Neutron Component Research Articles

Impact of neutrons on the RadFET dose response when exposed to mixed-fields

The Radiation MONitoring (RadMON) system is widely employed at CERN to measure the radiation levels in the accelerators, as well as the degradation of electronics located in the Large Hadron Collider (LHC) tunnel and shielded areas. Radiation Field Effect Transistors (RadFETs) integrated in the RadMON specifically measure the Total Ionizing Dose (TID) in the accelerators complex and are affected in turn by the CERN radiation field.The CERN High energy AcceleRator Mixed-field test facility (CHARM) has been built with the intention of reproducing different mixed-fields (atmospheric, space, accelerators, ground,…), to test electronics when exposed to specific radiation environments. Among these fields, LHC-like environments are reproduced to test the RadMON's electronic components: the main goal is a full characterization of the RadMON response and the monitoring of its degradation, when it is exposed to the LHC radiation field.FLUKA Monte Carlo simulations are crucial at this stage as a powerful tool to reproduce and calibrate the RadMON response. Our present FLUKA Monte Carlo model of the RadFET is well representative of its experimental dose response to the CHARM mixed-field, in unshielded layout. However, the simulations-experiments agreement in lateral shielded positions is less accurate, probably due to the neutron component of the field.This paper focuses on the study of the RadFET dose response to neutrons, when the dosimeter is irradiated by mixed-fields. FLUKA Monte Carlo simulations and neutron test campaigns performed at ILL (Institut Laue Langevin) and LPSC (Laboratoire de Physique subatomique et de Cosmologie) in Grenoble, as well as at CERN are compared, to further investigate and fully characterize the RadFET response to neutrons.The simulations-measurements agreement is within the experimental uncertainties, while an overall agreement within a factor 2 is found in positions shielded by the movable walls, at CHARM. The test campaign showed the RadFET is insensitive to the thermal neutron component of the mixed-field at CHARM.

Investigation of thermal neutron detection capability of a CdZnTe detector in a mixed gamma-neutron radiation field

Abstract The aim of this study was to investigate the thermal neutron measurement capability of a CdZnTe detector irradiated in a mixed gamma-neutron radiation field. A CdZnTe detector was irradiated in one of the irradiation tubes of a 241Am-Be source unit to determine the sensitivity factors of the detector in terms of peak count rate (counts per second [cps]) per neutron flux (in square centimeters per second) [cps/neutron·cm−2·s−1]. The CdZnTe detector was covered in a 1-mm-thick cadmium (Cd) cylindrical box to completely absorb incoming thermal neutrons via 113Cd(n,γ) capture reactions. To achieve, this Cd-covered CdZnTe detector was placed in a well-thermalized neutron field (f-ratio = 50.9 ± 1.3) in the irradiation tube of the 241Am-Be neutron source. The gamma-ray spectra were acquired, and the most intense gamma-ray peak at 558 keV (0.74 γ/n) was evaluated to estimate the thermal neutron flux. The epithermal component was also estimated from the bare CdZnTe detector irradiation because the epithermal neutron cutoff energy is about 0.55 eV at the 1-mm-thick Cd filter. A high-density polyethylene moderating cylinder box can also be fitted into the Cd filter box to enhance thermal sensitivity because of moderation of the epithermal neutron component. Neutron detection sensitivity was determined from the measured count rates from the 558 keV photopeak, using the measured neutron fluxes at different irradiation positions. The results indicate that the CdZnTe detector can serve as a neutron detector in mixed gamma-neutron radiation fields, such as reactors, neutron generators, linear accelerators, and isotopic neutron sources. New thermal neutron filters, such as Gd and Tb foils, can be tested instead of the Cd filter due to its serious gamma-shielding effect.

The CANDELLE Experiment for Characterization of Neutron Sensitivity of LiF TLDs

As part of the design studies of future power and research nuclear reactors, the validation of neutron and photon calculation schemes requires the implementation of nuclear heating measurements. Such measurements are usually performed in very low-power reactors, whose core dimensions are accurately known and where irradiation conditions are entirely controlled. The use of thermoluminescent dosimeters is particularly well suited to gamma heating measurements, although the TLDs are also sensitive to neutrons depending on their composition. Hence, for gamma heating assessment in a mixed gamma–neutron field, the neutron sensitivity correction factors of TLDs has to be accurately determined to ensure a better interpretation of doses measured in a reactor with reduced uncertainties. This paper presents the CANDELLE experiment, which is dedicated to the implementation of a pure neutron field calibration of lithium-enriched TLDs, by using the Platform for Studies and Research on Nuclear Energy platform of LPSC. This calibration step is part of a promising approach that has been recently developed at INFN for medical purposes, aiming at determining the gamma and neutron contributions to the doses measured by LiF TLDs in the mixed field, from the peak height ratios of the gamma and neutron calibration glow curves of this type of TLDs. The test irradiations conducted at LPSC within the first phase of the CANDELLE project allowed retrieving the peak height of LiF TLDs in fast neutron field, hence providing an early assessment of the neutron components of doses measured in the EOLE reactor at CEA Cadarache with around 10% uncertainty at $1\sigma$ . From these preliminary results, the second phase of the project will be devoted, on the one hand, to the use of moderator screens aiming at achieving a thermal neutron field while avoiding a too strong attenuation of the flux, and on the other hand, to the determination of the neutron spectrum at different locations within the irradiation area.

Dosimetry in mixed neutron-gamma fields with a Timepix detector

We used the hybrid semiconductor pixel detector Timepix as an area dosimeter in mixed neutron-gamma fields. The surface of the detector was covered with several converters based on 6Li, polyethylene, Th and enriched U. We used three different neutron sources for calibration of the device – thermal neutrons from graphite pile, 241Am-Be and 252Cf. The desired neutron component of dosimetry and operational quantities can be determined by counting events under the converters. The segmentation of the Timepix detector and its capability to measure energy deposition of each interacting quantum of ionizing radiation allows a separation of neutron events from X-ray/gamma or electron interaction. Thus, the device can also be used for simultaneous X-ray and gamma dosimetry, where it is in some aspects superior to most of the commercial devices, given its detection threshold of 3–5 keV.

Verification of cosmic neutron doses in long-haul flights from Japan

International Commission on Radiological Protection recommends that aircraft crew and frequent flyers be informed of their individual doses received from cosmic radiation onboard aircrafts. The cosmic radiation dose in aviation is generally assessed by model calculations. In Japan, the code “JISCARD EX” is used since 2007 for management of cosmic radiation exposure of aircraft crew. In the present study, the precision of this code was investigated in regard to neutrons which contribute the most to the effective dose in aviation. Measurements of cosmic neutrons were performed with two moderator-type neutron monitors having different response functions: a conventional-type rem meter (NCN1) and an extended energy-range rem meter (WENDI-II) in four long-haul flights to Singapore, Sydney, Washington, D.C. and London from Japan (Narita or Kansai airport). Through the combined analyses of these measurements, the contribution of high-energy (>15 MeV) neutron component was estimated. The ambient dose equivalents, H*(10), measured with WENDI-II agreed well with the calculations made by JISCARD EX, while the contribution of the high-energy component obtained as the difference between the measured H*(10) values of two monitors was systematically higher than the model calculations.

Operation of the prospective beamline calorimeter in the high-radiation forward environment of the international linear collider

Results on electromagnetically-induced radiation damage to silicon diode sensors, obtained from the T506 experiment at SLAC, are used in concert with detailed shower simulations to project the effects of radiation damage on the proposed International Linear Collider Beamline Calorimeter (BeamCal) detector system. The study makes use of the FLUKA Monte Carlo to simulate electromagnetic showers in both the T506 apparatus and the prospective BeamCal detector system. Under the conservative assumption that damage leading to sensor leakage currents is dominated by the neutron component of the electromagnetic shower, and assuming that resulting leakage currents depend linearly on neutron fluence, the power consumption required to operate the BeamCal detector at a temperature of −10° C would be expected to increase by approximately 100 W per year of operation. Lowering the operating temperature to −30°C would be expected to reduce the growth in power consumption to approximately 10 W per year. Under other assumptions about the source of damage, the accumulated power draw would be expected to be significantly less. Results on fluences of both electromagnetic and hadronic particles in regions peripheral to the bulk of the BeamCal detector system, where front-end electronics would be mounted, are also presented.

Scintillating Fiber Devices for Particle Therapy Applications

Particle therapy (PT) is a radiation therapy technique in which solid tumors are treated with charged ions and exploits the achievable highly localized dose delivery, allowing to spare healthy tissues and organs at risk. The development of a range monitoring technique to be used online, during the treatment, capable to reach millimetric precision is considered one of the important steps toward an optimization of the PT efficacy and of the treatment quality. To this aim, charged secondary particles produced in the nuclear interactions between the beam particles and the patient tissues can be exploited. Besides charged secondaries, neutrons are also produced in nuclear interactions. The secondary neutron component might cause an undesired and not negligible dose deposition far away from the tumor region, enhancing the risk of secondary malignant neoplasms that can develop even years after the treatment. An accurate neutron characterization (flux, energy and emission profile) is, hence, needed for a better evaluation of long-term complications. In this contribution, two tracker detectors, both based on scintillating fibers, are presented. The first one, named dose profiler (DP), is planned to be used as a beam range monitor in PT treatments with heavy ion beams, exploiting the charged secondary fragments production. The DP is currently under development within the Innovative Solutions for In-Beam DosimEtry in Hadrontherapy project. The second one is dedicated to the measurement of the fast and ultrafast neutron component produced in PT treatments, in the framework of the monitor for neutron dose in hadrontherapy project. Results of the first calibration tests performed at the Trento Protontherapy Center and at Centro Nazionale di Adroterapia Oncologica (Italy) are reported, as well as simulation studies.

TLD calibration for neutron fluence measurements at JET fusion facility

Measurements of neutron streaming through penetrations in biological shields are being carried out at JET fusion device by means of thermoluminescence (TL) detectors with the objective to validate the neutronics codes and nuclear data widely applied in ITER nuclear analyses in a real fusion environment. TLDs response due to the neutron component of the radiation field is related to the neutron fluence in a well-defined neutron energy spectrum. Therefore, a TLDs calibration in real fusion radiation fields is necessary to allow neutron fluence from TL measurements at JET to be more precisely calculated. Hence, a MCP-N and MCP-7 TLDs produced at the IFJ PAN in Kraków were calibrated at the ENEA facilities of Frascati and Casaccia laboratories. The obtained results have been analysed and new calibration factors are proposed. The detection system based on TLDs developed and calibrated for JET experiments can then be generally applied not only to fusion neutron fields, but also to ITER to monitor the neutron fluence outside the biological shield.

Investigation of the EAS Neutron Component with the PRISMA-32 Array

Investigation of the EAS Neutron Component with the PRISMA-32 Array

Identification of differentially expressed genes and pathways in mice exposed to mixed field neutron/photon radiation

BackgroundRadiation exposure due to the detonation of an improvised nuclear device remains a major security concern. Radiation from such a device involves a combination of photons and neutrons. Although photons will make the greater contribution to the total dose, neutrons will certainly have an impact on the severity of the exposure as they have high relative biological effectiveness.ResultsWe investigated the gene expression signatures in the blood of mice exposed to 3 Gy x-rays, 0.75 Gy of neutrons, or to mixed field photon/neutron with the neutron fraction contributing 5, 15%, or 25% of a total 3 Gy radiation dose. Gene ontology and pathway analysis revealed that genes involved in protein ubiquitination pathways were significantly overrepresented in all radiation doses and qualities. On the other hand, eukaryotic initiation factor 2 (EIF2) signaling pathway was identified as one of the top 10 ranked canonical pathways in neutron, but not pure x-ray, exposures. In addition, the related mTOR and regulation of EIF4/p70S6K pathways were also significantly underrepresented in the exposures with a neutron component, but not in x-ray radiation. The majority of the changed genes in these pathways belonged to the ribosome biogenesis and translation machinery and included several translation initiation factors (e.g. Eif2ak4, Eif3f), as well as 40S and 60S ribosomal subunits (e.g. Rsp19, Rpl19, Rpl27). Many of the differentially downregulated ribosomal genes (e.g. RPS19, RPS28) have been causally associated with human bone marrow failure syndromes and hematologic malignancies. We also observed downregulation of transfer RNA processes, in the neutron-only exposure (p < 0.005). Ingenuity Pathway Analysis (p < 0.05) of differentially expressed genes predicted significantly suppressed activity of the upstream regulators c-Myc and Mycn, transcription factors known to control ribosome biogenesis.ConclusionsWe describe the gene expression profile of mouse blood following exposure to mixed field neutron/photon irradiation. We have discovered that pathways related to protein translation are significantly underrepresented in the exposures containing a neutron component. Our results highlight the significance of neutron exposures that even the smallest percentage can have profound biological effects that will affect medical management and treatment decisions in case of a radiological emergency.

Effect of higher harmonics in the area-ratio pulsed neutron source technique

The area-ratio pulsed neutron source technique, which can yield a subcriticality in dollar units, is given by Ap/Ad, the area ratio of the prompt neutron component to the delayed neutron component. In this paper, both components are reconstructed by the summation of the spatial harmonics that are obtained by solving the α–mode eigenvalue equations based on the neutron transport and diffusion theories. Monte Carlo simulations for the area-ratio method in a one-dimensional slab are performed. The reconstructed prompt and delayed components agree well with the simulation results. The areas Ap and Ad contain a higher harmonic effect, and the ratio Ap/Ad differs from the true subcriticality. The effect of the higher harmonics in Ap can be reduced by the extrapolated area-ratio method if the earlier period after the pulse generation is successfully excluded from the fitting period. However, there is no way to remove the effect of the higher harmonics from the delayed neutron component, but it alleviates itself because it is given by the subtraction of the prompt component from the total (delayed and prompt) component. The subcriticality in dollar units adjusted by the extrapolated area-ratio method is considerably improved compared with the unadjusted Ap/Ad. The improvement is remarkable for a near-critical system in which the denominator Ad is relatively large, and the effect of the higher harmonics in Ad is minor.

Assessment of mixed neutron and photon radiation ratios using a tissue equivalent proportional counter on KSTAR

Tokamaks have a mixed radiation field consisting of neutrons, neutron-induced gamma rays, and hard X-rays due to runaway electrons. Neutron and gamma-ray diagnostics for characterization of the mixed radiation fields of tokamak in such an environment is essential for determining neutron emission rate as well as for understanding behaviors of fast ions in plasma operations.The experiment using a tissue equivalent proportional counter (TEPC) based on a microdosimetric technique has performed with the aiming of investigating its application to tokamaks through the measurement of dosimetric quantities at the KSTAR tokamak. For the work, a Bemjamin type of spherical TEPC with a 0.318 cm tissue equivalent wall of Shonka type A-150 plastic has applied to define lineal energy boundaries for secondary particles caused by each radiation component. The TEPC has placed on a deck at a distance of about 20 m from KSTAR tokamak. The mixture distributions have obtained from the measurement of lineal energy spectra. The mixture ratio of neutrons and gammas in the KSTAR tokamak has evaluated to be around 1:4. The present result shows not only the availability of the developed TEPC for the assessment of neutron and gamma components in the tokamak, but also its applicability for fusion reactors even though the application of TEPC on tokamak is still at experimental stage.

Search for dark matter effects on gravitational signals from neutron star mergers

Motivated by the recent detection of the gravitational wave signal emitted by a binary neutron star merger, we analyse the possible impact of dark matter on such signals. We show that dark matter cores in merging neutron stars may yield an observable supplementary peak in the gravitational wave power spectral density following the merger, which could be distinguished from the features produced by the neutron components.

INVESTIGATION ON RADIATION SHIELDING PROPERTIES OF SPECIAL CONCRETE IN NEUTRON FIELDS.

This paper presents the results on radiation shielding of special types of concrete, designed for nuclear reactor containments. The research focused on the study of shielding properties against neutron component of ionizing radiation. For this purpose, two types of ionizing source were used: the isotopic reference neutron field of 239Pu-Be in calibration laboratory and the MARIA Research Reactor.

Nonnegative Tensor Factorization Approach Applied to Fission Chamber’s Output Signals Blind Source Separation

Inside nuclear reactors, gamma-rays emitted from nuclei together with the neutrons introduce unwanted backgrounds in neutron spectra. For this reason, powerful extraction methods are needed to extract useful neutron signal from recorded mixture and thus to obtain clearer neutron flux spectrum. Actually, several techniques have been developed to discriminate between neutrons and gamma-rays in a mixed radiation field. Most of these techniques, tackle using analogue discrimination methods. Others propose to use some organic scintillators to achieve the discrimination task. Recently, systems based on digital signal processors are commercially available to replace the analog systems. As alternative to these systems, we aim in this work to verify the feasibility of using a Nonnegative Tensor Factorization (NTF) to blind extract neutron component from mixture signals recorded at the output of fission chamber (WL-7657). This last have been simulated through the Geant4 linked to Garfield++ using a 252Cf neutron source. To achieve our objective of obtaining the best possible neutron-gamma discrimination, we have applied the two different NTF algorithms, which have been found to be the best methods that allow us to analyse this kind of nuclear data.

Thermoluminescence properties of 30Y2O3·30P2O5·40SiO2 vitroceramics in mixed neutron-gamma fields

Powders of the 30Y2O3·30P2O5·40SiO2 vitroceramic were irradiated with broad spectrum d+Be (Eneutron = 0–14.5 MeV) and quasi-monoenergetic d+D neutrons (Eneutron = 12.4 ± 0.22 MeV). The absorbed dose of d+Be neutrons was Dn = 2.52 ± 8% Gy with Dγ = 0.22 ± 14% Gy accompanied gamma absorbed dose. The absorbed dose of d+D neutrons was Dn = 1.43 ± 8% Gy with Dγ = 0.21 ± 14% Gy gamma absorbed dose. The thermoluminescence (TL) induced in the vitroceramics was studied. Both the gamma and neutron component contributed to the TL signals. The relative neutron sensitivities were [(TLn/TLγ)/(Dn/Dγ)]d+Be = 0.04 ± 60% and [(TLn/TLγ)/(Dn/Dγ)]d+D = 0.11 ± 43%.

Natural Radiation Dose and Geomagnetic Effect

Earth keeps getting bombarded by high-energy particles that originate in the outer space and in Sun. Cosmic radiation in Earth’s atmosphere consists of a photon and directly ionizing component and a neutron component. Charged particles of cosmic radiation are deflected by the geomagnetic field that is more expressed at the equator than near the poles. Photon radiation was measured by Radiameter ESM FH 40G-L10 at 26 main meteorological stations in all parts of Croatia. The correlation between the photon dose rate and latitude was examined, as well as multiple correlations for the photon dose, latitude and altitude. The obtained positive correlation coefficients were statistically significant. The neutron component of the cosmic radiation was measured by series of nuclear track-etched detectors, at the same meteorological stations during one year period. The dependence of the neutron dose rate on the altitude was found and the associated equation of the linear regression was derived. Relation between the values of neutron dose N and altitude h, showed significant dependence of the neutron dose on altitude. However, the correlation of neutron dose and geographic (geomagnetic) latitude was not statistically significant, probably due to a small range of geographic latitudes for the measuring stations in Croatia.

Design of Moderator Neutron for Boron Neutron Capture Therapy in Kartini Nuclear Reactor Using Monte Carlo N Particle 5 Simulation

The optimation of moderator design on radial piercing beam port in Kartini Nuclear Reactor using MCNP5 simulation has been carried out. This optimation has been used for obtaining neutron flux according to International Atomic Energy Agency (IAEA) regulation. The methode used in this experiment was combination of shifting methode and filtering methode. Independent variables varied, were material and thickness of collimator wall, moderator, filter and gamma shielding. Optimized epithermal neutron flux of the collimator for BNCT has been achieved 1.20 × 101 n/cm2s. The result of beam quality are 0.8 for neutron current component, 0.03 for thermal neutron component, 312 × 10-13 Gy cm2s/n for fast neutron component and 38.5 × 10-13 Gy cm2s/n for gamma contamination component. It can be concluded that, the designed moderator is feasible and applicable for BNCT.

Design of beam shaping assembly based on 3.5 MeV radio-frequency quadrupole proton accelerator for boron neutron capture therapy

Boron neutron capture therapy (BNCT) is expected to be an effective method of improving the treatment results on malignant brain glioma and malignant melanoma, for which no successful treatment has been developed so far. The beam shaping assembly (BSA) of accelerator-based boron neutron capture therapy (A-BNCT) consists of a moderator, a reflector, gamma and thermal neutron shielding and a collimator. The BSA moderates the fast neutron produced in target to epithermal energy range. Design of BSA is one of the key jobs in BNCT project. An optimized study was conducted to design a beam shaping assembly for BNCT facility based on 3.5 MeV 10 mA radio-frequency quadrupole proton accelerator at Dongguan Neutron Science Center. In this simulation work, the neutron produced from the 7Li (p, n) 7Be reaction by 3.5 MeV proton is adopted as a neutron source term. In order to search for an optimized beam shaping assembly for accelerator-based BNCT, Monte Carlo simulation is carried out based on the parameters of moderator material and structure, the Gamma shielding, and the thermal neutron filter in the beam shaping assembly. The beam shaping assembly in this work consists of various moderator materials, teflon as reflector, Bi as gamma shielding, 6Li as thermal neutron filter, and lithium polyethylene as collimator. After comparing the simulation results of Fluental and LiF moderator materials, the beam shaping assembly configuration based on sandwich Fluental-LiF configuration is proposed. The sandwich Fluental-LiF configuration is made up of Fluental and LiF layer by layer, like a sandwich structure, and each layer is 2 cm thick. According to the beam quality requirement of the IAEA-tecdoc-1223 report, the optimized epithermal neutron flux in air at the exit of BSA of the sandwich Fluental-LiF configuration is 9.14×108 n/(cm2·s), which is greater than those of the Fluental configuration (7.81×108 n/(cm2·s)) and LiF configuration (8.79×108 n/(cm2·s)), when the ratio of fast neutron component to gamma ray component to thermal neutron is less than the limiting value of IAEA recommendation. Subsequently, the depth distribution of the equivalent doses in the Snyder head phantom is calculated to evaluate the treatment characteristic. The simulation results show that the therapy rate of the beam shaping assembly based on the sandwich Fluental-LiF configuration is basically equal to that of the Fluental configuration and better than that of the LiF configuration, and the therapy time is less than that of the Fluental configuration. This means that the beam shaping assembly based on the sandwich Fluental-LiF configuration is one of the suitable options for our accelerator-based BNCT.

The CANDELLE experiment for characterization of neutron sensitivity of LiF TLDs

As part of the design studies conducted at CEA for future power and research nuclear reactors, the validation of neutron and photon calculation schemes related to nuclear heating prediction are strongly dependent on the implementation of nuclear heating measurements. Such measurements are usually performed in low-power reactors, whose core dimensions are accurately known and where irradiation conditions (power, flux and temperature) are entirely controlled. Due to the very low operating power of such reactors (of the order of 100 W), nuclear heating is assessed by using dosimetry techniques such as thermoluminescent dosimeters (TLDs). However, although they are highly sensitive to gamma radiation, such dosimeters are also, to a lesser extent, sensitive to neutrons. The neutron dose depends strongly on the TLD composition, typically contributing to 10-30% of the total measured dose in a mixed neutron/gamma field. The experimental determination of the neutron correction appears therefore to be crucial to a better interpretation of doses measured in reactor with reduced uncertainties. A promising approach based on the use of two types of LiF TLDs respectively enriched with lithium-6 and lithium-7, precalibrated both in photon and neutron fields, has been recently developed at INFN (Milan, Italy) for medical purposes. The CANDELLE experiment is dedicated to the implementation of a pure neutron field “calibration” of TLDs by using the GENEPI-2 neutron source of LPSC (Grenoble, France). Those irradiation conditions allowed providing an early assessment of the neutron components of doses measured in EOLE reactor at CEA Cadarache with 10% uncertainty at 1σ.