1. Pre-concentration and selective separation of Ra2+ in the presence of a wide range of concurrent cations using a new developed resin 2. Direct Measurement of Ionization from Electron Recoils for 3γ Imaging with a Liquid Xenon Compton Camera XEMIS

jeudi 26 avr. 2018, 14:00 → 15:30 Europe/Paris

Amphi GALOIS (Subatech - IMT Atlantique)

Chloé Therreau

14:00 → 14:30 Pre-concentration and selective separation of Ra2+ in the presence of a wide range of concurrent cations using a new developed resin

Radium is the daughter nuclide of Naturally Occurring Radioactive Materials (NORM), uranium and thorium, which exists in several isotopes. Accordingly it incites great interest in various fields of application such as: environmental monitoring, analytical and medical uses (Gott et al. 2016). Due to its extensive use (in food products, in heating pads and suppositories, in cosmetics, as a fertilizer…) during the early 20th century, many sites across Europe and North America have been contaminated (Harvie 1999). Therefore, various regulatory authorities have shown an interest in monitoring and enforcing limits for radium levels in drinking water and industry (Morvan et al. 2001). Radium’s high mobility in the environment and its chemical similarity to calcium both explain its classification as a highly radiotoxic radioelement.
For all these reasons, the necessity to concentrate/separate radium has gained importance in scientific research academic or industrial fields. MnO2 resin or disks are the most common materials used to extract radium from ground and surface water of low Ra-activities. But these systems show some limitation, especially in salty or mineral waters, rich in calcium and magnesium. So there is a need for the development of more selective supports for radium based on Molecular Recognition Technology (MRT).
This question is at the center of this work, led by TRISKEM, which aims to develop a specific resin for a selective extraction of Ra in environmental applications. The developed resin consists of a metal-selective ligand, either chemically bonded to a silica support or impregnated onto another organic polymer support. This study characterizes the adsorption and desorption of Ra, on the newly developed Ra-resin, in the presence of high concentrations of interfering cations, especially calcium. Several French mineral waters and environmental samples have been tested to check the efficiency of the new Ra-resin compared to MnO2 disks and chelex resin. Resins were tested for selectivity and efficiency as a function of different key parameters (pH, time, Ca/Mg concentrations and Ba concentration). The results are very promising for environmental applications.

Key words: Radium, selective extraction, specific resin, concurrent cations, environment.

Orateur: Soumaya Khalfallah (Radiochimie)

14:30 → 15:00 Direct Measurement of Ionization from Electron Recoils for 3γ Imaging with a Liquid Xenon Compton Camera XEMIS

The 3γ imaging is an innovative functional imaging modality, based on the detection in coincidence of three γ-rays by using on liquid xenon Compton camera and a (β+,γ) radionuclide emitter, for purpose of obtaining a 3D image with 100 times less activity than in current Positron-emission tomography (PET) systems. The ability to successfully obtain a high-quality image is greatly dependent on the spatial and energy resolution of the detector, the data analysis process and the image reconstruction method. A succession of R&D programs XEMIS1 and XEMIS2, designed to detect simultaneously the UV scintillation light and ionization signals from ionizing radiation, has been developed to explore the feasibility and advantage of this new camera.
The experimental results of the first prototype XEMIS1 shown a spatial resolution along the z-axis of roughly 100 μm for 511 keV photoelectric events with an ultra-low noise front-end electronics (below 100 e- RMS). XEMIS2, a larger single-phase liquid xenon cylindrical camera dedicated to 3D image of small animals, is now under assembly and qualification. More than 20000 pixels will be equipped for charge collection; in addition, a new self-trigger analog ASIC, XTRACT, has been developped for the sake of continuous read-out with negligible dead-time during 20 minutes.
The objective of this thesis work is to realize the direct measurement of ionization signal in order to obtain the deposited energy and location for each γ-ray interaction vertex in the TPC. The simulation of electrons recoils trajectory in LXe reproduced a shift of 100 μm for 511 keV, which may explain the spatial resolution of XEMIS1. Besides, a complete simulation and study with XEMIS1 is still ongoing for optimizing the ionization signal measurement. Characterizations of ionization signal using Monte Carlo simulation and data analysis have shown a good performance for energy measurement. At the present stage, the main work is to characterize the performance of the new electronic chain from front-end electronics to data acquisition in XEMIS1 and developing the XEMIS2 data analysis program before the operation of XEMIS2. The resultat of the first test at LXe temperature will be presented. The data analysis for resolution optimizing will become the core mission for resolution optimizing to reach the desired performances in times to come.

Orateur: Yajing Xing (Xenon)