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JEE Main 2026 Preparation: Question Papers, Solutions, Mock Tests & Strategy Unacademy » JEE Study Material » Physics » Law of Radioactive Decay

Law of Radioactive Decay

This article comprises the study material notes on the Law of radioactive decay. Understand the concept of radioactivity, Law of radioactive decay, types of radioactivity decay and other related topics in detail.

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Introduction 

Initially coined in the year 1896, the phenomenon of radioactivity is exhibited by the atom’s nucleus as a result of nuclear instability. In simple terms, radioactivity can be described as a process through which the unstable atom’s nucleus tends to lose its energy after emitting radiation. A small quantity of Uranium compound was packed in the black paper and placed in a drawer that contained photographic plates. When examined, it was recorded that the plates had been exposed to some exposure which was later termed radioactive decay. There are mainly three types of radioactive decay. These include the Alpha decay, beta decay, and gamma decay which we will be studying in this article. 

Today, in this article on the Law of radioactive decay, you will get detailed information on the half life of radioactive elements, Types of radioactivity decay, their properties, and other related topics. So, without further ado, let us get started with the Law of radioactive decay in the physics study material.

Explain the Law of radioactivity decay

According to the radioactivity decay law, the probability per unit time that the nucleus will most likely decay remains the same and independent of time. radioactive disintegration is impossible to forecast due to the nucleus’s smaller size than the atom and the magnitude of the electromagnetic force. 

The atomic nucleus is located in the centre of the atom, which is shielded from the environment by surrounding electrons. As a result, the study of the element’s environment-independent degradation. 

In mathematical terms, the Law of radioactivity decay is described as –

A∝N

A=λN (mathematical representation)

A represents the no. of decays per unit time of a radioactive sample

N represents the total number of particles in the sample

λ is the constant of proportionality or decay constant

Types of the Radioactivity Decay

There are mainly three different types of radioactivity decay. These are as follows – 

  • Alpha Decay

Alpha decay can be described as the phenomena of alpha particles emission from the radioactive nucleus. The alpha particles hold the least amount of penetration power whereas the highest ionisation power. 

  • Beta Decay

Mostly, the beta particle is known as the electron; however, it can be positron as well. In case the overall reaction includes electrons, the neutrons are shredded by the nucleus one after another. Also, the proton number keeps on increasing. Beta particles are highly energetic which are present inside the nucleus. 

  • Gamma Decay

The photon is emitted in case the electron jumps from extremely high energy to extremely low energy levels. Similarly, it happens in the nucleus as well, which gives rise to the gamma rays. The gamma rays are the uncharged particles and have electromagnetic radiation. Gamma particles have the greatest penetrating power. 

Properties of Alpha, beta, and Gamma 

Although most of the properties of apha, beta and gamma have already been discussed. Here is the detailed comparison between the properties of alpha, beta and gamma radiations:

Property 

α ray

β ray

γ ray

Particle’s nature 

The alpha rays are positively charged particles that consist of 4He2  nuclei.

The beta rays are negatively charged. Note these are also known as electrons. 

The gamma rays are uncharged particles and have electromagnetic radiation.

Charge on the particles 

The alpha rays have two units of positive (+) charge. This means it is +2e.

The beta rays consist of only one unit of negative charge. This means it is e–.

The gamma rays contain absolutely no charge. 

Mass of the particles 

The mass of the alpha particles is 6.6466 × 10-27 kg.

9.109 × 10-31 kg is the mass of the beta particles.

The gamma rays have absolutely no mass. 

Range of the particles 

Alpha rays are ~10 cm in air. It can be stopped by 1 mm of aluminium metal sheet.

Beta rays are up to a few meters in the air. It can be stopped easily using a thin layer of aluminium mass.

Gamma rays are several metres in the air. It can be stopped through a thick lead layer. 

Natural sources of the particles 

The alpha rays are naturally radiated through the natural radioisotopes e.g. 236U92.

The beta rays are naturally radiated through the cobalt radioisotopes e.g. 68Co29.

The gamma rays form excited nuclei. 

Conclusion 

With this, we end our study material on the Law of radioactive decay. In this Introduction Law of radioactive decay, we studied that the loss of elementary particles from an unstable nucleus causes radioactive disintegration, transforming the unstable material into a more stable element. There are three types of radioactive decay. These include alpha decay, beta decay, and gamma decay.

 

We covered Introduction to the Law of radioactive decay, types of radioactive decay, a brief introduction of all three types of decay and other related topics in detail. We hope the Law of radioactive decay study material must have helped attain a greater understanding of this topic.

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Frequently asked questions

Get answers to the most common queries related to the IIT JEE Examination Preparation.

Mention two properties of alpha rays.

Ans: Here are the two properties of alpha rays-  ...Read full

What do you understand about alpha decay?

Ans: The Alpha decay can be described as the phenomena of alpha particles emis...Read full

How to determine whether it’s Alpha radiation?

Ans: To determine the Alpha, Beta, or Gamma radiation, the first step is to determine the count rate at the backgrou...Read full

Which radiation Is the Most Dangerous?

Ans: Alpha radiations are the most dangerous or hazardous among the other three forms of radiation because cells rap...Read full

Mention two properties of beta rays.

Ans: Here are the two properties of beta rays- ...Read full

Ans: Here are the two properties of alpha rays- 

  • The alpha rays are positively charged particles that consist of 4He2 nuclei.
  • The mass of the alpha particles is 6.6466 × 10-27 kg.

Ans: The Alpha decay can be described as the phenomena of alpha particles emission from the radioactive nucleus. 

Ans: To determine the Alpha, Beta, or Gamma radiation, the first step is to determine the count rate at the background, then source the count rate without any absorber. Position a thin sheet between the monitor and the source, in case the counts get reduced, it emits the alpha particles.

Ans: Alpha radiations are the most dangerous or hazardous among the other three forms of radiation because cells rapidly absorb them. Gamma and Beta radiation are less hazardous compared to alpha radiations because they are easily passed through the cells and absorbed less by cells.

Ans: Here are the two properties of beta rays-

  • The beta rays are negatively charged. Note these are also known as electrons.
  • 9.109 × 10-31 kg is the mass of the beta particles.

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