Suggestions or feedback? Previous image Next image. Massachusetts Institute of Technology. Search MIT. Search websites, locations, and people. Enter keywords to search for news articles: Submit. Browse By. Explained: rad, rem, sieverts, becquerels.
A guide to terminology about radiation exposure. David L. Publication Date :. Some reports talk about millisieverts while others talk about rem or becquerels, when what most people really want to know is much simpler: Can I drink the milk?
Is it safe to go home? Should people in California be worried? There are a number of reasons for the confusion. Different units of measure are used depending on what aspect of radiation is being measured. For example, the amount of radiation being given off, or emitted, by a radioactive material is measured using the conventional unit curie Ci , named for the famed scientist Marie Curie, or the SI unit becquerel Bq.
The radiation dose absorbed by a person that is, the amount of energy deposited in human tissue by radiation is measured using the conventional unit rad or the SI unit gray Gy. The biological risk of exposure to radiation is measured using the conventional unit rem or the SI unit sievert Sv. When the amount of radiation being emitted or given off is discussed, the unit of measure used is the conventional unit Ci or the SI unit Bq.
A radioactive atom gives off or emits radioactivity because the nucleus has too many particles, too much energy, or too much mass to be stable. The nucleus breaks down, or disintegrates, in an attempt to reach a nonradioactive stable state. As the nucleus disintegrates, energy is released in the form of radiation. The Ci or Bq is used to express the number of disintegrations of radioactive atoms in a radioactive material over a period of time.
For example, one Ci is equal to 37 billion 37 X 10 9 disintegrations per second. The Ci is being replaced by the Bq. Since one Bq is equal to one disintegration per second, one Ci is equal to 37 billion 37 X 10 9 Bq. Ci or Bq may be used to refer to the amount of radioactive materials released into the environment. For example, during the Chernobyl power plant accident that took place in the former Soviet Union, an estimated total of 81 million Ci of radioactive cesium a type of radioactive material was released.
When a person is exposed to radiation, energy is deposited in the tissues of the body. The amount of energy deposited per unit of weight of human tissue is called the absorbed dose. Absorbed dose is measured using the conventional rad or the SI Gy.
The rad, which stands for radiation absorbed dose, was the conventional unit of measurement, but it has been replaced by the Gy. One Gy is equal to rad. This number is known as the Quality Factor Q. When the amounts of radiation being measured are less than 1, prefixes are attached to the unit of measure as a type of shorthand. This is called scientific notation and is used in many scientific fields, not just for measuring radiation.
The table below shows the prefixes for radiation measurement and their associated numeric notations. When the amount to be measured is that is, 1 X 10 3 or higher, prefixes are attached to the unit of measure to shorten very large numbers also scientific notation. The table below shows the prefixes used in radiation measurement and their associated numeric notations. People are exposed to radiation daily from different sources, such as naturally occurring radioactive materials in the soil and cosmic rays from outer space of which we receive more when we fly in an airplane.
Some common ways that people are exposed to radiation and the associated doses are shown in the table below.
0コメント