Nuclear Reaction

A nuclear reaction is the reaction in which atomic nucleus and particles like proton, neutron etc react each other.
The reaction takes place by collide between two nuclei and form products. The nuclear reactions are spontaneous reaction. Thus the reaction involves a conversion of mass into decay products (kinetic energy).
Some are induced nuclear reaction like an alpha particle bombarding on a nitrogen nucleus.

₂He⁴ + ₇N¹⁴ → ₈O¹⁷ + ₁H¹

In the above reactions, the total mass of the elements on the left side of equation is less than the total masses of the products on the right side. To balance this or for proceeding the reaction, some kinetic energy must be supplied to the left side of reactants. This energy is responsible to complete the reaction

Types of Nuclear Reactions

There are two main type of nuclear reaction.

1. Nuclear fusion
2. Nuclear fission

Stimulated Nuclear Reactions

• The radioactive decay of many elements take place naturally but some nuclear reactions are also artificially stimulated.
• These are known as stimulated nuclear reaction.
• Two such types of nuclear reactions come in this category. One is nuclear fission and the other nuclear fusion.

Nuclear Fission Reactions

These are the nuclear reactions in which nucleus of an atom breaks into smaller parts with releasing a large amount of energy in the process. Generally the reaction is completed by firing of a neutron on the nucleus of an atom. Due to the energy of the neutron bullet, the target element (nucleus of atom) splits into two or more elements.

These produced elements are lighter than the parent atom. For example, the fission of U²³⁵ is the example of nuclear fission.

In the fission of U²³⁵, a neutron is fired on the uranium atom. By absorbing this neutron, the uranium atom releases three neutrons with large amount of energy and two daughter atoms. The daughter atoms that are produced are different. These daughter atoms are radioactive in nature and continue to decay.

Nuclear chain reactions

1. The nuclear chain reactions are the principle reactions of nuclear power.
2. In the nuclear fission reaction, if the released neutrons of nuclear fission collide with U²³⁵ nuclei, they can enhance the fission of these atoms and start a self nuclear chain reaction.
3. This chain reaction is the principle reaction of nuclear power.
4. A specific amount of energy is released from the chain reaction continues the splitting process of uranium atoms.
5. The released heat of this reaction is used to produce the electrical energy.

The nuclear chain reaction is of two types.

• Controlled nuclear chain reactions
• Uncontrolled nuclear chain reactions

Controlled Nuclear Chain Reactions

Out of the number of released neutron from nuclear, only one neutron should be strike another uranium nucleus to maintain a sustained controlled nuclear reaction.
If the neutron and uranium nucleus is less than one then the reaction will not be proceed but if it is more than one then it might cause an atomic explosion (uncontrolled). The amount of free neutrons in the reaction space is controlled by a neutron absorbing element.

In the reactors, control rods are used for the purpose of absorbing the fast moving neutrons. They are made by strong neutron absorbent material like Boron, Cadmium etc. The released neutrons possess too much of kinetic energy.

The neutron absorption reaction of boron is,

1. The moderator is used to reduce the speed of these fast neutrons.
2. The heavy water, ordinary water (light water reactors, LWR) or graphite can be used as moderator.

After slowing the speed of fast neutrons, they are produced to further the nuclear fissions. These type of reactions occurs within the nuclear reactor.
In the controlled chain fission reaction of reactor, fuel assemblies are connected and the control rods are lifted slowly to initiate the chain reaction. The fissionable atoms of fuel rod allow the reaction to proceed spontaneously in a controlled manner.

As the reaction starts, the uranium-235 nuclei become decreased while fission by-products are produced. These by-product absorbs the produced neutrons. The concentration of fissionable atoms becomes low during this situation which helps in controlling the reaction within. It helps in making only 3 to 4% of the fuel material.
The use of heavy water helps in slowing down the speed at which the nuclei react with other atoms, while the control rods are used to stop the reaction temporary.

Uncontrolled nuclear chain reaction

• The uncontrolled fission reaction takes place in the case of nuclear bomb.
• Each nuclei produce three neutrons by fission of which two neutrons are utilized in the chain reaction.
• Fissionable atom makes more than 80% of fuel in this process.
• Each nuclei in this uncontrollable manner reaction undergoes fission by two or more compared to two additional reactions.
• For example, if one atom proceeds with three other fission and then these three proceed with 9, 27, 81 fissions.
• Each of these steps completes only in fraction of seconds with large amount of heat and energy.
• This large amount of released heat energy is the main cause of expansion of the surrounding material.
• This usually results in nuclear explosion.

Nuclear Fusion

• These reactions produce one large element by the fusion of two or more elements together.
• This process takes place with releasing of energy.
• The amount of released energy of nuclear fusion reactions is very high and are also known as thermonuclear reactions.
• The common example of nuclear fusion is the formation of element helium which is produced by fusion of two isotopes of hydrogen.
• The one is deuterium (H₂) and second is tritium (H₃).
• The reaction occurs at very high temperature and pressure.
• A tokamak reactor is used to generate the magnetic field.
• The magnetic field is used to heat the hydrogen gas up to its plasma state and then bombardment is done on the plasma by a neutral beam of atom.
• Again the temperature is raised by use of radio frequency and magnetic compression.
• Under high temperature and pressure, many hydrogen nuclei are fused together to form a single atom.

Low Energy Nuclear Reactions

• This kind of reaction is also known as cold fusion.
• This idea is given for finding the alternative energy sources.
• Nuclear fusion reaction is very good source of energy. The fusion of hydrogen nuclei into helium produces a huge amount of energy.
• But these reactions are practically not easy or feasible as it requires a high temperature and pressure conditions as in Sun.
• The high temperature and pressure conditions cannot be fulfilled under lab condition and so for generating energy at low
• temperature and pressure conditions, the idea of cold fusion is generated.
• Cold fusion is produced more energy (approx 27 times) than gasoline without any kind of radioactivity and radioactive waste.
• The cost of the process is also very low (approx 1cent/ kwh) than fossil fuel.
• The cold fusion reactors are looks like electrolysis cells.
• In this process, the fusion of hydrogen into helium occurs at room temperature and is nothing but a type of electrolysis chemical process.
• For the excitation process the Palladium electrodes or Nickel electrodes are used.
• Large amounts of energy with Helium neutrons are produced.

But this process is still pending for verification and there is not much scientific explanation on the process of cold fusion.

Balancing Nuclear Reactions

In the balance nuclear reactions, the three main components should be balance between reactants and products.

1. Total atomic number (Z)
2. Mass number (A) – the mass number is also called nucleon number. This is equal to the sum of the protons and neutrons.
3. Total charge (Q) If we consider a nuclear reaction,

²⁴⁹Cf + ¹⁸O → X+4n

For determining the value of X, some steps are described below.

Step-1
Each component of the reaction should be written in the form of these three components. These are atomic mass, mass number and charge. So the equation is

²⁴⁹₉₈Cf⁹⁸⁺ + ¹⁸₈O⁺⁸ → ^b_aX^c +4¹₀n⁰

Step-2
Next step is balanced of atomic number, mass number, and total charge.

• Atomic number is equal to number of protons.

So, 98 + 8 → a + 4 (0)

So a = 98+ 8 - 0 = 106

As the Z= 106, so by periodic table,
it is trans uranium element Seaborgium (Sg).

• Now the mass number balance,

249 + 18 → b + 4 -----(1)

So,
b = 249 + 18- 4 = 263

As mass number = sum of the protons and neutrons.

Number of neutrons = 263 - 106 = 157

This shows that Seaborgium have 106 protons and 157 neutrons.

• Now the charge balance shows that,

98 + 8 → c + 4 (0)

So, c = 98 + 8 - 0 = 106

This is the charge of unknown species
and thus the unknown component is ²⁶³₁₀₆Sg¹⁰⁶⁺.

The balance nuclear reaction is ²⁴⁹₉₈Cf⁹⁸⁺ + ¹⁸₈O⁺⁸ → ²⁶³₁₀₆Sg¹⁰⁶⁺ + 4 ¹₀n⁰