What are Nuclear Reactions?

Nuclear reactions are processes in which the fundamental characteristics of a nucleus changes. They change into a completely different nucleus. These processes occur naturally in an unstable nucleus. Bombarding an energetic particle can induce nuclear reactions.  In this article, both the naturally occurring nuclear reactions are termed as radioactive decay and the induced nuclear reactions are further categorized as nuclear fission and nuclear fusion.

What are the types of nuclear reactions?

Two types of nuclear reactions are given below in detail:

• Radioactive decay
• Induced nuclear reactions

Radioactive decay

The most significant parameters used to identify a nucleus are the number of protons and neutrons. While representing an atom, Z  denotes the number of protons in a nucleus; N denotes the number of neutrons; A  denotes the sum of protons and neutrons known as the mass number.

A stable nucleus maintains definite Z and N combinations. An unstable nucleus either has excess neutrons or excess protons. Such excesses are seen in heavier nuclei, and these unstable nuclei split to emit particles and radiation. This disintegration of a nucleus into a different nucleus and different particles is known as radioactive decay.

The particles that are emitted during radioactive decay are used to classify radioactive decay. Also, note that these fast-moving emitted particles are generally termed radiation. There are three types of processes in which radioactive decay takes place:

• Alpha decay
• Beta decay
• Gamma decay

Alpha decay

In this process, the unstable nucleus emits something known as the alpha particle. This alpha particle is nothing but a pair of protons and a pair of neutrons. The remaining nucleus, which has two fewer neutrons and two fewer protons, is the new nuclei. Note that the alpha particles are helium nucleus.

The general equation for alpha decay is as follows:

${}_{z}X^A\to {}_{z}Y-1A+e^{+}+\nu$

An example of this nuclear reaction is as follows:

${}_{88}Ra^{226}\to {}_{86}Rn^{622}+H{e}_4^2$

In this example, the radium nucleus (known as the parent nucleus) breaks up into the radon nucleus (known as the daughter nucleus) and alpha particles (helium nucleus).

Another example of alpha decay using uranium-238 is visualized below. (Here, protons are represented as blue circles and neutrons in red circles.)

Beta decay

Beta decay is a type of radioactive decay. Either the neutron is transformed into a proton, or a proton is transformed into a neutron. During this process, the nucleus emits a beta particle. This beta particle emitted by this radioactive nucleus can be either an electron or positron. There are two kinds of beta decay: beta plus decay (${\beta }^{+}$) and beta minus decay (${\beta }^{-}$).

During the process of beta plus decay, a proton will disintegrate to form a neutron. This causes a decrease in atomic number. To satisfy the conservation of charges, a positron and neutrino will produce during this nuclear reaction. Positron is equivalent to the electron except in charge; it has a positive charge.

The general equation of beta plus decay is as follows:

${}_{z}X^A\to {}_{z}Y-1A+e^{+}+\nu$

An example of this nuclear reaction is as follows:

${}_{6}C^{10}\to {}_{5}B^{10}+e^{+}+\nu$

During the process of beta minus decay, a neutron will transform to produce a proton. This causes an increase in atomic number.  An electron and an antineutrino will be produced during this nuclear reaction to satisfy the conservation of charges. The general equation of beta plus decay is as follows:

${}_{z}X^A\to {}_{z}Y-1A+e^{+}+\nu$

An example of this nuclear reaction is as follows:

${}_{6}C^{10}\to {}_{7}N^{14}+e^{+}+\nu$

Gamma decay

Gamma decay is a nuclear reaction in which the emission of electromagnetic radiation of extremely high frequency occurs. Gamma decay helps the nucleus jump from a higher energy level to a lower energy level by emitting high-energy photons. The energy of these emitted photons will be in the order of MeV.

The parent and daughter nuclei are not undergoing any physical change in this nuclear reaction, similar to the other two decays. Most of the time, gamma decay occurs after alpha decay or beta decay. The daughter nuclei will be in an excited state after alpha or beta decay. This daughter nuclei will return to the ground state by emitting one or more high-energy gamma rays (photons).

An example of gamma decay of the nickel nucleus is given below:

First, consider cobalt nuclei undergoing beta minus decay to produce nickel, one electron and antineutrino.

${}_{27}C{o}^{60}\to {}_{28}N{i}^{60}+e^{+}+{\nu }^{-}$

This nickel nucleus will undergo gamma decay to attain a stable state by emission of energy in the form of photons.

${}_{28}N{i}^{60}\to {}_{28}N{i}^{60}+\gamma +1.33 \mathrm{MeV}$

Gamma rays have sources other than radioactive decay. These are lightning and thunderstorms from celestial bodies such as distant galaxies, pulsars, etc. Due to this high energy, gamma rays are extremely penetrating and harmful to biological life forms.

Induced nuclear reactions

Nuclear fission and fusion

In the first part of this topic, we studied that induced nuclear reactions are further categorized as nuclear fission and fusion. Nuclear fission is a nuclear reaction that involves the splitting of the nucleus into lighter nuclei. The combined mass of these daughter nuclei will be less than that of the parent nuclei, and the missing mass (the difference between the parent and daughter nuclei mass) will be converted into nuclear energy.

An example of nuclear fission is the splitting of uranium-235 nuclei.

${}_{92}U^{235}+{}_{0}n^1\to {}_{56}Ba^{144}+{}_{36}k{r}^{89}+2{}_{0}n^1+200 \mathrm{MeV}$

In this case, a uranium nucleus is splitting into barium and krypton nucleus by combining with one neutron. Also, the missing mass is converted into nuclear energy, and two neutrons are there in the end product.

One of the major applications of this nuclear fission is the production of electric energy from nuclear power plants.

Nuclear fusion is a nuclear reaction in which two or lighter nuclei combine to form a heavier nucleus. Like nuclear fission, this process also produces a massive amount of energy.

The second isotope of hydrogen with one proton and one neutron is deuterium. And the third isotope of hydrogen with one proton and two neutrons is tritium. The end product when these two isotopes undergo nuclear fusion will be a helium nucleus (with two protons and neutrons) and a neutron. The extra mass of this reaction will transform into kinetic energy.

This process forms energy in every star in the universe, including the sun.

Difference between nuclear fission and fusion

The two types of nuclear reactions are compared below:

Common Mistakes

The common mistake in this part is in the case of beta plus decay and beta minus decay. Electrons are used in the place of positrons and vice versa; in neutrino and antineutrino, one is used in place of the other.

Context and Applications

This topic is significant for professional exams for undergraduate and postgraduate courses, especially for

Bachelor of Science in Physics

Bachelor of Science in Biotechnology

Bachelor of Science in Atmospheric Science

Bachelor of Science in Chemistry

Master of Science in Physics

Master of Science in Atmospheric Science

Master of Science in Chemistry

Related Concepts

Radioactive elements

Radioactivity

Electromagnetic spectrum

Bohr’s atom model

Atomic orbital

Isotopes and isobars

Components of atom

Practice Problems

Q.1 According to Einstein’s equation, rest mass energy associated with 1 amu mass is?

(a) 1.6 eV

(b) 931 eV

(c) 931 MeV

(d) 9.31 MeV

Correct option: (b)

Q.2 The rest mass energy of an electron is?

(a) 1.61 MeV

(b) 0.51 MeV

(c) 1.02 MeV

(d) 1.51 MeV

Correct option: (b)

Q.3 During a nuclear reaction, some amount of mass gets converted into energy. Correct statement about total binding energy of reactants is:

(a) Less than the binding energy of products

(b) Greater than the binding energy of products

(c) equal to the binding energy of the products

(d) either greater or less than the binding energy of the products

Correct option: (a)

Q.4 Rest mass-energy relation given by Einstein is?

(a) $E=m{c}^2$

(b) $E=mc$

(c) $E=m^2{c}^2$

(d) $E=m^{2}c$

Correct option: (a)

Q.5 According to Einstein’s equation, rest mass energy of is 1×10-3 g:

(a) $9\times {10}^6 \mathrm{J}$

(b) $9\times {10}^8 \mathrm{J}$

(c) $9\times {10}^{10} \mathrm{J}$

(d) $9\times {10}^{12} \mathrm{J}$

Correct option: (c)