system
Given the following post, respond as if you're commenting on Reddit:
human
Does radiation stay close to the ground, rise, or go everywhere ? For example would it be "safe" to be inside a canyon or on top of a building ?

I want to write a short story set in a post nuculear war world and want to keep it as accurate as possible.

Also if you would be willing to share some more info (theories and such) on how the world would be after a nuculear war (what/who would survive, how would the enviroment be, where and how the last humans would settle if they survive) that would be great.

EDIT: okay thank you all guys for the replies. This thing kind of exploded (heh)

Seems that I will have to think of something different though to male the story a bit more realistic.
gpt
Please remember that most of the information you have received from popular culture about post war nuclear fallout dangers is complete rubbish.   Fallout is not nuclear waste with a long half life, it is normal matter that is briefly radioactive for a short period of time, with a few important exceptions.  The reality is that nuclear war will not cause long lasting radiation danger, permanent genetic mutations, nuclear winter, or any other permanent biological or environmental problems past 1 years time.  Please read free PDF download of Nuclear War Survival Skills for the actual facts as determined by scientists who studied Hiroshima, Nagasaki, and many other aspects of nuclear war.  

There are many horrible aspects of nuclear war but long term(years,decades) of radiation contamination is not one of them.