Radiation poisoning

Radiation poisoning, also called "radiation sickness", is a form of damage to organic tissue due to excessive exposure to ionizing radiation. The term is generally used to refer to acute problems caused by a large dosage of radiation in a short period. Many of the symptoms of radiation poisoning occur as ionizing radiation interferes with cell division. This interference causes particular problems for cells that normally divide rapidly, such as those lining the gastrointestinal tract. Likewise, this is one reason for the effectiveness of radiotherapy in treating cancer — cancer cells are among the fastest-dividing in the body, and will be killed by a radiation dose that adjacent normal cells are likely to survive.

Measuring radiation dosage

The rad is a unit of absorbed radiation dose defined in terms of the energy actually deposited in the tissue. One rad is an absorbed dose of 0.01 joules of energy per kilogram of tissue. The more recent SI unit is the gray, which is defined as 1 joule of deposited energy per kilogram of tissue. Thus one gray is equal to 100 rad.

Related Topics:
Rad - Absorbed radiation dose - Energy - Joule - SI unit - Gray

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To more accurately assess the risk of radiation, the absorbed dose energy in rad is multiplied by the relative biological effectiveness (RBE) of the radiation to get the biological dose equivalent in rems. Rem stands for "Röntgen equivalent man." In SI units, the absorbed dose energy in grays is multiplied by the same RBE to get a biological dose equivalent in sieverts (Sv). The sievert is equal to 100 rem.

Related Topics:
Rems - Röntgen - Sieverts (Sv)

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The RBE is a "quality factor," often denoted by the letter Q, which assesses of the damage to tissue caused by a particular type and energy of radiation. For alpha particles Q may be as high as 20, so that one rad of alpha radiation is equivalent to 20 rem. The Q of neutron radiation depends on their energy. However, for beta particles, x-rays, and gamma rays, Q is taken as one, so that the rad and rem are equivalent for those radiation sources, as are the gray and sievert. See the sievert article for a more complete list of Q values.

Related Topics:
Alpha particle - Neutron - Beta particle - X-ray - Gamma ray - Sievert

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