Evaluation of mercuric iodide ceramic semiconductor detectors

Mercuric iodide ceramic radiation detectors, which can act as nuclear particle counters, have been fabricated with single continuos electrical contacts and with linear strip contacts. They have been tested with different kinds of gamma and beta sources as well as in a high energy beam at CERN. The detectors were also successfully tested for radiation hardness with irradiation of 5(double dagger)10(14) neutrons/cm(2). The ratio of detected photons over the number of absorbed photons has been measured with gamma sources of different energies, and it ranges from 20% at 44 keV up to about 30% at 660 keV. An absolute efficiency of 70% has been measured for a 350 mu m thick detector for beta particles emitted by a Sr-90 source. Charge collection efficiency, defined as the amount of charge induced on the electrodes by a Minimum Ionizing Particle (MIP) traversing the detector, has been measured in two samples. The average collected charge fits well with a linear curve with slope of 35 electrons/(kV/cm) per 100 mu m. This result is well described by a dynamic device simulation, where the free carrier mean lifetime is used as a free parameter, adjusted to a value of 1.5 ns, i.e. about 1/100 of the corresponding lifetime in single crystal HgI2 detectors. The response to MIP has also been studied with a high energy (100 GeV) muon beam in CERN. A preliminary beam profile is presented while a more detailed analysis is still in progress and will be presented elsewhere. These results together with the low cost of the material make ceramic HgI2 detectors excellent candidates for large area particle tracking and imaging applications, even in a radiation harsh environment.