Radiation dosimetry
Radiation dosimetry is the science of measuring and calculating the exposure to ionizing radiation, such as X-rays and gamma rays, absorbed by matter and biological tissues over time. This field is particularly significant in contexts where radioactive materials may be illicitly obtained or disseminated, as it aids forensic scientists in investigating related crimes. Dosimetry allows for the assessment of how much radiation a sample has received, its source, and potential hazards it may pose to individuals who may have come into contact with it.
To measure radiation exposure, various devices are utilized, with dosimeters being the primary tools for tracking cumulative radiation levels. Unlike Geiger counters, which provide real-time readings, dosimeters offer a total exposure count. Dosage is reported in grays (Gy) for physical matter and sieverts (Sv) for biological tissues, adhering to international measurement standards. Occupational exposure limits are set by governments to safeguard health, with specific dose guidelines for whole-body exposure and specific organs.
Personal dosimeters, which can be electronic or film-based, are worn by individuals to monitor their radiation exposure continuously. These tools are essential in environments where radiation exposure is a risk, ensuring that safety guidelines are followed and biological impacts are minimized.
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Radiation dosimetry
DEFINITION: Calculation of radiation exposure (quantity or dose of ionizing radiation—such as X-rays or gamma rays—absorbed by matter in tissue) over a given period of time.
SIGNIFICANCE: A high degree of concern surrounds the illicit acquisition and dissemination of radioactive materials by criminals and terrorist organizations. Forensic scientists apply dosimetry in investigating such crimes through geological and archeological dating, retrospective dosimetry, and personnel dosimetry.
Using dosimetry, investigators can determine how much radiation exposure a given sample has received, the sample’s origination point, who has come in contact with the material, and whether the sample poses a potential hazard.
A radiation dosimeter is a device that measures cumulative (total) radiation exposure. Dosimeters differ from Geiger counters, which are also radiation detectors but give only moment-to-moment readings of radiation levels. Radiation doses are reported in grays (Gy) for matter and sieverts (Sv) for biological tissue. The non-SI (International System of Units) unit for radiation is rads, and that for dose equivalent is rems (1 Gy = 100 rads and 1 Sv = 100 rems). Mineral specimens produce radioactivity ranging from 0.5 to 200 millirems per hour measured at approximately one-half inch from the specimen.
The governments of most nations have established guidelines for permissible occupational radiation dose levels. Typically, the whole-body dose limit for routine exposures is 5 rems per year. This limit is based on the total amount of internal and external exposure. Specific limits have also been set for individual organs that must be met in addition to the whole-body dose limit: For the extremities the limit is typically 50 rems per year; for skin and other organs, 50 rems per year; and for the lens of the eye, 15 rems per year.
A personal radiation dosimeter is a small electronic device that resembles a pen; it is often worn clipped to clothing to measure an individual’s radiation exposure. By using a magnifying and illumination lens, the wearer can read the exposure level directly by looking into the dosimeter. This is considered to be the most effective method of determining personal radiation exposure, as the biological damage caused by radiation is cumulative. The film badge dosimeter is an inexpensive alternative to the electronic dosimeter. It is a plastic badge containing a piece of photographic film. The badge is worn on the individual’s clothing, and the film is gradually exposed with the wearer’s radiation exposure. The film is periodically removed from the badge and developed, and through analysis of the developed film’s optical density, the cumulative dosage measurement can be determined.
Bibliography
Ehmann, William D., and Diane E. Vance. Radiochemistry and Nuclear Methods of Analysis. New York: John Wiley & Sons, 1991.
Moody, Kenton James, Ian D. Hutcheon, and Patrick M. Grant. Nuclear forensic Analysis. Boca Raton, Fla.: CRC Press, 2005.
Stabin, Michael G. Radiation Protection and Dosimetry: An Introduction to Health Physics. New York: Springer, 2007.
Wojcik, Andrzejm et al. "Minimum Reporting Standards About Dosimetry of Radiation Sources Used in Radiation Research Studies." Radiation and Environmental Biophysics, vol. 63, 20 Feb. 2024, pp. 181-183, doi.org/10.1007/s00411-024-01063-6. Accessed 14 Aug. 2024.