Survey meter

Survey meters are portable radiation detection and measurement instruments used to check personnel, equipment and facilities for radioactive contamination, or to measure external or ambient ionizing radiation fields (to evaluate the direct exposure hazard). The hand-held survey meter is probably the most familiar radiation measuring device to society owing to its wide and highly visible use.

The most commonly used hand-held survey meters are the scintillation counter, which sees use in the measurement of alpha, beta and neutron particles; the Geiger counter, widely used for the measurement of alpha, beta and gamma levels; and the ion chamber, which is used for beta, gamma and X-ray measurements.

The instruments are designed to be hand-held, are battery powered and of low mass to allow easy manipulation. Other features include an easily readable display, in counts or radiation dose, and an audible indication of the count rate. This is usually the “click” associated with the Geiger type instrument, and can also be an alarm warning sound when a rate of radiation counts or dose has been exceeded. For dual channel detectors such as the scintillation detector it is normal to generate different sounds for alpha and beta. This gives the operator rapid feedback on both the level of radiation and the type of particle being detected. These features allow the user to concentrate on manipulation of the meter whilst having auditory feedback of the rate of radiation detected.

Meters can be fully integrated with probe and processing electronics in one housing to allow single-handed use, or have separate detector probe and electronics housings, joined by a signal cable. This latter is preferred for checking of convoluted surfaces for radioactive contamination due to the ease of manipulating the probe.

The readout for alpha and beta radiation is normally in counts, whilst that for gamma and X-ray is normally in a reading of radiation dose. The SI unit for this latter is the sievert. There is no simple universal conversion from count rate to dose rate, as it depends on the particle type, its energy, and the characteristic of the sensor. Count rate therefore tends to be used as a value which has been calculated for a particular application for use as a comparator or against an absolute alarm threshold. A dose instrument may be subsequently used if a dose reading is required. To help with this some instruments have both dose and count rate displays.

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