Radioactivity class 12th - Alpha (α), Beta (β) and Gamma (ɣ) decay


Have you seen those movies where some top secret experiment goes wrong resulting in some kind of radioactive explosion in the area ? but are all the radioactive explosions the same ?

Even in radioactivity, there are many kinds of radioactive decays. So in this article, we are going to uncover all about radioactivity such as radioactive radiation, types of radioactive decays, laws of radioactivity and many more things regarding radioactivity for class 11th and 12th students.

An unstable nucleus of atoms losses some energy to form a stable nucleus. This phenomenon of energy loss by nuclei is called Radioactivity. 

What is radioactivity ?

In nature, some elements containing atoms tend to have unstable nuclei and in order to get stable nuclei, they exhibit the phenomenon known as radioactivity in which energy is lost due to radiation emitted from the unstable nucleus of atoms.

Now, how will you decide whether the nucleus is stable or not ? Let me tell you!

Stability of the nucleus mainly depends on two main factors:
  1. Force of repulsion (Electrostatics). 
  2. Force of attraction. 
Both these forces are extremely powerful forces in nature. 

Force of attraction is the force that binds the nucleus together and the force of repulsion is due to the phenomena of electrostatics. 

You may have heard it somewhere: 

"Like charges repel each other and unlike charges attract"

This means, electric charge the "like" ones tend to repel each other and as the nucleus of an atom consists of positive charges, from the law of electrostatics there is some repulsion as well between them

Coming to the main point, So these two forces decide whether a nucleus is stable or not. The balance between both the forces (attraction and repulsion) keeps the nucleus stable but as the size of the nucleus increases, chances of an unstable nucleus increase due to an increase in the mass of the nucleus which disturbs the balance between the forces. 

Therefore you will notice, elements that show radioactivity tends to have higher atomic mass. For example, Plutonium (244 μ) and Uranium (238.028 μ) are extremely unstable and therefore they show radioactivity. 

This phenomenon of radioactivity was found by Henri Becquerel although that also by an accident. Before the discovery of radioactivity, people used to use crockery made from uranium due to its glowing property without knowing how harmful it was.

Watch this video if you want to know about how Uranium was discovered and why it was an accident:


Not only that, you now may be thinking that radioactivity is only of one type but there's more. With research, it's been found that radioactivity is also of many different types depending upon various factors such as emission which we will see further in this article.

For time being, only remember that there are three types of radioactivity:
  1. Alpha decay 
  2. Beta decay
  3. Gamma decay

Radioactive radiation:

As I mentioned earlier, radioactive decay is also categorized into three different types, 1. Alpha (α) decay 2. Beta (β) decay and 3. Gamma (ɣ) decay.

We will learn about them as well but for better understanding and concept. First look at these chemical equation, examples of α, β, and ɣ decay.

Radioactive reactions

So these equations show, the radioactivity of alpha (α), beta (β), and gamma (ɣ) decay. Now there are some laws as well of radioactivity. Which is essential to know before knowing alpha, beta, and gamma decay.

Laws of radioactivity:

There are some natural laws of radioactivity which you need to know for clear understanding and concept building. These laws are given in the table below:

Laws of radioactivity
1. Radioactivity is depended on the conservation of charges.
2. The rate of decay of the nucleus is not dependent on temperature and pressure.
3. Radioactivity is the result of the decay of the nucleus.
4. Physical and chemical properties are different for the daughter nucleus and mother nucleus.
5. The energy emitted from radioactivity is accompanied by alpha, beta, and gamma particles.
6. Rate of decay is also dependent on a number of atoms that are present at that time.

Radioactive decays:

Now you know all the necessary information needed before learning alpha (α), beta (β), and gamma (ɣ) decay.

Let me remind you again, elements with unstable nucleus show radioactivity to form the stable nucleus and in all these three types of decays, this transformation from the unstable nucleus to the stable nucleus is going to be the same in radioactivity.

So without wasting much of your time, let's start with alpha (α) decay.

Alpha decay (α):

When unstable atomic nuclei emit a helium nucleus to get a stable configuration, this kind of radioactive decay is called as alpha (α) decay.


This ejected alpha particle consists of four nucleons (2 protons and 2 neutrons). This emission reduces the number of protons and neutrons in the parent nucleus which brings it's to the more stable configurations.

The alpha particle is identical to the helium atoms. You may recall that the alpha particle was used in one of the famous science experiments, gold foil experiment by Rutherford as he was the one who first observed alpha decay in the elements.

Due to alpha particles getting emitted out in radioactivity, the atomic number of radioactive elements changes with 2 atomic numbers lesser and has 4 mass numbers lower.

For example, refer to this reaction of alpha decay where uranium gets changed to thorium.


So, the transformation of the nucleus in alpha decay can be written as:


Now, this was only the one example, but you may be wondering where actually this alpha decay is happening ? Is there any procedure of alpha decay or it happens automatically ? i.e What is the occurrence of alpha decays ?

So let's clear this query as well.

Occurrence of alpha decays:

Alpha decay occurs in the heaviest elements. The nucleus of these elements should be large enough as well as unstable enough to go in spontaneous (occur by themselves) fission type of reaction.

The alpha particle which ejected out travels approx at the speed 10% of the light which is around 2, 997, 924 580 m/s which is actually insane.

Alpha decay

Alpha particle contains the energy of 5MeV and has a charge of +2 because there is no electron present in them.

One thing to keep in mind is that the alpha particle reacts vigorously with its surroundings because of their charge and high mass and therefore they don't last long but this does not mean that they are not harmful. In fact, alpha particles react more violently when comes in contact with the human body. 

Due to their high ionizing power, it can even break tissues inside a body. Exposure to alpha radiation for a long period of time can cause blister and burns as well.

Burn due to radiation

Beta decay (β):

Beta decay is a kind of radioactivity in which either a proton is transformed into a neutron or neutron is transformed into a proton. By this, an unstable nucleus gets closer to become a stable nucleus.

During this transformation, the nucleus also emits either an electron or a positron. This happens to follow the law of conservation of charge because a neutron is transformed into a proton or visa-versa.

Depending upon the transformation, either an electron or positron is been released. Therefore beta decays are also further categorized into Beta-Plus decay and Beta-Minus decay.

Beta-Plus decay (β+):

In Beta Plus decay, proton gets transformed into a neutron which causes a decrease in an atomic number of a radioactive sample. Due to this transformation nucleus experiences a loss of proton but instead gains one neutron.

In order to maintain conservation of charge, during Beta-Plus decay, a positron is released which is equivalent to an electron in all the aspects such as mass but the only difference between a positron and electron is that positron is a positive charge.

Beta-Minus decay (β-):

In Beta-Minus decay, a neutron is transformed into a proton which causes an increase in an atomic number of radioactive samples.

During this process, to maintain the conservation of charge, nucleus produces an electron and an antineutrino. Don't worry, antineutrino is just the antimatter counterpart of neutrino. You don't need to dig that much in deep.

Beta Minus decay

Both neutrino and antineutrino are neutral particles so this maintains the law of conservation of charge as well.

Gamma decay (ɣ):

Gamma decay is basically the emission of electromagnetic radiation of extremely high energy and therefore nucleus is giving out the excess amount of energy in order to get stabilized.

As you may already have known that, atoms have various energy level so thus nucleus. Nucleus also has different energy levels and in gamma decay, the nucleus drops from high energy level to low energy level by emitting high energy photons.

Unlike alpha or beta decay, this time nucleus is not going into any physical changes and therefore daughter and parent nuclei both are the same, but why they don't go under any physical changes ?

Because most of the time, gamma decay occurs after alpha or beta decay. Alpha or Beta decays leave the daughter nuclei in the excited state and in order to get back to the ground state, daughter nuclei emit one or more high energy gamma rays.

Gamma decay

Uses of radioactivity:

So this was all about basics of radioactivity you needed to know. So now let's end this article with what are the uses and application of all these things and radioactivity which you have just learnt.

So here are the applications of radioactivity:
  1. In nuclear reactors to generate electricity and a source of energy.
  2. To study living organisms by using tracers which are radioisotopes.
  3. Sterilization of medical instruments and foods to kills microorganism. 
  4. A dentist uses radiation to X-ray teeth. 
  5. In many industries, radioactivity is used to determine whether the material is fit for application or not. 

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