Nuclear fission

Nuclear fission is known to be a new type of transmutation, it being discovered as a result of attempts to prepare isotopes of elements of atomic number greater than 92. It should be noted that unstable nuclei ordinarily disintegrate into particles of disparate mass and charge. In these cases the larger particle is usually an atom whose mass differs not at all, or only by a few units from that of the parent atom.

When it is attempting to prepare atoms of an atomic number higher than that of uranium, that element was bombarded with slow-moving neutrons, it was found that some of its atoms were split into 2 particles, their mass and charge being nearly equal.

Disintegration of this type was named nuclear fission, and was found to be accompanied by the evolution of the tremendous quantity energy.

It was verified by the direct calorimetric measurement that a very large amount of energy is liberated by fission. Since a pound of uranium contains about 2 gram-atoms, the complete fission of one pound of this element, or a similar heavy element, produces about 10×1012 calories. This may be compared with the heat of combustion of 1 pound of coal, which is approximately 4×105 calories. Thus uranium as a source of energy may be 2.5 million times more valuable than coal.

Uranium 235 and plutonium 239, which can be made from uranium 238, are found to be capable of undergoing fission when exposed to slow neutrons. It was shown that the thorium isotope undergoes fission under the influence of fast neutrons. It seemed likely that all of the elements with atomic number 90 or greater can be made to undergo this reaction.

Uranium and thorium are considered to be important source of heat and energy in the world.

The fission reactions can be chain reactions. These reactions prove to be initiated by neutrons. A nucleus of U235 may combine with a neutron to form U236. This isotope happens to be unstable, and to undergo spontaneous fission, into two particles of roughly equal atomic number, the sum of the atomic numbers being 92, that is, protons in the U236 nucleus are divided between the two daughter nuclei.

The foregoing text illustrates the great significance of the nuclear fission and fissionable elements as a source of energy. Taking into account that uranium and thorium are not rare elements, but are among the more common elements, we can understand the promise of nuclear energy for the world of the future, and the possibility of its contributions to human welfare.

Vocabulary

fission –розщеплення transmutation – перетворення nuclei – ядро disparate – непорівнянний neutron – нейтрон calory - тепло

initiate – покласти початок cause – причина explosive – вибуховий foregoing – вищезазначений thorium –торій