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A dose which is acute, that is, received over a short period of time, has a much greater biolgoical effect than one received over a longer period of time. This is because radiation acts by depositing energy in tissue, damaging your cells. Very minor damage, repeated often, will be better repaired than a major assault. Doses can then cause either deterministic effects, where X dose causes Y problems, or stochastic effects, where X dose raises the probability of Y by Z amount.
The most well-known deterministic effects are what's commonly known as radiation poisoning, while stochastic effects mostly consist of cancer of one sort or another. Both the timing and absolute dose determine the effect -- 1 Sv over the course of 20 years (a US radiation worker receiving his or her limit for the year 20 years in a row) will not cause radiation poisoning, but a dose of 1 Sv over 5 minutes certainly will.
A brief digression on units: All units in these charts are in sieverts, the SI unit of effective dose. The SI unit of dose, the gray, is a unit of energy deposited in matter. 1 Gy is equal to 1 Joule/kilogram. Sieverts are calculated by multiplying grays by a quality factor based on the type of radiation producing the dose.
The quality factor captures how bad the type of radiation is for you. For gamma rays, the most common and farthest-traveling form of radiation, the quality factor is 1. In the US, the government and many reactors use units of rem and rad, corresponding to sieverts and gray, respectively. 1 Gy = 100 Rad.
Confusingly, Roentgens (pronounced renkens), an outdated unit of exposure, is sometimes used interchangably with rem and rad.
What this means is, getting farther away from the radiation source goes a long way towards limiting your exposure.
If you can't get and stay far away from the radiation source, your second option to limit your dose is to just not spend that much time next to it. Radiation fields usually have units of dose rate, meaning the time you spend in them is just as important as the strength of the field.
Finally, if you have to spend a long time near a large radiation source, you can still limit your exposure by putting a lot of the appropriate shield between you and it. Lead is most commonly used, but if the source is giving off a lot of neutrons, you will want some water and boron instead. These three principles are often distilled down into just "time, distance, and shielding", and, along with the control of radiological contamination, form the motivation for almost every measure taken for radiation protection.
There are three fundamental concepts that are important when discussing radiation and its effects on physical objects:
(i) the actual radioactivity involved,
(ii) the amount of energy the radiation imparts on other objects, and
(iii) the question of the biological effects of that radiation, particularly on humans.
These concepts are behind the three units most commonly used to measure radiation. As it turns out, the sport of boxing provides a rather useful analogy for understanding these three concepts. From the point of view of a boxer facing a tough opponent, the three concepts of radiation mentioned above could be thought of as:
(i) how many punches are being thrown,
(ii) how powerful the punches are, as in a jab versus an uppercut, and
(iii) how much the punches actually hurt when they land.
The three units that measure the three concepts mentioned above are:
(i) The becquerel (ultimately after French nuclear physicist Atoine Henri Becquerel who shared a 1903 Nobel Prize in nuclear physics).
(ii) The gray (after British radiobiologist Louis Harold Gray).
(iii) The sievert (after Swedish radiologist Rolf Maximilian Sievert).
Originally posted by dvrt10
reply to post by pforkp
Thanks for posting this. It's nice to know that at least one person on this site is trying to calm nerves instead of agitate them.
If you look at the fact that cancer is now inflicting a huge slice of the population when it was non existant they say before Nuclear technology, it kinda makes the numbers MOOT.
...a becquerel would just be a measure of how many punches are thrown without regard to whether they are roundhouses, hooks, jabs, or even if they connect at all. They also say nothing about how much the punches hurt, once landed.
Garwin's criticism centers on what he sees as a glaring omission--the report's failure to cite the findings of a 1993 study produced by the U.N. Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), which estimated that the worldwide 'collective effective dose' from the Chernobyl accident was about 600,000 man-sieverts. He also refers to a report published last summer by the National Academy of Sciences on the effects of ionizing radiation, which concludes that each dose of whole-body radiation causes a lethal cancer at the rate of 0.04 cancer deaths per sievert of exposure.
Originally posted by Long Lance
reply to post by chocise
sources please, and remember that irradiation by an external gamma radiation source is different from being contaminated with alpha & beta emitters. Pu is chemically toxic beyond your imagination, so i'd go with caffeine, just saying.
i'll give you one link about the Cobalt 60 irradiation experiment in Taiwan, even though i strongly disagree with clandestine involuntary human experimentation, if you have links corroborating the rest of your stories please post them.
www.ncbi.nlm.nih.gov...edit on 2011.3.20 by Long Lance because: (no reason given)
Originally posted by chocise
Thank you Lance, I don't have the sources as I explained clearly from the outset this was a received email from a colleague. I felt it was relevant to the current discussion and decided to post it in its entirety.
The references you seek are in the text itself: whether quoted directly from The Times [New York or UK] or within the text directly, attributed to individual specialist professors on the subject. I could trace these links, but really, c'mon... I'm not writing a thesis, just carrying the banter along.