Note: In the descriptions below, the term "radiation" in the context of radiation detection refers to beta/gamma radiation unless noted otherwise. The detection of alpha radiation, or even low energy beta or gamma radiation (like that emitted from tritium), requires special probes or devices and is generally not included in the instruments discussed unless specifically mentioned. (1) Thermoluminescent Dosimeters (TLD): TLDs are devices that store radiation readings, which can later be measured using an electronic reader. They are rugged and can be stockpiled and rapidly issued. They are usually housed in cards that can color code for different technical specialties or be used as ID cards. TLDs do not have readouts that can be read by those wearing them, so they cannot be used as early warning devices or as indicators that radiation exposure limits have been reached. Once a TLD is read, its reading is cleared, so it can be reused many times. The TLD reader must be regularly calibrated and operated by a qualified and knowledgeable person. TLDs are appropriate for people involved in reentry and cleanup, but should not be used alone by first responders entering high-radiation areas. In the latter case, real-time detection instrumentation should also be carried by the first responders. (2) Self-Reading Dosimeters: This type of dosimeter, a small tube about the size of a ballpoint pen, is easy to use and does not require an expensive training program or a skilled technician. The wearer can look through the tube and get a reading of total absorbed dose in real time, so they can be used as an aid in controlling the amount of time spent in the radiation area. However, they are fragile and tend to go to a maximum reading when dropped, leading to lost data. They can be initialized by electronic chargers and reused many times. Self-reading dosimeters could be used by emergency responders, but because of their sensitivity to mechanical shock or environmental conditions dosimeter cards are preferred. (3) Dosimeter cards: These devices are about the size of a credit card and can be carried in a pocket. Successive dots on the card change color as levels of radiation exposure are exceeded. They can only be used once, and then must be thrown away, but the cost is minimal at $5.00 per card. Interpretation of the reading is instantaneous. They are recommended for immediate issue to emergency responders. Because their readings are only approximate and because they can only be used once, they are not recommended for reentry and cleanup personnel. Monitoring Devices for Decontamination Stations: Decontamination stations should be established as soon as possible after the event. People without serious injuries should be directed to these stations instead of to emergency rooms. Decontamination stations need instruments that can read radiation levels below normal background, but do not need a very high range. Accurate readings of high radiation levels have no practical value; if a person is contaminated, he or she should be immediately decontaminated. (1) Geiger-Mueller (GM) Counter: GM counters are sensitive radiation detection devices that can be capable of measuring alpha, beta, and gamma radiation. The GM counter, or Geiger counter, has a probe that can be aimed at the area of interest and a readout that measures in mR/hr or counts/minute. A special probe, generally referred to as a "pancake" probe, is required for detecting alpha radiation. GM counters also offer an audio option that allows the user to hear clicking proportional to the radiation level. Because they are directional and can give erroneous readings in extremely high radiation fields, GM counters are not recommended for general area readings by the teams entering intense radiation areas to save lives or to map the areas. They are easy to use, but require periodic calibration, which can be done by shipping to a service provider. Organizations using Geiger counters should have access to a qualified technician who can train the team members in use of the device. (2) Pancake Probe: A Geiger-Mueller counter with a wide, flat probe that is capable of detecting alpha, beta, or gamma radiation. The wide sensitive area of the probe allows for more rapid search of an area, and the shield on the back of the probe helps prevent radiation from some other source from interfering with the readings on the area of interest. The detector should be able to read levels below normal background. Because they are directional and can give erroneous readings in extremely high radiation fields, pancake probes are not recommended for general area readings by the teams entering intense radiation areas to save lives or to map the areas. They are easy to use, but require periodic calibration, which can be done by shipping to a service provider. Organizations using pancake probes should have access to a qualified technician who can train the team members in use of the device. (3) Alpha Detectors: An alpha detector must be very close to the alpha source to detect it. It should be noted that the measurement of alpha radiation can be confounded by the presence of beta/gamma radiation. However, since alpha emitters are internal hazards, not external hazards, if there is any concern about alpha emitters, first responders can enter with respiratory protection and not worry about the presence of the alpha emitting material. The decontamination station personnel can determine whether radioactive material is present using a pancake probe. Alpha detectors are only useful in the reentry and cleanup phase of the incident. (4) Portable Spectrometer: Portable spectrometers are used to determine the specific radioisotopes present. Since the presence or absence of radiation, and its magnitude, is all that emergency responders entering an area to save lives need to be aware of, knowing the specific radioisotope involved would not be immediately helpful. Therefore, portable spectrometers are not recommended for first responders. However, personnel making protective action recommendations need to know what radioisotopes are present, specifically to guide the treatment of internal contamination, so they need the capability of performing isotopic identification. (5) Area Monitor: These monitors are stationary devices set up to detect radiation over a wide area continuously. One form, the gate monitor, is an omnidirectional probe and meter mounted in a fixed location to check incoming or outgoing material for radiation. An area monitor should be capable of reading below normal background, and it would be worthwhile to connect it to a computer or data-logging device. Logged data would then enable the reconstruction of the extent of possible contamination or staff exposure, especially when emergency room or relocation center staff miss an alarm or choose to ignore it to take care of a gravely injured patient. (6) Portal Monitor: A portal monitor is a doorway-type device that allows people to walk through to detect the presence of radiation. A portal monitor can be used to check large numbers of people more rapidly than a technician with a hand-held meter so they are useful at decontamination stations established for screening mobile but possibly contaminated people. Many types of portal monitors are not wide enough to accommodate wheel chairs or gurneys and all require periodic calibration and testing. Some portal monitors can be expanded to allow vehicles to pass through, but most are for the monitoring of people. (7) Air Monitor/Air Sampler: These terms sometimes create confusion. An air monitor is technically an omnidirectional probe mounted in an area of concern, which can record or transmit dose rates in units such as rad per hour. An air sampler is a calibrated vacuum cleaner-type device that collects particles from the air on a filter that can be analyzed later. There are some hybrid devices, which pull air through a moving paper tape that is then counted by a detector, usually called an air particle detector. An air monitor is useful where there is concern over airborne radiation posing an immediate health risk. An air sampler is more sensitive than an air monitor, but it does not provide real time information. Samples can be analyzed in a laboratory for total counts, or for specific isotopes. For assistance in selecting a particular instrument or set of instruments, contact your state's Radiation Control Program Director. You can find the name and telephone number by contacting the Conference of Radiation Control Program Directors at (502) 227-4543 or on the Internet at www.crcpd.org