How powerful is the Atomic Bomb?

I just dropped my first A-Bomb. This sparked a few questions:

How long does the radiation or fallout last?

Can my units get damaged if they stay inside the fallout?

How much damage does the A-bomb do to a city? (If possible: provide a formula for damage done vs combat strength in cities)

Solution 1:

The fallout lasts until you clear it with a worker, it won't go away by itself. This should also answer your second question since it would be rather risky if you workers took damage while clearing the fallout so no your units do not take damage from fallout. Fallout simply makes the tile useless in terms of improvements and being worked by a city.

Solution 2:

The radiation lasts until it is removed by a worker.

Radiation does not damage units.

The bomb itself damages a city's health by 50% (not completely sure, but this is what I found in my experiences).