The effects of a nuclear explosion include shock waves (or referred as air blasts for an explosion in the air), thermal radiation, initial nuclear radiation
, and residual nuclear radiation.
Unlike the Hiroshima bomb, which was air-burst, a ground-burst IND would, in addition to the initial nuclear radiation
, generate a radioactive plume covering up to 1,000 square miles.
Initial nuclear radiation is generated by the processes of fission and fusion at the instant of detonation.
For larger fusion weapons, the lethal area for the initial nuclear radiation is smaller than the lethal areas for blast and thermal flash, for the 1Mt bomb described above, about 22[km.
A crude 1kt terrorist weapon would produce lethal initial nuclear radiation out to 800m from ground zero, although its lethal blast effect would extend only to 450m.
The 1Mt explosion described above, if above a large city, would cause many millions of immediate fatalities from blast, thermal flash, and initial nuclear radiation equivalent to the entire population living within a circle 21km across.
Its effects, although not unimportant, are relatively minor compared with the blast effects, thermal flash, initial nuclear radiation, and local fallout.