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Applied Chemistry and Physics
Published in Robert A. Burke, Applied Chemistry and Physics, 2020
Because radiation exposure can be cumulative, there are no truly safe levels of exposure to radioactive materials. Radiation does not cause any specific diseases. Symptoms of radiation exposure may be the same as those of exposure to cancer-causing materials. The tolerable limits for exposure to radiation that have been proposed by some scientists are arbitrary. Scientists concur that some radiation damage can be repaired by the human body. Therefore, tolerable limits are considered acceptable risks when the activity benefits outweigh the potential risks. The maximum annual radiation exposure for an individual person in the United States is 0.1 roentgen equivalent man (REM). Workers in the nuclear industry have a maximum exposure of 5 REM per year. An emergency exposure of 25 REM has been established by the National Institute of Standards and Technology for response personnel. This type of exposure should be attempted under only the most dire circumstances and should occur only once in a lifetime. There are currently efforts to increase this maximum emergency exposure.
Boilers
Published in A.J. Pansini, K.D. Smalling, Guide to Electric Power Generation, 2020
Nuclear plant operations introduce some slight addition of radiation into the atmosphere. These are well below the limits established as safe by the NRC. (Some background information may be reassuring. In the 1930’s, in connection with “radium” painted on watch dials, tests were made to determine the amount of radiation harmful to humans and it was established that humans could safely tolerate an exposure of 291,000 millirems a year. A rem or ‘roentgen equivalent man,’ is the unit of radiation which produces the same biological effect as a unit of radiation from ordinary X-rays. While the same regulatory bodies determined that 5,000 millirems per year was a permissible limit, it established a limit of 500 millirems as the permissible exposure for the general public. Plant designs further limit this value to about one-thousandth (0.001) or only 5 millirems per year. In contrast, natural background radiation may exceed 300 millirems per year.)
Toxic Pollution
Published in Kimon Hadjibiros, Ecology and Applied Environmental Science, 2013
The following units are used to measure emitted or absorbed radioactive radiation: One Curie (Ci) is the radioactive radiation emitted by radioactive material that undergoes 37 billion nuclear transformations per second (the transformation rate of 1 gram of Radium-226). The submultiple units millicurie (mCi), microcurie (μCi), nanocurie (nCi) and picocurie (pCi) are used, each of which is one-thousandth of the previous one.The Becquerel (Bq) is equal to one nuclear transformation per second, therefore 1 Bq = 27 pCi.The rad (Roentgen-absorbtion-dose) is equal to an energy absorption of 100 ergs per gram of irradiated material.The rem (rad-equivalent-man) is also a unit of energy absorption, which takes into account its biological effects as a function of the type of radiation and its distribution in the human body. It is the dose that has the biological effects of 1 rad of x-rays and is determined by multiplying rad by a quality factor QF. A unit usually used for smaller doses is the millirem (mrem), i.e. one one-thousandth of a rem.
Thirty Minutes Before the Dawn
Published in Nuclear Technology, 2021
The quickly prepared safety plan for Trinity was reasonably thorough, fairly elaborate, intentionally flexible, and in hindsight, somewhat lacking. Attributed to Hempelmann, the plan suggested a specific exposure limit for project participants: “It has been advised that no person should (of his own will) receive more than 5 R [roentgens, the common unit of measuring radiation at that time] at one exposure.” The upper dose limit over a 2-week period was set at 75 R by Dr. Hempelmann, Colonel Stafford Warren (chief medical officer of the Manhattan Project), and Warren’s deputy, Lt. Col. Hymer Friedell, during a conference at base camp on July 14 (Ref. 29). For perspective, today a DOE worker is limited to approximately 5 R over the course of a year.aalConsider “Electronic Code Federal Regulations, Title 10 (Energy),” Chapter III, Part 835. This law sets the limit at 5 rem/year, which is approximately 5 R. For civilians, “Evacuation of towns or inhabited places will be carried out by G-2 personnel if necessary on advice from the Medical Department.”aamK. T. Bainbridge, “Trinity,” p. 31. The plan was originally published as a July 20 memo “Hazards of TR #2,” LANL, NSRC, collection A-2020-019. That morning the three doctors, in consultation with Hubbard and a few other colleagues, also established the threshold for an evacuation: “The upper safe limit of radiation raised to 15 r/hr at peak of curve.”aan“Abstract of Conferences on Medical Hazards Held Before Trinity Shot,” p. 3.