In a nuclear reactor, moderators slow down the neutrons which come out in a fission process. The moderator used have light nuclei. The heavy nuclei will not serve the purpose, because:

1. they will break up
2. elastic collision of neutrons with heavy nuclei will not slow them down
3. the net weight of the reactor would be unbearably high
4. substances with heavy nuclei do not occur in the liquid or gaseous state at room temperature
Subtopic:  Nuclear Energy |
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Level 2: 60%+
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Fusion processes, like combining two deuterons to form a \({He}\)-nucleus are impossible at ordinary temperatures and pressure. The reasons for this can be traced to the fact:
(a) nuclear forces have short-range.
(b) nuclei are positively charged.
(c) the original nuclei must be completely ionized before fusion can take place.
(d) the original nuclei must first break up before combining with each other.
 
Choose the correct option:
1. (a) and (c) 2. (a) and (d)  
3. (b) and (d) 4. (a) and (b)    
Subtopic:  Nuclear Energy |
Level 3: 35%-60%
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