1,721,987 research outputs found
Response of LaBr3(Ce) scintillators to 14 MeV fusion neutrons
No full textThe response of a 3′′×3′′ LaBr3(Ce) scintillator to 14 MeV neutron irradiation has been measured at the Frascati Neutron Generator and simulated by means of a dedicated MCNP model. Several reactions are found to contribute to the measured response, with a key role played by neutron inelastic scattering and (n,2n) reactions on 79Br, 81Br and 139La isotopes. An overall 43% efficiency to 14 MeV neutron detection above an experimental threshold of 0.35 MeV is calculated and confirmed by measurements. Post irradiation activation of the crystal has been also observed and is explained in terms of nuclear decays from the short lived 78Br and 80Br isotopes produced in (n,2n) reactions. The results presented in this paper are of relevance for the design of γ-ray detectors in burning plasma fusion experiments of the next generation, such as ITER, where capability to perform measurements in an intense 14 MeV neutron flux is required. © 2015 Published by Elsevier B.V
Upgrade of the compact neutron spectrometer for high flux environments
No full textIn this paper new version of the 6Li-based neutron spectrometer for high flux environments is described. The new spectrometer was built with commercial single crystal Chemical Vapour Deposition diamonds of electronic grade. These crystals feature better charge collection as well as higher radiation hardness. New metal contacts approaching ohmic conditions were deposited on the diamonds suppressing build-up of space charge observed in the previous prototypes. New passive preamplification of the signal at detector side was implemented to improve its resolution. This preamplification is based on the RF transformer not sensitive to high neutron flux. The compact mechanical design allowed to reduce detector size to a tube of 1 cm diameter and 13 cm long. The spectrometer was tested in the thermal column of TRIGA reactor and at the DD neutron generator. The test results indicate an energy resolution of 300 keV (FWHM), reduced to 72 keV (RMS) excluding energy loss, and coincidence timing resolution of 160 ps (FWHM). The measured data are in agreement with Geant4 simulations except for larger energy loss tail presumably related to imperfections of metal contacts and glue expansion. © 2017 Elsevier B.V
Proton recoil telescope based on diamond detectors for the measurement of fusion neutrons
No full textDiamonds 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 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. © 2016 IEEE
Directionality properties of the nGEM detector of the CNESM diagnostic system for SPIDER
No full textThe 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. © 2018 Elsevier B.V
Proton recoil telescope based on diamond detectors for measurement of fusion neutrons
No full textDiamonds are very promising candidates for the neutron diagnostics in harsh environments such as fusion reactor. In the first place this is because of their radiation hardness, exceeding that of Silicon by an order of magnitude. Also, in comparison to the standard on-line neutron diagnostics (fission chambers, silicon based detectors, scintillators), diamonds are less sensitive to 7 rays, which represent a huge background in fusion devices. Finally, their low leakage current at high temperature suppresses the detector intrinsic noise. In this talk a CVD diamond based detector has been proposed for the measurement of the 14 MeV neutrons from D-T fusion reaction. The detector was arranged in a proton recoil telescope configuration, featuring a plastic converter in front of the sensitive volume in order to induce the (n, p) reaction. The segmentation of the sensitive volume, achieved by using two crystals, allowed to perform measurements in coincidence, which suppressed the neutron elastic scattering background. A preliminary prototype was assembled and tested at FNG (Frascati Neutron Generator, ENEA), showing promising results regarding efficiency and energy resolution. © 2015 IEEE
Monte Carlo simulation of the experimental pulse height spectra produced in diamond detectors by quasi-mono-energetic neutrons
No full textThis work was carried out in view of the possible use of diamond detectors as high resolution neutron spectrometers for the ITER project. An MCNP5(X) based computational tool has been developed to simulate the fast neutron response of diamond detectors. The source neutrons are generated by a source routine, developed earlier, that includes deuteron beam energy loss, angular straggling, and two-body relativistic kinematics. The diamond detector routine calculates a pulse height spectrum that is built up by elastic and inelastic scattering, (n,a), (n,p), and (n,d) reaction channels. A combination of nuclear data from ENDF/B-VII.0, TENDL-2010, and ENSDF is used. The simulated spectra are compared with measured spectra. It is shown that the simulation tool allows an interpretation of most of the characteristic features in the spectrum. This is an important step towards the use of diamond detectors for spectral analysis and fluence measurements. © 2001 Elsevier Science. All rights reserved. © 2012 Elsevier B.V
Single-crystal diamonds for neutrons
No full textSingle-crystal Chemical Vapour Deposition (CVD) diamond detectors feature a superb Signal-to-Noise ratio (S/N , timing response and good energy resolution. These properties make CVD diamonds interesting for neutron detection. In the present contribution we discuss different measurements of neutron energy with CVD diamonds applied to relatively low- and high-energy neutrons. For the low-energy range a compact neutron Time-of-Flight (ToF) spectrometer for high flux environments has been developed. Such a detector would allow the measurement of neutron spectra in the range from 250keV up to few MeV with 20–40% resolution in the neutron fluxes 105 < φn < 109 n/cm2/s. The first prototype of this spectrometer was tested at ENEA FNG 3MeV quasi-monochromatic neutron beam and demonstrated feasibility of the concept. However, the test evidenced inadequacy of existing amplifiers providing insufficient timing resolution to extract a sensible neutron spectrum in MeV range. This particular diamond detector application, among with many others, calls for a development of a fast amplifier featuring an order of magnitude higher Signal-to-Noise ratio. On the other hand, to measure the neutron flux in a wide neutron energy range (1–100 MeV) at counting rate ∼ 2 MHz a single diamond crystal coupled to a fast (tens of ns) shaping preamplifier was used. The test performed at the n_TOF neutron beam line at CERN revealed the capability of using such a detector for spectroscopic measurement: the energy resolution achieved is about 4% at the n-α peak at 9.3 MeV, i.e. for 15 MeV neutrons. CVD diamond detectors have been proposed, successfully tested and applied as neutron flux monitors in nuclear reactor and around tokamaks. Furthermore, the possibility to extend the application of diamond films to neutron spectroscopy for a wide range of applications can be envisaged and already tested in fusion tokamak and around accelerators
Test of a prototype neutron spectrometer based on diamond detectors in a fast reactor
No full textA prototype of neutron spectrometer based on diamond detectors has been developed. This prototype consists of a 6Li neutron converter sandwiched between two CVD diamond crystals. The radiation hardness of the diamond crystals makes it suitable for applications in low power research reactors, while a low sensitivity to gamma rays and low leakage current of the detector permit to reach good energy resolution. A fast coincidence between two crystals is used to reject background. The detector was read out using two different electronic chains connected to it by a few meters of cable. The first chain was based on conventional charge-sensitive amplifiers, the other used a custom fast charge amplifier developed for this purpose. The prototype has been tested at various neutron sources and showed its practicability. In particular, the detector was calibrated in a TRIGA thermal reactor (LENA laboratory, University of Pavia) with neutron fluxes of 108 n/cm2s and at the 3 MeV D-D monochromatic neutron source named FNG (ENEA, Rome) with neutron fluxes of 106 n/cm2s. The neutron spectrum measurement was performed at the TAPIRO fast research reactor (ENEA, Casaccia) with fluxes of 109 n/cm2s. The obtained spectra were compared to Monte Carlo simulations, modeling detector response with MCNP and Geant4. © 2015 IEEE
Development of a spectrometer to measure photon and electron decay heat from radionuclides
No full textNeutron activation of elements gives rise to an energy release during the subsequent radioactive decay. This paper deals with the development of a large, almost 4π, spectrometer for accurate and efficient measurements of photon and electrondecay heat of neutron activated elements. The spectrometer consists of a well-type 22.8 x 22.8 cm cylindrical CsI(Tl) scintillator (for photon detection) and a small plastic electron detector inserted in the well. The spectrometer was designed to have manyexcellent features such as the possibility to measure simultaneously the total activity of the sample and its electron and photon decay heat separately with high sensitivity and wide dynamic range. To demonstrate the feasibility of decay heat measurements with our spectrometer, we have irradiated twelve samples of different materials using the 14 MeV neutron generator FNG. The measurements have been compared with the prediction of the activation system EASY-99 and the results in term of the C/E (calculationvs. Experiment) are presented. While most of the C/E values are, within the uncertainties, equal to one, discrepancies for one radionuclide was found and are discussed in the paper. © 2014 Atomic Energy Society of Japan
Development of a low-noise amplifier for neutron detection in harsh environment
No full textA fast matching charge amplifier for neutron spectroscopy in harsh environment has been developed and tested at the JET Tokamak. This front-end circuit is capable to operate at a distance up to 100 meters from a sensor without increasing its equivalent noise charge. Further improvements are possible by exploiting the intrinsic performance of silicon-germanium bipolar junction transistors
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