Exercise 2. Match the two parts of the sentences. Look at Reading 4-A to help you.
1.Nuclear fission is a nuclear reaction...
2.If it occurs without neutron bombardment, as a type of radioactive decay, ...
3.However, most nuclear fission occurs as induced fission in a nuclear reactor...
4.This makes possible a self-sustaining chain reaction...
5.The isotopes that can sustain a fission chain reaction...
6.Uranium 235 is one of the few materials …
7.The energy released by a single fission comes from the fact that the fission products and the neutrons …
8.The difference in weight is converted directly to energy …
A. ... as a result of the bombardment of heavy nuclei by neutrons.
B.… at a rate given by Einstein’s equation E = mc2.
C.…weigh less than the original U-235 atom.
D. ... in which the nucleus of a heavy atom splits into lighter atoms, producing free neutrons and large amounts of energy.
E. ... that releases energy at a controlled rate in a nuclear reactor or at a very rapid uncontrolled rate in a nuclear weapon.
F. ... are called nuclear fuels, and are said to be fissile or fissionable. G. ... this type of fission is called spontaneous fission.
H. … that can undergo induced fission.
Exercise 3. Use Reading 4-A to find the English equivalents for the following Russian phrases.
Ядро – ядра – ядерная реакция; делиться на более легкие атомы, делящееся ядро, деление атома; радиоактивный распад; спонтанное деление, контролируемое деление; поддерживать цепную реакцию, самоподдерживающаяся цепная реакция; заставлять ядро делиться, вызвать дальнейшее деление; ядерное топливо, делящиеся материалы, подвергаться спонтанному делению (делиться спонтанно), период полураспада, природный уран, поглощать нейтрон, выделять огромное тепло, обогащать – обогащенный уран – обогащение, оружейный уран.
Exercise 4. Give the derivatives of the words below. 1. To heat – тепло, отопление.
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2.To weigh – вес.
3.To fission – деление, делящийся, способный к делению.
4.To collide – столкновение.
5.To bombard – бомбардировка.
6.To induce – индукция, индуцированный.
7.To cause – причина, потому что, из-за.
8.To absorb – поглощение.
9.To equal – равный, уравнение.
10.To remain – оставшаяся часть, остаток.
11.To convert – преобразование, преобразователь, обратимый.
12.To contain – содержание.
13.To compose – состав, разлагать.
14.To live – жизнь, период полураспада.
15.Possible – невозможный, возможность.
Exercise 5. Use Reading 4-A to answer the questions below:
1.What is nuclear fission?
2.What is meant by spontaneous fission? Induced fission?
3.What causes the atom to split in a nuclear reaction of fission?
4.What makes the self-sustaining chain reaction possible?
5.In what two ways can the chain reaction release energy?
6.What is meant by fissile/fissionable materials?
7.What are the two most common uranium isotopes?
8.How does U-238 behave and what is it finally transformed into?
9.What is the proportion of U-238 to U-235 in nature?
10.Why is U-235 the most important of all the uranium isotopes? 11.How much energy does the splitting of a U-235 atom release? 12.Where does this energy come from?
13.What is required for the fission reaction to occur in a nuclear reactor?
14.What enrichment is required for a NPP? For weapons-grade uranium?
Reading 4-B
Emission of Neutrons
Neutrons are ideal projectiles for nuclear bombardment because they have nо electrical charge and thus suffer no repulsion when they approach atomic nuclei. They are usually divided into thermal and fast neutrons according to their energy.
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A thermal neutron is a neutron with a relatively low energy of less than 1 MeV, and a speed of 2.2 km/s. Fast neutrons are fast! A fast neutron is a neutron with a kinetic energy close to 2 MeV, and a speed of 28,000 km/s. Fast neutrons can be made into thermal neutrons using a process called moderation. This is done with a neutron moderator. Most fission reactors use a neutron moderator to slow down the fast neutrons so that they are more easily captured, causing further fission. In reactors, heavy water, light water, or graphite is used to moderate neutrons.
The neutrons emitted as a result of the fission process can be divided into two categories, namely, prompt and delayed neutrons. The prompt neutrons are over 99 percent of the total fission neutrons. They are released within an extremely short interval of time, about 10-14 sec, of the fission process. Prompt neutrons are emitted directly by the fissioning nuclei. The delayed neutrons are produced by the decay of fission products and are emitted with a delay of a few seconds. The delayed neutrons are of great importance. They keep the chain reaction from developing into an uncontrolled process. Hence, they enable the reactor operation to be controlled.
Exercise 1. Match the two parts to make expressions from Reading 4-B. Read the text again if necessary.
1. ideal |
a) neutrons |
2. delayed |
b) moderator |
3. fission |
c) process |
4. neutron |
d) bombardment |
5. uncontrolled |
e) products |
6. reactor |
f) projectiles |
7. nuclear |
g) operation |
Now complete these sentences using the expressions above.
1.Neutrons are _______ for ______ because they have nо electrical charge.
2.Most fission reactors use a ______ to slow down the fast neutrons so that they are more easily captured, causing further fission.
3.The _______ are produced by the decay of ______ and are emitted with a delay of a few seconds.
4.The delayed neutrons keep the chain reaction from developing into an _______.
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Exercise 2. Use Reading 4-B to find the English equivalents for the following Russian phrases.
Бомбардирующая частица, отталкивать – испытывать отталкивание, быстрые и тепловые нейтроны, замедление – замедлитель нейтронов, замедлять (быстрые) нейтроны, захватывать нейтроны, мгновенные и запаздывающие нейтроны, испускать/излучать нейтроны, продукты деления, распад, задержка в несколько секунд, управлять работой реактора.
Exercise 3. Use Reading 4-B to answer the questions below.
1.Why are neutrons ideal projectiles for nuclear bombardment?
2.What is the difference between fast and thermal neutrons?
3.Into what two groups can fission neutrons be classified?
4.What is meant by “prompt” neutrons?
5.What is meant by “delayed” neutrons?
6.Why are delayed neutrons so important for fission reactors?
Reading 4-C
A Walk in the Snow
You are going to read a passage about the discovery of fission. Five sentences have been removed from the text. Choose from the sentences A-F the one which fits each gap (1-5). There is one extra sentence which you will not need to use.
A.Under the bombardment of neutrons, the uranium nuclei were splitting.
B.It was Frisch who introduced the term “fission”.
C.To his surprise, he only succeeded in producing isotopes of barium (Z=56).
D.But Meitner never received the Nobel Prize for her work.
E.He didn't know how the results of his research would be used.
F.In Germany in 1938, Otto Hahn was studying the effect of irradiating heavy elements with neutrons.
Who was the first to discover that heavy nuclei could undergo fission? 1).____________ He hoped the heavy nuclei would absorb the
neutrons, creating “transuranic elements”. These have a higher atomic number than uranium, with more than 92 protons in their nuclei (expressed as Z=92). 2)._________
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Hahn wrote to one of his colleagues, Lise Meitner, to tell her about his curious finding. Meitner was a Jew and had to leave Nazi Germany to live in Sweden. During a walk in the snow with her nephew, the nuclear physicist Otto Frisch, she realized the importance of Hahn’s discovery. 3)._________ If barium (Z=56) was being produced, then so much krypton (Z=36), since 36+56=92. It soon became clear that this is not the only pair of nuclei that can be produced. Another possible pair is rubidium (Z=37) and caesium (Z=55). 4).________ And it was Meitner who suggested that it releases energy.
A Nobel Prize was a suitable reward for the discovery of nuclear fission, and Hahn was awarded the chemistry prize for the work in 1944. 5)._________ It was a strange mistake that has provoked a lot of discussion among nuclear scientists.
Reading 4-D
Architect of the Nuclear Age
Read the passage about the famous Italian physicist Enrico Fermi and answer the question: What role did Fermi play in the American atomic bomb project?
Enrico Fermi discovered physics at the age of 14 and by 32 had developed the theory of beta decay. То explain it he had to introduce the fourth fundamental force of the universe, now known as Fermi’s ‘weak force’, the other three forces being gravity, electromagnetism and the strong force.
In 1934, Fermi and his team conducted а series of experiments that involved bombarding atomic nuclei with neutrons, and obtained many new isotopes. As a by-product, they found that slowing down neutrons by passing them through paraffin increased their effectiveness. That was the most important discovery of his life, as it would allow the controlled release of nuclear energy in а reactor. For these two discoveries, Fermi was awarded the Nobel Prize in1938.
In 1934 he had missed another Nobel Prize discovery - nuclear fission. The foil in which the uranium samples had been wrapped during experiments was too thick and the instruments were not sensitive enough to record the fission fragments. It was а blessing in disguise
(something that at first appears to be bad or unlucky but is actually
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