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.
In a nuclear explosion, energy is released as blast (~50%), thermal flash (~35%), initial nuclear radiation (~5%), residual nuclear radiation or fallout (~10%), and electromagnetic pulse (~5%).