4. Translate the text in writing

The advantage of a nuclear reactor is based on the liberated binding energy in the form of heat.

The disintegration is turned into a continuous process a chain reaction is only due to the fact that the nuclei under fission eject neutrons which cause other fission in nuclei. The number of fissile material can be increased by slowing-down high-speed neutrons by collisions with atoms of such substances which do not absorb them. Such moderators, e.g. heavy water or graphite are necessary because, although fast neutrons are not lost in the analysis, since they are absorbed by U238, they are indispersible to maintain the chain reaction. An ordinary atomic bomb is known to consist of a few pounds of U235 and Pu239 and mechanism for suddenly compressing the metal. The process of nuclear fission is stated to liberate energy. The fission of a very heavy nucleus converts about 0.1% of its mass into energy.

GASES

Gases are made up of1 atoms and molecules, which are in constant and rapid motion. In the gaseous state molecules tend to behave as independent particles; for this reason many simple relationships occur in that state alone. In short, the gaseous state gives the scientist an opportunity to observe matter in its most dilute condition, where molecular properties are most easily evaluated. Such properties as the masses and average velocities of individual molecules may be calculated from simple laboratory data. However, no real progress in developing experimental techniques was apparent until the sixteenth and seventeenth centuries. One of the early contributers was Jean Baptist von Helmont (1577-1644) who introduced the word "gas" as a contraction of "chaos". Another significant advance was made in 1643 when E. Torricelli invented the mercurial barometer, which is essentially the instrument used today to measure atmospheric pressure.

A reasonable understanding of the behaviour of gases was achieved with the invention of the air pump (vacuum pump) in 1656 by Otto von Guericke. With this device he was able to evacuate closed chambers and demonstrate the existence of rarefied atmospheres. A classic experiment involved the evacuation of a spherical chamber formed by a physical contact of two metallic hemispheres. When the chamber was evacuated atmospheric pressure prevented separation of the two halves by the pulling force of two teams of eight horses each.

Vocabulary

afford - дозволяти evaluate - оцінювати alone - тільки hemisphere - напівсфера apparent - дійсний opportunity - можливість behave - поводити себе prevent - попереджувати chamber - камера

chaos - хаос pump - насос constant - постійний rarefy - розряджувати contraction - стискання technique - метод evacuate - викачувати tend - намагатися