Nuclear fission
Nuclear fission is the splitting of a large and unstable
nucleus , such as uranium or plutonium Spontaneous fission is rare. Usually the unstable nucleus must first
absorb a neutron
The nucleus splits into two smaller nuclei , roughly equal in size,
and emits two or three neutrons plus gamma rays . Energy is
released
All the fission products have kinetic energy , which heats the
surroundings: in a reactor this heat boils water to drive turbinesThe neutrons may go on to be absorbed by other nuclei and cause further
fissions: a chain reaction
In a nuclear reactor the chain reaction is controlled , with
control rods that absorb neutrons, to control the energy released. In a
nuclear weapon the chain reaction is uncontrolled , releasing
the energy in an instant
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A fission chain reaction 1 a neutron is absorbed U a large unstable nucleus — uranium-235 or plutonium-239 2 the nucleus splits Kr Ba two smaller daughter nuclei three more neutrons, plus gamma rays and a lot of energy gamma rays 3 each one splits another nucleus U U U and so on — the number of fissions doubles and doubles again: a CHAIN REACTION Fission is the SPLITTING of a large unstable nucleus. It usually needs a neutron to be absorbed first; very occasionally it happens on its own. The two daughter nuclei are roughly equal in size, and are themselves radioactive. Energy is released as the kinetic energy of everything produced, and as gamma radiation. In a nuclear reactor the chain reaction is CONTROLLED: control rods absorb some of the neutrons so that on average exactly one neutron from each fission goes on to cause the next. Uncontrolled, the reaction runs away — that is a nuclear bomb. Fission chain reaction: a neutron absorbed by a uranium nucleus, the nucleus splitting into two smaller nuclei with three neutrons and gamma rays released, each neutron going on to split another nucleus
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In the full topic
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