Beta gauge particulate monitor

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July 2003 Analytical Instrumentation & Environmental Monitoring

Verewa's F-701 beta gauge particulate monitor determines particulate concentration by measuring the amount of radiation a sample absorbs when exposed to a radioactive source. In general, the more energy absorbed, the greater the particulate concentration. Depending on their energy, the emitted electrons will be absorbed by any material (solid, liquid, gas) within their reach. The absorption constant is therefore based on both the energy (in MeV) of the emitted electrons and the chemical composition of the absorbing material. Simplified, the correlation is: the lower the energy of the electrons, the lesser the absorption's dependence on the chemical composition of the absorbing material.

The F-701 incorporates a three-step procedure to ensure accurate and reproducible particulate measurements. At the start of each measurement cycle, the F-701 measures the amount of radiation absorbed by an unloaded filter tape. This is in essence an automatic zero correction. Once this 'zero reading' is taken, the sample is drawn through the filter tape at a controlled rate of 1 m³ per hour and any particulates in the gas stream deposited on the filter tape. After a pre-selected sample collection period, the F-701 again measures the amount of radiation absorbed by the loaded filter tape. The difference between the original zero reading and the final reading is directly proportional to the additional mass (ie dust particulates) collected on the tape.

The F-701 utilises a flat top C-14 source with a half-life of 5730 years. This particular isotope offers several advantages over other emitting isotopes in that its emitted electrons are very low energy (0,156 MeV) and decay into a non-radioactive chemical.

In addition, beta absorption using a C-14 source is virtually independent of the chemical composition of the collected particulates, eliminating the need for a site-specific reference calibration.

The monitor, which is CE approved and TUV Certified, provides accurate particulate measurements with a minimum of operator interaction and maintenance. It can be configured as either a 19" rack mounted unit or as a bench-top instrument.

The Model F-701 beta gauge particulate monitor consists of four main modules and is designed for a wide range of ambient air monitoring applications. Typical applications include ambient air monitoring networks, occupational health studies, indoor monitoring, heavy metal analysis, particulate monitoring at hazardous waste sites and landfills, secondary emissions monitoring (coal storage yards, quarries) and dust monitoring in fresh air and exhaust air pipes.

For more information contact Mike Andrews, OEN Enterprises, 011 792 2859, [email protected], www.oenenterprises.co.za

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Analytical Instrumentation & Environmental Monitoring

Beta gauge particulate monitor

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