2. Who is the discovery of neutron due to?
3. Why are neutrons the ideal projectiles for nuclear bombardment?
4. What may the impact of a neutron result in?
5. What process is known as the radiative capture of neutrons?
6. Why is this process of particular importance for heavy nuclcartargcts?
7. What nuclear targets do you know?
8. What were the investigators looking for while experimenting with heavy nuclear targets?
9. What heavy nucleartargets did Otto Hahnand Fritz Strassman bombard with neutrons?
10. What did they expect to observe in the experiment?
11. What result did they really observe?
12. Could Otto Hahn and Fritz Strassman interpret the results of their experiment?
13. Who was the mystery of their discovery cleared up by?
14. What did Meitnerand Frisch suggest concerning Hahn's experiments?
15. What energy does uranium fission liberate in this artificial nuclear transformation?
16. Who carried out detailed theoretical studies ofthe process of artificial nuclear fission?
17. What is the fission of heavy nuclei according to Bohr and Wheeler?
• Be prepared to say a few words about:
1. Characteristics of neutron and its discovery.
2. Different types of artificial nuclear transformations.
• Choose the proper word to fill up the blanks in the sentences below.
(capture, incident, collisions, fission, releases, results in)
1. Particle ... take place at locations known as integration regions.
2. This nuclear fission ... large quantities of energy which finally takes the form of heat energy.
3. Neutron absorption frequently ... the emission of secondary gamma rays.
4. In other cases the... neutron can be captured by the nucleus.
5. The spontaneous... of neutrons into positrons within 12 minutes through the emission of an electron is an evidence that neutrons can be considered as an electric modification of protons.
6. If it were not for the radiation... of the neutron no heavier isotope ofthe bombarded element would be formed.
• Translate into English making use of according to.
1. Согласно молекулярной теории, молекулы находятся в постоянном движении.
2. По утверждению автора, эта гипотезадовольно сомнительна.
3. Твердые тела классифицируются по их электрическим свойствам.
4. По словам докладчика, эти факты можно объяснить по-разному.
5. Что представляет собой деление тяжелых ядер, по утверждению Бора и Уилера?
CLASS WORK
READING (10В)
• Skim the passage as fast as you can and choose the answer that suits the following questions best.
1. Why arc the two fragments ineffective in producing further fission
processes?
a) They do not carry enough energy.
b) They carry too high electric charges.
c) They carry no charge at all.
2. What process is responsible for nuclear energy liberation?
a) uranium fission.
b) a secondary process accompanying nuclear fission.
c) breakup of a uranium nucleus.
FISSION NEUTRONS
In spite of the fact that each of the two fragments produced in the fission of a uranium nucleus carries about 100 Mev of energy, these fragments are quite ineffective in producing further fission processes; this is due to the fact that the fission fragments carry a very high electric charge and are consequently strongly repelled by the other uranium nuclei with which they may collide. *Thus, the discovery of uranium fission would not contribute anything to the problem of the large-scale liberation of nuclear energy if it were not for a secondary process that was found to accompany nuclear fission.
*It was discovered that apart from the two large fragments of the original nucleus, there are always several extra neutrons emitted in the breakup. In the case of U235 the average number of "fission neutrons" formed is 2.5 per uranium nucleus. *These fission neutrons formed in the breakup of one uranium nucleus may collide with the surrounding uranium nuclei and produce more fission and still more fission neutrons and if the conditions are favourable, the breeding (расширенное воспроизводство) of fission neutrons goes crescendo as does the breeding of pl248. Thus we get a branching chain reaction (разветвленная цепная реакция) and in practically no time all the nuclei of uranium in a given pile of this material break up with the liberation of a tremendous amount of energy.
• Read the passage again and translate the sentences marked with an asterisk.
• Give a free translation of the following text.
В 1930 году немецкий физик Бете (Boethe) заметил, что бомбардировка бериллия природными сс-частицами из полония вызывала весьма специфическое излучение. Бете полагал, что это излучение было образовано у-квантами высоких энергий, и только через два года Чадвик (Chadwick) доказал, что это излучение было ни чем иным, как быстро движущимся пучком частиц, которые имеют ту же массу, что и протоны, но не несут электрического заряда. Эти новые частицы получили имя нейтроны. Нейтроны самопроизвольно (spontaneously) распадаются на протоны в течение 12 минут с испусканием электрона. Общее (collective) название для нейтронов и протонов — нуклон, нейтроны — нейтральные нуклоны, тогда как протоны — нуклоны, несущие положительный элементарный заряд. Не имея электрического заряда, нейтроны не подвержены (are not subjected to) действию электрических отталкивающих сил при приближении к ядру и могут легко проникать (penetrate) в заряженные ядра. Благодаря этому нейтроны являются идеальными бомбардирующими частицами.
HOMEWORK
(to be done in writing)
1. Translate into Russian.
1. Providing such states existed, they could be produced by electron-positron collisions and could be detected by their characteristic decays.
2. Supposing an antinucleus were dressed with a cloud of positrons it would be an atom of antimatter.
3. In case a potential were applied to gas at low pressure, ionization ofthe molecules would result.