Fast Neutron Beam Research Articles

MCNP optimization of fast neutron beam thermalization device based on D-T neutron generator

The 14 MeV neutrons generated by Deuterium-Tritium (D-T) fusion reaction usually need to be moderated for Prompt Gamma Neutron Activation Analysis (PGNAA) applications. A fast neutron beam thermalization device was developed in Northeast Normal University based on a D-T neutron generator (model NG-9). A simple experimental system was set up firstly to validate the feasibility of simulation. The materials and dimensions of moderator and the size of multiplier, reflector and collimator were then optimized through MCNP5 to improve the efficiency of the thermalization device. The thermal, epithermal, fast and total neutron flux across the output surface in final system were increased for a factor of 9.65, 8.70, 5.84 and 6.94 times compared to the initial experimental system, respectively. And the optimized thermalization efficiency is 13.28 times higher than that of the original model of experimental system.

Assessment of gamma-rays and fast neutron beam attenuation features of Er2O3-doped B2O3–ZnO–Bi2O3 glasses using XCOM and simulation codes (MCNP5 and Geant4)

The authors aim to study the gamma-rays and neutron beam shielding capabilities of zinc bismuth borate glasses doped with erbium ions. Mass attenuation coefficient (MAC) (μ/ρ) values were computed employing XCOM and two different simulation codes, MCNP5 and Geant4, within 0.015–15 MeV photon energy, which showed good agreement within the derived values. The effective atomic number (Zeff), electron density (Ne), half-value layer (HVL) and mean free path (MFP) values were derived using MAC values. To account on the scattering effects of photons from the samples, exposure buildup factor (EBF) were determined, applying geometric progression (G-P) method, within 0.015–15 MeV photon energy and penetration depth of 1–40 mfp (intervals: 1, 5, 10, 15, and 40 mfp). The high MAC, Zeff values and low HVL, MFP values of 16.93B2O3‒22.57ZnO‒60Bi2O3‒0.5Er2O3 (mol%) glass optimized its shielding effects against gamma-rays. The macroscopic effective removal cross-section for fast neutron (ΣR) values lie within the range of 0.1142–0.1232 cm−1 for the selected Er2O3-doped samples. The studied parameters of the experimented glasses revealed their dominant radiation shielding features compared to commercial shielding glasses, concretes, and alloys.

Mass yield distributions in the Th232(n,f) reaction with fast neutrons

The cumulative yields of 48 fission products in the mass range of 77--153 have been measured for the $^{232}\mathrm{Th}(n,f)$ reaction with the average neutron energies of 7.46, 13.4, and 18.0 MeV using an off-line \ensuremath{\gamma}-ray spectrometric technique. Fast neutron beams were generated using the $^{9}\mathrm{Be}(p,n)$ reaction with the proton energies of 25, 35, and 45 MeV from the MC-50 Cyclotron at the Korea Institute of Radiological and Medical Sciences. Post-neutron mass chain yields were obtained from the cumulative fission yields using the charge distribution correction of the medium energy. From the mass yield data, the peak-to-valley ratio, average light mass, and heavy mass, as well as the average neutron numbers were obtained. The fine structure of the mass yield distribution in the $^{232}\mathrm{Th}(n,f)$ reaction is explained by considering the nuclear structure effects such as the even--odd effect and shell closure proximity. The effect of deformed shells closure proximity arising due to the octupole deformation of fragments is discussed. The difference in the mass yield distribution between the $^{232}\mathrm{Th}(n,f)$ and $^{238}\mathrm{U}(n,f)$ reactions at various excitation energies is explained based on the different types of potential energy surfaces between the two fissioning systems. The role of excitation energy on the standard I and standard II asymmetric mode of fission is also discussed. In the $^{232}\mathrm{Th}(n,f)$ reaction with the excitation energies of 11--13 MeV, the onset of symmetric product yields, peak-to-valley ratio, average light mass, and heavy mass, as well as the average neutrons number have been observed, which are explained from the point of second chance fission.

Determining the Energy Spectrum of Fast Neutrons in the n + 1H → n + p Reaction on the W–Be Source at the Institute for Nuclear Research, Russian Academy of Sciences

The neutron spectrum produced in the γ +9Be → 8Be + n reaction at different boundary energies of the photon spectrum is modeled in order to examine the possibility of measuring nuclear cross sections with fast quasi-monoenergetic neutron beams of the W–Be photoneutron source at the Institute for Nuclear Research. The obtained spectra are used to model the response of a hydrogen-containing detector to neutrons in the n + 1H → n + p reaction. An experimental setup for determining the energy spectrum of neutrons of the W–Be source is constructed. The spectra of secondary neutrons detected in an active hydrogen-containing target irradiated with neutrons are measured and compared to the ones modeled.

Hyperthermia with photon radiotherapy is thermoradiobiologically analogous to neutrons for tumors without enhanced normal tissue toxicity

The depth dose profiles of photons mirror those of fast neutrons. However, in contrast to the high linear energy transfer (LET) characteristics of neutrons; photons exhibit low LET features. Hyperthermia (HT) inhibits the repair of radiation-induced DNA damage and is cytotoxic to the radioresistant hypoxic tumor cells. Thus, thermoradiobiologically, HT simulates high LET radiation with photons. At temperatures of 39–45 °C, the physiological vasodilation allows rapid heat dissipation from normal tissues. On the contrary, the chaotic and relatively rigid tumor vasculature results in heat retention leading to higher intratumoural temperatures. Consequently, the high LET attributes of HT with photon radiations are mostly limited to the confines of the heated tumor while the normothermic normal tissues would be irradiated with low LET photons. HT thereby augments photon therapy by conferring therapeutic advantages of high LET radiations to the tumors akin to neutrons, while the ‘heat-sink’ effect spares the normal tissues from thermal radiosensitization. Thus, photon thermoradiotherapy imparts radiobiological advantages selectively to tumors analogous to neutrons without exaggerating normal tissue morbidities. The later has been the major concern with clinical fast neutron beam therapy. Outcomes reported from several clinical trials in diverse tumor sites add testimony to the enhanced therapeutic efficacy of photon thermoradiotherapy.

Directionality properties of the nGEM detector of the CNESM diagnostic system for SPIDER

The ITER project requires additional heating by two neutral beam injectors, each accelerating up to 1 MV a 40 A beam of negative deuterium ions for one hour. Such requirements have never been reached, so it was decided to build in Padova a facility (PRIMA) that hosts two experimental devices: SPIDER, a 100 kV negative H/D RF beam source, and MITICA, a full-scale injector for the ITER NBI. SPIDER has begun operation in 2018, while MITICA is expected to start after 2020. In both devices the accelerated deuterium beam impinges on an actively cooled beam dump used to stop the deuterons. Detection of fusion neutrons produced between beam–deuterons and dump-embedded deuterons will be used as a means to resolve the horizontal beam intensity profile. A neutron detection system called Close-contact Neutron Emission Surface Mapping (CNESM) is installed right behind the SPIDER beam dump, with the aim to provide the neutron emission map of the beam dump surface. The core of this diagnostic system is an nGEM (neutron-Gas Electron Multiplier) detector which will be able to reconstruct the fast neutron beam profile with an efficiency of about 10−4. A crucial point in order to correctly reconstruct the profile of the deposited D− power is the directionality discrimination capability of the detector. This paper reports on the results of the characterization of the nGEM directionality capabilities, performed at the Frascati Neutron Generator (FNG) using 2.5 MeV neutrons, before installation of the detector inside the SPIDER vacuum vessel.

A novel vertebrate system for the examination and direct comparison of the relative biological effectiveness for different radiation qualities and sources

Purpose: The recent rapid increase of hadron therapy applications requires the development of high performance, reliable in vivo models for preclinical research on the biological effects of high linear energy transfer (LET) particle radiation.Aim: The aim of this paper was to test the relative biological effectiveness (RBE) of the zebrafish embryo system at two neutron facilities.Material and Methods: Series of viable zebrafish embryos at 24-hour post-fertilization (hpf) were exposed to single fraction, whole-body, photon and neutron (reactor fission neutrons (<En = 1 MeV>) and (p (18 MeV)+Be, <En> = 3.5 MeV) fast neutron) irradiation. The survival and morphologic abnormalities of each embryo were assessed at 24-hour intervals from the point of fertilization up to 192 hpf and then compared to conventional 6 MV photon beam irradiation results.Results: The higher energy of the fast neutron beams represents lower RBE (ref. source LINAC 6 MV photon). The lethality rate in the zebrafish embryo model was 10 times higher for 1 MeV fission neutrons and 2.5 times greater for p (18 MeV)+Be cyclotron generated fast neutron beam when compared to photon irradiation results. Dose-dependent organ perturbations (shortening of the body length, spine curvature, microcephaly, micro-ophthalmia, pericardial edema and inhibition of yolk sac resorption) and microscopic (marked cellular changes in eyes, brain, liver, muscle and the gastrointestinal system) changes scale together with the dose response.Conclusion: The zebrafish embryo system is a powerful and versatile model for assessing the effect of ionizing radiation with different LET values on viability, organ and tissue development.

Effect of heating on physical, mechanical, and nuclear radiation shielding properties of modified concrete mixes

Four concrete mixes, goethite-limonite concrete (G.L), barite-limonite concrete (B.L), steel slag-limonite concrete (S.L), and dolomite concrete (D.C) were prepared and designed to investigate the influence of heating (25, 100, 200, and 450 °C) on their performance as nuclear radiation shielding barriers. Slabs of different thicknesses from the investigated concrete mixes were exposed to a collimated beam of fast neutrons emitted from 252Cf like fission spectrum, with activity of 1.05 mCi. Measurements of the attenuation properties of fast neutrons as well as total, primary and secondary, gamma rays were performed. Organic scintillation detector with stilbene crystal was used to detect fast neutrons and total gamma-rays intensities. Results show that G.L concrete has the highest value of total removal macroscopic cross-section, Σ, for samples exposed to temperature up to 200 °C. However, for samples heated at 450 °C, G.L concrete has the poorest attenuation for fast neutrons. On the other hand, for total gamma rays, as temperature raising up to 450 °C, the B.L. concrete mix has the highest value of total linear attenuation coefficients (μ). Nevertheless; at 450 °C the S.L. concrete mix has almost the same value of μ as that of B.L.

Progress of the Scientific Commissioning of a fast neutron beamline for Chip Irradiation

ChipIr is a new beamline at the ISIS spallation source dedicated to accelerated testing of microelectronics. ChipIr features an atmospheric-like neutron spectrum to study the so-called Single Event Effects, a major concern for the reliability of modern electronics at ground level and flight altitudes. A bespoke design was needed to extract a fast neutron beam from a neutron source designed for thermal neutron applications.The main objective of the Scientific Commissioning is to measure the flux, spectrum and profiles of the fast neutron beam in the different configurations of the beamline. In this work we present preliminary results of fast neutron measurements performed with a 70×70 mm2 neutron beam and the accelerator at 700 MeV. The neutron flux above 10 MeV was found to be 4.9 · 106 cm2s-1. The beam profile was found to be uniform within the 70×70 mm2 area. ChipIr is now in an advanced stage of scientific commissioning and beta-users have started the first tests in late 2016. The first ‘official’ deliberate error was measured in a SRAM chip on the 29 June 2016; an 8 bit memory containing 1’s had the 7th bit inverted to a 0 – just the kind of error that can occur in the atmosphere due to neutron interaction.These results are promising for an imminent start of the ChipIr user programme.

Separation of gamma-ray and neutron events with CsI(Tl) pulse shape analysis

Fast neutrons are a large background to measurements of gamma-rays emitted from excited nuclei, such that detectors which can efficiently distinguish between the two are essential. In this paper we describe the separation of gamma-rays from neutrons with the pulse shape information of the CsI(Tl) scintillator, using a fast neutron beam and several gamma-ray sources. We find that a figure of merit optimized for this separation takes on large and stable values (nearly 4) between 5 and 10 MeV of electron equivalent deposited energy, the region of most interest to the study of nuclear de-excitation gamma-rays. Accordingly this work demonstrates the ability of CsI(Tl) scintillators to reject neutron backgrounds to gamma-ray measurements at these energies.

Fast neutron detection at near-core location of a research reactor with a SiC detector

The measurable charged-particle produced from the fast neutron interactions with the Si and C nucleuses can make a wide bandgap silicon carbide (SiC) sensor intrinsically sensitive to neutrons. The 4H-SiC Schottky detectors have been fabricated and tested at up to 500 °C, presenting only a slightly degraded energy resolution. The response spectrum of the SiC detectors were also obtained by exposing the detectors to external neutron beam irradiation and at a near-core location where gamma-ray field is intense. The fast neutron flux of these two locations are ∼4.8×104cm−2⋅s−1 and ∼2.2×107cm−2⋅s−1, respectively. At the external beam location, a Si detector was irradiated side-by-side with SiC detector to disjoin the neutron response from Si atoms. The contribution of gamma ray, neutron scattering, and charged-particles producing reactions in the SiC was discussed. The fast neutron detection efficiencies were determined to be 6.43×10−4 for the external fast neutron beam irradiation and 6.13×10−6 for the near-core fast neutron irradiation.

Investigations of Properties of 89Y Levels with Reactor Fast Neutrons

By employing a beam of reactor fast neutrons, the spectrum of gamma rays up to an energy of 4.6MeV and their angular distributions with respect to the neutron-beamaxis aremeasured in the reaction 89Y(n, n'γ). The multipolarities and multipole-mixture parameters for 34 gamma transitions and the spin–parities Jπ of states excited in this reaction are determined. The lifetimes of the lowest 32 levels of 89Y were measured by the Doppler shift attenuation method, and the reduced probabilities for the respective gamma transitions were calculated. Levels of the Kπ = +5/2+ and Kπ = −7/2+ bands associated with, respectively, prolate and oblate deformation shapes are found in 89Y at low excitation energies.

Response of a telescope proton recoil spectrometer based on a YAP: Ce scintillator to 5–80 MeV protons for applications to measurements of the fast neutron spectrum at the ChipIr irradiation facility

A telescope proton recoil spectrometer consisting of a 500μm thick silicon detector and a 2.54 cm × 2.54 cm YAP:Ce inorganic scintillator has been developed to measure the neutron spectrum at ChipIr, a fast neutron beam line that has recently started operations at the ISIS neutron source in the UK. The spectrometer has been tested with protons in the range 5–80 MeV at the INFN-LNS cyclotron accelerator. The light yield of the YAP scintillator to protons has been characterized relative to gamma-rays of same energies and found to scale linearly with the proton energy in the whole range. Background rejection using a ΔE-E technique by combining data from the silicon and YAP:Ce detectors has also been tested successfully.

Оценка терапевтического фактора выигрыша в нейтронной терапии на основе линейно-квадратичной модели

Purpose: To study the dependencies of therapeutic gain factor (TGF) on dose of cyclotron-produced fast neutron beams using the linear-quadratic model (LQM) parameters characterizing radiation response in tumor and normal tissues.&#x0D; Material and methods: The TGF in neutron therapy was calculated as the ratio of the relative biological effectiveness of neutrons for tumor (RBE tumor) to relative biological effectiveness for normal tissue (RBE normal tissue). The LQM was used to calculate the dependencies of neutron RBE on the dose and therapeutic gain factor. We considered two cases: 1) neutron therapy for 3 types of tumors with different radiation response, where the same normal tissue was critical; 2) neutron therapy for the same tumor, when 3 types of normal tissues were taken as critical.&#x0D; Results: Based on calculations and analysis of published data, the dependencies of neutron RBE on dose for selected types of tumors and normal tissues were obtained. The following variants were considered: 1) RBE tumor &amp;#62; RBE normal tissue; 2) RBE tumor &amp;#60; RBE normal tissue, in both two variants, the dependen-&#x0D; cies in the therapeutic dose rate were convergent; 3) the dependencies of RBE tumor and RBE normal tissue on dose are crossed. The dependencies of TGF for neutron therapy on single boost doses and quantitative ratios between the LQM parameters characterizing radiation response of tumor and normal tissues were found. A multivariate ratio between the dependencies on dose of RBE tumor and RBE normal tissue was the cause of variety in the dependencies of TGF on dose. In the first case, the TGF increased with increasing (α/β)γ ratio and decreasing single dose, and the maximum value of TGF was equal to ~ 1.4. In the second case, TGF was &amp;#60; 1, i.e. the effectiveness of neutron therapy was lower than the effectiveness of gamma irradiation, but it was increased with higher single dose and lower radiosensitivity of normal tissue. In the third case, the dose at the intersection point (Di) was the boundary, and TGF was &amp;#62; 1 to the left of the boundary, and TPV was &amp;#60;1 to the right of the boundary, provided that D &amp;#60;Di, RBEtumor &amp;#62; OBEnormal tissue.&#x0D; Conclusion: The obtained results with known parameters of the LQM for tumor and normal tissues allowed us to make an appropriate choice between neutron and gamma- ray therapy in order to increase the effectiveness of treatment for cancer patients. It was shown that in the case of neutron therapy, the analysis of dependencies of TGF on dose allowed the optimal dose fractionation regimen to be selected.

On the possible use of the MASURCA reactor as a flexible, high-intensity, fast neutron beam facility

In recent work [1, 2], we have shown that the MASURCA research reactor could be used to deliver a fairly-intense continuous fast neutron beam to an experimental room located next to the reactor core. As a consequence of the MASURCA favorable characteristics and diverse material inventories, the neutron beam intensity and spectrum can be further tailored to meet the users' needs, which could be of interest for several applications. Monte Carlo simulations have been performed to characterize in detail the extracted neutron (and photon) beam entering the experimental room. These numerical simulations were done for two different bare cores: A uranium metallic core (∼30% 235 U enriched) and a plutonium oxide core (∼25% Pu fraction, ∼78% 239 Pu). The results show that the distinctive resonance energy structures of the two core leakage spectra are preserved at the channel exit. As the experimental room is large enough to house a dedicated set of neutron spectrometry instruments, we have investigated several candidate neutron spectrum measurement techniques, which could be implemented to guarantee well-defined, repeatable beam conditions to users. Our investigation also includes considerations regarding the gamma rays in the beams.

On the possible use of the MASURCA reactor as a flexible, high-intensity, fast neutron beam facility

In recent work [1, 2], we have shown that the MASURCA research reactor could be used to deliver a fairly-intense continuous fast neutron beam to an experimental room located next to the reactor core. As a consequence of the MASURCA favorable characteristics and diverse material inventories, the neutron beam intensity and spectrum can be further tailored to meet the users' needs, which could be of interest for several applications. Monte Carlo simulations have been performed to characterize in detail the extracted neutron (and photon) beam entering the experimental room. These numerical simulations were done for two different bare cores: A uranium metallic core (∼30% 235U enriched) and a plutonium oxide core (∼25% Pu fraction, ∼78% 239Pu). The results show that the distinctive resonance energy structures of the two core leakage spectra are preserved at the channel exit. As the experimental room is large enough to house a dedicated set of neutron spectrometry instruments, we have investigated several candidate neutron spectrum measurement techniques, which could be implemented to guarantee well-defined, repeatable beam conditions to users. Our investigation also includes considerations regarding the gamma rays in the beams.

Level structure of 164Dy from the (n, n′γ) reaction

By employing a beam of reactor fast neutrons, gamma-ray spectra and angular distributions of gamma rays with respect to the neutron-beam axis were measured in the reaction 164Dy(n, n′γ). The scheme of levels and gamma transitions in 164Dy was composed on the basis of data published earlier and new levels, rotational bands, gamma transitions, and multipole-mixing parameters. It is concluded that the scheme of J = 0–4 levels is complete up to the excitation energy of 1.95 MeV. The commonly accepted rule in constructing K n π = 02 + and 11 + rotational bands is found to be violated. The nature of the 2+ level at the energy of 1796.68 keV is discussed.

Effects of combined neutron and gamma irradiation upon silicone foam

The total dose effect of combined fast-neutron beam and 60Co γ-ray radiation on silicone foam in air and nitrogen were investigated, respectively. The results show that foam hardening occurs and crystallization of polymer matrix decreases with increasing dose. Gas chromatograph was used to identify the kinetics of volatile products generating, which generally increase with increasing total dose. The study indicates that combined neutron and gamma irradiation would influence silicone foam property obviously during the investigated dose range.

Measuring the Density of Different Materials by Using the Fast Neutron Beam and Associated Alpha Particle Technique

It was demonstrated in the previous work that various threat materials could be detected inside the sea going cargo container by measuring the three variables, carbon and oxygen concentration and density of investigated material. Density was determined by measuring transmitted neutrons, which is not always practical in terms of setting up the instrument geometry. In order to enable more geometry flexibility, we have investigated the possibility of using the scattered neutrons in cargo material identification. For that purpose, the densities of different materials were measured depending on the position of neutron detectors and neutron generator with respect to the target position. One neutron detector was put above the target, one behind and one in front of the target, above the neutron generator. It was shown that all three positions of neutron detectors can be successfully used to measure the target density, but only if the detected neutrons are successfully discriminated from the gamma rays.

Commissioning optically stimulated luminescence in vivo dosimeters for fast neutron therapy.

Clinical in vivo dosimeters intended for use with photon and electron therapies have not been utilized for fast neutron therapy because they are highly susceptible to neutron damage. The objective of this work was to determine if a commercial optically stimulated luminescence (OSL) in vivo dosimetry system could be adapted for use in fast neutron therapy. A 50.5 MeV fast neutron beam generated by a clinical neutron therapy cyclotron was used to irradiate carbon doped aluminum oxide (Al2O3:C) optically simulated luminescence dosimeters (OSLDs) in a solid water phantom under standard calibration conditions, 150 cm SAD, 1.7 cm depth, and 10.3 × 10.0 cm field size. OSLD fading and electron trap depletion studies were performed with the OSLDs irradiated with 20 and 50 cGy and monitored over a 24-h period to determine the optimal time for reading the dosimeters during calibration. Four OSLDs per group were calibrated over a clinical dose range of 0-150 cGy. OSLD measurement uncertainties were lowered to within ±2%-3% of the expected dose by minimizing the effect of transient fading that occurs with neutron irradiation and maintaining individual calibration factors for each dosimeter. Dose dependent luminescence fading extended beyond the manufacturer's recommended 10 min period for irradiation with photon or electron beams. To minimize OSL variances caused by inconsistent fading among dosimeters, the observed optimal time for reading the OSLDs postirradiation was between 30 and 90 min. No field size, wedge factor, or gantry angle dependencies were observed in the OSLDs irradiated by the studied fast neutron beam. Measurements demonstrated that uncertainties less than ±3% were attainable in OSLDs irradiated with fast neutrons under clinical conditions. Accuracy and precision comparable to clinical OSL measurements observed with photons can be achieved by maintaining individual OSLD calibration factors and minimizing transient fading effects.