Radioactive material

[slimjim]

If radioactive material has such unimaginably long half-lives, how come Hiroshima and Nagasaki are populated?

[j2buttonsw]

Different radioactive isotopes have different half-lives eg C14 has a half-life of >5000 years whereas P32 is a couple of weeks. The half-life of the radioactive material in nuclear bombs is short.

[darth vader]

j2b can you expand? How do you describe "short"? - months? years? also is this because of the geneva convention, or the limitations of nuclear weapons?

[j2buttonsw]

I was wrong. They used U235 in Little Boy (the Hiroshima bomb) which has half-life of 73 million years! A small proprtion of it (1.5 %) is used in the fission reaction which gives out the energy and the rest is distributed with the blast. So the reason that the area is still not radioactive is because the radioactivity has been distributed over a vast area. http://science.howstuffworks.com/nuclear-bomb.htm

[incitatus]

also if you think about it, long half life equals relatively little radioactivity. I deal with stuff with half lives measured in minutes and you definitely dont want much around.

[mattparker]

Radioactive particles can actually be transferred between objects, by quite litterally rubbing them onto another object. In the worst affected areas a cleanup operation is required to remove the particles by doing just this, transferring the particles to other objects and then removing these objects to storage (the UK it seems is a great dumping ground for radioactive waste)