Section 1 atomic nature of matter icon

Section 1 atomic nature of matter



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preface


The given educational edition on professional English “Nuclear Physics” is a class book intended for the fourth year students of the Physical-Technical Department. It can also be used for teaching professional English at other departments where this subject is taught. The edition is planned for 36 hours and corresponds to the topics of the modules on “Professional English” for the fourth year at the Physical-Technical Department.

The edition is aimed at teaching terminology and vocabulary on nuclear physics and their use in the situations of professional communication.

The class book consists of 7 sections with authentic texts forming their basis. Every section has tuning-in activities, exercises aimed at learning vocabulary and grammar units and developing communication skills. There are also tasks for preparing presentations and practicing listening skills. All sections are accompanied by formulas, equations, tables and diagrams.

The edition includes 3 appendixes with mathematical symbols and Greek alphabet.

Further a practice book and a teacher’s book are planned to be developed.

The class book is prepared at the Interdepartmental Chair of Professional Foreign Language of the Department of Natural Sciences and Mathematics of Tomsk Polytechnic University by a senior teacher Demjanenko N.V. and a teacher Grebenkova A.V.



SECTION 1


^ ATOMIC NATURE OF MATTER


LEAD-IN


Study this list of points to consider when deciding whether to study engineering. Tick [√] the statements which refer to you. Then ask your partner which statements refer to him or her.


^ 1 You enjoy practical projects - creating and investigating things.

2 You like finding out how things work.

3 You are interested in improving the environment.

4 You like helping people.

5 You enjoy solving problems.

6 You enjoy organizing activities.

7 You enjoy science programmes on TV or on the radio.


If you have ticked most of these statements, engineering is the right course of study for you.


Read the following text and do the tasks below (1-3):


In 1661 the English chemist Robert Boyle published the modern criterion for an element. He defined an element to be a basic substance that cannot be broken down into any simpler substance after it is isolated from a compound, but can be combined with other elements to form compounds. To date, 105 different elements have been confirmed to exist, and researchers claim to have discovered three additional elements. Of the 105 confirmed elements, 90 exist in nature and 15 are man-made.

Another basic concept of matter that the Greeks debated was whether matter was continuous or .discrete. That is, whether matter could be continuously divided and subdivided into ever smaller particles or whether eventually an indivisible particle would be encountered. Democritus in about 450 B.C. argued that substances were „ultimately composed of small, indivisible particles that he labeled atoms. He further suggested that different substances were composed of different atoms or combinations of atoms, and that one substance could be converted into another by rearranging the atoms. It was impossible to conclusively prove or disprove this proposal for more than 2000 years.

The modern proof for the atomic nature of matter was first proposed by the English chemist John Dalton in 1803. Dalton stated that each chemical element possesses a particular kind of atom, and any quantity of the element is made up of identical atoms of this kind. What distinguishes one element from another element is the kind of atom of which it consists, and the basic physical difference between kinds of atoms is their weight.


1. Complete the following sentences using the information from the text and your knowledge.


  1. The English chemist Robert Boyle …

  2. The Greeks debated …

  3. Democritus argued …

  4. The English scientist John Dalton proposed …


^ 2. Work in pairs. Decide whether the statements below (1-3) are true or false. Correct the false sentences. Share your ideas with other students in your group.


  1. Robert Boyle argued that an element can be broken down into any simpler substance after it is isolated from a compound.

  2. It was impossible to finally prove or disprove the Democritus suggestion that different substances were composed of different atoms or combinations of atoms, and that one substance could be converted into another by rearranging the atoms.

  3. Robert Boyle was the first to prove the atomic nature of matter.



^ 3. Using information from the text say a few words about:


  1. the modern criterion for an element published by Robert Boyle

  2. continuous or .discrete matter

  3. Democritus proposal that was impossible to conclusively prove or disprove this proposal for more than 2000 years

  4. the modern proof for the atomic nature of matter proposed by John Dalton in 1803



READING


TEXT 1


^ 1.1. Before reading the text below complete the sentences 1-3.


1. Subatomic particles are …

2. Gravity, electromagnetism, strong nuclear force and weak nuclear force are …

3. A gauge boson is …


1.2. You are going to read a text about subatomic particle theory. Six phrases have been removed from the text. Choose from the sentence A – G the one which fits each gap (1 – 6). There is one extra phrase, which you don’t need to use.


A which governs the aggregation of matter

B that emerges when a neutron changes by beta decay into a proton

C that is independent of charge

D which transmits the electromagnetic force between electrically charged objects

^ E that provide this mortar are associated with four basic forces

F which acts only between quarks

G which incorporates all four fundamental forces


The Present State of Subatomic Particle Theory


Since the 1950s physicists have discovered that protons and neutrons consist of quarks with spin 1/2 and that antiprotons and antineutrons consist of antiquarks. Neutrinos, too, have spin 1/2 and corresponding antineutrinos. Indeed, it is an antineutrino, rather than a neutrino, 1__________. This reflects an empirical law regarding the production and decay of quarks and leptons: in any interaction the total numbers of quarks and leptons seem always to remain constant. Thus, the appearance of a lepton—the electron—in the decay of a neutron must be balanced by the simultaneous appearance of an antilepton, in this case the antineutrino.

In addition to such familiar particles as the nucleons and the electron, studies have slowly revealed the existence of more than 200 other subatomic particles. These “extra” particles do not appear in the low-energy environment of everyday human experience; they emerge only at the higher energies found in cosmic rays or particle accelerators. Moreover, they soon decay to the more familiar particles after brief lifetimes of only fractions of a second. The variety and behaviour of these extra particles initially bewildered scientists but have since come to be understood in terms of the quarks and leptons. In fact, only six quarks, six leptons and their corresponding antiparticles are necessary to explain the variety and behaviour of all the subatomic particles, including those, that form normal atomic matter.

These quarks and leptons are the building blocks of matter, but they require some sort of mortar to bind themselves together into more complex forms, whether on a nuclear or a universal scale. The particles 2 __________.

On the largest scales, the dominant force is gravity, 3 __________ to form stars and galaxies and which influences the way that the universe is evolving from its initial big bang. The best-understood force, however, is the electromagnetic force, which underlies the related phenomena of electricity and magnetism. The electromagnetic force binds negatively charged electrons to positively charged atomic nuclei and gives rise to the bonding between atoms to form matter in bulk.

Gravity and electromagnetism are well known at the macroscopic level. The other two forces act only on subatomic scales, indeed on subnuclear scales. The strong nuclear force binds quarks together within protons, neutrons, and other subatomic particles; and, rather as the electromagnetic force is ultimately responsible for holding bulk matter together, so the strong force keeps protons and neutrons together within atomic nuclei. The fourth force is the weak nuclear force. Unlike the strong force, 4 __________, the weak force acts on both quarks and leptons. This force is responsible for the beta decay of a neutron into a proton and for the nuclear reactions that fuel the Sun and other stars.

Since the 1930s physicists have recognized that they can use field theory for all four basic forces. In mathematical terms, a field describes something that varies continuously through space and time. A familiar example is the field that surrounds a piece of magnetized iron. The magnetic field maps the way that the force varies in strength and direction around the magnet. The appropriate fields for the four basic forces appear to have an important property in common: they all exhibit what is known as gauge symmetry. Put simply, this means that certain changes can be made that do not affect the basic structure of the field. It also implies that the relevant physical laws are the same in different regions of space and time.

At a subatomic, quantum level, these field theories display a significant feature. They describe the action of a force in terms of subatomic particles, called gauge bosons, which in a sense carry the force. These particles differ from the building blocks—the quarks and leptons—by having integer values of the spin quantum number, rather than a value of 1/2. The most familiar gauge boson is the photon, 5 __________, such as the electrons and protons within the atom. The photon acts as a private, invisible messenger between these particles, influencing their behaviour with the information it conveys, rather as a ball influences the actions of children playing catch. Other gauge bosons, with varying properties, are involved with the other basic forces.

In developing a gauge theory for the weak nuclear force in the 1960s, physicists discovered that the best theory, which would always yield sensible answers, must also incorporate the electromagnetic force. The result was what is now called electroweak theory. It was the first workable example of a unified theory linking forces that manifest themselves differently in the everyday world. The unified theory reveals the outwardly diverse forces as separate facets of a single underlying force. The search for a unified theory of everything, 6 __________, is one of the major goals of particle physics. It is leading theorists to an exciting area of study that involves not only subatomic particle physics but also cosmology and astrophysics.


^ 1.3. Find the single words in the text above which mean the following:

a)

1. essential, important

2. special, particular

3. individual , independent

4. short , concise

5. chief , main

6. invariable, permanent, continual

7. composite, combined, complicated

8. fundamental, primary

9. primary, incipient

10. known , acquainted , intimate

11. judicious , reasonable , sane

12. hardy, powerful, tough


b)

1. arise, appear

2. realize, become aware

3. confuse, embarrass, perplex

4. show, demonstrate

5. disclose, reveal

6. mean, hint

7. tie, fasten

8. need, deserve

9. circumscribe, enclose

10. mirror, image, show

11. differ, alter

12. affect, sway


^ 1.4. Work in pairs or groups. Read the following definitions and decide what they mean.


1. any of the subatomic particles, the proton and the neutron, constituting atomic nuclei

2. type of fundamental particle with no electric charge, little or no mass, and one-half unit of spin

3. any member of a group of subatomic particles having odd half-integral angular momentum (spin 1/2, 3/2); named for the Fermi-Dirac statistics that describe its behaviour

4. a stable subatomic particle that has a unit-positive charge and a mass of 1.6726231 × 10−27 kg, which is 1,836 times the mass of an electron

5. also called elementary particle any of various self-contained units of matter or energy

6. a lightest stable subatomic particle known. It carries a negative charge which is considered the basic charge of electricity

7. one of the constituent particles of every atomic nucleus except ordinary hydrogen; it has no electrical charge and its mass is nearly 1,840 times that of the electron

8. any member of a class of fermions that respond only to electromagnetic, weak, and gravitational forces and do not take part in strong interactions

9. a subatomic particle with integral spin that is governed by the Bose-Einstein statistics (q.v.).

10. any of a group of subatomic particles believed to be among the fundamental constituents of matter. Constitute all hadrons (baryons and mesons)—i.e., all particles that interact by means of the strong force; the force that binds the components of the nucleus


^ 1.5. Make a list of collocations with the words below and use them in sentences of your own.


Example: motion → molecular motion, motion of the fluid Molecular motion is induced by the heat.


appearance particle environment force

experience scale matter reaction

field structure behavior


^ 1.6. Mind the translation of the Passive Voice.


1. The charge of an atom is not affected by the number of neutrons present, but depends on the balance between electrons and protons.

2. The results of the third experiment, unlike the other two, have been affected by ambient temperature.

3. The program will be effected with the aid of numerical analysis technique.

4. Simulating the reaction was not effected for lack of suitable computing devices.

5. The angular momentum of an object is proportional to its rotational velocity and also influenced by the distribution of its mass.

6. Sound levels are acted upon by the loss of energy upon reflection.

7. A transition from one phase to another (solid, liquid, vapour) is accomplished by a change in temperature, pressure, density and volume.

8. A great deal of research is being done to reduce the expenses of mini computer production.

9. At Fermi lab the main proton synchrotron has been modified by addition of superconducting magnets that will double its energy.

10. The immediate effect of temperature has not yet been accounted for.

11. The system of molecules is -governed by the laws of thermodynamics and statistical mechanics, where an important role is ascribed to temperature and entropy.

12. We are guided by the laws of conservation and transformation of energy in describing natural phenomena.

13. An appreciable distortion of the signal has been brought about by the environmental conditions.

14. In spite of the unfavourable operating conditions appropriate precautions arc taken to avoid the trouble.

15. Care is taken to overcome the difficulties in adjusting the device.


^ 1.7. Make up a report on the topics below.


1. «Robert Boyle (or other famous scientist) and his Discoveries»

2. «Subatomic Particles»

3. «Nuclear Forces»


(See appendix 4)


TEXT 2


^ 2.1. Work in pairs or groups. Before reading the text below, answer the question: What do you know about:


- Thomson's model of atomic structure

- Rutherford's nuclear model

- Moseley’s model

- Bohr model of the atom


Now read the text and check your guesses.


Models of Atomic Structure


A. Models of atomic structure


Thomson's discovery of the negatively charged electron had raised theoretical problems for physicists as early as 1897, because atoms as a whole are electrically neutral. Where was the neutralizing positive charge and what held it in place? Between 1903 and 1907 Thomson tried to solve the mystery by adapting an atomic model that had been first proposed by Lord Kelvin in 1902. According to this theoretical system, often referred to as the “plum pudding” model, the atom is a sphere of uniformly distributed positive charge about one angstrom in diameter. Electrons are embedded in a regular pattern like raisins in a plum pudding to neutralize the positive charge. The advantage of the Thomson atom was that it was inherently stable: if the electrons were displaced, they would attempt to return to their original positions. In another contemporary model, the atom resembled the solar system or the planet Saturn, with rings of electrons surrounding a concentrated positive charge. The Japanese physicist Hantaro Nagaoka, in particular, developed the “Saturnian” system in 1904. The atom, as postulated in this model, was inherently unstable because, by radiating continuously, the electron would gradually lose energy and spiral into the nucleus. No electron could thus remain in any particular orbit indefinitely.


B. Rutherford's nuclear model


Rutherford overturned Thomson's model in 1911 with his well-known gold foil experiment in which he demonstrated that the atom has a tiny, massive nucleus. Five years earlier Rutherford had noticed that alpha particles, beamed through a hole onto a photographic plate, would make a sharp-edged picture, while alpha particles beamed through a sheet of mica only 20 micrometres (or about 0.002 centimetre) thick would make an impression with blurry edges. For some particles, the blurring corresponded to a two-degree deflection. Remembering those results, Rutherford had his postdoctoral fellow, Hans Geiger, and an undergraduate student, Ernest Marsden, refine the experiment. The young physicists beamed alpha particles through gold foil and detected them as flashes of light or scintillations on a screen. The gold foil was only 0.00004 centimetre thick. Most of the alpha particles went straight through the foil, but some were deflected by the foil and hit a spot on a screen placed off to one side. Geiger and Marsden found that about one in 20,000 alpha particles had been deflected 45° or more. Rutherford asked why so many alpha particles passed through the gold foil while a few were deflected so greatly. “It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper, and it came back to hit you,” Rutherford said later. “On consideration, I realized that this scattering backwards must be the result of a single collision, and when I made calculations I saw that it was impossible to get anything of that order of magnitude unless you took a system in which the greater part of the mass of the atom was concentrated in a minute nucleus. It was then that I had the idea of an atom with a minute massive centre carrying a charge.”

Many physicists distrusted Rutherford's nuclear model because it was difficult to reconcile with the chemical behaviour of atoms. The model suggested that the charge on the nucleus was the most important characteristic of the atom, determining its structure. On the other hand, Mendeleyev's periodic table of the elements had been organized according to the atomic masses of the elements, implying that the mass was responsible for the structure and chemical behaviour of atoms.


C. Moseley’s model


Henry Gwyn Jeffreys Moseley, a young English physicist killed in World War I, confirmed that the positive charge on the nucleus revealed more about the fundamental structure of the atom than Mendeleyev's atomic mass. Moseley studied the spectral lines emitted by heavy elements in the X-ray region of the electromagnetic spectrum. He built on the work done by several other British physicists—Charles Glover Barkla, who had studied X-rays produced by the impact of electrons on metal plates, and Sir William Bragg and his son Lawrence, who had developed a precise method of using crystals to reflect X-rays and measure their wavelength by diffraction. Moseley used a crystal of potassium ferrocyanide as a diffraction grating to examine the spectra of X-rays produced by different metals. He arranged his crystal so that he could control and vary the angle between the crystal face and the X-ray beam. The X-rays from each element were reflected at a uniqueset of angles. By measuring the angle, Moseley was able to obtain the wavelength of the X-ray hitting the crystal.

Moseley found that the X-rays radiated by each element have a characteristic frequency that differs according to a regular pattern. The difference in frequency is not governed by Mendeleyev's change in mass, however, but rather by the change in charge on the nucleus. He called this the atomic number. In his first experiments, conducted in 1913, Moseley used the K-series of X-rays (X-radiation associated with the K-energy state of an atom) and studied the elements up to zinc. The following year he extended his work up to gold in the periodic table, using the L-series of X –rays (X-radiation associated with the L-atomic-energy state). Moseley was conducting his research at the same time that the Danish theorist Niels (phys.) Bohr was developing his quantum shell model of the atom. The two conferred and shared data as their work progressed and Moseley framed his equation in terms of Bohr's theory. Moseley presented formulas for the X-ray frequencies that were closely related to Bohr's formulas for the spectral lines in a hydrogen atom. Moseley showed that the frequency of a line in the X-ray spectrum is proportional to the square of the charge on the nucleus. The constant of proportionality depends on whether the X-ray is in the K- or L-series. This is the same relationship that Bohr used in his formula applied to the Lyman and Balmer series of spectral lines. The regularity of the differences in X-ray frequencies allowed Moseley to order the elements by atomic number from aluminum to gold. He observed that, in some cases, the order by atomic weights was incorrect. For example, cobalt has a larger atomic mass than nickel, but Moseley found that it has atomic number 27, while nickel has 28. When Mendeleyev constructed the periodic table, he based his system on the atomic masses of the elements and had to put cobalt and nickel out of order to make the chemical properties fit better. In a few places where Moseley found more than one integer between elements, he predicted correctly that a new element would be discovered. Because there is just one element for each atomic number, scientists could be confident for the first time of the completeness of the periodic table; no unexpected new elements would be discovered.


D. Bohr Model of the Atom


The British physicist Ernest Rutherford postulated that the positive charge in an atom is concentrated in a small region called a nucleus at the center of the atom with electrons existing in orbits around it. Niels Bohr, coupling Rutherford's postulation with the quantum theory introduced by Max Planck, proposed that the atom consists of a dense nucleus of protons surrounded by electrons traveling in discrete orbits at fixed distances from the nucleus. An electron in one of these orbits or shells has a specific or discrete quantity of energy (quantum). When an electron moves from one allowed orbit to another allowed orbit, the energy difference between the two states is emitted or absorbed in the form of a single quantum of radiant energy called a photon. Figure 1 is Bohr's model of the hydrogen atom showing an electron as having just dropped from the third shell to the first shell with the emission of a photon that has an energy = hv. (h = Planck's constant = 6.63 x 10-34 J-s and v = frequency of the photon.) Bohr's theory was the first to successfully account for the discrete energy levels of this radiation as measured in the laboratory. Although Bohr's atomic model is designed specifically to explain the hydrogen atom, his theories apply generally to the structure of all atoms.




Properties of the three subatomic particles are listed in the Table below.


TABLE


^ Properties of Subatomic Particles

Particle

Location

Charge

Mass

Neutron

Nucleus

none

1.008665 amu

Proton

Nucleus

+1

1.007277 amu

Electron

Shells around nucleus

-1

0.0005486 amu
  1   2   3   4   5   6   7




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