capable of performing essentially at room temperature thus the device employs a cadmium telluride crystal and because of the preferred low energy levels of radiation which it is called upon to detect must be capable of operatively reacting to low energy gamma ray interactions the interaction of gamma rays with such crystals is primarily through three processes namely the photo electric effect compton scattering and pair production in the photo electric effect a photon of energy hv interacts with an atom as a whole its energy is completely transferred to an electron usually in the innermost shell the electron is ejected with a kinetic energy e kin hv e b is the binding energy of the orbital electron h is planck 39 s constant and v is the frequency associated with the wave nature of the gamma radiation such electrons undergo many collisions until this energy is shared with some thousands of other electrons each of these electrons leaves behind a positively charged region called in the literature a 34 hole 34 at the energies of 125 i compton scattering is of minor importance pair production refers to the reaction of an electron and a photon by the gamma ray since this process requires more than 1 0 mev it does not occur in the present application in compton scattering the primary photon may interact with any one of the orbital electrons the electrons are considered essentially as free electrons under the condition that the primary photon energy is large compared with the.