Words and word combinations to be remembered

indivisible – неделимый, неразложимый	designate – называть	reject – отвергать, отказываться
X-rays – рентгеновские лучи	extract – вытаскивать, извлекать, получать	account for – объяснять
inner structure – внутренняя структура	to take the first step – сделать первый шаг	arrange – расставлять, устраивать
charge carriers – носитель заряда	distribute – распределять, рассредоточивать	point out – указывать. показывать
nucleus – ядро	scatter – разбрасывать, раскидывать	revolve – вращаться

Ex.1. Match Russian words and their English equivalents:

Atom

разрушенный	foreign
исходный	parent
возбужденный	daughter
водородоподобный	displaced
атом примеси	destroyed
дочерний	excited
смещенный	hydrogen-like

Ex. 2. Translate into English

Не цельный и неделимый, электрически нейтрален, внутренняя структура, положительный заряд, альфа-частица, ядро атома, расположение планет, равное число, химическое взаимодействие, удивительный результат, быть распределенным во всем атоме, быть рассеянным вокруг, отскакивать назад, вращаться, выдвинуть гипотезу, сделать вывод, в соответствии с этой теорией.

Ex. 3. Fill in the blanks:

1. As a branch of science atomic physics is concerned with ... .

2. Its origin may be ascribed to the discovery of ... .

3. Röntgen's discovery of X-rays enabled J. J. Thomson to understand ... .

4. Thus, in 1903 J. J. Thomson discovered the nature of ... and put forward the first hypothesis concerning ... .

5. According to Thomson's model the atom ... .

6. The word “atom” comes from ... and means ... .

7. Тhomson's model of the atom didn't account for ... and therefore was ... .

8. In their experiments Rutherford and his colleagues observed ... .

9. Rutherford came to the conclusion that atom ... .

10. Rutherford's model of the atom is called ... because ... .

Ex. 4. Answer the following questions:

1. What does the word "atom" come from? 2. What is an atom? 3. What can the origin of atomic physics be attributed to? 4. Who advanced the first hypothesis concerning the structure of the atom? 5. Why is the Thomson's model often called the plum-pudding model of the atom? 6. Who understood that atoms had nuclei? 7. Why was Rutherford's model of the atom called nuclear atom or solar system atom?

Ex. 5. Say a few words about:

• the origin of the word “atom”

• X-rays

• Thomson's model of the atom structure

• Rutherford's model of the atom

Unit14. The discovery of radioactivity

As is the case with so many other discoveries, the discovery of the phenomenon of radioactivity was purely accidental. It was discovered in 1896 by a French physicist, A. H. Becquerel (1852 – 1908), who was interested at that time in the phenomenon of fluorescence, i.e. the ability of certain substances to transform the ultraviolet radiation that falls on them into visible light. In one of the drawers of his desk Becquerel kept a collection of various minerals that he was going to use for his studies, but because of other pressing matters, the collection remained untouched for a considerable period of time. It happened that in the drawer there were also several unopened boxes of photographic plates, and one day Becquerel took one of the boxes in order to photograph something or other. When he developed the plates he was disappointed to find that they were badly fogged as if previously exposed to light. A check on other boxes showed that they were in the same poor condition, which was difficult to understand since all the boxes were sealed and the plates inside were wrapped in thick black paper. What could be the cause of this mishap? Could it have something to do with one of the minerals in the drawer? Being of an inquisitive mind, Becquerel investigated the situation and was able to trace the guilt to a piece of uranium ore. At that time the name “uranium” was not in vogue as it is today, in fact, only very few people, even among scientists have ever heard about that comparatively rare and not very useful chemical element. But the ability of a uranium compound to fog photographic plates through a thick cardboard box and a layer of black paper rapidly brought this obscure element to a prominent position in physics.

The existence of penetrating radiation that could pass through layers of ordinary opaque materials as if they were made of clear glass was a recognized fact at the time of Becquerel’s discovery. In fact, only a year earlier a German physicist, Wilhelm Roentgen (1845 – 1932) discovered what are now known as X-rays, which can penetrate equally well through cardboard, black paper, or the human body.

Although special high voltage equipment is required to produce X-rays, the radiation discovered by Becquerel was flowing quite steadily and without any external excitation from the peace of uranium ore resting in his desk. What could be the origin of this unusual radiation? Why was it specifically associated with the element uranium and, as studies found, with two other heavy elements known as thorium and actinium? The early studies of the newly discovered phenomenon which was called “radiation” showed that the emission of mysterious radiation was completely unaffected by physical and chemical conditions. We can stick a radioactive element into a very hot flame or drop it into liquid air without the slightest effect on the intensity of the mysterious radiation it emits. No matter whether we have pure metallic uranium, or its oxide which is contained in pitchblende, the radiation flows out at a rate proportional to the amount of uranium in the sample. These facts ruled out any possibility of ascribing the phenomenon of radioactivity to any kind of chemical properties of this element and led the early investigators to the conclusion that the phenomenon of radioactivity is the intrinsic property of the atoms of these peculiar elements and that its cause must be deeply rooted in the atomic interior.

In order to study the nature of the discovered radiation, Becquerel arranged the following experiment. He placed a small amount of uranium in a deep hole made in a lead block so that only a thin beam of radiation emerged from the groove. He also placed a magnet over the block in such a way that the magnetic lines of force were running perpendicular to the direction of the emerging beam. Under these conditions one could expect three different results.

If the radiation emitted by uranium were short electromagnetic waves similar to X-rays, no deflection should take place. If on the other hand, the radiation were fast moving electric particles, the beam should be deflected to the left in the case of a negative charge and to the right in the case of a positive one. In Becquerel’s experiment all three things happened, and the original beam emerging from the hole split into three parts: the part that consisted of particles carrying a positive charge was named α-rays and was later proved to be a steam of doubly ionized helium atoms, i.e. a stream of helium nuclei. The part consisting of negatively charged particles which turned out to be ordinary electrons was named β-rays, whereas the undeflected beam formed by short-wave electromagnetic radiation similar to X-rays received the name of γ-rays.