Radiation Detection: Dosimeters Plus Common Sense

The reality of a radiation emergency differs little from that caused by a chemical or biological release – any or all of them are either accidental or intentional. But in either case the emergency-response community is tasked with determining the type, size, and impact that the incident has on the population. Today there are many agencies involved with the development of detection equipment; however, the initial response is often carried out using secondary indications of the hazards – e.g., labels, signs, or placards indicating the possible presence of a hazardous material, the appearance of various medical symptoms in exposed individuals, and/or readings from specialized instruments.

Radiation is colorless, odorless, tasteless, and invisible. The only way to determine whether radioactive material has been involved in an event is to perform radiological surveys with specialized equipment. That equipment is designed to assist the responder, in the simplest of terms, in determining how much radiation is present and where it is. It also has, or should have, the capability of indicating how much radiation has been absorbed by the responder. The terms that are most commonly used in these measurements are dose and dose rate. The dose is the total amount of radiation accumulated by the responder or victim during a given period of time. The dose rate is how fast the radiation is traveling.

Many agencies have used current funding streams to purchase quick-response equipment for radiological incidents. Most if not all of these agencies are equipped with and now using dosimeters that are much more technologically accurate and more user-friendly than predecessor systems. Prior to the late 1990s, the most common dosimeter used was the so-called analog pen filament type. The analog radiation dosimeter is cylindrical, and about the size of a pen. It is called, appropriately enough, a pen dosimeter. The readout of the pen dosimeter is displayed by looking through the cylinder, in front of a light source, to see a red hash mark on a scale that marks the exposure. The pen dosimeter is then zeroed with a dosimeter charger.

New, Better, More Precise, Easier to Use

Recent advances have led to the introduction of an electronic self-reading dosimeter, which is in the shape and size of a pager. The dosimeter displays the dose in the form of a digital readout and sounds an alarm when the radiation level exceeds the threshold level.  Both types of dosimeters are usually clipped to the exterior of the user’s clothing. The pen dosimeters are made to measure in different ranges. Occupational exposure ranges for dosimeters usually measure up to 500 mrem [Milli  Roentgen] (5 mSv) [MilliSievert], which exceeds the normal U.S. yearly dose of 360 mrem (3.6 mSv), whereas the newer electronic self-reading dosimeters are auto-scaling – a feature that permits a larger range of measurement as well as greater accuracy.

A more modern-design dosimeter is the thermoluminescent dosimeter (TLD). Although not a direct reading instrument, the TLD plays an important role in the several dose-control issues that develop for responders over a longer period of time. The TLD contains a tiny crystal of lithium fluoride that undergoes cumulative structural changes when it is exposed to ionizing radiation. When heated, the crystal glows, giving off an amount of light proportional to its radiation exposure. This light is observed by an electronic sensor in a readout unit and recorded digitally. After the incident or exposure has ended the TLD is collected and sent to a lab to be read.

Time and experience have shown that local emergency-response agencies – e.g., fire departments and both EMS and law-enforcement agencies – will play the most important roles in the initial responses to a radiological emergency. The radiological emergency may be accidental – e.g., caused by an accidental release from a nuclear power plant – or intentional (in a terrorist attack). Whatever the cause, federal officials may well have an important role to play in supporting the response at the local level. However, the local response still will be key in determining the course of actions during the crucial early stages of a radiation incident.

Glen Rudner
Glen Rudner

Glen Rudner retired in 2022 as a manager of environmental operations for the Norfolk Southern (NS) Railway with environmental compliance and operations responsibilities in Tennessee, Alabama, Mississippi, and Louisiana. Previously, he was the hazardous materials compliance officer for NS’s Alabama Division (covering Alabama, Mississippi, Louisiana, and southwestern Tennessee). Prior to NS, he served as one of the general managers at the Security and Emergency Response Training Center in Pueblo, Colorado. He worked as a private consultant and retired as a hazardous materials response officer for the Virginia Department of Emergency Management. He has nearly 42 years of experience in public safety. He spent 12 years as a career firefighter/hazardous materials specialist for the City of Alexandria Fire Department, as well as a former volunteer firefighter, emergency medical technician, and officer. As a subcontractor, he served as a consultant and assisted in developing training programs for local, state, and federal agencies. He serves as secretary for the National Fire Protection Association Technical Committee on Hazardous Materials Response. He is a member of the International Association of Fire Chiefs Hazardous Materials Committee, a member of the American Society of Testing and Materials, and a former co-chairman of the Ethanol Emergency Response Coalition. He served as a member of the FEMA NAC RESPONSE Subcommittee.



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