trottiey
Nuclear
- Jul 8, 2010
- 237
There are two types of exposure to radiation: internal and external. External exposure refers to direct irradiation, like exposure to the sun. If you can shield it or walk away, the external exposure stops. Internal exposure refers to inhaling or ingesting radioactive contaminants, or otherwise absorbing them into your body. These will stay with you until your body can eliminate them, and they may come extremely close to your cellular DNA. Very small amounts of radioactive contamination that poses no external risk can become life-threatening if it becomes internal. Conversely, intense radioactive sources pose no internal risk as long as they are contained in a sealed container, but could be life-threatening to nearby personnel if the container does not provide adequate shielding.
In the course of normal operation of a nuclear plant or x-ray machine, everything is contained and external exposure is the greatest hazard. But in the Chernobyl and Fukushima crises, the greatest concern is with environmental releases and internal exposures. Highly radioactive fission products have been released into the environment through a combination of controlled venting, failure of containment, and fire. This is comparable to the release of toxic pollutants from major industrial disasters. Initial releases in the first three days of the crisis were low and unlikely to cause health effects in the population. The situation deteriorated on the fourth day.
Release of radioactive contaminants is best measured in units of becquerels or curies. Unfortunately, I have seen no such estimates to date; please post if you know a good source.
Microsieverts (µSv) and millirems (mrem) are units of radiation dose that measure biological effect on human tissue. The concept of "radiation dose" is primarily used to quantify external exposures, but it can be used to measure internal exposure if the nature of the contaminant and quantity ingested is known.
The worldwide average background dose for human beings subject to natural environments is 2400 µSv per year. An effective dose of 10,000 µSv carries with it a 0.056% chance of developing cancer or other health effect. For people who receive extremely high doses in short periods of time, (say, in excess of 500,000 µSv in a single day) there is an additional risk of acute radiation poisoning.
I welcome questions.
In the course of normal operation of a nuclear plant or x-ray machine, everything is contained and external exposure is the greatest hazard. But in the Chernobyl and Fukushima crises, the greatest concern is with environmental releases and internal exposures. Highly radioactive fission products have been released into the environment through a combination of controlled venting, failure of containment, and fire. This is comparable to the release of toxic pollutants from major industrial disasters. Initial releases in the first three days of the crisis were low and unlikely to cause health effects in the population. The situation deteriorated on the fourth day.
Release of radioactive contaminants is best measured in units of becquerels or curies. Unfortunately, I have seen no such estimates to date; please post if you know a good source.
Microsieverts (µSv) and millirems (mrem) are units of radiation dose that measure biological effect on human tissue. The concept of "radiation dose" is primarily used to quantify external exposures, but it can be used to measure internal exposure if the nature of the contaminant and quantity ingested is known.
The worldwide average background dose for human beings subject to natural environments is 2400 µSv per year. An effective dose of 10,000 µSv carries with it a 0.056% chance of developing cancer or other health effect. For people who receive extremely high doses in short periods of time, (say, in excess of 500,000 µSv in a single day) there is an additional risk of acute radiation poisoning.
I welcome questions.