Characteristics Of Neutron Beam Research Articles

Measurement of the applicability of various experimental materials in a medically relevant reactor neutron source part two: Study of H3BO3 and B-DTPA under neutron irradiation

Experiments related to Boron Neutron Capture Therapy (BNCT) accomplished at the Institute of Nuclear Techniques (INT), Budapest University of Technology and Economics (TUB) are presented. Relevant investigations are required before designing BNCT for vivo applications. Samples of relevant boron compounds (H3BO3, BDTPA) usually employed in BNCT were investigated with neutron beam. Channel #5 in the research reactor (100 kW) of INT-TUB provides the neutron beam. Boron samples are mounted on a carrier for neutron irradiation. The particle attenuation of several carrier materials was investigated, and the one with the lowest attenuation was selected. The effects of boron compound type, mass, and compound phase state were also investigated. To detect the emitted charged particles, a traditional ZnS(Ag) detector was employed. The neutron beam's interaction with the detector-detecting layer is investigated. Graphite (as a moderator) was employed to change the neutron beam's characteristics. The fast neutron beam was also thermalized by placing a portable fast neutron source in a paraffin container and irradiating the H3BO3. The obtained results suggest that the direct measurement approach appears to be insufficiently sensitive for determining the radiation dose committed by the Alpha particles from the 10B (n,α) reaction. As a result, a new approach must be used.

Evaluation of neutron beam characteristics for D-BNCT01 facility

Evaluation of neutron beam characteristics for D-BNCT01 facility

High Spatial Resolution Neutron Transmission Imaging Using a Superconducting Two-Dimensional Detector

Neutron imaging is one of the most powerful tools for nondestructive inspection owing to the unique characteristics of neutron beams, such as high permeability for many heavy metals, high sensitivity for certain light elements, and isotope selectivity owing to a specific nuclear reaction between an isotope and neutrons. In this study, we employed a superconducting detector, current-biased kinetic-inductance detector (CB-KID) for neutron imaging using a pulsed neutron source. We employed the delay-line method, and high spatial resolution imaging with only four reading channels was achieved. We also performed wavelength-resolved neutron imaging by the time-of-flight method for the pulsed neutron source. We obtained the neutron transmission images of a Gd–Al alloy sample, inside which single crystals of GdAl <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_3$</tex-math></inline-formula> were grown, using the delay-line CB-KID. Single crystals were well imaged, in both shapes and distributions, throughout the Al–Gd alloy. We identified Gd nuclei via neutron transmissions that exhibited characteristic suppression above the neutron wavelength of 0.03 nm. In addition, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{155}$</tex-math></inline-formula> Gd resonance dip, a dip structure of the transmission caused by the nuclear reaction between an isotope and neutrons, was observed even when the number of events was summed over a limited area of 15 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m × 12 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m. Gd selective imaging was performed using the resonance dip of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{155}$</tex-math></inline-formula> Gd, and it showed clear Gd distribution even with a limited neutron wavelength range of 1 pm.

GEANT4 simulations of the neutron beam characteristics for 9Be/7Li targets bombarded by the low energy protons

9Be(p,xn) and 7Li(p,xn) are two reactions for the accelerator-based compact neutron source at low energy protons conditions, especially for BNCT facilities and it is necessary to simulate the beam characteristics accurately. The different reference physics lists recommended by GEANT4 have been used to calculate the neutron beam characteristics for the 9Be and 7Li targets bombarded by proton beams of 5 ∼ 10 MeV and the accuracy of GEANT4 simulations has been discussed. By comparing with the reference data such as experimental data, MCNP6 simulations and numerical calculations, the results calculated by QGSP_BIC_AllHP show good agreement with a relative error of less than 10%. The neutron yields level out and have a tendency to move forward, when the thickness is greater than the range of protons in targets. However, the neutron yields are significantly underestimated by other physics lists except for QGSP_BIC_AllHP. In addition, two fitted curve equations are acquired to quickly estimate the neutron yield for 9Be and 7Li targets below 20 MeV. Therefore, due to the limitation of the particle type and energy range in this study, GEANT4 with QGSP_BIC_AllHP is recommended to calculate hadronic interactions of protons with matter below 20 MeV.

First beams at neutrons for science

The neutrons for science facility (NFS), the first operational experimental area of the new GANIL/SPIRAL-2 facility, received its first beams in December 2019. Proton-induced reaction cross-sections as well as neutron beam characteristics were measured during the first commissioning phases. The first results, showing the features of the facility, are presented here and compared with previously published data. The physics cases and the first accepted experiments are presented as well.

Evaluation of photon and neutron dose distribution from the Varian Clinac 2300EX 15 MV medical LINAC with MCNP6 Code

The X-ray and neutron beam characteristics of the Varian Clinac 2300EX LINAC were obtained by simulation and computation using the MCNP6 software. An electron source with an energy of 15 MeV is used to produce an X-ray beam which is then directed to the phantom 100 cm distance from the electron source. With an irradiated area (10 × 10) cm2, the average X-ray dose on the phantom surface obtained was (2,91 ± 0,47) 10−15 Gy/e. For better isodosis, a triangular prism-shaped within nickel material flattening filter was installed to produce an X-ray beam profile with an average dose of (2,04 ± 0,22) 10−16 Gy/e. During LINAC 15 MV operation, the mean neutron dose was detected (8,57 ± 0,55) 10−20 Sv/e. The neutron energy spectrum has been simulated, the distribution of thermal energy intensity is 0,06%, epithermal energy is 0,74%, and the most distribution is fast energy 99,20%. The ratio of neutron equivalent dose to the central axis X-ray dose (ξ) was calculated. The value of ξ meets the allowable limit of < 1/1000 Sv/Gy, recommended by the International Electrotechnical Commission (IEC). The ξ values obtained at several phantom depths in this study indicate the values allowed by the IEC.

Back-n white neutron source at CSNS and its applications

Back-streaming neutrons from the spallation target of the China Spallation Neutron Source (CSNS) that emit through the incoming proton channel were exploited to build a white neutron beam facility (the so-called Back-n white neutron source), which was completed in March 2018. The Back-n neutron beam is very intense, at approximately 2 × 107 n/cm2/s at 55 m from the target, and has a nominal proton beam with a power of 100 kW in the CSNS-I phase and a kinetic energy of 1.6 GeV and a thick tungsten target in multiple slices with modest moderation from the cooling water through the slices. In addition, the excellent energy spectrum spanning from 0.5 eV to 200 MeV, and a good time resolution related to the time-of-flight measurements make it a typical white neutron source for nuclear data measurements; its overall performance is among that of the best white neutron sources in the world. Equipped with advanced spectrometers, detectors, and application utilities, the Back-n facility can serve wide applications, with a focus on neutron-induced cross-sectional measurements. This article presents an overview of the neutron beam characteristics, the experimental setups, and the ongoing applications at Back-n.

Neutron yields of Be-9(p,xn) reactions and beam characterization for accelerator-based boron neutron capture therapy facility using MCNP6, PHITS, and GEANT4 simulation results

Neutron yields from 9Be(p,xn) reactions with a 2-cm thick beryllium target bombarded by proton beams of 5, 6, 7, 8, 9, and 10 MeV were investigated. Neutron beam characteristics through a pilot design of beam shaping assembly were calculated by using MCNP6, PHITS, and GEANT4. The neutron yield with a 10 MeV beam by MCNP6 was 7.7 times larger than values by the other codes, but close to the experimental data. The neutron spectrum and directionality were different among the codes. These differences could stem from different cross-section libraries and models used in the codes. The epithermal flux at the beam irradiation port by MCNP6 was 1.4 × 109 cm−2 s−1 for a proton current of 8 mA hitting the target. The ratio of thermal and epithermal flux was less than 0.01 and the forward directionality was 0.78. However, we suggest a new criterion regarding a ratio of fast and epithermal flux.

An instrument for measuring T-odd asymmetries in the fission of heavy nuclei

We describe an experimental setup used to measure the T-odd asymmetry effects for prompt fission neutrons and γ-rays in binary fission of some heavy nuclei induced by polarized neutrons with resonance energy. The overall setup as well as the details of the design and performance of the key components like fission fragment detectors, neutron and γ detectors, and the electronics used in the data acquisition and processing system are presented. The experimental setup on beam line POLI of the FRM II reactor (Garching, Germany), as well as the neutron beam characteristics, polarization measurements are described, too.

Designing a new graphite illuminator for imaging facility of INUS to improve neutron beam uniformity and intensity

A cylindrical graphite illuminator with a thickness of 6.5 cm and diameter of 18 cm was installed inside the collimator of INUS (Instalatie de Neutronografie UScata) neutron imaging facility in the past. The graphite illuminator is usually utilized inside the collimator of neutron imaging facility to provide an intense and approximately uniform beam of neutrons at the outlet of collimator. With the mentioned existing illuminator in INUS imaging facility, the thermal neutron flux at the exit of collimator was measured 7.2 × 104 n/cm2/s. Also the obtained neutron beam profile in this facility shows that it is not completely uniform at the imaging screen and the intensity of neutrons at the top and bottom of beam profile are not the same. Hence, in this paper a new graphite illuminator is proposed to improve the neutron beam characteristics in INUS imaging facility. Monte Carlo N-Particle (MCNP) code was implemented in this study for evaluating the proposed illuminator. The shape of proposed illuminator is a cylinder whose one side is inclined. Three quality factors of thermal neutron intensity, thermal neutron beam uniformity and gamma radiation dose rate were used to evaluate performance of the new illuminator. In order to obtain optimum illuminator shape, three effective parameters of thickness, angle of inclined side and position of the illuminator inside the collimator were investigated in this research. The investigation was carried out on thicknesses in the range of 5 to 25 cm with a step of 5 cm, angles in the range of 10 to 60° with a step of 10° and positions of −5, 0 and 5 cm with respect to center of reactor core. After investigating and interpolating the results, it was found that the proposed illuminator with a thickness of 10 cm, angle of 54.5° and position of 0 can produce a uniform beam profile, increase the thermal neutron intensity up to 7.1% and also decrease the neutron to gamma ratio up to 5% in comparison with the existing one.

Novel method exploration of monitoring neutron beam using Cherenkov photons in BNCT

Ensuring the stability of the neutron beam during boron neutron capture therapy (BNCT) is essential. The goal of this work was to explore a novel method using Cherenkov photons for real-time monitoring of neutron beam in BNCT. The Monte Carlo toolkit Geant4, was used to calculate the Cherenkov photons and dose based on a cubic phantom and Chinese hybrid radiation phantom under different conditions. Based on the study on the cubic phantom, the change of neutron beam characteristics indeed have an impact on dose, which needs quality assurance. The relationship between Cherenkov photons and gamma dose was favorable. The maximum relative variation of the generation of Cherenkov photons is approximately 3.51%, even when the relative change of boron concentration reaching 60%. However, comparing the results of the neutron beam with the original characteristics, the maximum relative variation of Cherenkov photons reaches 14.75% and 14.68% for the usage of Neuboron- spectrum and 5-degree rotation of neutron beam field orientation, respectively. Therefore, the intensity and distribution of Cherenkov photons can only be observably changed by neutron beam characteristics. Based on the Chinese hybrid radiation phantom, the changes in the intensity and distribution of Cherenkov photons can also be observed inside the phantom, and these changes are evident by a detector outside the phantom. Thus, Cherenkov photons has the potential application for neutron beam monitoring.

Design of back-streaming white neutron beam line at CSNS

A white neutron beam line using back-streaming neutrons from the spallation target is under construction at China Spallation Neutron Source (CSNS). Different spectrometers, to be installed in the so-called Back-n beam line for nuclear data measurements, are also being developed in phases. The physical design of the beam line is carried out with the help of a complicated collimation system and a sophisticated neutron dump, taking the overview of the neutron beam characteristics into account. This includes energy spectrum, flux and time structure, the optimizations of neutron beam spots and in-hall background. The wide neutron energy range of 1eV–100MeV is excellent for supporting different applications, especially nuclear data measurements. At Endstation#2, which is about 80m away from the target, the main properties of the beam line include neutron flux of 106n/cm2/s, time resolution of a few per mille over nearly the entire energy range, and in-hall background of about 0.01/cm2/s for both neutron and gamma. With its first commission in late 2017, Back-n will not only be the first high-performance white neutron source in China, but also one of the best white neutron sources in the world.

Abstract ID: 97 A Monte Carlo study of resolving the radiation dose through the detection of Cerenkov radiation in Boron Neutron Capture

Radiation dose in boron neutron capture therapy (BNCT) is determined by both the epithermal neutron beam and Boron-10 distribution [1] , [2] . It is thus more complex and important to monitor the radiation dose comparing to other radiation treatment modalities. In this study, we investigated the feasibility of resolving the radiation dose with respect to the change of beam property and Boron-10 concentration through the detection of Cerenkov radiation during BNCT. Monte Carlo toolkit Geant4 was used to simulate the irradiation of epithermal neutron beam on phantom containing tumor region [3] . Cerenkov can be generated during BNCT and it is expected to be correlated with gamma dose. The depth and radial distributions of gamma dose were obtained under different characteristics of boron concentration and epithermal neutron beam. The relationship between the number of Cerenkov photons and gamma dose was explored based on simple phantom and Chinese reference radiation phantom. Results showed that the gamma dose is almost unchanged under different boron concentration distributions, even if the relative change of boron concentration reached 60 percent. The changes in the characteristics of epithermal neutron beam directly leads to the changes in the gamma dose. This indicated that gamma dose can be used to reflect the stability and delivery accuracy of epithermal neutron beam. Meanwhile, the response relationship between the number of Cerenkov photons and gamma dose was observed. As a preliminary result, it suggests the potential feasibility to monitoring the gamma dose and the stability of the epithermal neutron beam through the detection of Cerenkov radiation emitted during BNCT.

Construction of a head phantom for mixed neutron and gamma field dosimetry in TRR

Boron Neutron Capture Therapy (BNCT) project in Tehran Research Reactor (TRR) is currently ongoing and an appropriate neutron beam for BNCT has been provided by modification of TRR thermal column. In order to measure the neutron beam characteristics inside of a phantom, a standard phantom is needed. The present paper describes details of the head phantom construction and its different potential. The constructed head phantom permits us to put different dosimeters with different sizes in many locations of the phantom volume. Foils, wires, TLDs and ion chamber can be placed inside of its volume. Gel dosimeter can also be poured into the phantom volume and removed from it easily.

SU‐E‐T‐470: Monte Carlo Simulation of Fast Neutron Treatments for Head and Neck Cancers

Purpose: To quantify the physical characteristics of a therapeutic fast neutron beam at the University of Washington (UW) using a Monte Carlo model validated against measured percentage depth‐dose (PDD) and lateral profiles. Methods: MCNPX modeling and simulation of the UW neutron therapy system's treatment head is divided into three stages. In Stage I, 50.5 MeV protons are directed at a Be target. Neutrons produced in the target pass through the primary collimator and flattening filter; photons and neutrons produced in Stage I are saved to a 100×100 cm2 phase space file located just below the flattening filter. In Stage II, neutrons and photons are transported through the MLC and saved to a second phase space file. Automatic adjustment of the 40 individual MLC to create regular or irregular field shapes with or without a wedge is controlled by an in‐house developed python script. In Stage III, neutral particles are transported from the phase space file at the bottom of the MLC into a 40×40×40 cm3 water phantom (150 cm source to surface distance). PDD curves and lateral dose profiles are computed from dose tallies in rectangular (0.1 cm3) volumes. Results: PDD simulation for an open 10.4×10.3 cm2 field agrees with measurement to within 4% up to 17 cm and within 8% up to 30 cm. A lateral dose profile at a depth of 1.7 cm matches well the overall shape of the profile. A representative simulation (1011 source particles) requires about 150 hours of CPU time on a dual, 2.4 GHz 8‐core Intel Xeon server. Conclusion: The developed MCNPX model is capable of reproducing measured data with sufficient accuracy for clinical applications. Efforts to improve agreement in the penumbra of lateral profiles are underway as well as tests of the model for various sizes of open and wedged fields.

Resumption of JRR-4 and characteristics of neutron beam for BNCT

The clinical trials of Boron Neutron Capture Therapy (BNCT) have been conducted using Japan Research Reactor No. 4 (JRR-4) at Japan Atomic Energy Agency (JAEA). On December 28th, 2007, a crack of a graphite reflector in the reactor core was found on the weld of the aluminum cladding. For this reason, specifications of graphite reflectors were renewed; dimensions of the graphite were reduced and gaps of water were increased. All existing graphite reflectors of JRR-4 were replaced by new graphite reflectors. In February 2010 the resumption of JRR-4 was carried out with new graphite reflectors. We measured the characteristics of neutron beam at the JRR-4 Neutron Beam Facility. A cylindrical water phantom of 18.6 cm diameter and 24 cm depth was set in front of the beam port with 1cm gap. TLDs and gold wires were inserted within the phantom when the phantom was irradiated. The results of the measured thermal neutron flux and the gamma dose in water were compared with that of MCNP calculation. The neutron energy spectrum of the calculation model with new reflector had little variation compared to that with old reflector, but intensities of the neutron flux and gamma dose with new reflector were rather smaller than those with old reflector. The calculated results showed the same tendency as that of the experimental results. Therefore, the clinical trials of BNCT in JRR-4 could be restarted.

Implementation of Neutron Mirror Modeling Capability into MCNPX and Its Demonstration in First Applications

Reflection of thermal and cold neutrons by polished surfaces and so-called supermirrors effect radiation fields in and around neutron beamlines. To allow the prediction of these radiation fields with MCNPX 2.5.0, two new input cards were implemented for defining mirror properties of surfaces. Mirror properties can be linked to any type of surface, in contrast to other neutron optics codes, where the mirror properties are part of component descriptions, allowing the simulation of very complex neutron optical devices. First calculations are under way to verify the new capability against combinations of MCNPX and MCSTAS (neutron optics code) simulations. Also, simulations are under way to compare the predicted neutron beam characteristics against measurements conducted at Paul Scherrer Institut.

Monte Carlo study of the neutron time emission spectra at the Manuel Lujan Jr. Neutron Scattering Center

A campaign of neutron-beam characterization measurements was carried out in 2001–2002 at the Manuel Lujan Jr. Neutron Scattering Center (Lujan Center) at the Los Alamos Neutron Science Center (LANSCE), Los Alamos National Laboratory. These experiments provided a valuable comprehensive data set to define the neutron-beam characteristics of the Lujan Center's target–moderator–reflector–shield assembly. To validate the current computer models of the target assembly, we carried out multiple Monte Carlo calculations of the neutron time emission pulses. The results of our simulations are directly compared with the experimental data characterizing five of the six moderators installed in the Lujan target–moderator–reflector–shield system. Our results not only present an important benchmark test of the MCNPX Monte Carlo transport model of the target assembly, but also show the capabilities of the MCNPX code in designing upgrade and future spallation neutron sources.

Evaluation of D(d,n) 3 He reaction neutron source models for BNCT irradiation system design

A mathematical method was developed to calculate the yield, energy spectrum and angular distribution of neutrons from D(d,n) 3 He (D-D) reaction in a thick deuterium-titanium target for incident deuterons in energies lower than 1.0MeV. The data of energy spectrum and angular distribution were applied to set up the neutron source model for the beam-shaping-assembly (BSA) design of Boron-Neutron-Capture-Therapy (BNCT) using MCNP-4C code. Three cases of D-D neutron source corresponding to incident deuteron energy of 1000, 400 and 150 keV were investigated. The neutron beam characteristics were compared with the model of a 2.45 MeV mono-energetic and isotropic neutron source using an example BSA designed for BNCT irradiation. The results show significant differences in the neutron beam characteristics, particularly the fast neutron component and fast neutron dose in air, between the non-isotropic neutron source model and the 2.5 MeV mono-energetic and isotropic neutron source model.

Development and characteristics of the HANARO neutron irradiation facility for applications in the boron neutron capture therapy field

The HANARO neutron irradiation facility for various applications in the boron neutron capture therapy (BNCT) field was developed, and its characteristics were investigated. In order to obtain the sufficient thermal neutron flux with a low level of contamination by fast neutrons and gamma rays, a radiation filtering method was adopted. The radiation filter was designed by using a silicon single crystal, cooled by liquid nitrogen, and a bismuth crystal. The installation of the main components of the irradiation facility and the irradiation room was finished. Neutron beam characteristics were measured by using bare and cadmium-covered gold foils and wires. The in-phantom neutron flux distribution was measured for flux mapping inside the phantom. The gamma-ray dose was determined by using TLD-700 thermoluminescence dosimeters. The thermal and fast neutron fluxes and the gamma-ray dose were calculated by using the MCNP code, and they were compared with experimental data. The thermal neutron flux and Cd ratio available at this facility were confirmed to be 1.49 × 109 n cm−2 s−1 and 152, respectively. The maximum neutron flux inside the phantom was measured to be 2.79 × 109 n cm−2 s−1 at a depth of 3 mm in the phantom. The two-dimensional in-phantom neutron flux distribution was determined, and significant neutron irradiation was observed within 20 mm from the phantom surface. The gamma-ray dose rate for the free beam condition was expected to be about 80 cGy h−1. These experimental results were reasonably well supported by calculation using the facility design code. This HANARO thermal neutron facility can be used not only for clinical trials, but also for various pre-clinical studies in the BNCT field.