I was researching the Kyshtym (nuclear) Disaster, and it said that it released 20 MCi (20 megacuries) of radiation into the air in a dust cloud.

I read from this Yahoo Answers answer that:

The curie is the old unit of activity and a very big unit it was.

1 curie = 3.70 x 10^10 disintegrations per sec.

In today's units 1 curie is about 30 Giga Becquerel.

So a curie of any radioactivity (alpha, beta or gamma) would fry you.

A sealed microcurie source could be safely handled.

If a single curie is this powerful, then what would twenty million curies (a 20 MCi) be like? Could you give any examples of events that exemplify this scale of radiation and damage (if you can't think of any real ones, then maybe a theoretical example)?

  • $\begingroup$ “So a curie of any radioactivity (alpha, beta or gamma) would fry you.” is nonsense. $\endgroup$
    – user7951
    Nov 9, 2015 at 19:09

1 Answer 1


There are a lot of factors at play here:

  • The curie and becquerel only tell you the number of disintegrations per unit time—they convey no information of the type or energy of radiation produced.

  • How dangerous a radioactive source is depends on the type of radiation produced and how one is exposed to it. External exposure to alpha particles is not very dangerous because alpha particles are easily stopped by skin, but inhaling alpha emitters can be very dangerous because there is direct access to sensitive alveolar cells.

  • How the radioisotopes are dispersed will greatly affect individual exposure to the radiation. A large amount of radioisotopes spread over a large area may increase the incidence of cancer slightly for a large number of people, but a smaller amount concentrated in one place may be very rapidly fatal to a single person.

20 MCi (740 PBq) is indeed a very large amount of radiation (~1/7 that released by the Chernobyl accident), but in a big cloud spread over thousands of square kilometres may not be acutely dangerous to people. That many radioisotopes is equivalent to 231,000 kg of cesium-137 and all that (magically) concentrated into a point source would produce a dose of .62 Gy/s for a person 1 m away—fatal in seconds.

  • $\begingroup$ I didn't realize the factors that could be at play here. Thanks for the explanation! $\endgroup$ Nov 9, 2015 at 19:31
  • $\begingroup$ But back to the original question (and assuming that this radiation was concentrated), what kind of an event could this be compared to? You told me the effects if you stand so close- but what could have a similar effect? $\endgroup$ Nov 9, 2015 at 19:33
  • $\begingroup$ @Jonathan I'm not sure what you mean by what "event could this be compared to". Except at very high levels, radiation exposure isn't immediately noticeable. If we're talking about .62 Gy/s, that's around 42 W of power dissipated as heat in a person of average mass, so there would be some heating. I could only speculate what that exposure actually feels like. Some reports from criticality accidents (e.g. demon core) described what might have been Cherenkov radiation visible in the eye. $\endgroup$ Nov 9, 2015 at 21:23

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