Oil in water injection from a submerged nozzle

International audienceWhen a certain amount of oil is injected upwardly through a vertical nozzle submerged in water, the oil-water interface evolves, for large orifices, from a sessile shape, to a cap profile with a roll-up border. The numerical simulation of such liquid-liquid interface evolution was made through the Boundary Element Method (BEM), by assuming a potential flow of a viscous fluid. At the end of the computed process, the velocity field behaviour leads to an inward rolling up movement of the cap border, simultaneously with the interface necking near the orifice level. Such velocity field precedes typically a vortex ring formation. An olive oil-water couple has been selected, because of the appropriate physical properties of those liquids: comparable densities, huge difference of viscosities, and very small interfacial tensio

Fast and Efficient Detection of 511 keV Photons using Cherenkov Light in PbF2_2 Crystal coupled to a MCP-PMT and SAMPIC Digitization Module

International audienceWe study the possibility to use the Cherenkov light for the efficient detection of 511 keV photons with the goal to use it in TOF-PET. We designed and tested two detection modules consisting of PbF$_2$ crystals attached to Planacon MCP-PMT XP85012. Amplified PMT signals are digitized by the SAMPIC module with high readout rate, up to $10^5$ events/s, and a negligible contribution to the time resolution, below 20 ps (FWHM). We developed a fast 2D scanning system to calibrate the PMT time response and studied in details the timing characteristics of the Planacon PMT. Using a radioactive $^{22}$Na source we measured a detection efficiency of 24% for 511 keV photons in a 10 mm thick crystal and a coincidence resolving time of 280 ps. We analyzed the main factors limiting the time resolution of the large-surface detection module and proposed solutions to improve it, which will be tested in our future project

A Pseudo-TOF Image Reconstruction Approach for Three-Gamma Small Animal Imaging

International audienceIn this article, we propose a novel image reconstruction technique for three-gamma (3- γ ) imaging systems that aims at reaching high image quality with a low statistics. The proposed approach is based on the utilization of a ( β+ , γ ) emitter and a liquid xenon (LXe) camera, the Xenon Medical Imaging System 2 (XEMIS2), that is currently being manufactured. The third gamma emitted is more energetic than the two 511-keV photons and interacts mostly through Compton scattering in LXE; therefore, we utilize the interactions’ position and the deposited energy to define a Compton cone that gives the direction from where the third gamma was emitted. The intersection point between the cone and the two coincidence photons’ lines of response (LOR) is the center of the probability distribution function (PDF), a resolution model similar to that of time-of-flight (TOF)-positron emission tomography (PET). The third gamma’s information is used to narrow the LOR portion employed during reconstruction. In this article, we show reconstruction results from simulation using highly realistic Geant4 Application for Emission Tomography (GATE) Monte Carlo simulation of the imaging device and a NEMA-like phantom

Efficient and fast 511-keV γ detection through Cherenkov radiation: the CaLIPSO optical detector

International audienceThe CaLIPSO project aims to develop a high precision brain-scanning PET device with time-of-flight capability. The proposed device uses an innovative liquid, the TriMethyl Bismuth, as the detection medium. It detects simultaneously the ionization and optical signals from the 511 keV gamma conversion. In this paper we present the design, the Monte Carlo simulation, and the tests results for the CaLIPSO optical prototype. In this prototype we demonstrated the ability to detect efficiently the low number of the optical photons produced by the relativistic electron from the gamma conversion through the Cherenkov effect. The time resolution of the current prototype is limited by the moderate time transition spread of the PMT, but should be improved to the level better than 100 ps (FWHM) by using micro-channel-plate PMT according to the Geant 4 simulation

Studies and optimization of scintillation light measurements for the development of the 3-gamma medical imaging XEMIS2 liquid xenon compton camera

International audienceWe report the studies and optimization of scintillation light measurements in an updated version of the XEMIS1 prototype for the development of the XEMIS2 camera. A novel monolithic liquid xenon Compton camera, named XEMIS2 (XEnon Medical Imaging System), attempts to achieve low-activity small-animal imaging using the 3-gamma imaging technique. This emerging detector relies on the time projection chamber technique: it will be able to perform a simultaneous detection of the three γ-rays emitted by a specific radionuclide, such as scandium-44, and to produce a good quality image with a remarkable diminution of radiopharmaceutical activity at the same time. Vacuum Ultraviolet (VUV) scintillation light and ionization charge carriers generated from the recoiling particles within the detector are detected and used to reconstruct the interaction position and deposited energy. A cost-effective self-triggering scintillation signal read-out and data acquisition (DAQ) system has been developed to achieve a continuous data read-out with negligible electronics dead time. The DAQ prototype has been installed and qualified in an updated version of the XEMIS1 detector. It reaches the performance specifications in scintillation light measurements. Moreover, scintillation signals can also be used for the virtual segmentation of the monolithic detection volume through the matching algorithm of the scintillation and ionization signals based on the Light Collection Map (LCM). This spatial pre-localization of the physical events, called the virtual fiducialization of the active volume, is used to lower the detector occupancy rate when the administered activity is increased to lessen the examination time. The XEMIS1 experimental LCMs indicate that each PMT owns an individual field of view so as to segment the active volume virtually. The preparation work for the XEMIS2 camera operation has been completed in the updated XEMIS1 detector while the XEMIS2 scintillation light measurement system is under commissioning in Nantes Centre Hospitalier Universitaire. •The XEMIS2 camera oriented to the whole-body small animal 3-gamma medical imaging is presented.•The XEMIS2 system is a monolithic liquid xenon Compton camera with a 24 cm axial field of view.•A cost-effective 16-channel self-triggering scintillation signal front-end read-out electronics named XSRETOT is reported.•The XEMIS1 experimental light collection maps can be used for the virtual segmentation of the monolithic detection volume