EPSILON: a gamma ray imaging system for the nuclear environment

EPSILON is a position-sensitive detector system for gamma ray imaging applications in the nuclear industry. This system is based on the use of a 3" circular position-sensitive photomultiplier tube (Hamamatsu R2486) coupled to a segmented CsI:Tl array and is optimised for imaging photons in the energy range 60 keV to 662 keV. The detector when mounted on a pan and tilt head combines the flexibility of a scanning system with the sensitivity and high angular resolution of an imager. This paper describes the design and optimisation of the collimator, detection system and readout for imaging the radiation environment. The performance of the imager has been evaluated using Cs137 point sources at distances of 2 to 5 metres. The radiation scene may be mapped with a 0.8 precision across an 11° diameter field of view. The sensitivity of the system and the improvements in image quality achievable by image processing are discussed