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Explain the source of stellar energy. Explain the carbon - nitrogen cycle, proton cycle occurring in stars. |
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Answer» Solution :Scientists proposed two types of cyclic processes for the sources of energy in the sun and STARS. The first is know as carbon - nitrogen cycle and the scond is proton - proton cycle. 1. Carbon - Nitrogen Cycle : According to Bethe carbon - nitrogen cycle is mainly responsible for the production of solar energy. This cycle consists of a chain of nuclear reactions in which hydrogen is converted into Helium, with the help of Carbon and Nitrogen as catalysts. The nucleasr reactions are as given below. `._(6)^(12)C+ ._(1)^(1)H to ._(7)^(13)N + gamma` `._(7)^(13)N to ._(6)^(13)C + ._(+1)^(0)e + v` `._(6)^(13)C + ._(1)^(1)H to ._(7)^(14)N + gamma` `._(7)^(14)N + ._(1)^(1)H to ._(8)^(15)O + gamma` `._(8)^(15)O to ._(7)^(15)N + ._(+1)^(0)e + v` `._(7)^(15)N + ._(1)^(1)H to ._(6)^(12)C + ._(2)^(4)He` 2. Proton - Proton Cycle : A star is FORMED by the condensation of a large amount of matter at a point in space. Its temperature rises to `2,00,000 .^(@)C` as the matter contracts under the influence of gravitational attraction. At this temperature the thermal energy of the protons is sufficient to form a deuteron and a positron. The deuteron then COMBINES with another protobn to form LIGHTER nuclei of helium `._(2)^(3)He`. Two such helium nuclei combine to form a helium nucleus `._(2)^(4)He` and two protons releasing a total amount of energy 25.71 MeV. The nuclear fusion reactions are given below. `._(1)^(1)H+ ._(1)^(1)H to ._(1)^(2)H+ ._(1)^(0)e + v` `._(1)^(2)H + ._(1)^(1)H to ._(2)^(3)H + gamma` `._(2)^(3)He + ._(2)^(3)He to ._(2)^(4)He + 2._(1)^(1)H` The net result is `4 ._(1)^(1)H to ._(2)^(4)He + 2 ._(+1)^(0)e + 2v + 2gamma` |
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