Gamma Ray Detectors

Following a capture reaction in the gas target, the product nucleus emits one or more gamma rays very quickly (typically before it has travelled more than a few micrometers). The gamma rays pass readily through the thin wall of the target vacuum box and into the bismuth germanate (BGO) detectors, where their probability of interaction is high. Most of the energy of a gamma ray is converted into kinetic energy of an electron or an electron-positron pair. As electrons lose energy in BGO they produce light-- about 3 photons per keV of energy loss. Photomultipliers attached to the BGO counters convert the light into an electrical current which is registered by the data acquisition electronics.