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When radioactive materials are released, the human senses cannot detect radioactivity. The only way responders will know whether radioactive materials are present is with the use of instruments specially designed to detect radioactivity. Four general types of radiation monitors are available for emergency response:
• Geiger counter – You can use a portable Geiger counter to detect radiation coming from samples in many different settings. It contains a cigar-sized, high-voltage vacuum tube, called a Geiger-Muller tube, that registers many kinds of ionizing radiation, including X-rays, gamma rays and alpha particles. The Geiger counter indicates radiation by making a clicking sound and showing the intensity level on a meter or digital display.
• Lithium fluoride crystal – People who work around radiation wear badges called dosimeters. The dosimeter keeps track of radiation they encounter on the job. A lithium fluoride crystal in the badge stores energy whenever ionizing radiation hits it. Technicians test the exposed crystal to make certain a worker’s radiation dose stays within safe limits.
• Bubble detector – Most radiation monitors cannot detect neutrons, so another device is needed for this kind of radiation. Bubble detectors serve as inexpensive, simple-to-use dosimeters. Neutrons produce tiny vapor trails in a special gel. The vapor forms bubbles that accumulate. The number of bubbles relates to the number of neutrons, which helps determine exposure to neutron radiation.
• Helium 3 detector – A helium 3 detector can monitor levels of neutron radiation much as a Geiger counter does for ionizing radiation. The high cost of helium 3 detectors limits their use to specialized laboratory and industrial applications.
While knowing the technology behind monitors may be interesting and useful to some, it is “nice-to-know” information and not necessary to use the instruments appropriately. What is necessary is that responders know how to maintain, calibrate and properly use the monitoring instruments they have access to. They must also be able to select the proper instruments for the chemical(s) present when on the scene of a hazardous materials incident. The instrument manufacturer is the best source of information about specific monitoring instruments and important information for use and care. n