Question

______________ is the principle reaction responsible for the energy output of the Sun.
A) Gamma decay
 B) Nuclear fusion
C) Alpha decay
D) Positron emission

Answer 1

Hint: The sun is a source of heat and energy. The nuclear reaction takes place inside the core. The sun has an abundant amount of hydrogen. These lighter hydrogen atoms combine to form heavier nucleus helium. The mass is converted into energy and it acts as the ultimate source of energy. The reaction which is responsible for the energy output of the sun is as: \[\text{4}{{\text{ }}^{\text{1}}}\text{H+2}{{\text{e}}^{-}}{{\to }^{\text{4}}}\text{He + 2 neutrinos + 6 photons}\]

Complete step by step answer:
The sun is a hot mass. The nuclear reaction takes place deep inside the core of the sun. The temperature of the core is as high as 15 million kelvin. The sun has an abundant level of hydrogen gas. The hydrogen gas combines to form a heavier nucleus of helium. The small nuclei combine to give heavier nuclei is called nuclear fusion.
The hydrogen combines to form helium such that during this conversion the mass is converted into the energy which is released as the heat energy. The overall reaction is depicted as follows:
\[\text{4}{{\text{ }}^{\text{1}}}\text{H+2}{{\text{e}}^{-}}{{\to }^{\text{4}}}\text{He + 2 neutrinos + 6 photons}\]

This reaction takes place in several steps.
Step 1) The two hydrogen atoms combine to form hydrogen gas. This releases the antielectron and neutrino.
\[^{\text{1}}\text{H +}{{\text{ }\!\!~\!\!\text{ }}^{\text{1}}}\text{H }\!\!~\!\!\text{ }\to {{\text{ }}^{\text{2}}}\text{H + antielectron + neutrino}\]
This step is nearly impossible to take place. Because both protons can repel each other as they have \[+\text{ }1\]a charge. But the reaction is feasible in very hot conditions. Such that the protons can hit each other with high speed. This lets them come closer to each other even though they repel each other.

Step 2) The electron reacts with the antielectron to give photon energy.
\[\text{electron + antielectron }\to \text{ photon + photon}\]
The antielectron hits with an electron and they annihilate to make two photons. These high energy photons are absorbed in the gas and eventually give the low energy photons.

Step 3) Step 3 involves the reaction of hydrogen gas with that of the hydrogen atom and liberates a helium isotope along with a photon.
\[{{\text{ }}^{\text{2}}}\text{H + }\!\!~\!\!\text{ }{{\text{ }}^{\text{1}}}\text{H }\to {{\text{ }}^{\text{3}}}\text{He + photon}\]
The emitted high energy photon is absorbed in the gas and eventually gives out the low energy photon.

Step 4) In step 4, the two \[^{\text{3}}\text{He}\] nuclei combine and form a helium gas and liberate the 2 neutrons and 4 protons and rearrange themselves into the helium nucleus and two free protons.
${{\text{ }}^{\text{3}}}\text{He + }\!\!~\!\!\text{ }{{\text{ }}^{\text{3}}}\text{He }\to {{\text{ }}^{\text{4}}}\text{He + }\!\!~\!\!\text{ }{{\text{ }}^{\text{1}}}\text{H + }{{\text{ }\!\!~\!\!\text{ }}^{\text{1}}}\text{H}$
Therefore the net reaction is:
\[\begin{matrix}
 \text{6}{{\text{ }\!\!~\!\!\text{ }}^{\text{1}}}\text{H + 2 }{{\text{e}}^{-}}\text{ }\to {{\text{ }\!\!~\!\!\text{ }}^{\text{4}}}\text{He + 2}{{\text{ }\!\!~\!\!\text{ }}^{\text{1}}}\text{H + 2 neutrinos + 6 photons} \\
 \text{or} \\
\text{4}{{\text{ }\!\!~\!\!\text{ }}^{\text{1}}}\text{H + 2 }{{\text{e}}^{-}}\text{ }\to {{\text{ }\!\!~\!\!\text{ }}^{\text{4}}}\text{He + 2 neutrinos + 6 photons} \\
\end{matrix}\]
The net energy released during the nuclear fusion reaction which occurs at the sun is\[\text{ 26 MeV}\] .
Here we can say that nuclear fusion is responsible for the energy output of the sun.

Hence, (B) is the correct option.

Note: Nuclear fission reactions are opposite to the nuclear fusion reaction. In a nuclear fission reaction, the heavy and unstable nuclei are broken down into smaller nuclei. Example uranium breaks down into smaller nuclei and acts as the source of energy.