Positron annihilation monitor and method for detecting hazardous materials

A device for measuring constituents of a gaseous sample comprising:

• a source of positrons;
• an annihilation region spaced apart from said source and occupied by said gaseous sample, wherein at least one positronium species is formed through interaction of said positrons with said gaseous sample;
• and two gamma ray detectors disposed adjacent to said annihilation region for detecting gamma rays generated by the decay of said at least one species of positronium within said annihilation region, wherein at least one gamma ray detector is substantially insensitive to water.

A device for measuring the presence of a small concentration of at least one hazardous material within a vessel having walls comprising:

• a positron source;
• an annihilation region spaced apart from said positron source for receiving positrons from said positron source and wherein at least one species of positronium comprising a population of ortho-positronium is formed by an interaction of said positrons with said at least one hazardous material, said annihilation region being located within said walls of said vessel and being positioned such that at least a portion of said at least one hazardous material to be measured passes within positron-capture-proximity of said positrons.