Particle counters are instruments that use optical technology to detect and count particulates in air, liquids or on surfaces. The particles can originate from diverse sources such as smoke, ash, dust, oil, metals or biological contaminants, for example mould or micro-organisms. The devices can be simple handheld units or advanced fixed manifolds depending on the purpose. Aerosol particle counters are commonly used to measure air for particulate contamination in critical environments such as cleanrooms for producing food, drugs or microchips. Cleanroom standards set the limits for particulates per unit volume depending on the level of classification.
Nuclear Counter instruments are used to check both the environment and/or specific items for radioactivity. A Geiger counter works by detecting the ionization produced by a radioactive particle. Every time a particle of radiation is detected, the counter records and the total number of particles recorded over a period of time indicates the amount of radiation present. Typically this is done over one minute intervals, resulting in "counts per minute" or CPM. Higher CPM equals increased radiation levels. A proportional counter is a measurement device to count particles of ionizing radiation and measure their energy. It works on the same principle as the Geiger counter, but uses a lower operating voltage.
Several gas mixtures are used for measurement of radioactivity and ionisation. For example, carrier gas for proportional counter, P-5 and P-10 mixtures (5% and 10% methane in argon); carrier gas for Geiger counter, 0.95% iso-butane in helium; and quench gas, 1.3% n-butane in helium.