Читать книгу Introduction to the World of Nuclear Physics - Lidiya Strautman - Страница 3

foil 1) станиолевый 2) станиоль 3) фольга 4) фольговый

foil paper фольга

investigate 1) исследовать 2) обследовать 3) производить исследование 4) разбираться 5) разведать 6) разведывать

exclude исключать (from ); не впускать; не допускать (возможности и т. п. )

deflect 1) отклонять(ся) от прямого направления ( from ); изменить направление; отклонить от курса

deflection 1) девиация 2) деформация 3) изгибный 4) отводящий 5) отклонение

Oersted discovered that an electric current would deflect a magnetic needle. Эрстед открыл, что электричесткий ток способен вызывать отклонение магнитной стрелки. This special metal shield will deflect a bullet from its course. – Этот специальный металлический щит изменит траекторию пули.

repel отбрасывать, отталкивать particles repel one another – частицы взаимно отталкиваются

bounce off отскакивать рикошетом от чего-л.

infinity 1) бесконечность; безграничность to infinity – до бесконечности Syn: eternity , endlessness 2) что-л. бесконечное, безграничное; бесконечное время; бесконечное пространство

fuzzy 1) нерезкий 2) нерезок 3) пушист 4) пушистый 5) размыт 6) размытый 7) расплывчат 8) расплывчатый

fuzziness а) неясность, неопределенность, смутность; расплывчатость, размытость, нечеткость; б) нерезкость изображения или записи; кудрявость

MODELS OF THE ATOM

In the early 1900's many scientists turned their attention to the investigation of the structure of the atom. Many models were proposed, and a handful were adopted as ways to describe the atom. Neither of them was perfect but they have brought us a long way toward understanding of these building blocks. Three of particular interest to us in physics are:

1. The Rutherford Model

2. The Bohr Model

3. The Cloud Model

Even though these models are different, neither one excludes the other two. Accepting one model does not cancel out the other two. It is possible to accept all three models at the same time.

The Rutherford model

In 1909 Ernest Rutherford conducted what is now a famous experiment where he bombarded gold foil with alpha particles (Helium nuclei). A source which underwent alpha decay was placed in a lead box with a small hole in it. Any of the alpha particles which hit the inside of the box were simply stopped by the box.

Only those which passed through the opening were allowed to escape, and they followed a straight line to the gold foil.

Observations

. Most of the alpha particles passed straight through the gold foil.

. Some of the alpha particles deflected by very small amounts.

. A very few deflected greatly.

. Even fewer bounced of the foil and back to the left.

Considering the deflection of the alpha particle through large angles and even bouncing off the gold foil you must keep in mind that the gold nuclei have a charge of +79 and the alpha particle has a charge of +2. These two positive charges repel each other. The closer they get, the greater the force. The greater the force, the greater the amount of deflection.

The Bohr Model

While the Rutherford model focused on describing the nucleus, Niels Bohr turned his attention to describing the electron. Prior to the Bohr Model, the accepted model was one which depicted the electron as an orbiting planet. The flaw with the planet-like model is that an electron particle moving in a circular path would be accelerating. An accelerating electron creates a changing magnetic field. This changing magnetic field would carry energy away from the electron, eventually slowing it down and allowing it to be “captured” by the nucleus.

Bohr built upon spectroscopic observations of atoms. Spectroscopists noticed that an atom can only absorb certain energies (colors) of light (the absorption spectrum) and, once excited, can only release certain energies (the emission spectrum) and these energies happen to be the same. Bohr used these observations to argue that the energy of a bound electron is “quantized.” Quantized is a fancy word meaning only certain quantities of energy are allowed. This explanation addresses the true origin of light. Since only certain energy levels are allowed, it is actually possible to diagram the atom in terms of its energy levels. In the figure below you see a model of a Hydrogen atom and to the right of it, a Bohr energy level diagram.

The Hydrogen Atom

If the energy of the photon of light is just right, it will cause the electron to jump to a higher level. When the electron jumps back down, a photon is created for each jump down. A photon without the right amount of energy passes through the atom with no effect. Photons with too much energy will cause the electron to be ejected, which ionizes the atom. An ionized electron is said to be in the n=infinity energy level. Keep in mind that these rings are not actually orbits, but are levels that represent the location of an electron wave. The number n corresponds to the number of complete waves in the electron.

EXERCISES

Ex. 1. Make the following sentences negative.

1. We will limit our discussions to protons, neutrons and electrons. 2. Protons and neutrons are believed to be made up of even smaller particles called quarks. 3. The electrons actually change their orbit with each revolution. 4. Quantized is a fancy word meaning that only certain quantities of energy are allowed. 5. The number n corresponds to the number of complete waves in the electron.

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

1. Photons with too much energy will cause the electron to be ejected which ionizes the atom. 2. The number n corresponds to the number of complete waves in the electron. 3. He developed the probability function for the Hydrogen atom. 4. The cloud model represents a sort of history of where the electron has probably been and where it is likely to be going. 5. The nucleus is made up of positively charged particles called protons and neutrons which are neutral. 6. Prior to the Bohr Model, the accepted model was one which depicted the electron as an orbiting planet.

Ex. 3 Translate the sentences using the examples given below.

The institute installed modernized equipment. В институте установлено модернизированное оборудование. The equipment installed modernized our laboratory too. Установленное оборудование модернизировало и нашу лабораторию.

A. 1. The Conference attended by scientists from different countries discussed new trends and methods in this field of research. 2. One of the rights enjoyed by University scientists is that of combining research with teaching. 3. The discovery followed by further experimental work stimulated research in this area.

B. 1. Mathematics, mechanics, statics and geometrical optics referred to as classical disciplines started mathematical traditions in the history of natural science. 2. The heads of the laboratories were asked questions formulated and agreed upon by a group of sociologists. 3. The scientist's eloquence substituted for logical argu-entation in defending an “extreme” viewpoint failed to win the audience. 4. The mixture allowed to stay overnight gradually decomposed. 5. Physicists showed that particles thought of as “elementary” were in fact “non-elementary”. 6. The subjects dealt with under this topic aroused a heated discussion.

Ex. 4. Identify the structures including what and give Russian equivalents of the relevant part of the sentence.

1. What is done cannot be undone. 2. I would here refer to what I have already said about these substances. 3. This article will review what has been achieved in this field since 1981. 4. From what has been said one concludes that the results obtained depend principally on the technique employed. 5. What we want to stress is indivisibility and complexity of the environment. 6. What follows is extremely significant in its bearing on the problem of the relationship of physics with other sciences. 7. Much of what we do in space, much of what is expected of us strains our technology to the breaking point. 8. In this article Dyson states what may be considered three rules of managing a research laboratory. 9. What goes into a system must eventually come out.

Ex. 5. Learn to distinguish between modal and auxilliary to have and to be. State their function and give Russian equivalents.

1. The argument is that by that time the resources of the plane may have been exhausted and man may have had to leave the Earth in search for another habitable place. 2. To get anywhere and back in a lifetime the speed would have to be very high so as to take advantage of the relativistic change in clock rates. 3. The maximum value which is to be expected is only reached in the range of variables used in the tests. 4. If Mars were a testing ground for our notion about the origin of life, we must avoid using the same notion to conclude in advance that Mars is lifeless. 5. As it is true of the author, we have had to be a little arbitrary in deciding what to include and what to omit. 6. If we built a scale model with the Earth as a ball 100 feet in diameter, this ocean would be less than half an inch deep.

The Cloud Model

Erwin Schredinger built upon the thoughts of Bohr yet took them in a new direction. He developed the probability function for the Hydrogen atom (and a few others). The probability function basically describes a cloudlike region where the electron is likely to be found. It cannot say with any certainty, where the electron actually is at any point in time, yet can describe where it ought to be. Clarity through fuzziness, is one way to describe the idea. The model based on this probability equation can best be described as the cloud model.

The cloud model represents a sort of history of where the electron has probably been and where it is likely to be going. The red dot in the middle represents the nucleus while the red dot around the outside represents an instance of the electron. Imagine, as the electron moves it leaves a trace of where it was. This collection of traces quickly begins to resemble a cloud. The probable locations of the electron predicted by Schredinger's equation happen to coincide with the locations specified in Bohr's model.

What is an atom composed of?

An atom is the smallest particle of any element that still retains the characteristics of that element. However, atoms consist of even smaller particles. Atoms consist of a central, dense nucleus that is surrounded by one or more lightweight negatively charged particles called electrons. The nucleus is made up of positively charged particles called protons and neutrons which are neutral. An atom is held together by forces of attraction between the electrons and the protons. The neutrons help to hold the protons together. Protons and neutrons are believed to be made up of even smaller particles called quarks. We will limit our discussions to protons, neutrons and electrons.

Niels Bohr was a Danish scientist who introduced the model of an atom in 1913. Bohr's model consists of a central nucleus surrounded by tiny particles called electrons that are orbiting the nucleus in a cloud. These electrons are spinning so fast around the nucleus of the atom that they would be just a blur if we could see particles that small. In our pictures and exercises the electron appears to orbit in the same path around the nucleus much like the planets orbit the Sun. But, please be aware that electrons do not really orbit in the same path. The electrons actually change their orbit with each revolution.