Читать книгу Introduction to the World of Nuclear Physics - Lidiya Strautman - Страница 4

penetrate 1) а) проникать внутрь, п–оходить сквозь, пронизывать The water has penetrated into the bedrooms. Вода проникла в спальни. These new ideas are penetrating into the framework of society. – Эти новые идеи проникают в общество.

penetration 1) внедрение 2) пенетрация 3) проникание 4) проникновение 5) проницательность 6) проплавление

scatter 1) затрусить 2) натрясти 3) разбрасывать 4) разброс 5) разбросать 6) развеивать 7) разволакивать 8) разворошить

scatter electrons рассеивать электроны

scatter plot график рассеяния

breakthrough 1) крупное научное / техническое достижение; прорыв (в науке) 2) внезапный рост цен

capture 1) захват 2) захватывание 3) захватывать 4) каптаж 5) каптировать 6) уловить

capture electron захватывать электрон

compelling необоримый, неодолимый, неотразимый, непреодолимый

compelling reason неопровержимые доводы

attraction 1) привлечение 2) притяжение 3) притяжимость

attractive interaction взаимное притяжение

Coulomb’s attraction кулоновское притяжение

determine 1) определять, устанавливать (с помощью расчетов, рассуждений, проведения расследования и т. п.) to determine the answer to the problem – определить ответ на поставленный вопрос

THE ATOM

By the early 20th century, there was rather compelling evidence that matter could be described by an atomic theory. That is, matter is composed of relatively few building blocks that we refer to as atoms. This theory provided a consistent and unified picture for all known chemical processes at that time. However, some mysteries could not be explained by this atomic theory. In 1896, A.H. Becquerel discovered penetrating radiation. In 1897, J J. Thomson showed that electrons have negative electric charge and come from ordinary matter. For matter to be electrically neutral, there must also be positive charges lurking somewhere. Where are and what carries these positive charges?

A monumental breakthrough came in 1911 when Ernest Rutherford and his coworkers conducted an experiment intended to determine the angles through which a beam of alpha particles (helium nuclei) would scatter after passing through a thin foil of gold.

Models of the atom. The dot at the center of the Rutherford atom is the nucleus. The size of the dot is enlarged so that it can be seen in the figure.

What results would be expected for such an experiment? It depends on how the atom is organized. A prevailing model of the atom at the time (the Thomson, or “plum-pudding,” atom) proposed that the negatively charged electrons (the plums) were mixed with smeared-out positive charges (the pudding). This model explained the neutrality of bulk material, yet still allowed the description of the flow of electric charges. In this model, it would be very unlikely for an alpha particle to scatter through an angle greater than a small fraction of a degree, and the vast majority should undergo almost no scattering at all.

The results from Rutherford’s experiment were astounding. The vast majority of alpha particles behaved as expected, and hardly scattered at all. But there were alpha particles that scattered through angles greater than 90 degrees, incredible in light of expectations for a “plum-pudding” atom. It was largely the evidence from this type of experiment that led to the model of the atom as having a nucleus. The only model of the atom consistent with this Rutherford experiment is that a small central core (the nucleus) houses the positive charge and most of the mass of the atom, while the majority of the atom’s volume contains discrete electrons orbiting about the central nucleus.

Under classical electromagnetic theory, a charge that is moving in a circular path, loses energy. In Rutherford’s model, the electrons orbit the nucleus similar to the orbit of planets about the sun. However, under this model, there is nothing to prevent the electrons from losing energy and falling into the nucleus under the influence of its Coulomb attraction. This stability problem was solved by Niels Bohr in 1913 with a new model in which there are particular orbits in which the electrons do not lose energy and therefore do not spiral into the nucleus. This model was the beginning of quantum mechanics, which successfully explains many properties of atoms. Bohr’s model of the atom is still a convenient description of the energy levels of the hydrogen atom.

EXERCISES

Ex. 1 Make the following sentenses negative.

1. Becquerel decided to develop his photographic plates. 2. In this model, it would be very unlikely for an alpha particle to scatter through an angle greater than a small fraction of a degree. 3. The size of the dot is enlarged so that it can be seen in the figure. 4. The results from Rutherford’s experiment were astounding. 5. By the early 20th century, there was rather compelling evidence that matter could be described by an atomic theory.

Ex. 2 Make up questions to which the following sentences are the answers.

1. At high enough energy, the addition of energy creates new particles rather than frees the quarks. 2. Bohr’s model of the atom is still a convenient description of the energy levels of the hydrogen atom. 3. Energy brought into a nucleus to try to separate quarks increases the force between them. 4. This hypothesis was disproved on the 26-27th of February, when his experiment “failed” because it was overcast in Paris. 5. Because gamma rays carry no electric charge, they can penetrate large distances through materials. 6. A sheet of aluminum one millimeter thick or several meters of air will stop these electrons and positrons.

Ex. 3 Give Russian equivalents of whether. ..

1. The question is whether he will send you to the conference or go himself.

2. Whether the project will be approved at present is a matter of importance.

3. One of the fundamental questions is whether petroleum migrated over considerable distances to form pools, or whether it was formed essentially in place. 4. There was a disagreement whether they should continue along the same line or whether they should take another approach. 5. Whether this difference of approach played a decisive role in the final solution to the problem remains a subject for speculation. 6. One of the fundamental problems of today is whether we will be able to meet the challenge of the environmental crisis.

Ex. 4. Fill in the blanks with the proper words from the list below

1. World science is faced with the all-important task of finding effective … of protecting the atmosphere from pollutants. 2. The data available to man concerning the physical phenomena of space might not be very exciting to those who cannot interpret their … 3. Natural scientists are so interested in their selfmade problems that they tend to neglect the problems that are most.. for human life. 4. The name atom comes from the Greek word and.. indivisible. 5. The information on the physical phenomena of space is a part of the answer to space exploration, but is.. the total explanation 6. Radar techniques have recently been employed to obtain more accurate measurements of the.. distance between the Earth and the Sun. 7. The main task of ecology is to support survival of plant, animal and human life …

means, meaning, meaningful, means, by no means, by all means, mean.

Ex. 5 Translate the sentences into English using who, which, which of, what

1. Трудно найти человека, который бы не задумывался над этим. 2. Это вопрос, который касается всех. 3. Трудно сказать, какая из этих проблем сложнее. 4. Необходимо решить, кто из них возглавит эту работу. 5. Трудно сказать, какие вопросы будут нас волновать через два десятка лет. 6. Никто не знает, кто первым применил это устройство. 7. Лектор сказал, какую литературу надо прочитать по этому предмету. 8. Трудно было решить, кто из них был прав.

Ex. 6. From the list below choose an adequate English word group to explain the meaning of the italicized words.

1. It took him some time to bring home the fact that the experiment was dangerous. 2. Nowadays most people find it difficult to keep pace with the information accumulated in their special field of interest. 3. It is not quite clear at the moment who will see to it that all is in balance. 4. It is not very wise of you to cut your life short by ignoring your doctor's advice. 5. The problem was to get rid of the unwanted impurities. 6. I don't quite understand what this symbol stands for. 7. It was only in this century that aluminium was produced in quantity. to represent; to make shorter; to make clear; to take care; in large amounts; to remove; to keep up with.

The Nucleus

The atomic nucleus consists of nucleons-protons and neutrons. Protons and neutrons are made of quarks and held together by the strong force generated by gluon exchange between quarks. In nuclei with many nucleons, the effective strong forces may be described by the exchange of mesons (particles composed of quark-antiquark pairs). A proton consists of two up quarks and one down quark along with short-lived constituents of the strong force field. A neutron is similar except that it has two down quarks and one up quark. Although scientists are convinced that nucleons are composed of quarks, a single quark has never been isolated experimentally. Energy brought into a nucleus to try to separate quarks increases the force between them. At high enough energy, the addition of energy creates new particles rather than frees the quarks.

The Discovery of Radioactivity

In 1896 Henri Becquerel was using naturally fluorescent minerals to study the properties of x-rays, which had been discovered in 1895 by Wilhelm Roentgen. He exposed potassium uranyl sulfate to sunlight and then placed it on photographic plates wrapped in black paper, believing that the uranium absorbed the sun’s energy and then emitted it as x-rays. This hypothesis was disproved on the 26-27th of February, when his experiment “failed” because it was overcast in Paris. For some reason, Becquerel decided to develop his photographic plates anyway. To his surprise, the images were strong and clear, proving that the uranium emitted radiation without an external source of energy such as the sun. Becquerel discovered radioactivity.

Becquerel used an apparatus similar to that displayed below to show that the radiation he discovered could not be x-rays. X-rays are neutral and cannot be bent in a magnetic field. The new radiation was bent by the magnetic field so that the radiation must be charged and different from x-rays. When different radioactive substances were put in the magnetic field, they deflected in different directions or not at all, showing that there were three classes of radioactivity: negative, positive, and electrically neutral l.

Ernest Rutherford, who did many experiments studying the properties of radioactive decay, named these alpha, beta, and gamma particles, and classified them by their ability to penetrate matter. Rutherford used an apparatus similar to that depicted in the figure. When the air from the chamber was removed, the alpha source made a spot on the photographic plate. When air was added, the spot disappeared. Thus, only a few centimeters of air were enough to stop the alpha radiation.

Because alpha particles carry more electric charge, are more massive, and move slowly compared to beta and gamma particles, they interact much more easily with matter. Beta particles are much less massive and move faster, but are still electrically charged. A sheet of aluminum one millimeter thick or several meters of air will stop these electrons and positrons. Because gamma rays carry no electric charge, they can penetrate large distances through materials before interacting – several centimeters of lead or a meter of concrete is needed to stop most gamma rays.