Fabrication of mercuric iodide radiation detectors

The technologies developed at CTC to synthesize and purify mercuric iodide and to grow single crystals have made it possible to routinely produce detectors, which find applications in hand-held instruments operating at ambient temperatures. The dimensions of the detectors are specified, depending on the application, by a combination of sensitivity, spectral resolution and instrument dimensions. A short description will be given of the methods used to prepare the material and grow the crystals, of the cutting and shaping of the detector bodies and of the surface preparation and contact application, including the coating with parylene. Additional methods of encapsulation are used to protect the detectors against mechanical damage and to reduce the microphonic noise. As a result modular units are produced which are very rugged and can be used in instruments of different designs. The testing of the detectors follows the consecutive steps in the fabrication, and data will be presented to show that generally the performance improves as a result of the procedures used by us. Since the modular approach reduces the electronic noise levels processed by the preamplifier it is possible to use long shaping times up to 50 μs which optimizes the spectral resolution.