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Studies of Liquid-Gaseous Two-Phase Systems by Positron Emitting RadiotracersHensel, F.
For a more detailed knowledge and understanding of various industrial processes an in-situ visualization is required. Positron Emission Tomography is an imaging technique used in medical research as a tool to study brain and heart diseases, allowing a non-invasive in-vivo concentration measurement of labeled substances. The mentioned features got us to carry out feasibility investigations for PET-like radiotracer applications in the field of two-phase flow systems. The main aim was to observe mixing and flow phenomena in efficient spatial and time resolution.
Typical values for the stopping ranges of positrons produced by common PET isotopes in water are approximately 2mm. Typical densities of the liquid-gaseous two phase systems that were to investigate are below 10% of the density of water under normal conditions. So the positron range effect becomes very important. Therefore as a first step the spatial annihilation distribution of a solid positron source has been measured using a Ti-45 source and solid blocks of polystyrene and polyurethane foam. The experiments have been carried out using a double head spherical PET-scanner for treatment plan verification of 3D conformable radiation therapy . The foam density amounted from 15 kg/m3 to 38 kg/m3. The feasibility of a range based density measuring technique using the positron range was successfully shown. The next steps in this field could be the setup of a density measurement system for foams, including a detector optimization that results in an easy to handle low cost experimental assembly. It should comprise an encapsulated positron source and 2-4 pairs of detectors to cover an enlarged density range.
Liquid positron emitting tracers were used for monitoring phenomena in bubbly flows. PET experiments often require high activities and quite long integration times for an image reconstruction. Due to activity limitations it has been tried to optimize the experimental setup. Good results were achieved using a nearly two-dimensional geometry in combination with a midplane backprojection. In the experiments mixing processes in bubbly flows were observed using a F-18 solution. The bubbly flows were created by air injection. The event data were collected in list mode. The time resolution for these experiments was below 1s (integration time for the data evaluation). Best choice was a time step value of 500ms. In a further experiment the drainage of a surfactant stabilized foam was investigated.
Transport processes in bubbly flows and foams seem to be adequate topics for investigation using a PET technique. Time resolutions of about 1 s and below can be achieved, depending on the problem. The main advantage of PET tracers is the fact that many organic substances can be labeled with positron emitting isotopes which is important for the component sensitive investigation of many industrial processes.
Contribution to proceedings
3rd Topical Meeting on Industrial Radiation and Radioisotope Measurements and Applications, Conference Program and Abstracts, Raleigh, NC (USA), October 6-9, 1996, p. 101, ISBN 0-89448-645-2
- Applied Radiation and Isotopes 48 (1997), 1485 - 1492
3rd Topical Meeting on Industrial Radiation and Radioisotope Measurements and Applications, Raleigh, NC (USA), October 6-9, 1996
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