Read the text: Nuclear fusion

When two light nuclei come into very close contact with each other it is possible for the strong force to fuse the two together. It takes a great deal of energy to push the nuclei close enough together for the strong or nuclear forces to have an effect, so the process of nuclear fusion can only take place at very high temperatures or high densities. Once the nuclei are close enough together the strong force overcomes their electromagnetic repulsion and squishes them into a new nucleus. A very large amount of energy is released when light nuclei fuse together because the binding energy per nucleon increases with mass number up until nickel-62. Stars like our sun are powered by the fusion of four protons into a helium nucleus, two positrons, and two neutrinos. The uncontrolled fusion of hydrogen into helium is known as thermonuclear runaway. Research to find an economically viable method of using energy from a controlled fusion reaction is currently being undertaken by various research establishments.

Nuclear fission

For nuclei heavier than nickel-62 the binding energy per nucleon decreases with the mass number. It is therefore possible for energy to be released if a heavy nucleus breaks apart into two lighter ones. This splitting of atoms is known as nuclear fission.

The process of alpha decay may be thought of as a special type of spontaneous nuclear fission. This process produces a highly asymmetrical fission because the four particles which make up the alpha particle are especially tightly bound to each other, making production of this nucleus in fission particularly likely.

For certain of the heaviest nuclei which produce neutrons on fission, and which also easily absorb neutrons to initiate fission, a self-igniting type of neutron-initiated fission can be obtained, in a so-called chain reaction. [Chain reactions were known in chemistry before physics, and in fact many familiar processes like fires and chemical explosions are chemical chain reactions]. The fission or "nuclear" chain-reaction, using fission-produced neutrons, is the source of energy for nuclear power plants and fission type nuclear bombs such as the two that the United States used against Hiroshima and Nagasaki at the end of World War II. Heavy nuclei such as uranium and thorium may undergo spontaneous fission, but they are much more likely to undergo decay by alpha decay.

For a neutron-initiated chain-reaction to occur, there must be a critical mass of the element present in a certain space under certain conditions (these conditions slow and conserve neutrons for the reactions). There is one known example of a natural nuclear fission reactor, which was active in two regions of Oklo, Gabon, Africa, over 1.5 billion years ago. Measurements of natural neutrino emission have demonstrated that around half of the heat emanating from the earth's core results from radioactive decay. However, it is not known if any of this results from fission chain-reactions.

I. Reading exercises:

Exercise1. Read and memorize using the dictionary:

nuclear fusion, electromagnetic repulsion, fuse together, squish, thermonuclear runaway, nuclear fission, self-igniting type of neutron, initiated fission, spontaneous fission, neutron-initiated chain reaction, critical mass, neutrino emission, emanate from

Exercise 2. Answer the questions:

1. How can the process of nuclear fusion take place?

2. Why is a very large amount of energy released when light nuclei fuse together?

3. What is known as thermonuclear runaway?

4. What is known as nuclear fission?

Exercise 3. Match the left part with the right:

1. When two light nuclei come into very close contact with each other	a. as a special type of spontaneous nuclear fission.
2. A very large amount of energy is released	b. by the fusion of four protons into a helium nucleus, two positrons, and two neutrinos.
3. Stars like our sun are powered	c. when light nuclei fuse together.
4. The process of alpha decay may be thought of	d. it is possible for the strong force to fuse the two together.

Exercise 4. Open brackets using the right words:

For nuclei (lighter/heavier) than nickel-62 the binding energy per nucleon (decreases/increases) with the mass number. It is therefore (impossible/possible) for energy to be released if a heavy nucleus (divides/breaks) apart into two lighter ones.

The Speaking Module

II. Speaking exercises:

Exercise 1. Describe nuclear force; star; fission; fusion; binding energy using the suggested words and expressions as in the example:

nuclear force between nucleons; that part of the force; which is not electromagnetic; it is much stronger; but drops off; than electromagnetic forces; very rapidly; at distances greater than 10-13 centimeter example: Nuclear force – that part of the force between the nucleons which is not electromagnetic; it is much stronger than electromagnetic forces, but drops off very rapidly at distance greater than 10-13 centimeter.

star consisting of a large; a celestial body; self-luminous mass; of hot gas; by its own gravity; held together; the sun is a typical star

fission into parts of comparable mass; the division of an atomic nucleus; usually restricted to heavier nuclei; such as isotopes of uranium, plutonium and thorium

fusion to form a heavier nucleus; combination of two light nuclei; and perhaps other reaction products; with release of some binding energy

binding energy to decomposed the system; the net energy required; into its constituent particles

Exercise 2. Ask questions to the given answers:

1. Question: ____________________________________ ?

Answer: The process of alpha decay may be thought of as a special type of spontaneous nuclear fission.

2. Question: ____________________________________ ?

Answer: This process produces a highly asymmetrical fission.

3. Question: ____________________________________ ?

Answer: The process of nuclear fusion can only take place at very high temperatures or high densities.

The Writing Module

III. Writing exercises:

Exercise 1. Complete the sentences with the suggested words: end; for; fission; against; explosions; bombs; physics; using; chain; in:

Chain reactions were known ______ chemistry before______ , and in fact many familiar processes like fires and chemical ______ are chemical ______ reactions. The ______ or "nuclear" chain-reaction, ______ fission-produced neutrons, is the source of energy ______ nuclear power plants and fission type nuclear ______ such as the two that the United States used ______ Hiroshima and Nagasaki at the ______ of World War II.

Exercise 2. Fill in the table with words from the text. Group the antonyms:

fusion	weak
light	uncontrolled
close	unfamiliar
possible	fission
strong	heavy
high	low
repulsion	long ago
large	decrease
controlled	at the beginning
currently	far
increase	attraction
easy	unknown
familiar	passive
at the end	difficult
active	small
known	impossible

Exercise 3. Compose a story on one of the topics (up to 100 words):

“Chain reaction”

“The process of alpha decay”

“Nuclear power plants”

Lesson 5

The Reading Module

Read the text: Research in Elementary Particle and Nuclear Physics

Particle and Nuclear Physics are concerned with the elementary building blocks of matter and the fundamental symmetries and interactions governing the foundations of our world.