Beta attenuation monitors (BAMs) are typically used in outdoor settings to quantify the amount of particulate matter in the air. The primary application is for air quality measurement. This applies to environmental monitoring carried out by government entities, as well as monitoring carried out by industrial facilities subject to air quality regulations. Although there are many competing technologies, BAMs have the advantage that the measurement principle is relatively simple, and the monitors can be left unattended for long stretches of time, typically for several weeks.

The principle of operation depends on radioactive decay. Beta rays or beta particles are one of the common forms of radiation produced by radioactive nuclei when they decay. In order to operate, a BAM requires a source of beta rays, typically a small quantity of carbon 14. A filter tape is placed between the radioactive source and the scintillation detector. When the filter is clean, the instrument makes a baseline measurement. Then a pump is used to drive a given quantity of air through the filter, trapping dust and other particulates. The mass of the dust on the filter blocks some of the beta rays from reaching the detector, producing an attenuated signal with respect to the baseline measurement. A simple mathematical calculation converts the signal into a measurement of the mass of the suspended particles per volume of air. Before the next measurement is made, the filter tape is advanced to a new position, so that the filter is clean. Given practical lengths of filter tape, the monitor can be left unattended for as long as two months. Typically, data is transmitted electronically to a central reporting station. Different sampling accessories can be used to conform to standard methods. Other sampling accessories simulate the load of particulate matter inhaled by a human being under the given circumstances.

The major application for beta attenuation monitors is for fixed location monitoring. The main source of demand is from government organizations charged with monitoring air quality. Other uses are for monitoring regulated industries, such as mining, cement, pharmaceuticals, chemicals, power plants, and pulp and paper. Portable instruments are used by first responders in situations involving hazardous materials or disasters. These systems do not pose any particularly strong hazard, as the radioactive materials are not very strong. Beta attenuation can also be used for other applications—primarily as a thickness gauge—but those products are not considered here.

The market for beta attenuation monitors is less than $10 million annually. There are also not very many market participants. The primary vendors sell many different technologies that relate to air quality measurement. The leading vendor is Met One Instruments. Other vendors: Opsis, based in Sweden; ESM Andersen Instruments, a small German business that is part of Thermo Fisher Scientific; and Ecotech, an Australian firm.

Beta Attenuation Monitors

at a Glance:

Leading Suppliers

• Met One

• Opsis

• ESM Andersen (Thermo)

Largest Markets

• Government

• Mining

• Cement

Instrument Cost

• $10,000–$25,000