Speaker
Marco Cortesi
(Weizmann Institute of Science)
Description
We present our recent results on development of high-resolution instrumentation and measurement techniques for investigating various practical thermal-hydraulic processes, such as dynamic gas-liquid two-phase flow. Included in these activities, two projects are currently under development: -) A novel high-efficiency, one-dimensional fast-neutron imaging detector intended for fan-beam tomography applications. The detector consists of a multi-layer neutron-to-proton converter made of a hydrogenous polymer coupled to a position-sensitive THick Gaseous Electron Multiplier (THGEM) detector; the latter collects and multiplies the proton-induced electrons released in the gas gap between the converter foils, thereby localizing the neutron interaction. The design, operational principles, and performance of the new detector concept is discussed. In particular, we report on the characterization studies and results of electron transport along the small gas gaps of the converter, which affects the performance of the detector in terms of both detection efficiency and localization behavior. Measurements performed with a multi-foil converter and a 10x10 cm2 THGEM imaging detector prototype with monoenergetic 2.5 MeV and 14 MeV are presented and compared to Monte-Carlo simulat! ions. For irradiation with 2.5 MeV neutrons and a total of 300 converter foils, detection efficiencies of ~7% and a spatial resolution of ~1 mm are expected. -) A cold-neutron imaging detector prototype based on a THGEM. The detector consists of a thin Boron layer, for neutron-to-charged particle conversion, coupled to two THGEM electrodes in a cascad for charge amplification, and a position-sensitive charge-readout anode. The detector operates in Ne/(5%)CF4 at atmospheric pressure with a stable gain of around 104. Due to the geometrical structure of the detector elements (THGEM geometry and charge read-out anode), the image of the detector active area shows a large inhomogeneity, corrected using a dedicated flat-field correction algorithm. The prototype provides a detection efficiency of 5% and an effective spatial resolution on the order of 1.3 mm. Some possible applications include dynamic visualization of combustion engine fluid dynamics, non-destructive monitoring of capillary processes, investigation of heat exchange in fluidized-bed heat exchangers for the steel industry, or investigations of turbulent oil-gas flow through a pipe in petrochemical industry. Another class of important application includes the investigation of phenomena relevant for development of nuclear power plant technologies, such as gas-liquid or gas-solid two-phase flow, study of steam explosion processes, nuclear fuel inspection, and monitoring of special nuclear materials.
