Nuclear chain reaction
By: Tajamul Fayaz
Tags: Science, Nuclear Weapons, NASA, Space, Nuclear

Introduction:

Nuclear chain reactions, 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.

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👉young's double slit experiment

👉: Rutherford's nuclear model

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

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.

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points to consider for a Nuclear chain reactions:

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 …..http://www.themegaguide.com/2020/05/Nuclear-chain-reaction5.html