Radiation detector, 'mini-monitor g-m meter type 5.10', metal / plastic, made by Mini Instruments Inc, Burnham on Crouch, Essex, England, 1963-2005
The detector is encased in a grey metal casing. The front of the unit is grey and shows a 'counts per second' meter in a window, a black 2 position switch, and a grey rotary 3 position switch (off, battery check,on). On the top of the unit is mounted a rod shaped grey probe with a red tip and is attached with a curly electrical cord.
The mini monitor is well established in teaching, research, hospital and industrial laboratories as a reliable, convenient, and inexpensive contamination meter. The machine has a large logarithmically scaled meter with an open scale at the lower end to show background levels of radiation while displaying high levels without switching. There is also a speaker to give an audible estimation of radiation intensity. There is an alarm which can be set to trip at any level on the scale. The unit can be battery or mains operated.
Geiger counters are used to detect ionizing radiation, usually alpha and beta radiation, but other types of radiation as well. The sensor is a Geiger-Müller tube, a gas-filled tube (usually helium, neon or argon with halogens added) that briefly conducts electricity when a particle or photon of radiation temporarily makes the gas conductive. The tube amplifies this conduction by a cascade effect and outputs a current pulse, which is indicated by a needle or lamp and/or audible clicks. Modern instruments can report radioactivity over several orders of magnitude.