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1) When the fissionable material can sustain a chain reaction by itself, the chain reacting system is in balance.
2) The capture of the neutron forms a new compound nucleus.
3) First of all, neutrons are in motion in a nuclear reactor.
4) By raising or lowering the number of neutrons, the rate of the generator can be decreased or increased to get the required power level.
5) Furthermore, at the thermal energies of slow neutrons the fission cross-section becomes very large for nuclei with odd number of neutrons.
6) In fact, the velocity of the passing neutron influences the fission and capture happens.
7) A certain group of neutrons is delayed and decayed within the fission process, which is the important factor providing the control over a chain reacting system.
8) For example, the compound nucleus of U-235 used in a thermal reactor is not very stable and may break into the fragments.
9) These are the examples of typical reaction products.
10) Heat is generated in the reactor even if it stops because of the radioactive decay; that’s why it needs cooling.
11) When the neutron velocity decreases, the fission and cross-sections go up in any neutron-induced reactions.
12) Fission can occur after capture of a neutron, but if the neutrons are low-energy, fission can take place in the isotopes of the elements with odd number of their nuclei.
ǃ The passive is formed with the appropriate tense of the verb to be + past participle. Only transitive verbs can be put into the passive
The passive is used
- when we are more interested in the action than the agent, such as processes, instructions, reports etc.
- when the person who performs the action (agent is unknown, unimportant or obvious from the context.
Look at this sentence from the article and underline the passive form of the verb: Using U-235 in a thermal reactor as an example, when a neutron is captured the total energy is distributed amongst the 236 nucleons (protons & neutrons) now present in the compound nucleus.
- to emphasize the agent.
Look at this sentence from the article and underline the passive form of the verb: When a neutron passes near to a heavy nucleus, for example uranium-235 (U-235), the neutron may be captured by the nucleus and this may or may not be followed by fission.
For more information about Passive consult English Grammar in Use by R. Murphy Units 42-44
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