Tritium discrimination using cluster size information from a DGEM detector

This report describes a method to effectively discriminate between tritium and other interfering airborne radioactive gases using ionization cluster size information from a double gas electron multiplier (DGEM) and a suitable readout array. The readout array consists of 121 pads (an 11×11 matrix of 4×4 mm pads on 6 mm centres) on a printed circuit board, each connected to a charge sensitive amplifier. The prototype-automated discriminating monitor typically indicated a spillover fraction, in the tritium channel, in the order of ±5% for binary mixtures of tritium and 14C, 85Kr, 133Xe or 41Ar. A custom-made dynamic cluster-fitting algorithm gives results in real-time with very good accuracy under extreme conditions.