How do you use a Geiger counter?

Answer 1

Geiger counter instruments consist of two main elements, the Geiger-Muller tube, and the processing and display electronics. The radiation sensing element is an inert gas-filled Geiger-Muller tube (usually containing helium, neon or argon with halogens added) which briefly conducts electrical charge when a particle or photon of radiation makes the gas conductive by ionization. The tube amplifies each ionization event by a cascade effect and outputs a current pulse, which can be passed to the processing electronics. The signal is amplified and can be displayed by an analogue or digital display. The electronics also generates the relatively high voltage, typically 400-600 volts that has to be applied to the GM tube to enable its operation.

There are fundamentally two types of radiation readout; counts or radiation dose. The counts display is the simplest and is the number of ionizing events displayed either as a count rate, commonly "counts per second", or as a total over a set time period (an integrated total). The counts readout is normally used when alpha or beta particles are being detected. More complex to achieve is a display of radiation dose rate, displayed in a unit. This type of display is normally used for measuring gamma or X-ray dose rates and requires the use of an "energy compensated" GM tube, so that the absorbed dose displayed relates to the count events. The electronics will apply known factors to make this conversion.

There is usually an option to produce audible clicks representing the number of ionization events. This is the distinctive "click" normally associated with hand held or portable Geiger counters. The purpose of this is to allow the user to concentrate on manipulation of the instrument, whilst retaining auditory feedback on the radiation rate.