Ramamurti, was willing to shift his residence because government had decided to start a nuclear power plant near his village. His daughter Radha, a science student convinced him not to shift since adequate safety measures to avoid any mishap had already been taken by the government before starting the nuclear thermal plant. (1) What are the values displayed by Radha? (any two) (2) What is the principle of working of nuclear reactor? (3) Lighter elements are better moderators for a nuclear reactor than heaviour element, why?

Dear Student ,

The nucleus of a lighter element contains a relatively larger number of protons. When fast neutrons are passed through such an element , they make elastic collisions with its protons, which have smaller velocities . After few interaction , the final velocities of the neutrons become equal to the low velocities of protons and hence the get slowed down.
(b)For a controlled chain reaction , the average number a available neutrons should never exceed one per fission . Any excess neutrons over  the critical unit should be absorbed . This is what the control rods do. They are made of cadmium because cadmium has a high cross-section for neutron absorption. 
(c) the overcome coulomb repulsion , the fusing nuclei are given enough thermal energy by raising their temperature to 106-107K. Such a high temperature is available in the interior to the sun.

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