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Tamil Nadu Board of Secondary EducationSSLC (English Medium) Class 10
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Nuclear Fission

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Estimated time: 8 minutes
CBSE: Class 12

Introduction

When the study of nuclei goes beyond natural radioactive decay and includes reactions produced by bombarding nuclei with particles such as protons, neutrons, and alpha particles, new nuclear possibilities emerge.

One of the most important neutron-induced nuclear reactions is fission.

CBSE: Class 12

Definition: Nuclear Fission

Nuclear fission is a neutron-induced nuclear reaction in which a heavy nucleus, such as uranium-235, breaks into two intermediate-mass nuclear fragments.

CBSE: Class 12

Main Fission Reaction

When uranium-235 is bombarded with a neutron, it first forms uranium-236 and then splits into two lighter nuclei with the release of neutrons.

\[_0^1n+_{92}^{235}U\to_{92}^{236}U\to_{56}^{144}Ba+_{36}^{89}Kr+3_0^1n\]

This is one example of a fission reaction.

CBSE: Class 12

Other Possible Fission Products

The same neutron-induced reaction can also produce other pairs of intermediate-mass fragments.

\[_0^1n+_{92}^{235}U\to_{92}^{236}U\to_{51}^{133}Sb+_{41}^{99}Nb+4_0^1n\]

Another example is:

\[_0^1n+_{92}^{235}U\to_{54}^{140}Xe+_{38}^{94}Sr+2_0^1n\]

Important Observation

The same uranium nucleus can split into different pairs of intermediate-mass fragments.

CBSE: Class 12

Outcomes of Nuclear Fission

  • The fragment products formed during fission are radioactive nuclei.
  • These radioactive nuclei emit beta particles in succession to achieve stable end products.
  • The disintegration energy in fission events first appears as the kinetic energy of the fragments and neutrons.
  • Eventually, this energy is transferred to the surrounding matter and appears as heat.
CBSE: Class 12

Energy Released in Fission

The energy released, or Q value, in the fission reaction of nuclei like uranium is of the order of 200 MeV per fissioning nucleus.

Estimation of Energy Release

Consider a nucleus with mass number 240 breaking into two fragments, each with mass number 120.

  • Binding energy per nucleon for the nucleus with A = 240 is about 7.6 MeV.
  • Binding energy per nucleon for each fragment with A = 120 is about 8.5 MeV.
  • Therefore, the gain in binding energy per nucleon is about 0.9 MeV.
  • Hence, the total gain in binding energy is: 240 × 0.9 = 216 MeV

So, the total gain in binding energy is about 216 MeV.

CBSE: Class 12

Applications

  • Nuclear Reactors: The source of energy in nuclear reactors, which produce electricity, is nuclear fission.
  • Atom Bomb: The enormous energy released in an atom bomb comes from uncontrolled nuclear fission.

Related QuestionsVIEW ALL [22]

How long can an electric lamp of 1000 W be kept glowing by fusion of 2.0 kg of deuterium? Take the fusion reaction as:

\[{}_{1}^{2}\mathrm{H}+_{1}^{2}\mathrm{H}\rightarrow{}_{2}^{3}\mathrm{He}+\mathrm{n}+3.27\mathrm{MeV}\]

Calculate and compare the energy released by a) fusion of 1.0 kg of hydrogen deep within Sun and b) the fission of 1.0 kg of 235U in a fission reactor.

Distinguish between nuclear fission and fusion giving an example of each.

Calculate the energy that can be obtained from 1 kg of water through the fusion reaction 2H + 2H → 3H + p. Assume that 1.5 × 10−2% of natural water is heavy water D2O (by number of molecules) and all the deuterium is used for fusion.

(Use Mass of proton mp = 1.007276 u, Mass of `""_1^1"H"` atom = 1.007825 u, Mass of neutron mn = 1.008665 u, Mass of electron = 0.0005486 u ≈ 511 keV/c2,1 u = 931 MeV/c2.)

As compared to 12C atom, 14C atom has

If three helium nuclei combine to form a carbon nucleus, energy is liberated. Why can't helium nuclei combine on their own and minimise the energy?

Suppose India had a target of producing by 2020 AD, 200,000 MW of electric power, ten percent of which was to be obtained from nuclear power plants. Suppose we are given that, on an average, the efficiency of utilization (i.e. conversion to electric energy) of thermal energy produced in a reactor was 25%. How much amount of fissionable uranium would our country need per year by 2020? Take the heat energy per fission of 235U to be about 200MeV.

In a typical fission reaction, the nucleus is split into two middle-weight nuclei of unequal masses. Which of the two (heavier or lighter) has greater kinetic energy? Which one has greater liner momentum?

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