Source:http://linkedlifedata.com/resource/umls/id/C0017230
UMD: Radiation survey meters designed to be sufficiently sensitive to detect a single ionization event. These meters usually consist of a cylinder that is pressurized (typically from 70 to 200 mm Hg) and contains a mixture of helium, neon, or argon and a quenching gas. A metal rod running through the center of the cylinder acts as an anode, and the cylinder wall acts as a cathode. Ionization radiation enters the chamber through a window on the front of the cylinder, producing an ionization avalanche. Over a period of time (e.g., a minute), a pulse counter registers each ionization avalanche and quenching as a pulse and displays the results on a meter. An audio speaker may be added to broadcast each ionization avalanche as a cracking sound. Geiger-Muller survey meters are used to detect low-level radiation (less than 100 milliroentgen/hour); they are useful for detecting radioactive spills and contamination of work areas as well as in instrumentation.,MSH: A radiation counter that uses a radiation-counter tube