How many miles were the atomic bomb on japan?

Answer 1

Cannot answer; depends on the yield, burst height/depth, etc. Some examples of optimal altitude airbursts:

• Low yield tactical weapon, blast radius < 0.1 mile.
• Tzar Bomba (over 50MTon yield), blast radius 60 miles.

Above or below the optimal altitude the blast radius of an airburst is reduced.

Surface and subsurface bursts have much smaller blast radius values than airbursts. A deep enough subsurface burst can be entirely contained and have no effect on the surface (except for a brief earthquake if underground, or millions of tiny radioactive bubbles rising to surface if underwater).

Answer 2

Half a mile was the evaporation of humans. Further away was the roasting of humans or animals.

Answer 3

at least 100