What is Radioactive Decay? Explained

In a previous article, we learned about radioactivity. There we learned that radioactivity is a nuclear phenomenon where the unstable nucleus tries to come to a steady state by spontaneously emitting alpha particle (𝛼), beta particle (𝛽), and gamma (𝛾) radiation. In this article, we are going to discuss radioactive decay to complete radioactivity.

If you do not know what is Radioactive decay, this article is for you. Today, I am going to unlock the details of Radioactive decay. In this article, you will know -

1. What is Radioactive decay?
2. Types of Radioactive decay
a) Alpha emission
b) Bita emission
c) Gamma emission

What is Radioactive decay?

Radioactive decay is the spontaneous breaking of an atomic nucleus. In the process of radioactive decay, very massive nuclei break into small nuclei by releasing energy (gamma radiation) and particles (alpha particle, and beta particle).

What is Radioactive Decay

The radioactive substance or radioisotope has unstable nuclei that do not have sufficient binding energy to hold the nuclei together. They want to be stable so they are continually changing to stabilize. This process will continue until a new element is formed that has a stable nucleus and is not radioactive.

Types of Radioactive decay

Radioactive decay is three types - alpha, beta, and gamma decay.

a) Alpha Decay:

If an unstable nucleus contains a number of neutrons much more than the number of protons, it may emit two protons and two neutrons tightly bound together in a single particle, known as the alpha particle.

A stream of alpha-particles called alpha-rays. In the nuclear disintegration process, the emission of these alpha-rays is called alpha decay.

Alpha-disintegration law:

If the nucleus of a radioactive element X of mass number A and atomic number Z emits an alpha-particle, a new element Y ( daughter nucleus) is formed which has a mass number equal to (A-4) and an atomic number equal to (Z-2). These changes can be expressed in the form of a reaction as follows -


When a radioactive element like uranium nucleus (U-238) emits an alpha particle, a new type of nucleus thorium (Th-234) is formed.

b) Beta Decay:

When an unstable nucleus contains more neutrons than the protons, a neutron may change into a proton by emitting an electron (for charge conservation). The electron emitted by the nucleus at a high speed is called the beta particle.

A stream of beta-particles called beta-rays. In the nuclear disintegration process, the emission of these beta-rays is called beta decay.

Beta-disintegration law:

In emitting a beta particle, the number of nucleons in the nucleus (i.e protons and neutrons) remains the same, but the number of neutrons is decreased by one and the number of protons is increased by one.

If a radioactive nucleus P with mass number A and atomic number Z emits a beta particle to form a daughter nuclei Q, then according to radioactive law the change can be represented as follows -


A radioactive carbon nucleus C-14 having 14 nucleons ( 6 protons and 8 neutrons) emits a beta particle and changes to new nucleus nitrogen N-14 having 14 nucleons (7 protons and 7 neutrons).

c) Gamma Decay:

In many cases, an alpha or beta emission is found to be followed by gamma emission. It occurs when the daughter or parent nucleus is in a state of excitation ( i.e it has an excess of energy).

This extra energy is released in the form of electromagnetic radiation known as gamma radiation. This is known as gamma decay.

The gamma rays take no mass and no electric charge from the nucleus i.e no neutrons or protons are lost, hence the nucleus does not decay into a different nucleus i.e there is no change in mass number A and atomic number Z of the nucleus in gamma emission. The emission is represented as follows -


In the alpha decay of uranium (U -238), two gamma rays of different energies are emitted in addition to the alpha particle.

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