2. Read and translate text 1. Text 1 Emission

The emission of electrons from metals can occur in several ways. If a metal is heated to a sufficiently high temperature, emission will occur. This is known as primary or thermionic emission. Secondary emission is that which occurs when high-velocity electrons or ions strike a metal and knock out other electrons. Almost all metals and some insulators emit secondary electrons. Emission may also occur when light rays strike a material and give up energy that libe­rates electrons; this is known as photoemission. Thermionic and secondary emission are of most importance in ordinary vacuum tubes.

Theory of Emission. In any conductor there are a large number of free electrons moving around with various velocities. As the tem­perature of the conductor increases the average velocity of the free electrons increases. At the surface of the conductor there exists a restraint upon the movement of the electrons in the form of an elec­trostatic gravitational force. Were it not for this all the electrons in the metal would soon escape. Only those electrons, which have enough energy to overcome the surface forces, manage to get away. The energy in electron volts that an electron must have before it can leave a metal is known as the work function of the metal. The emission of electrons primarily depends upon the temperature of the metal and the work function of the metal.

The only metal besides tungsten that has possibilities as a practical emitter is tantalum. Although tantalum cannot be made as hot as tungsten because its melting temperature is 3300° K, com­pared with 3655° K for tungsten, its work function is sufficiently lower. A disadvantage of tantalum is that it is easily contaminated by residual gases, which form oxides that greatly reduce the emission.

Emission of Thoriated Tungsten. There are many metals, that have a higher emission than tungsten, but it is not possible to take advantage of this by using the metals in the pure form, because most of them melt at a relatively low temperature. It is, however, possible to coat tungsten with a thin layer of other metals and thus take advantage of the high melting temperature of tungsten and the high emission of the other metals. It has been discovered that thorium on tungsten gives the highest emission of any practical combination of this character.

3. Find English equivalents for the following terms.

Cредняя скорость, температура плавления, свободные электроны, изолятор, вольфрам, первичное излучение, быстрый электрон, вторичное излучение, остаточные газы, поверхностные силы, фотоэмиссия, вторичный электрон, работа выхода, плавить, термоэлектронная эмиссия, электростатическая гравитационная сила, окись, тантал, световые лучи, ион, уменьшить излучение, тонкий слой металла, при относительно низкой температуре.

4. Choose Russian equivalents for the following words from the list given below.

Increasing, using, shown, placed, decreasing, resulting in, increased, amplified, occurring, applied, emitting, switched on, competing, described, influencing, reduced.

Усиленный, уменьшая, включенный, уменьшенный, увеличивающий, давая в результате, излучающий, влияя, показанный, примененный, описанный, используя, увеличенный, помещенный, происходящий, конкурирующий.