique for particle identification, a basic requirement for the rejection of charged particles from neutron-induced reactions in carbon. Extensive Monte Carlo simulations were performed to characterize proton transport through the different slabs of silicon and scintillation detectors, to optimize the experimental set-up and to deduce the efficiency of the whole PRT detector. In this work we compare measured data collected with the PRTs with a full Monte Carlo simulation based on the Geant-4 toolkit.

CoolGAL: a Galinstan bathed Be fast neutron production target at the NEPIR facility

In this contribution, we present the CoolGAL fast neutron production target system, to be used in the initial phase of the NEPIR irradiation beamline at the SPES facility, that will be operational in 2022. Initially, NEPIR will be used for shielding studies against fast neutrons for space applications and to investigate neutron-induced single event effects in microelectronic devices and systems. In CoolGAL, the neutron production component, a thick Be cylinder, is immersed in a static bath of Galinstan, a liquid alloy of Ga, In and Sn, contained by an outer water cooled copper cladding. MCNPX calculations indicate that, by using a 1 μA current of 70 MeV protons, it can produce a fast neutron energy spectrum that is somewhat flat the 30-65 MeV energy range and with a sharp cut-off at the beam energy. At the standard test point, located 2.6 m downstream from the source, the beam spot diameter, defined by the peculiar collimation scheme of the initial phase of NEPIR, is 10 cm and the integral fast neutron flux is Φn(1< En<65 MeV) ~ 3×106 n cm-2s-1. Using proton beams with two different energies, one can calculate, by subtraction, the effects due to the neutrons in the energy interval defined by the two cut-off values. Preliminary results of ANSYS calculations, for a 1 μA proton current of 70 MeV protons (70 W), show a limited regime temperature (28 °C) of the Be component, capable of ensuring the exceptional safety level required for the operation at SPES. The thermal reliability of CoolGAL is very promising for future developments that require higher proton currents.

Design of the Neutron Imaging Differential Pumping Line at LLNL*This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

The neutron imaging system at LLNL is a radiographic capability for imaging objects with fast, quasi-monoenergetic neutrons at ⩽1mm spatial resolution. The neutron production source is a deuteron beam (4 or 7 MeV) incident upon a rotating, high-pressure, windowless, pure-deuterium gas target. The windowless nature of the target combined with the high pressure leads to significant gas leakage upstream of the neutron production target. This leakage degrades the imaging quality by (1) increasing the depth-of-field blurring and (2) increasing the beam diameter and divergence in the transverse direction via angular straggling in the residual gas. To mitigate these effects, and guided by bench tests and simulations, we designed a differential pumping line (DPL) to ensure the highest quality imaging system. The system consists of three primary stages (chambers), each separated by carefully shaped apertures. These apertures can be long and thin with low-angle tapers due to the high quality of the beam optics (convergence at the target < 5mrad) and low emittance of the beam (~5 pi mm- mrad). The primary cascaded roots pumps are sized to remove >99% of the incoming mass flow in each stage, ensuring that by the third stage furthest from the target, turbomolecular pumps are able to operate in a nominal ~mTorr range. We anticipate full system testing with helium in mid 2019.

Choice of accelerator type for Boron Neutron Capture Therapy system

There are briefly considered physical and medical aspects contemporary development of Boron Neutron Capture Therapy (BNCT) system. Choice of accelerator for neutron produce is discussed. Three of accelerator types are compared: electrostatic accelerator, compact cyclotron and RFQ with working frequency of P-diapason. A few factors determine choice: providing required neutron flux, compactness of accelerator and whole BNCT system, economical power consumption. Our choice is radio-frequency quadrupole. Two of RFQ variants are considered: compact RFQ and universal one, which has possibility to accelerate two of types particles (proton and deuteron) and to use two of types targets (Lithium and Beryllium) for neutron production.

Development of an Accelerator-Based Epithermal Neutron Source for Boron Neutron Capture Therapy

The paper presents a review of the current state of development of accelerator-based epithermal neutron sources for boron neutron capture therapy (BNCT), a promising method for the treatment of malignant tumors. Special attention is paid to an epithermal neutron source based on a new type of accelerator of charged particles: a tandem accelerator with vacuum insulation and a lithium neutron-producing target.

Development of a Neutron Imaging Station at the n_TOF Facility of CERN and Applications to Beam Intercepting Devices

A neutron radiography testing station has been developed exploiting the neutron beam of CERN’s n_TOF Experimental Area 2, located at the shortest distance to the neutron producing-target. The characteristics of the n_TOF neutron beam for the imaging setup are presented in this paper, together with the obtained experimental results. The results focused on the testing of several particle producing targets, including a spent antiproton production targets as well as targets from two different HiRadMat’s experiments. The possible developments of neutron imaging capabilities of the n_TOF facility in terms of detection-systems and beam-line upgrades are as well outlined.

Study on secondary electron suppression in compact D–D neutron generator

A compact D–D neutron generator, with a peak neutron yield of D–D reactions up to 2.48 × 108 n/s is being developed at Lanzhou University in China for application in real-time neutron activation analysis. During tests, the problem of back acceleration of secondary electrons liberated from the neutron production target by deuterium ions bombardment was encountered. In this study, an electric field method and a magnetic field method for suppressing secondary electrons are designed and experimentally investigated. The experimental results show that the electric field method is superior to the magnetic field method. Effective suppression of the secondary electrons can be achieved via electrostatic suppression when the bias voltage between the target and the extraction-accelerating electrode is > 204 V. Furthermore, the secondary electron emission coefficient for the mixed deuterium ion (D1+, D2+, and D3+) impacting on molybdenum is estimated. In the deuterium energy range of 80–120 keV, the estimated secondary electron emission coefficients are approximately 5–5.5 for the mixed deuterium ion glancing incidence of 45° and approximately 3.5–3.9 for the mixed deuterium ion normal incidence.

Study on background shielding for a compact photoneutron source

A compact photoneutron source (PNS), based on an electron LINAC was designed and constructed to provide required experimental nuclear data for Thorium Molten Salt Reactor (TMSR). All devices including the LINAC, the neutron production target and the detector systems were arranged in a shared hall, leading to a high background of neutron and γ-ray. The necessary shielding design was made to reduce the backgrounds. A series of preliminary measurements of total cross section in thermal neutron energy region for some key nuclides of TMSR, such as 232Th and 7Li, have been performed at this PNS. It was found, however, that additional shielding needs to be constructed to further reduce the neutron and γ-ray backgrounds. MCNP is a major tool for the background shielding design since it has the calculation capability for a coupled neutron-photon-electron transport problem. A two-step subsection simulation based on MCNP involving with variance reduction techniques (Sub-Var method) was performed to provide required flux and spectrum calculation for the new background shielding design. Based on the simulated results, a new local shielding was designed and constructed, which can reduce the thermal neutron background by three orders of magnitude and the γ-ray background by two orders of magnitude. The neutron flux and energy spectrum were measured under the new shielding condition and compared with the simulated ones, showing a good agreement with each other in the thermal energy region. Therefore, a significant improved shielding for the PNS is achieved, which is expected to provide a required assurance for the future measurements of neutron cross section at the PNS.

Compact Plasma Reflex Triode for Neutron Generation

Original neutron generator on the base of pulse accelerating vacuum tube with two targets, symmetrically located on both sides of deuteron source, is discussed. Two immersion lenses in front of each other use as accelerating and focusing systems. Lenses cathodes are Faraday cups with targets for neutron production on the bottom. Symmetric ring magnetic elements cover immersion lenses for correcting focusing conditions. Computer simulation allows us to choose electrodes geometry and accelerating pulse value for electron flow from ion–electron emission oscillate between the targets and provide device operation as reflex triode. Estimations show that four times less energy for deuteron flow acceleration requires to obtain neutron flow production at the level of the best sealed accelerating tubes with the same tube geometry sizes.

Estimating the Reactivity of the Yalina-Booster Fast-Thermal Subcritical Assembly without Fuel in the Fast Zone

The geometry and material content of the Yalina-Booster two-zone subcritical assembly driven by external neutron sources are described, along with the instrumentation and conditions of experimental measurements. 252Cf isotope and a neutron generator with a TiT or TiD neutron-producing target are used as external neutron sources. The results are presented from analytical and experimental estimates of the levels of subcriticality in two core configurations: (1) with a fueled core (uranium dioxide of 10% enrichment in the thermal zone and uranium dioxide of 21% enrichment in the fast zone) and (2) with uranium dioxide of 10% enrichment in the thermal zone and without fuel in the fast zone. The calculated effective fractions of delayed neutrons in the considered thermal zone are compared. It is shown that the main kinetic parameters are defined by the thermal zone. The calculated results are compared to experimental ones, and the discrepancies are analyzed.

Neutron field study of p(35) + Be source reaction at the NPI Rez

The cyclotron-based fast neutron sources of the white- and quasi-monoenergetic spectra are operated at the NPI Rez Fast Neutron Facility utilizing the variable proton (up to 36 MeV) and deuteron (up to 20 MeV) beams delivered by the U-120M isochronous cyclotron and target stations with the Be(thick), D2O(thick), and Li(C) neutron production targets. The upgraded beryllium target station provides the high intensity neutron field of broad spectra up to 33 MeV with mean energy of 14 MeV. The energy range corresponds to the main energy part of IFMIF (International Fusion Material Irradiation Facility) neutron spectrum. This IFMIF-like source is appropriate for the radiation hardness tests of materials and electronics, validation of activation cross-section data within the fusion relevant research programs, and fast neutron activation analysis experiments. At the NPI CAS, the neutron field of p + Be source reaction was studied for proton beam energy of 35 MeV using the multi-foil activation technique. The modified version of SAND-II deconvolution tool was used for neutron spectrum reconstruction up to 33 MeV (i.e. energy region with a lack of experimental neutron spectral data).

The SNS Moderator Demonstration Facility

We describe a moderator demonstration facility at the Spallation Neutron Source (SNS). We will use the Beam Test Facility (BTF) at SNS to provide a moderator neutronics test stand with which we will verify the performance gains expected from the innovative moderator concepts central to the SNS Second Target Station. These concepts include large-volume para-hydrogen moderators and high-brightness moderators, as well as new moderator materials. The BTF provides a test facility for the new Radio-Frequency Quadrupole accelerator (RFQ) to be installed at SNS and produce a pulsed H− beam of 2.5 MeV energy. We will add to the BTF a beam chopper similar to that already used in the SNS at the RFQ exit, various beam transport components, a neutron-producing target, a cryogenic moderator test stand, a reflector-shielding assembly, and a performance assessment neutron beamline.

Damage evaluation of proton irradiated titanium deuteride thin films to be used as neutron production targets

Titanium deuteride thin films have been manufactured under different conditions specified by deuterium gas pressure, substrate temperature and time. The films were characterized by different techniques to evaluate the deuterium content and the homogeneity of such films. Samples with different concentrations of deuterium, including non deuterated samples, were irradiated with a 150 keV proton beam. Both deposits, pristine and irradiated, were characterized by optical profilometry and scanning electron microscopy.

High wavelength-resolution Bragg-edge/dip transmission imaging instrument with a supermirror guide-tube coupled to a decoupled thermal-neutron moderator at Hokkaido University Neutron Source

Bragg-edge neutron transmission imaging is one of several useful material characterization tools available at a compact-acceralator driven pulsed-neutron source (a pulsed CANS). Quantitative imaging experiments for crystalline phase, crystallographic texture, and crystallite size have been successfully performed at a pulsed CANS using a coupled (high intensity type) cold-neutron moderator. However, imaging experiments for strain and grain orientation have not been achieved due to the low wavelength-resolution of the coupled moderator. In this study, we demonstrated that both strain imaging using the Bragg-edge transmission method and grain-orientation imaging using the Bragg-dip transmission method are feasible at a pulsed CANS; both types of imaging are made possible with an efficient neutron beam transport system using a supermirror guide-tube combined with a decoupled thermal-neutron moderator (300 K polyethylene), which can supply short neutron pulse. Using this system, we achieved high wavelength-resolution (about 0.5%) Bragg-edge/dip neutron transmission imaging experiments, which correctly visualized the strain values and grain orientations in several polycrystalline materials. On the other hand, it was also found that the neutron flux and the neutron beam angular divergence (L/D) were insufficient with this approach. For this reason, we performed Monte-Carlo simulation studies to investigate a new geometry of moderator system which achieves not only high wavelength-resolution (short pulse width) but also high neutron brightness which is necessary for a high L/D experiment. The simulation results suggest that the most promising candidates use a thin and low-height cold-neutron moderator (20 K methane) with decoupled pre-moderators or poisoned pre-moderators with large solid-angle coverage for fast neutrons emitted from a neutron production target. This system offers higher peak intensity than a coupled moderator for cold neutrons emitted from the highest brightness region on the moderator surface, while achieving narrow pulse widths and decay times as fast as those of decoupled/poisoned moderators.