4: Main Conclusions
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The following are the main conclusions which were reached after thorough
examination of the effects of the bombs dropped on Hiroshima and Nagasaki:
1. No harmful amounts of persistent radioactivity were present after the
explosions as determined by:
A. Measurements of the intensity of radioactivity at the time of the
investigation; and
B. Failure to find any clinical evidence of persons harmed by persistent
radioactivity.
The effects of the atomic bombs on human beings were of three main types:
A. Burns, remarkable for (1) the great ground area over which they were
inflicted and (2) the prevalence of "flash" burns caused by the
instantaneous heat radiation.
B. Mechanical injuries, also remarkable for the wide area in which
suffered.
C. Effects resulting from penetrating gamma radiation. The effects from
radiation were due to instantaneous discharge of radiation at the moment of
explosion and not to persistent radioactivity (of either fission products
or other substances whose radioactivity might have been induced by
proximity to the explosions).
The effects of the atomic bombs on structures and installations were of two
types:
A. Destruction caused by the great pressure from the blast; and
B. Destruction caused by the fires, either started directly by the great
heat radiation, or indirectly through the collapse of buildings, wiring,
etc.
4. The actual tonnage of T.N.T. which would have caused the same blast
damage was approximately of the order of 20,000 tons.
5. In respect to their height of burst, the bombs performed exactly
according to design.
6. The bombs were placed in such positions that they could not have done
more damage from any alternative bursting point in either city.
7. The heights of burst were correctly chosen having regard to the type of
destruction it was desired to cause.
8. The information collected would enable a reasonably accurate prediction
to be made of the blast damage likely to be caused in any city where an
atomic explosion could be effected.
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