system
Given the following post, respond as if you're commenting on Reddit:
human
Why is Hiroshima and Nagasaki inhabitable after the nuclear bombings? Shouldn't there be lingering cancer-causing radiation?

Would your answers be the same if more bombs were exploded over those cities?
gpt
There are a few answers here. 

First. When the bomb explodes there is a large radiation burst, which then goes away. This would not necessarily cause an area to be radioactive, as the radiation is only there while the bomb is fissioning. 

Second. When you fission atoms, the waste products are what cause contamination. The Hiroshima and Nagasaki bombs fissioned less than 1% of their fuel. As a result there was very little contamination, and most of it got spread into the atmosphere and dispersed. This would keep residual contamination low enough to not have much of an impact. 

If you detonated present day weapons, or weapons designed specifically to contaminate, you may make an area uninhabitable.