Introduction to the World of Nuclear Physics. Lidiya Strautman
Читать онлайн книгу.
like copper, the electrons are so loosely held by the atom and so close to the neighboring atoms that it is difficult to determine which electron belongs to which atom. Under these conditions, the valence or free electrons tend to drift randomly from one atom to its neighboring atoms. Under normal conditions the movement of the electrons is truly random, meaning they are moving in all directions by the same amount. However, if some outside force acts upon the material, this flow of electrons can be directed through materials and this flow is called electrical current. Materials that have free electrons and allow electrical current to flow easily are called conductors. Many materials do not have any free electrons. Because of this fact, they do not tend to share their electrons very easily and do not make good conductors of electrical currents. These materials are called insulators.
Any material that is composed of only one type of atoms is called a chemical element, a basic element, or just an element. Any material that is composed of more than one type of atoms is called a compound. Every element has a unique atomic structure. Scientists know of only about 109 basic elements at this time. (This number has a habit of changing.) All matter is composed of combinations of one or more of these elements. Ninety-two of these basic elements occur naturally on or in the Earth. The other elements are man-made. You may recognize the names of some of these basic elements, such as: hydrogen, helium, oxygen, iron, copper, gold, aluminum, uranium. The periodic table of elements lists the basic elements and some of their properties
1. An element is material composed of only one kind of atom.
2. A compound is material composed of more than one kind of atom.
3. Some examples of elements that can be found on the periodic table are hydrogen, helium, oxygen, iron, copper, gold, aluminum, uranium.
UNIT 2
Vocabulary list
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
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.
2.
3.
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.
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 . Since only certain energy levels are allowed, it is actually possible to diagram the atom