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How Is Radiation Measured?
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When people talk about radiation measurements, they usually refer to ionizing radiation. Most types of lightwaves "radiate," or transfer through a medium, but only some of these waves are ionizing to living tissue, which means that energy is exchanged as the radiation passes through an organism. Atoms change, borrowing energy from the radiation and passing that energy through living tissue. This can produce effects as simple as sunburn or as complicated as radiation sickness. There are many different types of measurements used to define radiation, how it is stored in objects, how it affects tissue and how it affects humans.
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The curie, named after scientist Marie Curie, is a unit of measurement used to measure how radioactive an object is, or how much radiation it produces. This is done by examining how fast its atoms disintegrate and measuring their disintegration per second. A curie is about 37 billion disintegrations per second, but curies are divided into millicuries and picocuries to measure tiny amounts of radioactivity. All objects have a certain amount of curies. Roentgen, on the other hand, is a radiation unit that indicates how much radiation is present in the air of a specific environment. This is used to show how much radiation may be absorbed by standing in a particular place for a certain amount of time.
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More common than these two are the rad and the rem. These two units can measure any type of ionizing radiation, including alpha, beta, neutron, gamma and "X," and deal with how much radiation is absorbed by objects. Rad stands for "radiation absorbed dose." One rad equals 100 ergs (an energy unit) absorbed by 1 g of material. Rads are used to show how much radiation any object, especially things like metal and stone, has absorbed.
Rem is a strictly biological measurement, and stands for "roentgen equivalent man," meaning that it is the same essential measurement as a roentgen, only applied to the human body--although this works only with gamma and "X" types of radiation. Rem is used to define limits of exposure for people who work in nuclear power plants. Rem is often divided in millirems and assigned a length of time, such as millirems per hour.
Technically, rad and rem measurements have been replaced by the metric measurements gray and sievert. Gray is a precise measurement of how much energy the ionizing radiation gives to the tissue it passes through, an exact measurement. Sieverts take into account the type of radiation and produces a biological measurement of how dangerous the absorbed radiation is to the body. However, rads and rems are still used in many practical settings.
eHow Article: How Is Radiation Measured?
