system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why places like Hiroshima and Nagasaki are inhabitable after being nuked while places like Pripyat, outside of Chernobyl, will be uninhabitable for centuries?
gpt
The bombs that were dropped on Hiroshima and Nagasaki were detonated at 500 m above the surface.  This allows the energy of the explosion to be spread out more evenly across a wider area - maximizing the blast radius, essentially.  It also limits how much radioactive material actually ends up on the ground.

The US couldn't be sure that their nuclear bombs would force Japan into surrender, and they wanted to be able to invade if necessary.  So making sure that it would be safe to invade Hiroshima with ground troops was a design priority.