The use of wide-band-gap solid-state neutron detectors is expanding in environments where a compact size and high radiation hardness are needed, such as spallation neutron sources and next-generation ...fusion machines. Silicon carbide is a very promising material for use as a neutron detector in these fields because of its high resistance to radiation, fast response time, stability and good energy resolution. In this paper, measurements were performed with neutrons from the ISIS spallation source with two different silicon carbide detectors together with stability measurements performed in a laboratory under alpha-particle irradiation for one week. Some consideration to the impact of the casing of the detector on the detector's counting rate is given. In addition, the detector response to Deuterium-Deuterium (D-D) fusion neutrons is described by comparing neutron measurements at the Frascati Neutron Generator with a GEANT4 simulation. The good stability measurements and the assessment of the detector response function indicate that such a detector can be used as both a neutron counter and spectrometer for 2-4 MeV neutrons. Furthermore, the absence of polarization effects during neutron and alpha irradiation makes silicon carbide an interesting alternative to diamond detectors for fast neutron detection.
Background: the gamma-emitting radionuclide Technetium-99m (99mTc) is still the workhorse of Single Photon Emission Computed Tomography (SPECT) as it is used worldwide for the diagnosis of a variety ...of phatological conditions. 99mTc is obtained from 99Mo/99mTc generators as pertechnetate ion, which is the ubiquitous starting material for the preparation of 99mTc radiopharmaceuticals. 99Mo in such generators is currently produced in nuclear fission reactors as a by-product of 235U fission. Here we investigated an alternative route for the production of 99Mo by irradiating a natural metallic molybdenum powder using a 14-MeV accelerator-driven neutron source. Methods: after irradiation, an efficient isolation and purification of the final 99mTc-pertechnetate was carried out by means of solvent extraction. Monte Carlo simulations allowed reliable predictions of 99Mo production rates for a newly designed 14-MeV neutron source (New Sorgentina Fusion Source). Results: in traceable metrological conditions, a level of radionuclidic purity consistent with accepted pharmaceutical quality standards, was achieved. Conclusions: we showed that this source, featuring a nominal neutron emission rate of about 1015 s−1, may potentially supply an appreciable fraction of the current 99Mo global demand. This study highlights that a robust and viable solution, alternative to nuclear fission reactors, can be accomplished to secure the long-term supply of 99Mo.
A compact DT neutron generator (NG) based on the mixed-beam operation was used as a calibration neutron source in the latest in-situ calibration of neutron detectors at the Joint European Torus ...(JET). In order to meet the requirement for the total uncertainty of the neutron detector calibration below ±10 %, the neutron emission properties had to be experimentally characterized and reproduced through detailed modelling of the neutron source characteristics and geometry of the neutron generator.
The detailed neutronics simulations were an essential part of both NG characterization and JET neutron detector calibration. The complex neutron emission properties of the NG were reproduced through a combination of simulations and highresolution neutron spectroscopy measurements. This meant that six different DT neutron source components resulting from NG's mixed beam operation were explicitly simulated and their relative intensities scaled based on experimentally obtained neutron spectrum measurements. Furthermore, the detailed model of the NG's geometry was produced based on information from the supplier of the NG and images from a computer tomography (CT) scan. Finally, the positioning of the neutron source inside the JET tokamak during in-situ calibration was reproduced based on the information from the remote handling system (RHS) at JET, the system responsible for the positioning of the source during the calibration experiment.
The extensive effort presented in the paper significantly contributed to the total uncertainties of the calibration factors well within the target value of ±10 %.
In the 2019 C38 Deuterium-Deuterium campaign at JET several different ITER-relevant materials and dosimetry foils were irradiated in a specially designed long-term irradiation station located inside ...the vacuum vessel with the purpose of testing the activation of ITER materials by fusion neutrons. The samples were exposed to a neutron fluence of 1.9E14 n/cm
2
during JET discharges performed in the experimental campaign over a period of 5 months. Gamma ray spectroscopy measurements were performed on irradiated samples to determine the activation of different long-lived isotopes in the samples. Monte Carlo computational analysis was performed to support the experiment by using the measured neutron yield and irradiation time. In this paper we focus on the computational analysis of the dosimetry foils that are used in order to measure the local neutron energy spectrum and flux. The foils were chosen to cover different neutron energies: thus Yttrium and some of the Nickel and Cobalt reactions were used to determine the Deuterium-Tritium fusion fraction, while Scandium and Iron and some of the Nickel and Cobalt reactions were used for comparison of the computed activity with the experimental measurements. The obtained C/E values show a reasonably good agreement between calculated and measured activity, thus validating the computational methodology and providing the basis for the analysis of the ITER-relevant materials and future experiments performed at JET in the Deuterium-Tritium campaign.
Diamonds are very promising candidates for the neutron diagnostics in harsh environments such as fusion reactors because of their proven radiation hardness. In comparison to the standard neutron ...diagnostics currently used (i.e., fission chambers, silicon based detectors, scintillators) CVD diamonds are less sensitive to y rays, which represents a huge background in fusion devices. Furthermore, their low leakage current provides a high energy resolution. A CVD diamond based detector has been proposed for the measurement of the 14 MeV neutrons from DT fusion reaction. The prototype was arranged in a proton recoil telescope configuration, featuring a plastic converter in front of the sensitive volume, in order to induce the (n, n) reactions which generate the recoil protons. The segmentation of the sensitive volume, achieved using two crystals with two dedicated electronic readouts, allowed to perform measurements in coincidence, which suppressed the neutron-carbon elastic scattering background. A preliminary prototype was assembled and tested at FNG (Frascati Neutron Generator), showing promising results regarding efficiency and energy resolution.
A neutronics integral benchmark experiment on a pure copper block, aimed at testing and validating recent copper nuclear data libraries, has been performed at Geel Electron LINear Accelerator ...Facility (GELINA). GELINA is a powerful photoneutron source using a 75-<inline-formula> <tex-math notation="LaTeX">\mu \text{A} </tex-math></inline-formula>, 110-MeV electron beam impinging on a depleted U rotating target, producing a white neutron spectrum ranging from the epithermal region up to about 20 MeV with a mean energy of about 1.4 MeV and intensity up to <inline-formula> <tex-math notation="LaTeX">3.2 \times 10^{13} </tex-math></inline-formula> n/s. A large nat Cu block (dimensions <inline-formula> <tex-math notation="LaTeX">60 \times 60 \times 60 </tex-math></inline-formula> cm 3 ) has been positioned at 100 cm from the target. Thin activation foils were used as neutron flux probes and located inside the block in six positions at different depths with respect to the main neutron propagation direction. Materials whose activation cross section are sensitive to different neutron energy ranges were used, and the measured fluxes were compared with calculations performed using the MCNP6 neutron transport code coupled to different neutron cross-sectional databases (FENDL3.1, JEFF33_T2, and ENDF 7.1). The MCNP6 calculation also used the neutron spectrum produced by the GELINA accelerator. This is the first time that a neutronics integral experiment on copper is performed using such a white neutron spectrum and the results of our comparison could be used to validate the neutron copper cross sections in the neutron energy range covered by GELINA. The C/E results, taking into account the sources of uncertainties, are satisfactory: no large differences are observed among the result obtained using the three cross-sectional databases; however, the JEFF-3.3 seems, slightly, better predict the results.
First neutron and X‐ray beam tests on a novel 12‐pixel single‐crystal diamond mosaic detector are presented and discussed. Preliminary characterization of single‐pixel electronic properties, ...performed with α particles, results in charge carrier mobilities >2000 cm2 Vs−1 and saturation velocities of the order of 107 cm s−1. Signal stability over time, measured with a 241Am source (37 kBq activity), is longer than 5 h. Tests under an intense X‐ray beam (1 Gy h−1 dose‐rate) show a very good response uniformity (down to about 1% of relative standard deviation from mean value), suggesting a high level of pixel reproducibility at intermediate bias voltages (ranging from 20 to 100 V). Response uniformity reduces at voltages >200 V, due presumably to radiation‐assisted detrapping effects. Preliminary results of 12‐pixel simultaneous acquisitions of X‐ray beam profiles and pulse height spectra under a fast neutron beam (14 MeV) are also presented.
A Monte Carlo model for low energy D–D neutron generators Milocco, Alberto; Trkov, Andrej; Pillon, Mario
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
01/2012, Letnik:
271
Journal Article
Recenzirano
Deuteron–deuteron (D–D) fusion reactions are foreseen for the next stage fusion reactors. A computational model is developed for simulating the neutron production by accelerating deuterons with ...energy less then 10
MeV onto solid targets containing deuterium. It requires the specification of the beam and target characteristics (e.g. deuterons energy, deuterium atomic fraction). The model is implemented in the subroutines of the MCNPX and MCNP5 codes, which need so far to be recompiled. The deuterons are transported inside the solid target by a Monte Carlo method. The neutrons are generated with the angle – energy distribution as defined by the laws and nuclear data for the deuteron–deuteron reaction in the ENDF/B-VII.0 library. The sensitivity studies on the input parameters of the D–D model are presented. The D–D source model is finally validated by an experiment, which has been performed by the FNG team at the IRMM with a high energy resolution detector. The results of the simulations indicate that the source model may be useful for the evaluation of the D–D neutron source term and associated uncertainties in experimental facilities.
•Fast neutron and gamma-ray spectra were measured in a copper assembly irradiated with DT neutrons.•The results were compared with MCNP calculations.•Primary aim was to provide experimental data for ...checking and validation of nuclear data evaluations of copper.
A neutronics benchmark experiment on a pure Copper assembly was performed at the Frascati Neutron Generator. The work aimed at testing of recent nuclear data libraries. This paper focuses on the measurement of fast neutron and gamma-ray flux spectra in the Copper assembly under DT neutron irradiation in two selected positions with a spectrometer based on the organic liquid scintillator NE-213. The measurement results were compared with Monte Carlo radiation transport calculations using MCNP and nuclear data from the JEFF-3.1.1 library. Calculations have been done with Cu data from JEFF-3.1.1, JEFF-3.2, FENDL-3 and ENDF/B-7.0. Discrepancies appear in the intermediate neutron energy range between experiment and calculation. Large discrepancies were observed in the gamma-ray spectra calculated with JEFF-3.2.
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