Characteristics Of Neutron Fields Research Articles

Characterisation of neutron fields at the n-lab, a fast neutron facility at the University of Cape Town

The n-lab is a fast neutron facility based in the Department of Physics, University of Cape Town, offering collimated neutron beams produced by an MP 320 deuterium–tritium sealed tube neutron generator, and a 220 GBq americium–beryllium radioisotopic source. Characterisations of the spatial and energy distributions of the fast neutron beams were performed using an EJ-301 organic liquid scintillator detector and digital data acquisition system. Neutron energy spectra were obtained through unfolding analyses with MAXED, and a Monte Carlo approach to the propagation of uncertainties was implemented. Measurements of fluence and neutron emission rates were determined through the neutron activation of copper foils and subsequently used to validate the scaling of the unfolded neutron energy spectra.

Characteristics of neutron fields at pool-type research nuclear reactors

The article presents results of experimental determination of the characteristics of neutron fields behind the biological shielding of reactor facilities in the physical hall of pressurized water research reactors of the pool type . In the work , measurements of the energy distribution of the neutron radiation flux density , determination of anisotropy and correction factors for individual dosimeters were carried out . The energy distribution of the neutron radiation flux density was obtained using an MKS-AT1117M multi-sphere dosimeterradiometer w ith a BDKN-06 d etection u nit a nd a s et o f p olyethylene m oderator s pheres . Based o n t he r esults o f d etermining t he e nergy d istribution o f t he n eutron r adiation f lux d ensity , t he a verage v alues o f t he n eutron e nergy w ere e stablished , w hich a re i n t he e nergy r ange : 0.06–0.35 M eV . The d ifference b etween n eutron f ields a t t he s urveyed p ersonnel w orkplaces a nd n eutron f ields i n w hich i ndividual d osimeters a re c alibrated l eads t o a n a dditional e rror i n e stimating s uch d osimetric q uantities a s a mbient d ose e quivalent , i ndividual d ose e quivalent o r e ffective d ose . The p erformed s tudies a llow t o i mprove t he s ystem o f i ndividual d osimetric c ontrol b ased o n t he c ycle o f i mprovements : n ew k nowledge – e xperimental s tudies – i mplementation o f r esearch r esults – r egulation o f a ctivities t o r educe t he e xposure o f w orkers – a nalysis o f t he d ata o btained – n ew k nowledge . The r adiation a nisotropy w as e stimated f rom t he r esults o f m easurements o f t he a ccumulated d ose o f n eutron r adiation b y i ndividual t hermoluminescent d osimeters p laced o n f our v ertical p lanes o f a h uman p hantom . A dequate e stimates o f t he e ffective d ose t o p ersonnel c an b e o btained u sing c orrection f actors f or i ndividual d osimeters . For v arious w orkplaces a nd m ethods , t he c orrection f actors r ange f rom 0.04 t o 0.7.

Characterisation of neutron field in large graphite insertion in special core of the LR-0 reactor

Graphite is important reactor material used as a neutron moderator in various reactor designs. It is not only structural material used in previous reactors design but even material to which attention is focused due to the very high-temperature reactor design, which uses graphite as moderator and reflector. Due to the well-characterised cross-section of graphite, it is also a good candidate for neutron shaping experiments. In this kind of experiment, the neutron spectra are modified to the unconventional shape of neutron spectra which can be used to validate cross-section. This paper deals with validation of neutron field in graphite block surrounded by driver core arranged in large special core in LR-0 reactor. The experimentally determined shape of neutron spectra and spatial distribution of neutron flux is compared with the calculation. It is worth noting that the agreement for flux distribution is satisfactory in regions below the moderator level.

Using Thin-Film Breakdown Counters for the Neutron Field Characterization in Experiments on “Quinta” Setup

Using Thin-Film Breakdown Counters for the Neutron Field Characterization in Experiments on “Quinta” Setup

Cobalt and silver nanocoatings for reactor dosimetry

Activation foils are an important tool for the characterization of neutron fields. Some of the materials that are used in these foils have large interaction cross-sections that cause unwanted self-shielding effects. In practice experimenters minimize these effects by using aluminium alloys. An alternative approach can be a nanocoating of a pure material on a carrier. The validity of this approach is investigated in this work. Nanocoatings can be more flexible compared to alloys and can probably reduce the number of required post-irradiation gamma spectrometry measurements.Cobalt and silver nanocoatings were deposited by physical vapour deposition on nickel and aluminium carrier foils. The nanocoatings were tested in two irradiation campaigns in the Belgian Reactor 1 at SCK CEN. By depositing nanocoatings with different thickness and determining the corresponding number of activated atoms the inherent flexibility of the technique is demonstrated.When the dosimeters were punched from the carrier foils, the metal cylindrical punch damaged the nanocoatings which increased the spread on the number of atoms between different dosimeters. This is prevented by including a Ti interlayer of 5 nm between the carrier and the cobalt and silver layers. It was shown that this results in a coating with good homogeneity or minimal spread.This study shows that applying nanocoatings on a carrier is a valid technique to make dosimeters.

Characterisation of neutron field in the polyethylene neutron irradiator

The paper describes neutron field characterisation of low-flux multipurpose educational irradiator developed at Czech Technical University in Prague. The irradiator is aimed for demonstration experiments including neutron activation analysis, delayed neutron counting, or studies related to neutron and/or gamma detection and spectrometric devices. It may accommodate various neutron sources including 252Cf or AmBe radionuclide sources, D-D generator, or in-reactor irradiated nuclear material serving as delayed neutron source, or gamma sources including radionuclide ones or short-lived sources produced in the adjacent reactor.The characterisation was performed based on neutron activation technique using gold foils. It included two experimental parts. The first one verified the level of response symmetry in the four irradiation channels and characterisation of the axial distribution in the irradiation channels. Within the second one, the responses to thermal and epithermal neutrons and the cadmium ratio in the central irradiation position were determined. Whereas the former was determined solely with the 252Cf source, the latter was performed for all available sources: 252Cf, AmBe, and the D-D generator. The experimental results were further compared to calculations by the MCNP Monte Carlo code.

JSIR2S code for delayed radiation simulations: Validation against measurements at the JSI TRIGA reactor

Interest on development of computational tools for calculations of radiation field due to decay of radioactive activation and fission products (delayed radiation) has increased in recent years, mainly due to requirements on shutdown dose rate for the future ITER fusion reactor and material testing reactors (MTR), where gamma heating values of several 10 Wg−1 can be reached in reactor structural components during reactor steady state operation and for characterization of research reactor irradiation facilities. Previous experimental work shows a roughly 30% contribution of delayed gamma rays to the total gamma ray flux.An extensive experimental campaign at the JSI TRIGA reactor has been carried out using multiple ionization and fission chamber detectors for gamma and neutron field characterization. A series of reactor power steps was performed with said detectors in different irradiation positions during steady reactor power and after shutdown. The reactor and the used detectors, along with irradiation power steps have been modelled in detail using the JSIR2S code system framework to compare measured and calculated fluxes and dose rates. Simulated results are in good agreement with measurements and with experimentally obtained values of delayed gamma fractions from previous work.

DIAMON: A portable, real-time and direction-aware neutron spectrometer for field characterization and dosimetry

An innovative portable detection system based on real-time spectrometry was developed for neutron field characterization and dosimetry. This system, called DIAMON (Direction-aware Isotropic and Active neutron MONitor with spectrometric capabilities), relies on a multi-detector geometry and a built-in unfolding code to provide in real time all field and operational quantities of interest. A patent pending design provides a quasi-ideal isotropic response and an optimized spectrometric performance from thermal to high energies. Furthermore, the custom signal processing and acquisition system is conceived for deriving continuously the 3D directional distribution of incoming neutrons. This work describes the characterization of DIAMON performances carried out at the neutron calibration facility of Politecnico di Milano. Neutron spectra, field quantities and dosimetric values are reported and compared with those assessed by a reference, calibrated, Bonner Sphere System. The overall variability of the DIAMON angular response and the gamma sensitivity are presented and discussed. An example of the continuous monitoring capabilities is also shown. Results demonstrate DIAMON is an all-in-one detection system able to characterize accurately all neutron field properties in real-time.

JSI TRIGA neutron and gamma field characterization by TLD measurements

A well characterized radiation field inside a research nuclear reactor irradiation facilities enables precise qualification of radiation effects to the irradiated samples such as nuclear heating or changes in their electrical or material properties. To support the increased utilization of the JSI TRIGA reactor irradiation facilities in the past few years mainly on account of testing novel detector designs, electronic components and material samples, we are working on increasing the neutron and gamma field characterization accuracy using various modeling and measurement techniques. In this paper we present the dose field measurements using thermo-luminescent detectors (TLD’s) with different sensitivities neutron and gamma sensitivities, along with multiple ionization and fission chamber. Experiment was performed in several steps from reactor start-up, steady operation and a rapid shutdown, during which the ionization and fission chamber signals were acquires continuously, while the TLD’s were being irradiated at different stages during reactor operation and after shutdown, to also capture response to delayed neutron and gamma field. The results presented in this paper serve for validation of JSI designed JSIR2S code for delayed radiation field determination, initial results of its application on the JSI TRIGA TLD measurements will also be presented.

Thermal neutron field characteristics in the neutron exposure accelerator system for biological effect experiments (NASBEE) facility

Abstract The neutron exposure accelerator system for biological effect experiments (NASBEE) facility was constructed to investigate the biological effects of fast neutrons produced by the 9Be(p, n)9B and 9B(D, n)10 B reactions. In this work, we describe the modification of the NASBEE facility for the development of thermal neutron detectors and radiology applications. We characterized thermal neutron fields created with a polyethylene (PE) moderator. The maximum thermal neutron fluxes via proton (600 μ A) and deuteron (350 μ A) beams were estimated to be 5.7 × 107 and 1.2 × 108 cm−2 s−1 , respectively, by using the 30-mm-thick PE moderator set in front of the irradiation sample The ratios of the gamma ray absorbed dose to thermal neutron fluence were 3.6 × 10−12 Gy cm2 for the 9Be(p, n)9B reaction and 6.1 × 10−11 Gy cm2 for the 9B(D, n)10B reaction. The thermal neutron field in the NASBEE facility can be used for various applications of thermal neutrons and is now open to external users.

The methodology of characterization of neutron leakage field from PET production cyclotron for experimental purposes

During the production of 18F isotope for radiopharmaceuticals in 18O(p,n)18F reactions, the leakage neutrons are mostly considered as a waste product. The utilization of a cyclotron based neutron source might be an interesting application because its average energy is relatively high and emissivity is quite strong. Thus its use might be useful in many fields of neutron based research. This paper aims to define the methodology and its following use for the characterization of the secondary neutron field leaking from 18O enriched H2O target in IBA Cyclone 18/9. Experimental characterization is based on the employment of independent methods, namely the proton recoil method using a stilbene scintillation detector and neutron activation analysis with selected IRDFF materials. Neutron field characteristics were also tested by calculation in the standard MCNP6 code model and using FENDL-3, TENDL-2017 nuclear data libraries for (p,n) reactions. The calculation models have been found as discrepant in some quantities more or less, thus it is recommended to use experimental characterization as a sole method.

Characterization of the Radiation Field in the ATLAS Experiment With Timepix Detectors

We present a study of the radiation field at various locations in the ATLAS experiment, using compact detector systems based on pixelated silicon sensors assembled with Timepix readout chips. The hodoscope design of the ATLAS-Timepix (TPX) detectors includes neutron converters in between two sensors, allowing the characterization of both neutron and charged particle fields on a track by track basis. Thermal and fast neutrons are discriminated by segmenting the sensor area with dedicated sensitive materials. Using specific pattern recognition algorithms, clusters from electrons and photons above ~10 keV, minimum ionizing particles (MIPs), and highly ionizing particles are classified. A coincidence method using the time-over-threshold mode of the chip is developed to extract stopping power and directional information of energetic charged particles. Thermal neutron fluences are obtained for each ATLAS-TPX unit, illustrating the effect of detector material and shielding in the experimental cavern. Reconstructed trajectories of energetic charged particles point out radiation coming from the interaction point and other hot spots.

An active Bonner sphere spectrometer capable of intense neutron field measurement

A Bonner sphere spectrometer (BSS) was developed compensating for the lack of active BSSs for intense neutron field characterization. The spectrometer combines the merits of present active and passive BSSs, namely, online data acquisition capability and intense neutron field resistance, respectively. The key elements of the development are the utilization of diamond detectors as thermal neutron sensors of BSSs and the incorporation of the air gap into the design of the diamond detector for optimizing the pulse height spectrum in order to enhance the rejection capability to γ ray backgrounds and to decrease the impacts of spectrometer instabilities. A two-step method capable of >100 times of calculation time saving compared to the whole geometry model was suggested to establish the response function for neutrons below 20 MeV whose reliability was verified by the two other models. The applicability of the BSS to intense neutron field characterization was demonstrated by the good performance in the Experimental Advanced Superconducting Tokamak (EAST) neutron field with an emission rate of ∼1013–1014 neutrons/s. The spectrometer is dedicated to the characterization of intense neutron fields around tokamaks. These devices may find an application in future tokamaks, such as the International Thermonuclear Experimental Reactor, the Demonstration Power Station, and the China Fusion Engineering Test Reactor, whose neutron emission rates will be >104 times higher than those of current tokamaks.

Characterization of JET neutron field in irradiation locations for DD, DT and TT plasmas

The neutron fluxes and spectra were characterized for four locations close to the plasma and related to activation experiments, as the preparation for the upcoming experimental campaigns in JET. The focus was on the study of a variance reduction technique in order to obtain statistically significant results in the parts of the neutron energy spectra, important for irradiation experiments. The DD, DT and TT plasmas were studied with the Monte Carlo hybrid method and the use of the ADVANTG program for generation of weight windows as variance reduction method to accelerate Monte Carlo simulations. The calculations were optimized to obtain low statistical uncertainties for all energy bins in the 640 energy group structure and for all three plasma sources. This included the acceleration of calculations for reaction rates of capture reactions, i.e. in the thermal flux region in irradiation positions on the first wall. Speed-ups due to use of the hybrid method in excess of two orders of magnitude were found with respect to analog calculations despite the vicinity of the plasma source.

Neutron field characterization at the independent spent fuel storage installation of the Trillo nuclear power plant

Neutron fields inside and outside the independent spent fuel storage installation of Trillo Nuclear Power Plant are characterized exhaustively in terms of neutron spectra and ambient dose equivalent, measured by Bonner sphere system and LB6411 monitor. Measurements are consistent with storage casks and building shield characteristics, and also with casks distribution inside the building. Outer values at least five times lower than dose limit for free access area are found. Measurements with LB6411 and spectrometer are consistent with each other.

High-Sensitivity Fast Neutron Detector KNK-2-8M

The design of the fast neutron detector KNK-2-8M is outlined. The results of he detector study in the pulse counting mode with pulses from 238U nuclei fission in the radiator of the neutron-sensitive section and in the current mode with separation of functional section currents are presented. The possibilities of determination of the effective number of 238U nuclei in the radiator of the neutron-sensitive section are considered. The diagnostic capabilities of the detector in the counting mode are demonstrated, as exemplified by the analysis of reference data on characteristics of neutron fields in the BR-1 reactor hall. The diagnostic capabilities of the detector in the current mode are demonstrated, as exemplified by the results of measurements of 238U fission intensity in the power startup of the BR-K1 reactor in the fission pulse generation mode with delayed neutrons and the detector placed in the reactor cavity in conditions of large-scale variation of the reactor radiation fields.

DEVELOPMENT, CHARACTERIZATION AND TESTING OF A SIMPLIFIED BONNER SPHERE SYSTEM FOR RAPID NEUTRON FIELD CHARACTERIZATION.

Personal neutron dosimetry requires workplace specific correction factors from detailed neutron field characterization. A Bonner sphere system (BSS) with a 3He proportional counter and a 3 inch an a 9 inch sphere was developed at SCK·CEN for rapid neutron field characterization. The BSS energy and angular responses were simulated with MCNPX and validated by irradiations with a thermal neutron beam at the Belgian Reactor 1 (BR1) and 252Cf and Am-Be sources at the SCK·CEN Laboratory for Nuclear Calibration (LNK). The BSS unfolding performance was tested using the FRUIT unfolding code for measurements of the scattered neutron field at the LNK. The unfolded spectra were in good agreement with MCNPX simulations.

Measurement of the energy spectrum of secondary neutrons in a proton therapy environment

Abstract Measurement of the energy spectrum of secondary neutrons were carried out at the OncoRay Proton Therapy facility in Dresden, following an approach originating in neutron metrology which is well suited for both the characterization of secondary neutron fields at proton therapy facilities and the validation of Monte Carlo simulations. For the experiment, a brass target was placed in the proton beam and Bonner spheres measurements were made at a distance of 2 m from the target and at different angles, 15° to 120°, with respect to the incoming proton beam. The measured spectra were compared to Monte Carlo simulations.

TWO NEW SINGLE-EXPOSURE, MULTI-DETECTOR NEUTRON SPECTROMETERS FOR RADIATION PROTECTION APPLICATIONS IN WORKPLACE MONITORING.

This communication describes two new instruments, based on multiple active thermal neutron detectors arranged within a single moderator, that permit to unfold the neutron spectrum (from thermal to hundreds of MeV) and to determine the corresponding integral quantities with only one exposure. This makes them especially advantageous for neutron field characterisation and workplace monitoring in neutron-producing facilities. One of the devices has spherical geometry and nearly isotropic response, the other one has cylindrical symmetry and it is only sensitive to neutrons incident along the cylinder axis. In both cases, active detectors have been specifically developed looking for the criteria of miniaturisation, high sensitivity, linear response and good photon rejection. The calculated response matrix has been validated by experimental irradiations in neutron reference fields with a global uncertainty of 3%. The measurements performed in realistic neutron fields permitted to determine the neutron spectra and the integral quantities, in particular H*(10).

INFLUENCE OF SCATTERED NEUTRON RADIATION ON METROLOGICAL CHARACTERISTICS OF АТ140 NEUTRON CALIBRATION FACILITY

Today facilities with collimated radiation field are widely used as reference in metrological support of devices for neutron radiation measurement. Neutron fields formed by radionuclide neutron sources. The aim of this research was to study characteristics of experimentally realized neutron fields geometries on АТ140 Neutron Calibration Facility using Monte Carlo method. For calibration, we put a device into neutron field with known flux density or ambient equivalent dose rate. We can form neutron beam from radionuclide fast-neutron source in different geometries. In containercollimator of АТ140 Neutron Calibration Facility we can install special inserts to gather fast-neutron geometry or thermal-neutron geometry. We need to consider neutron scattering from air and room’s walls. We can conduct measurements of neutron field characteristics in several points and get the other using Monte Carlo method. Thermal neutron collimator forms a beam from radionuclide source with a significant amount of neutrons with thermal energies. From found relationship between full neutron flux and distance to neutron source we see that inverse square law is violated. Scattered radiation contribution into total flux increases when we are moving away from neutron source and significantly influences neutron fields characteristics. While source is exposed in shadow-cone geometry neutron specter has pronounced thermal component from wall scattering. In this work, we examined main geometry types used to acquire reference neutron radiation using radionuclide sources. We developed Monte Carlo model for 238 Pu-Be neutron source and АТ140 Neutron Calibration Facility’s container-collimator. We have shown the most significant neutron energy distribution factor to be scattered radiation from room’s walls. It leads to significant changes of neutron radiation specter at a distance from the source. When planning location, and installing the facility we should consider radiation quality requirements.