How Do Dosimeters Work?

Dosimeters measure prolonged exposure to potentially dangerous effects. They are used by workers and scientists in a variety of situations, but the most common dosimeters measure either ionising radiation or noise over periods of time.

They are small objects often worn in pockets that take readings over a day or several days.The wearer may self-monitor the dosimeter to see what the average level of radiation or noise has been. Other dosimeters are sent to technicians who put the dosimeter through a standardised test to measure the average levels. This gives companies a good idea of how dangerous certain areas are for their workers, and shows how well they are following safety regulations mandated by state and federal governments.

Radiation and noise dosimeters both sense the prolonged "dose" of a particular type effect, but work in vastly different ways. When measuring light amounts of radiation over an extended period of time, two different methods can be used. The first kind is the whole-body dosimeter, which measures x, beta and gamma radiation rays. This is a simple, disposable device in the shape of a packet that is created with a very thin layer of aluminum oxide. All radiation passes through this packet, but some passes through a copper filter, while some passes through a tin or imaging filter, and some is allowed to go straight through to the aluminum oxide layer. The dangerous types of radiation will have a specific interaction with this layer, giving it energy. At the end of the day the layer is taken from the dosimeter and tested with a blue laser, causing the oxide to give off luminescence in different areas based on how much radiation it received.

The second type of radiation dosimeters works in a similar method, but uses small crystals or chips instead of an aluminum oxide layer. These crystal "catch" ionising radiation, which leaves traces of energy as it passes through objects, exchanging electrons and ultimately changes the processes of tissues. Since the crystal is not living it has no processes to change, but the electrons are captured within its structure. When heated, the crystal chip produces light equal to the amount of gamma, x and beta radiation it has received. This light is carefully measured and used to identify how much radiation a person wearing the dosimeter has encountered. This process is referred to as thermoluminescent dosimetry.

Noise dosimeters measure sound levels instead of radiation. Noise dosimeters use sound meters to measure how many average decibels they are exposed to over a certain number of hours per day, usually six to eight. Anything above an 80-decibel average over eight hours is considered unacceptably high.

Noise dosimeters measure sound in several different ways because there are different regulations concerning types of sound. While the primary microphone may pick up and record the average decibels workers are exposed to, other internal instruments monitor more specific jumps in sound. Modern dosimeters are created in the form of small badges with an opening for the microphone and no accessible parts, so workers cannot alter readings. Data is communicated to a main computer through wireless or infrared connections.