Recent Developments in Count Rate Processing Associated with Radiation Monitoring Systems

This chapter presents some recent data processing developments associated with radiation monitoring systems. Radiation monitors have to continuously provide count rate estimations with accuracy and precision. A filtering technique based on a Centered Significance Test coupled with a Brown’s double exponential filter has been developed and used in compensation measurement and moving sources detection schemes

Détection de rayonnements neutroniques à base de gadolinium

The search for alternatives to helium-3 neutron counters forms a driving topic in today’s nuclear instrumentation. The cross section of gadolinium for thermal neutron capture makes this element a promising candidate. This thesis aims at scaling and evaluating different counting schemes based on the signature of these captures inside the detection medium. Three research areas have been explored: plastic scintillator-based detection, semiconductor-based detection and magnetic phase transition in gadolinium. The theoretical study of the ferromagnetic-paramagnetic transition in gadolinium has been concluded by a practical infeasibility. A method built on the insertion of a metal gadolinium core at the center of a large plastic scintillator has been designed. A significant signal between 3 and 8 MeV in the presence of a californium-252 source allows pulse height discrimination from natural gamma-ray background. Gadolinium-loaded plastic scintillators, compensated by bismuth-loaded scintillators, have been modeled, synthetized and tested in presence of gamma and neutron emitters. The concept of a compensation of gadolinium foil-covered sensors by terbium-covered sensors has been studied. The detection scheme has received a first experimental validation via cesium-137 and californium-252 exposures, for bismuth-loaded scintillating media and CdZnTe crystals.La recherche d’alternatives aux compteurs neutroniques à hélium 3 forme un thème de premier plan dans l’instrumentation nucléaire contemporaine. La section efficace de l’élément gadolinium pour la capture des neutrons thermiques en fait un candidat prometteur. L’objectif de cette thèse est de dimensionner et d’évaluer des schémas de comptage fondés sur la signature de ces captures dans le milieu de détection. Trois domaines de recherche ont été explorés : la détection à base de scintillateurs plastiques, la détection à base de semi-conducteurs et la détection par transition de phase magnétique dans le gadolinium. L’étude théorique portant sur la transition ferromagnétique-paramagnétique du gadolinium a été conclue par une non-faisabilité pratique. Une méthode reposant sur l’insertion d’un cœur métallique de gadolinium dans un scintillateur plastique de grand volume a fait l’objet d’un dimensionnement. Un signal significatif entre 3 et 8 MeV en présence d’une source de californium 252 autorise une discrimination, par la hauteur des impulsions, de la radioactivité gamma naturelle. Des scintillateurs plastiques dopés au gadolinium, compensés par des scintillateurs dopés au bismuth, ont été modélisés, synthétisés et testés en présence d’émetteurs gamma et neutron. Le principe d’une compensation de capteurs couverts de feuilles de gadolinium par des capteurs couverts de terbium a fait l’objet de deux études. Le schéma de détection a reçu une première validation expérimentale via une exposition à des sources de césium 137 et de californium 252, pour des milieux plastiques dopés au bismuth ainsi que des cristaux de CdZnTe

Shadow-shielding compensation for moving sources detection

International audienceTo monitor radioactivity emitted by a vehicle such as a pedestrian, a car, a train, or a truck, radiation portal monitors (RPMs) are commonly employed. It has been noted that these RPM suffer from a shadow-shielding effect when the source is transported by a dense and large vehicle such as a truck or a train. While methods using databases are listed as state of the art, we have developed an approach based on a state model, ensuring a gain in performance and flexibility. This new study presents a technique applied to RPM, efficiently compensating the shadow-shielding effect. A simulation study has been performed to highlight the efficiency and reliability of the method

Neutron detection using a Gadolinum covered CdZnTe detector

International audienceGain in efficiency and miniaturization is an issue for portable neutron detectors. $^{157}$ Gd, $^{155}$ Gd and $^{113}$Cd nuclei show the highest neutron capture cross-sections available in the stable element list. They are then a subject of interest for neutron detection and could be considered as suitable competitors with regards to detectors using $^3$He, $^{10}$B, $^6$Li or proton recoils. A neutron detector using a Gd converter and a CdZnTe diode is studied to address portable neutron detection. To exploit the low energy signature from the Gd, a reliable compensation technique with a guard sensor has been designed. Some innovations have been done on algorithmic part and sensor part of the system. The concept has been experimentally proved. It has notably been demonstrated that a Tb cover on the guard sensor allows a reduction of the overcompensation and then a maximization of the sensitivity of the detector

Compensation scheme for online neutron detection using a Gd-covered CdZnTe sensor

International audienceThe development of portable and personal neutron dosimeters requires compact and efficient radiation sensors. Gd-157, Gd-155 and Cd-113 nuclei present the highest cross-sections for thermal neutron capture among natural isotopes. In order to allow for the exploitation of the low and medium-energy radiative signature of the said captures, the contribution of gamma background radiation, falling into the same energy range, needs to be cancelled out. This paper introduces a thermal neutron detector based on a twin-dense semiconductor scheme. The neutron-sensitive channel takes the form of a Gd-covered CdZnTe crystal, a high density and effective atomic number detection medium. The background compensation will be carried out by means of an identical CdZnTe sensor with a Tb cover. The setting of a hypothesis test aims at discriminating the signal generated by the signature of thermal neutron captures in Gd from statistical fluctuations over the compensation of both independent channels. The measurement campaign conducted with an integrated single-channel chain and two metal Gd and Tb covers, under Cs-137 and Cf-252 irradiations, provides first quantitative results on gamma rejection and neutron sensitivity. The described study of concept gives grounds for a portable, online compatible device, operable in conventional to controlled environments

Multilayer phoswich scintillators for neutron / gamma discrimination

International audienceMultiLayer Phoswich (MLP) scintillators have been studied for fission neutron detection by Monte-Carlo simulations and experimental tests. n/γ discrimination behavior of these systems and their angular dependencies have been characterized. The possibility to carry on a neutron counting system based of such an approach has been proven, and according to the results, an optimal thickness of layers for fission neutron counting was found around [100–150] μm. But, contrary to current liquid or solid-state discrimination scintillators, it appears that MLP-based neutron counting systems cannot directly classify neutron and gamma-ray interaction events from pulse shape analysis. To operate properly, it is therefore required to implement a compensation algorithm in the system readout

Managing religious diversity in secular organizations in France

International audienc

Large-volume and room-temperature gamma spectrometer for environmental radiation monitoring

The use of a room-temperature gamma spectrometer is an issue in environmental radiation monitoring. To monitor radionuclides released around a nuclear power plant, suitable instruments giving fast and reliable information are required. High-pressure xenon (HPXe) chambers have range of resolution and efficiency equivalent to those of other medium resolution detectors such as those using NaI(Tl), CdZnTe, and LaBr3:Ce. An HPXe chamber could be a cost-effective alternative, assuming temperature stability and reliability. The CEA LIST actively studied and developed HPXe-based technology applied for environmental monitoring. Xenon purification and conditioning was performed. The design of a 4-L HPXe detector was performed to minimize the detector capacitance and the required power supply. Simulations were done with the MCNPX2.7 particle transport code to estimate the intrinsic efficiency of the HPXe detector. A behavioral study dealing with ballistic deficits and electronic noise will be utilized to provide perspective for further analysis

Estimation of nuclear counting by a nonlinear filter based on a hypothesis test and a double exponential smoothing

International audienceOnline nuclear counting represents a challenge due to the stochastic nature of radioactivity. The counting data have to be filtered in order to provide a precise and accurate estimation of the count rate, while ensuring a response time compatible with the application in view. An innovative filter is presented in this paper to address this issue. The filter is nonlinear and based on a Centered Significance Test (CST) providing a local maximum likelihood estimation of the signal. This nonlinear approach allows enables to smooth the counting signal while maintaining a fast response when brutal change in activity occurs. The filter is then improved by the implementation of a Brown's double Exponential Smoothing (BES). The filter has been validated and compared to other state-of-the-art smoothing filters. The CST* filter shows a significant improvement compared to all tested smoothing filters

Recruitment discrimination: how organizations use social power to circumvent laws and regulations

International audienc