CHAPTER III

The Scientific Experiment

     The aim of Operation "Grapple" is to test the performance of nuclear weapons dropped from Royal Air Force aircraft, and it is in connection with these tests that the scientists from the Atomic Weapons Research Establishment will be primarily concerned. A small group of scientists from the Ministry of Supply's Royal Aircraft Establishment and the Admiralty Research Laboratory will collaborate with the personnel from A.W.R.E. in certain specialized aspects associated with the weapons and the tests  
     When nuclear weapons are exploded in the air, as they will be in the Operation, light and heat and nuclear radiations are emitted in all directions at very high speeds and therefore their effects are instantaneous. The blast produced by the explosion also travels in all directions but at a much slower rate-at a few miles from the ground zero it is travelling at the speed of sound, 1,100 feet per second. The blast is in the form of a pressure wave and blast wind of short duration. The pressure produced near to the explosion may be 50 times the atmospheric pressure but drops rapidly as the blast wave travels outwards. The pressure in the wave is reinforced by reflections from the ground but the extent of this depends, among other things, on the height of the burst
     Within a very short time after the explosion an ascending column of gas and smoke in the form of a cloud rises to a great height. The suction resulting from the immense heat draws up water droplets and dust from the surrounding atmosphere where they unite with the products of the explosion. As the rising cloud loses its upward momentum the winds in the upper atmosphere take control and carry it away.
      The immediate result of the explosion is the production of very highly radioactive effects, called nuclear radiations, consisting of alpha, beta and gamma rays and neutrons.
      The alpha and beta rays do not constitute a serious problem, but the gamma rays and the neutrons are dangerous. It is, however, important to remember that the distance to which these can travel is limited and therefore the danger from an airburst depends upon the height the bomb explodes above the ground. The gamma rays have great power of penetration, over the limited distance of their travel, and heavy shielding is needed to protect people and materials within this distance from the harmful effects. The amount of radiation absorbed in a given time is usually referred to as a "dose" of radiation, the unit of dose being the roentgen or, for short, r. The neutrons, like the gamma rays, have great power of penetration but as they do not travel very far compared with

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