Exact figures on the thicknesses of various substances to provide
complete or partial protection from the effects of radiation in
relation to the distance from the center of explosion, cannot be
released at this time. Studies of collected data are still under way.
It can be stated, however, that at a reasonable distance, say about 1/2
mile from the center of explosion, protection to persons from radiation
injury can be afforded by a layer of concrete or other material whose
thickness does not preclude reasonable construction.
Radiation ultimately caused the death of the few persons not killed by
other effects and who were fully exposed to the bombs up to a distance
of about 1/2 mile from X. The British Mission has estimated that
people in the open had a 50% chance of surviving the effects of
radiation at 3/4 of a mile from X.