NUCLEI
Essay Question Answers
Q1. Explain the principle and working of a nuclear reactor with the help of a labelled diagram.
Ans. Principle of nuclear reactor: Nuclear reactor works on the. principle of achieving controlled chain reaction,.
- Fuel: Fissionable material, commonly Uranium isotopes are used.
- Moderator: The purpose of moderator is to slow down the fast moving neutrons. Eg: Heavy water, Graphite
- Control rods: To control the chain reaction. Eg: Cadmium (or) Boron rods
- Coolant:The substance used to absorb heat generated in the reactor
- Radiation shielding: Lead blocks and concrete walls of thickness. $10m$ areused for the reactor. Turbines
Working:- Nuclear reactor works on the principle of controlled and sustained chain reaction and releases large amount of energy
Q2. Explain the source of stellar energy. Explain the carbon - nitrogen cycle, proton-proton cycle occurring in stars
Ans.The source of stellar energy is nuclear fusion reaction, for which hydrogen is the fuel.
Energy from Sun and Stars : Sun and Stars have been radiating huge amounts of energy by nuclear fusion reactions taking place in their core, where the temperature is of the order 107 K. More scientists proposed two types of cyclic processes for the source of energy in the Sun & Stars. They are
Carbon - Nitrogen Cycle : Carbon - Nitrogen cycle is one of the most important nuclear reactions for the production of solar energy by fusion.
$$\begin{gathered}
{}_{6}^{12}C\:+{}_{1}^{1}H\:\rightarrow\:N\:+\:\gamma \\
_{7}^{13}N\:\rightarrow\:{}_{6}^{12}C\:\:+\:e^{+}\:+\:\nu \\
\begin{aligned}&{}_{6}^{13}C\:+{}_{1}^{1}H\:\to\:{}_{7}^{14}N\:\:+\:\nu\\&{}_{7}^{14}N\:+{}_{1}^{1}H\:\to\:_{8}^{15}O\:+\:\gamma\end{aligned} \\
_{8}^{15}O\:\rightarrow\:{}_{7}^{15}N\:+\:e^{+}\:+\:\nu \\
{}_{7}^{15}N\:+{}_{1}^{1}H\:\rightarrow\:{}_{6}^{12}C\:+\:{}_{2}^{4}He\:+ \:\gamma
\end{gathered}$$
The entire cycle can be summed up as, $4_{1}^{1}H\to{}{}{}{}_{2}^{4}He+2e^{+}+3\nu+3\gamma$
The energy released during this process is $26.70\:\: MeV$
Proton - Proton Cycle : At higher temperature the thermal energy of the protons is sufficient to form a deuteron and a positron. The deuteron then combines with another proton to form higher nuclei of helium ${}_2^3He$ Two such helium nuclei combine with another proton releasing a total amount of energy 25.71 MeV. The nuclear fusion reactions are given below ..
$$\begin{array}{c} \\{{_2^4He\:+\:H\:\to\:H\:+\:e^{+}\:+\:\nu}}\\{{_1^2H\:+\:_1^1H\:\to\:He\:+\:\gamma}}\\{{_1^2H\:+\:_1^1H\:\to\:He\:+\:\gamma}}\end{array}$$
For this equation to takes place first three equations must occur twice.
$$_2^3He+_2^3He\to_2^4He\:+\:2_1^1H$$
The net result of the above reactions is $4_{1}^{1}H\to{}{}{}{}{}^{4}He+{}{}2e^{+}+{}2v+{}2\gamma$
The energy released during this process is $26.70\:\: MeV$