Nuclear chain reaction - chain reaction discovery and types



Nuclear chain reaction, discovery and types. Nuclear chain reactions  are the reactions where we obtain nuclear energy , through the  process of nuclear fission. The energy  released in nuclear power plants by nuclear fission process are utilized by the people for domestic purposes as well.

Neutrons generated in these reactions, by the fission process ,which causes fission in other atoms and so on . These reactions generally occur with isotopes which are heavier such as uranium-235 ,an isotope of uranium , where there is a continuous release and absorption of neutrons .

"Critical mass" : mass of uranium 235 that is required to produce a particular nuclear reaction. 

What is a Nuclear reaction? 

The transformation of one stable nucleus into the another nucleus by bombarding the former with a suitable high energy is called a nuclear   reaction.

The nuclear reaction is symbolically represented as :

       ZXA  + 2He4 →    z+2CA+4    →       Z+1YA+3 + 1H1 + Q

Rutherford was the first scientist to perform an experiment in 1919 on artificial transmutation of elements. 

 Law of conservation of total energy , Law of conservation of linear momentum, Law of conservation of charge and conservation of number of nucleons are followed in each type of Nuclear chain reaction.

Let me first provide you some information about, what happens in a nuclear reaction :

The fission reaction of ₉₂U²³⁵  is represented as :

                                     ₉₂U²³⁵ + ₀n¹ → ₅₆Ba¹⁴¹ + ₃₆kr⁹² + 3 ₀n¹ + 200Mev

in this fission reaction of uranium 235 , as it is clear from the reaction that three secondary neutrons are produced. These three secondary neutrons may bring about the fission of three more uranium 235 nuclei and produce 9 neutrons. These neutrons may bring about the fission of 9 more uranium nuclei and so on.

Thus there occurs continuous reactions called as Nuclear chain reactions. It should be noted that in this case a huge amount of energy will be released.

Nuclear chain reaction, fission chain reaction
Nuclear chain reaction

The energy produced by the nuclear fission process can be utilized for a peaceful purposes, if we can have a control over this reaction. This led to the construction of a nuclear reactor.

However,  if the nuclear reaction cannot be controlled, then the energy released during the process of nuclear fission will bring a disastrous effects. This led to the discovery of an atom bomb.

points to consider :

1) Leakage of neutrons from the system :

Some of the secondary neutrons, which are produced during the nuclear fission reaction may escape out of the system. This leakage may be stopped by properly designing the system.

2) Absorption of neutrons by impurities :

The secondary neutrons which are produced during the nuclear fission process may be absorbed by impurities which are not fissionable. This loss may be reduced by having a fissionable material free from impurities.

3) Absorption of neutrons by U-238 :-

If we think of a natural uranium it consists of three isotopes that is ₉₂U²³³, ₉₂U²³⁵,  ₉₂U-238. Their percentage is 0.006% , 0.714% and 99.28% respectively.

Again it is found that uranium -238 is fissionable only with fast neutrons and it absorbs slow neutrons, whereas uranium -235 is fissionable only with slow neutrons.

Since the percentage of uranium -238 in natural uranium is very large, hence neurons collide with uranium - 238. Due to this, neutrons are slowed down on collision with uranium - 238 isotope and hence these slowed neurons are absorbed by uranium - 238. That is why, chain reaction in natural uranium can not occur. 

To sustain the process of nuclear chain reaction, uranium-235 is first of all separated from the natural uranium. The uranium 235 so obtained after this process is called an "enriched uranium ".The enriched uranium is bombarded with slow neutrons and hence we can sustain chain reaction. 

4)  Reproduction Factor :

The reproduction factor is defined as the ratio of the rate of production of neutrons to the rate of  loss of  neurons due to leakage and absorption. 

                                 K =  production / loss 

  If K = 1 , the chain reaction will be steady. This chain reaction is also called as controlled chain reaction.  The size of the fissionable material (uranium)  used in this case is said to be critical size.

 If K > 1 , then the reaction in this case is also called uncontrolled chain reaction. The size of the material in this case is super critical. 

If K < 1 , the chain reaction would gradually comes to halt. The size of the material used is said to be subcritical.

Discovery :

An Italian born Nobel Prize winning physicist named Enrico Fermi ,who directs and controls the first nuclear chain reaction in his laboratory. when he succeeded in his experiment, he sent a coded message  “The Italian navigator has landed in the new world ”to president Roosevelt. 

A full-time professor of physics at the University of Florence  named Enrico Fermi  focused on producing the radioactivity by breaking neutron speed which were derived from the radioactive beryllium. Fermi remained skeptical about his discoveries. 

He was awarded with Nobel Prize in 1938 , for the identification of a new radioactive elements. The persons dealing with national security are restricted to travel abroad.

Enrico Fermi was permitted by government to go Italy and receive Nobel Prize . 
His wife " Laura " a Jew and both never returned to Italy, due to the fascist regime of Mussolini.

Enrico Fermi performed many of his experiments with Danish born physicist named Neil Bohr, Who suggested the possibility of a nuclear chain reaction.  when he immigrated to New York City.

when Enrico Fermi and others saw the military possibility of such an explosive power, he wrote a letter to president Roosevelt warning against German atomic bomb. The letter was finally signed and delivered by Albert Einstein, which resulted in American program to create it's own atomic bomb. 

Controlling the chain reaction was important . If the balance between produced and absorbed neutrons was not correct, it would not proceed any reaction or it may lead to disastrous consequences. 

Types of nuclear reaction:

There are two types of nuclear reaction named Fission Chain reaction and Fusion chain reaction. 

Nuclear fusion:

The process of fusing two or more light nuclei to form a single nucleus, with the release of a large amount of energy.

Nuclear chain reaction, fusion chain reaction
fusion chain reaction

Some of the examples of nuclear fusion reactions are :-

                                          ₁H² + ₁H² → ₂He⁴ + 24Mev 

In nuclear fusion the energy released is much more than energy released during nuclear fission.  
clear fusion takes place under the conditions of a very high temperature and pressure.

These conditions are met with in the interior of the sun and are not easy to arrange in laboratory. 

 Nuclear fission:

The process of splitting of a heavy nucleus having atomic number greater than 230 , into two or more lighter nuclei, with the release of a large amount of energy.

Bombarded of U-235 with thermal neutrons, splits into Ba-141 and kr-92  with the emission of three more neutrons along with the release of 200 M e v of energy per fission. 

The neutrons produced after fission reaction are called secondary neutrons. 
The reaction is given below :

                                   ₉₂U²³⁵ + ₀n¹ → ₅₆Ba¹⁴¹ + ₃₆kr⁹² + 3 ₀n¹ + 200Mev


The energy released in the fission reaction appears in the form of gamma rays,  Kinetic energy of fission fragments and the released neutrons .

According to researches, U-235 of uranium on complete fission releases energy equivalent to burning of about 600 tonne of coal. 


The article has discussed about Nuclear  chain reaction and the types of Nuclear chain reactions . It has also discussed about the discovery of nuclear chain reaction and has provided you an exact information related to it.

I hope the article was helpful for you and had helped you a lot . Please share this article to other people on social media , so that they can also get some benefits from reading the article about Nuclear chain reactions

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