Use of thick HgI₂ detectors as intelligent spectrometers

Abstract

Mercuric iodide is a very attractive material to detect ionizing radiation due to its high stopping power and wide energy gap, which allows the use of a small and compact detectors at room temperature. However, the spectroscopic performances of these detectors are poor in comparison with other more popular semiconductors with better transport characteristics. This effect becomes dramatic when thick crystals are used. The partial charge-collection method is reported to be the most suitable one for enhancing the energy resolution achieved with thick detectors. A Monte Carlo simulation of the behavior of the model and its dependence with crystals and electronic parameters is presented, giving operating rules that optimize the system performance in each situation. Specially designed hardware has been developed to extract the maximum information of the charge pulse produced by photon-detector interaction, according with the results of the simulation. As a final step, an automatic isotope-identification process, based on the use of neural networks, is performed, the identification being the true output of the whole system. Due to the strong dependence of this output on the free hardware parameters, an adaptive network is designed to act on these parameters in such a way that the system converges automatically to the best identification.