Spectrométrie gamma

La spectrométrie gamma est une technique de mesure nucléaire permettant d'identifier certains éléments radioactifs par la mesure de l'énergie des rayonnements gamma qu'ils émettent. Elle diffère de la technique du compteur Geiger, qui ne détecte que la présence de rayonnements gamma sans fournir d'information sur la nature de la source détectée. La mesure par spectrométrie gamma permet de construire des spectres, qui sont des histogrammes donnant les quantités de photons détectés en fonction de leur énergie. Principe Les noyaux atomiques ont une structure en niveaux d'énergie comparable à celle des niveaux d'énergie des atomes, de sorte qu'ils peuvent émettre (ou absorber) des photons d'énergie particulière. Comme les atomes, les niveaux d'énergie des noyaux sont caractéristiques de chaque espèce d'atome. De sorte que l'énergie des photons gamma émis, qui correspond aux différences d'énergie dans les noyaux, peuvent servir à identifier des éléments et des isotopes. La di

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Characterisation of the activation in Crocus

The aim of this study is to characterize the activation of the crocus cavity. For this purpose, the concrete plug of the irradiation channel crossing the cavity shielding was used to measure the activation by gamma spectrometry. In a first time measurements were made after a long cooling time to determine the residual activation. Then, the plug was irradiated at 40Watts for 2 hours to provide a sufficient irradiation to the concrete. At the same time, measurements were led thanks to the dosimetry by thermoluminescence in the cavity. TLDs measurements gave reaction rates in Li6 at strategical positions detailed on this report. TLDs positions were defined in a Cartesian system centred on the centre core. 2D plans based on previous plan were designed to improve the calculation accuracy of the neutrons flux simulations. The analysis shown a very low activity of the concrete plug, below the low level waste thresholds. However results provided by TLDs and the Nagra’s calculations allowed to highlight a greater neutrons fluence in the upper part of the cavity. So, it might be relevant to pursue the gamma ray spectrometry measurements with concrete plugs from other cavity areas where the neutron flux should be higher.

2018

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CROCUS Concrete Activation Study by γ-ray Spectrometry and TLD Neutron Flux Measurements

Isabelle Tanseri

The semester project was under the course Physics lab IVb at EPFL. At EPFL site, the experimental fission reactor CROCUS is shielded by concrete which becomes radioactive as a result of neutron interaction. The activation is of interest to study for validation of models and cal- culations, and to quantify the amount of radioactive waste when the reactor will be recycled. In this project, measurements on concrete ac- tivation by NaI- and HPGe-detectors were performed on an in-cavity concrete block, together with TLD measurements on neutron flux in- side the core of CROCUS and in the cavity. The concrete activation and neutron flux allows for comparison and validation of models. The in-cavity concrete block had a low activation, trace elements of 60Co and 65Zn seem to be existing. The relative flux was the highest for structures close to the core and at the ceiling. In future projects, more experimental data on both concrete activation and neutron flux would be performed to acquire uncertainty estimations and correction factors.

2017

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In-core dosimetry for the validation of neutron spectra in the CROCUS reactor

Pavel Frajtag, Yifeng Jiang, Vincent Pierre Lamirand, Axel Guy Marie Laureau, Andreas Pautz

The present article describes the preliminary validation study of simulated in-core and reflector n eutron spectra in preparation of oncoming experimental programs in the zero-power reactor CROCUS at EPFL. For this purpose, a set of activation foils were irradiated at three characteristic positions in the CROCUS reactor, and the subsequent activities were analyzed via gamma spectrometry. The experimental setup was then modeled with the Monte Carlo neutron transport code Serpent2 and associated with an analysis tool to include the effect of the reactor power history during experiments. The comparison of calculated and measured reaction rates (C/E) indicates a general consistency (at 2 sigma) between calculated and measured spectra. However, offsets of C/E values were observed in (n,gamma) reactions, up to 18% for In-115 and 8% for Cu-63 dosimeters. This could be caused by an unexpected isotopic composition, uncertainties in nuclear data, or the spectrometry analysis. In addition, a 100-groups spectrum unfolding was performed using the experimentally determined reaction rates and the Serpent2 spectra as the prior knowledge. The unfolded spectra were mainly adjusted in the thermal and fast ranges, while few modifications were made in the epithermal region due to the low contribution of epithermal neutrons in activation processes. Moreover, within energy groups where the capture reactions show resonant behavior, flux depletion (up to 38% as compared to the prior spectra) is observed due to the absence of self-shielding effect in the unfolding process. For this purpose, an unfolding method based on energy groups weighting is developed and tested.

E D P SCIENCES2020

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PHYS-452: Radiation detection

The course presents the detection of ionizing radiation in the keV and MeV energy ranges. Physical processes of radiation/matter interaction are introduced. All steps of detection are covered, as well as detectors, instrumentations and measurements methods commonly used in the nuclear field.

PHYS-439: Introduction to astroparticle physics

We present the role of particle physics in cosmology and in the description of astrophysical phenomena. We also present the methods and technologies for the observation of cosmic particles.

PHYS-400: Selected topics in nuclear and particle physics

This course presents the physical principles and the recent research developments on three topics of particle and nuclear physics: the physics of neutrinos, dark matter, and plasmas of quarks and gluons. An emphasis is given on experimental aspects in these three research fields.

Détecteur à scintillation

Un détecteur à scintillation, également appelé compteur à scintillation ou plus souvent scintillateur, est un instrument composé d'un matériau qui émet de la lumière à la suite d'un dépôt d'énergie p

Scintillateur

Un scintillateur est un matériau qui émet de la lumière à la suite de l'absorption d'un rayonnement ionisant (photon ou particule chargée). Il existe deux grandes familles de scintillateurs :

les s

Césium

Le césium est l'élément chimique de numéro atomique 55, de symbole Cs. Dans les conditions standard, le corps simple césium est un métal mou et ductile, blanc ou argenté à doré. Son point de fusion