immediate Effects
An experimental nuclear explosion, like all nuclear explosions, produces immediate effects
that are limited mm space or time.
The inhabitants of the Japanese cities of Hiroshima and Nagasaki experienced direct
etlects from atomic bombs. Using the observations made in those two cities, the evtent of the
area exposed to the effects of the nuclear explosion has heen pinpomicd
Tt has been found that ao
inhabitant of Hiroshima living more than 1.8 miles from the point ol explosion wir exposed to the
immediate effects of the bomb.
Delayed Effects
Nuclear tests also produce radioactive fallout, which is usually divided into Jocal, distant
and global fallout that is spread over a long period of time.
Local fallout is made up of activated heavy debris and fragments of earth torn from the
soil at the time of the explosion that fall back by the force of gravity. These materials reach the
earth’s surface in a few hours and scatter over a distance that varies with the explosion’s vield.
They can drift from 60 to 250 miles with the direction of the wind and about 30 milcs perpen-
dicular to the wind. They contain a high proportion of short-lived radioactive products.
Distant fallout is composcd of finer particles projected into the lower layers of the atmosphere—up to 7 miles on the average or in the troposphere—and is carried around the earth by the
prevailing winds. These fine particles fall slowly, often dropping to the surface in atmospheric
Precipitation, and scatter in a wide latitudinal band centered approximately on the proving grounds.
Global fallout comes from very fine particles carried into the stratosphere (above 7 miles)
on which pravity has a very slight effect. These particles, exposed to the movements of stratospheric
winds, have great difficulty crossing back through the tropopause—a layer between the stratosphere
and the troposphere—and take several years to fall to the earth’s surface. By that time, the shortlived products that these particles contain have all disappeared, and the level of radioactivity due
to the remaining products is insignificant.
Local fallout aione is therefore dangerous.
were oy
lt affects only the testers and the zone located in immediate proximity to the firing grounds