(1) A type of gamma-ray detector. Consists of a gas-filled cylindrical metal shell containing a center rod (i.e., electrode) maintained at about 100 volts positive to the cylinder wall. An incident gamma ray interacts with the cylinder wall material or the gas maintained at high pressure in order to produce a high-speed electron. The high-speed electron, drawn to the positively charged center rod, produces additional electrons and ions in the collision with gas atoms. The electrons (along with some negative ions) moving to the center electrode constitute a minute flow of electrical cur rent, the size of which is proportional to the number of gamma-ray interactions. Long chamber lengths and high gas pressures are used in order to improve detector efficiency, but vertical resolution suffers with increased chamber size. See also pair production. Compare Geiger-Mueller counter, proportional counter, and scintillation counter.
(2) Has been used as a slow-neutron detector.