A scaler is essentially a device that counts the electrical pulses generated by the radiosensitive detector. A Geiger counter is a familiar example of a radiation measuring instrument that measures the ionizing radiation of electrons (beta particles), gamma rays, and, in some cases, alpha particles (helium nuclei).
Ionizing radiation is any type of radiation that has sufficient energy per particle, or per quantum, to break apart atoms into charged particles (ions). A Geiger counter combines, in a single unit, a Geiger-Müller tube (the radiosensitive detector) and a scaler unit.
In many radiation measuring instruments, a "scaler mode" is one measurement mode of several that may be available to accommodate different radiation measurement requirements. An example of such a mode is counts per minute (cpm).
High voltage must be applied to the Geiger-Muller tube to make it radiosensitive.
In addition to its role as a pulse counter the scaler (or multi-mode unit) serves as the high voltage (HV) supply for the tube. A cable at one end of the tube connects to a power supply contained within the scaler unit.
The tube contains an inert gas at low pressure (helium, neon or argon) with halogens (chlorine, bromine or fluorine) added. The gas becomes electrically conductive when its molecules are struck by ionizing particles or photons. The high voltage tube acts as an amplifier: When radiation enters the tube through a thin window, it ionizes some of the gas molecules inside. The electrons produced are accelerated toward a collector wire in the tube, striking other molecules in their path with sufficient energy to cause further ionization. The electrons produced, in turn, are accelerated in the electric field, causing further ionization. The result is a brief avalanche of electrons that produces a pulse of output current through the collector wire.
A scaler usually displays the current pulses produced by radiation as "counts" in a LCD or LED register. The pulses can be displayed as counts per minute by a needle on a meter, or individually in a count register. Many Geiger counters can produce an audible noise in response to an ionizing particle entering the tube.
A scaler can count pulses for a set period of time, usually in minutes, or it can count time for a set number of pulses.
The register is cleared before beginning a new set of counts.