How long does radioactivity from a nuclear blast last for?

Question

are hiroshima and nagasaki still radio active?

Answer 1

When Uranium or Plutonium fission (in a nuclear explosion or a nuclear reactor), they produce elements that are rougly half the atomic number of the original U-235 or Pu-238, but it doesn't always happen that they split *exactly* in two. There is, more like, a distribution of created (daughter) elements from the fissions, with a double-peak at atomic weights 95 and 135 (don't ask me why there is a double-peak).

Some of these isotopes around those weights have half-lives measured in decades, while others only last seconds. Some of these isotopes are very energetic (high energy, high intensity gamma emitters), while others emit beta particles, and some emit low-energy alpha particles. It's mostly the long-life isotopes (such as strontium-90 and cesium-137) that are most worrisome.

Hiroshima and Nagasaki are back to being 'normal' cities, but for the memorials at ground-zero.

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Answer 2

Radio active material has what is called 'A Half Life,' If that is 100 years the radio activity will be reduced by 50% in that length of time, and so on. The two cities that were nuked are now safe to wander ariund in.

Answer 3

it gets diluted but what do they say, a half life of millions of years.

Answer 4

too long