Gamma ray energy measurement using the multiple Compton technique

Modern developments in detector and electronics technology now enable a new generation of gamma ray detectors based on recording each and every energy loss associated with an incident gamma ray. The energy of an incident gamma ray is determined by measuring the positions of the first three interactions, and the energy loss of the first two. The direction of the incident gamma ray is restricted to a conical range of possible directions. The significance of such a detector is at least three-fold: first, a gamma ray need not be totally absorbed in order to measure its full energy. Thus, relatively thinner detectors are possible. Detection efficiencies approaching 40% at 1 MeV are possible in a Si detector system of only 40 g/cm² thickness. Second, these detectors are naturally imaging without the need for a complex aperture or collimator. Third, these detectors have little or no Compton shelf, thus Compton rejection or heavy shielding is no longer required. We report on a simple demonstration measurement using three position sensitive detectors