Notes : Nuclear Fission: Definition, Reaction, Energy Released and Applications

Defination of Nuclear Fission 

Nuclear fission is the process in which a heavy nucleus splits into two or more lighter nuclei when bombarded by a neutron. A large amount of energy and neutrons are released during this process.

Example of Nuclear Fission

When a slow neutron strikes a Uranium-235 nucleus, it first forms an unstable Uranium-236 nucleus. This unstable nucleus then splits into two lighter nuclei.

Nuclear Reaction

$${}^{1}_{0}n + {}^{235}_{92}U \rightarrow {}^{236}_{92}U$$ $${}^{236}_{92}U \rightarrow {}^{144}_{56}Ba + {}^{89}_{36}Kr + 3\,{}^{1}_{0}n + \text{Energy}$$

Important Points About Nuclear Fission

• Uranium-235 is a fissile material.
• Nuclear fission is a neutron-induced reaction.
• Two or more lighter nuclei are formed.
• 2 to 4 neutrons are released.
• The fission fragments are radioactive.
• They emit beta particles and eventually become stable.

Energy Released in Nuclear Fission

The energy released during fission is called the Q-value.

$$Q \approx 200 \, \text{MeV}$$

Thus, each fission of Uranium-235 releases approximately 200 MeV of energy.

Numerical: Estimation of Fission Energy

Consider a heavy nucleus of mass number 240 splitting into two nuclei each having mass number 120.

Given Data

Binding energy per nucleon of parent nucleus:

$$E_{bn} = 7.6 \, \text{MeV}$$

Binding energy per nucleon of daughter nuclei:

$$E_{bn} = 8.5 \, \text{MeV}$$

Step 1: Increase in Binding Energy per Nucleon

$$\Delta E_{bn} = 8.5 - 7.6$$ $$\Delta E_{bn} = 0.9 \, \text{MeV}$$

Step 2: Total Energy Released

$$\text{Energy Released}=240 \times 0.9$$ $$=216 \, \text{MeV}$$

Result

$$\boxed{\text{Energy Released}=216 \, \text{MeV}}$$ $$\approx 200 \, \text{MeV}$$

Therefore, approximately 200 MeV of energy is released during one fission reaction.

Form of Released Energy

Initially, the released energy appears as:

• Kinetic energy of fission fragments
• Kinetic energy of emitted neutrons

Later, this energy is converted into heat energy.

Applications of Nuclear Fission

Nuclear Reactors

Controlled nuclear fission is used to generate electricity in nuclear power plants.

Atomic Bombs

Uncontrolled nuclear fission releases enormous energy and is used in atomic bombs.

Key Points for Revision

• Heavy nucleus splits into lighter nuclei.
• Uranium-235 is commonly used for fission.
• About 200 MeV energy is released per fission.
• Neutrons released during fission can produce a chain reaction.
• Fission products are radioactive.
• Controlled fission is used in nuclear reactors.
• Uncontrolled fission is used in atomic bombs.

Frequently Asked Questions (FAQs)

1. What is Nuclear Fission?

Nuclear fission is the splitting of a heavy nucleus into lighter nuclei with the release of energy and neutrons.

2. Which isotope is commonly used in Nuclear Fission?

Uranium-235.

3. How much energy is released during one fission of Uranium-235?

Approximately 200 MeV.

4. Why are fission products radioactive?

Because they are unstable and emit beta particles to become stable.

5. What is the source of energy in nuclear power plants?

Controlled nuclear fission reactions.