Nuclear fission is defined as the process of splitting heavy unstable nucleus into two or more than two lighter nuclei. It is one of the types of nuclear reaction. It is exothermic process as huge amount of energy is released during the reaction process.
Examples of Nuclear Fission
Nuclear fission reaction of Uranium-235
When 92U235 is bombarded with thermal neutron, it splits up into 56Ba141 and 36Kr92 with the emission of 3 neutrons. There is also release of 200MeV energy per fission. Splitting of 92U235 by absorbing neutron is best example of nuclear fission reaction.
92U235 + 0n1 →56Ba141 + 36Kr92 + 30n1 + Q
Atom bomb are based on uncontrolled nuclear fission reaction.
Nuclear reactors are powerful device used to generate tremendous amount of energy with the help of fission reactions. This tremendous amount of energy is used for generation of electricity and construction purposes.
Nuclear fission in nuclear power plant is used for production of electricity. Power plants are also a type of nuclear reactor. These plants constructed in many parts of world are meant for production of electricity.
Nuclear Fission Vs Nuclear Fusion
|It is the splitting of heavy unstable nucleus into two or more nuclei.
|It is the formation of heavy stable nucleus from two or more lighter nuclei.
|It requires a projectile(i.e neutron) for reaction.
|It does not require any projectile.
|High energy of about 200MeV is produced during each reaction.
|Low energy of about 24MeV is produced during each reaction.
|The mass converted into energy is 0.1%.
|The mass converted into energy is 1%.
|It occurs at relatively low temperature and pressure as compared to fusion.
|It produces less products which are also less radioactive.
|Nuclear reactors, atom bomb etc. are based on fission reaction.
|Hydrogen bomb, reaction occurring inside sun are based on fusion reaction.
Some Nuclear Fission Reaction Equations
a) 92U235 + 0n1 →56Ba141 + 36Kr92 + 30n1 + Q
b) 94Pu230 + 0n1 →54Xe137 + 40Zr103 + 30n1 + Q
c) 7N14 + 0n1 →6C14 + 1H1
Necessary conditions for Nuclear Fission
- The binding energy per nucleons should be low.
- The nuclei should be unstable.
- The minimum mass to initiate reaction called critical mass, is required.
- There must be at least one neutron to take part in fission reaction.
Nuclear Fission Process
It is a complex process which is carried out in nuclear reactor. Many fission reactions are carried out in nuclear reactors to generate tremendous amount of energy. This tremendous amount of energy is used for constructive purposes as well as production of electricity.
When a heavy unstable nucleus is allowed to absorbs neutrons(0n1), it splits into two or more nuclei. This process releases high amount of energy along with 2 or 3 neutrons. The produced neutrons are kinetically energetic (about 2MeV) and may again take part in further fission reactions by combing with the available fissionable fuels.
Therefore, neutrons may escape from reaction to initiate a series of reaction called as chain reaction. The released energy during the process is given by Einstein’s famous equation,
Where, m= mass defect [total mass(M)-total mass of products(m)]
c=velocity of light
The uncontrolled nuclear reaction is called chain reaction. In chain reaction, the produced neutrons from reaction again and again combine with products as well as reactants (i.e fuel) until no fissionable fuel remains in the nuclear reactor device. The number and energy of neutrons produced can be controlled inside nuclear reactor as per the reaction need.
Image: showing chain reaction, Source: wikipedia
Moderator are used to slow down the highly energetic neutrons.Some examples of moderator are heavy water(D2O), graphite, beryllium etc. There are 2-types of chain reaction.
- Controlled chain reaction
- Uncontrolled chain reaction
Controlled Chain Reaction
- Rate of production of neutron in controlled reaction is equal to one.
- Multiplication factor or reproduction factor (K) is equal to one i.e K=1.
- In this type of reaction, energy liberated is less as the production of neutrons is controlled.
- It is used in constructive purposes.
- Nuclear reactors work on this principle.
Uncontrolled Chain Reaction
- It is uncontrolled reaction. i.e violent reaction.
- In this type of reaction, more than one neutron take part in reaction. This leads to series of reaction.
- Multiplication factor or reproduction factor (K) is greater than one i.e K>1.
- Large amount of energy is produced during this violent reaction.
- An atom bomb works on this principle.
Multiplication Factor or Reproduction Factor
It is the ratio of number of neutrons produced to the number of neutrons present before reaction. It is represented by ‘K’. Multiplication factor (K) = number of neutrons produced/number of neutrons present before reaction
- If K<1, the chain reaction finally stops.
- If K>1, chain reaction will continue.
Facts of Fission Reaction
- Mass converted in energy is 0.1%. The mass converting into energy can be calculated by using Einstein’s famous equation, E=mc2.
- It requires neutron as projectile to initiate reaction process.
- During nuclear fission, the sum of masses of product nuclei is slightly less than parent nucleus. This difference in mass is called defect mass. Defect mass is converted into energy.
- The minimum mass to start reaction is called critical mass.
- Nuclear fuel is the fissionable substance that is used as reactant during reaction in presence of neutron.
- The commonly used nuclear fuel are isotopes of uranium U235, U236. Isotopes of plutonium Pu239, Pu240, Pu241 and isotopes of thorium.
- The best nuclear fuel is Pu239.
- Naturally occurring Uranium consists of 2-isotopes of it. 0.7% U235 and 99.3% U238.
- Solar energy from sun is due to fusion not fission.
What is nuclear fission used for?
It is used for production of tremendous amount of energy. The produced energy during the reaction is used for production of electricity and for constructive purposes. It’s principle is also used in making Atom bombs.
Which is more powerful fission or fusion?
The energy produced during fission is very high as compared to energy produced during fusion. In fission there is production of 200MeV (for uranium-235) and in fusion there is only 24MeV (for deuterium-D2) energy produced during single reaction. Also, there are many radioactive isotopes produced during fission but only few products are formed during fusion. So, fission is more powerful than fusion.
How does nuclear fission reaction work?
When radioactive fissionable nucleus is allowed to absorb neutron, it becomes highly unstable. The unstable nucleus splits into 2 or more smaller nuclei along with production of high amount of energy. This process is carried out in a device called nuclear reactor. Nuclear reactors are safer and protects the radiations from entering the environment which are fatal for living beings as well as our environment.