New thermal neutron solid-state electronic detector based on HgI2 crystals

We describe the development of a new solid-state electronic neutron detector, based on HgI2 single crystals. Incident neutrons are absorbed in high neutron absorbing foils, such as cadmium or gadolinium, which are placed in front of a HgI2 detector. Gamma rays, emitted as a result of the neutron absorbtion, are then absorbed in the HgI2, generating free charge carriers, which are collected by the electric field. The advantage of this system lies in it's manufacturing simplicity, low weight and small physical dimensions, compared to gas-filled conventional neutron detectors. The disadvantage is that the system does not discriminate between gamma rays and neutrons. A method to minimize this disadvantage is pointed out. It is as well possible to count neutrons by direct exposure of the HgI2 to neutrons. The neutron-to-gamma transformation in that case takes place by the material nuclei themselves. This method, however, is impractical due to the interference of delayed radioactivity whose origin are 129I nuclei. They are generated from 128I by absorbing a neutron, and decay with a 25 min half lifetime involving gamma emissions. (author)