Energy from Matter Help

By — McGraw-Hill Professional
Updated on Sep 5, 2011


The splitting up of an atomic nucleus is known as nuclear fission . This is, in a sense, the opposite of nuclear fusion, which occurs inside the Sun and other stars. The very first atomic bombs, developed in the 1940s, made use of fission reactions to produce energy. More powerful weapons, created in the 1950s, used atomic fission bombs to produce the temperatures necessary to generate hydrogen fusion.

Human-caused And Natural Fission

The preceding problems involving oxygen and beryllium are given for illustrative purposes, but the actual breaking up of atomic nuclei is not such a simple business. A physicist can’t snap an atomic nucleus apart as if it were a toy. Nuclear reactions must take place under special conditions, and the results are not as straightforward as the foregoing problems suggest.

To split atomic nuclei in the laboratory, a particle accelerator is employed. This machine uses electric charges, magnetic fields, and other effects to hurl subatomic particles at extreme speeds at the nuclei of atoms to split them apart. The result is a fission reaction, often attended by the liberation of energy in various forms.

Some fission reactions occur spontaneously. Such a reaction can take place atom-by-atom over a long period of time, as is the case with the decay of radioactive minerals in the environment. The reaction can occur rapidly but under controlled conditions, as in a nuclear power plant. It can take place almost instantaneously and out of control, as in an atomic bomb when two sufficiently massive samples of certain radioactive materials are pressed together.

Matter And Antimatter

The proton, the neutron, and the electron each has its own nemesis particle that occurs in the form of antimatter . These particles are called antiparticles . The antiparticle for the proton is the antiproton; for the neutron it is the antineutron; for the electron it is the positron . The antiproton has the same mass as the proton, but in a negative sort of way, and it has a negative electric charge that is equal but opposite to the positive electric charge of the proton. The antineutron has the same mass as the neutron, but again in a negative sense. Neither the neutron nor the antineutron have any electric charge. The positron has same mass as the electron, but in a negative sense, and it is positively charged to an extent equal to the negative charge on an electron.

You might have read or seen in science-fiction novels and movies that when a particle of matter collides with its nemesis, they annihilate each other. This is true. What, exactly, does this mean? Actually, the particles don’t just vanish from the cosmos, but they change from matter into energy. The combined mass of the particle and the antiparticle is liberated completely according to the same Einstein formula that applies in nuclear reactions:

E = ( m + + m ) c 2

where E is the energy in joules, m + is the mass of the particle in kilograms, m is the mass of the antiparticle in kilograms, and c is the speed of light squared, which, as you recall, is approximately equal to 9 × 10 16 m 2 /s 2 .

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