test difference between the atomic bomb and the T.N.T.
explosion is the fact that the atomic bomb gives off greater amounts of
radiation. Most of this radiation is "light" of some wave-length
ranging from the so-called heat radiations of very long wave length to
the so-called gamma rays which have wave-lengths even shorter than the
X-rays used in medicine. All of these radiations travel at the same
speed; this, the speed of light, is 186,000 miles per second. The
radiations are intense enough to kill people within an appreciable
distance from the explosion, and are in fact the major cause of deaths
and injuries apart from mechanical injuries. The greatest number of
radiation injuries was probably due to the ultra-violet rays which have
a wave length slightly shorter than visible light and which caused
flash burn comparable to severe sunburn. After these, the gamma rays
of ultra short wave length are most important; these cause injuries
similar to those from over-doses of X-rays.

The origin of the gamma rays is different from that of the bulk of the
radiation: the latter is caused by the extremely high temperatures in
the bomb, in the same way as light is emitted from the hot surface of
the sun or from the wires in an incandescent lamp. The gamma rays on
the other hand are emitted by the atomic nuclei themselves when they
are transformed in the fission process. The gamma rays are therefore
specific to the atomic bomb and are completely absent in T.N.T.
explosions. The light of longer wave length (visible and ultra-violet)
is also emitted by a T.N.T. explosion, but with much smaller intensity
than by an atomic bomb, which makes it insignificant as far as damage
is concerned.

A large fraction of the gamma rays is emitted in the first few
microseconds (millionths of a second) of the atomic explosion, together
with neutrons which are also produced in the nuclear fission. The
neutrons have much less damage effect than the gamma rays because they
have a smaller intensity and also because they are strongly absorbed in
air and therefore can penetrate only to relatively small distances from
the explosion: at a thousand yards the neutron intensity is negligible.
After the nuclear emission, strong gamma radiation continues to come
from the exploded bomb. This generates from the fission products and
continues for about one minute until all of the explosion products have
risen to such a height that the intensity receive