Imaging with polycrystalline mercuric iodide detectors using VLSI readout

Abstract

Potentially low cost and large area polycrystalline mercuric iodide room-temperature radiation detectors, with thickness of 100–600 μm have been successfully tested with dedicated low-noise, low-power mixed signal VLSI electronics which can be used for compact, imaging solutions. The detectors are fabricated by depositing HgI 2 directly on an insulating substrate having electrodes in the form of microstrips and pixels with an upper continuous electrode. The deposition is made either by direct evaporation or by screen printing HgI 2 mixed with glue such as Poly-Vinyl-Butiral. The properties of these first-generation detectors are quite uniform from one detector to another. Also for each single detector the response is quite uniform and no charge loss in the inter-electrode space have been detected. Because of the low cost and of the polycrystallinity, detectors can be potentially fabricated in any size and shape, using standard ceramic technology equipment, which is an attractive feature where low cost and large area applications are needed. The detectors which act as radiation counters have been tested with a beta source as well as in a high-energy beam of 100 GeV muons at CERN, connected to VLSI, low noise electronics. Charge collection efficiency and uniformity have been studied. The charge is efficiently collected even in the space between strips indicating that fill factors of 100% could be reached in imaging applications with direct detection of radiation. Single photon counting capability is reached with VLSI electronics. These results show the potential of this material for applications demanding position sensitive, radiation resistant, room-temperature operating radiation detectors, where position resolution is essential, as it can be found in some applications in high-energy physics, nuclear medicine and astrophysics.