Radioactivity Unit of Measurement and Types of Radioactivity Upsc

Units of Radioactivity

There are four common units of measurement in Radioactivity in nuclear Physics. They are Curie, Rutherford, Becquerel, and Roentgen.


It is defined as the quantity of a radioactive substance that undergoes 3.7 x 10 10 disintegrations per second. Referred from 1 gm of radium 226.

Rutherford (RD)

It is defined as the number of radioactive substances that undergoes 10 6 disintegrations per second.  1RD = 10 6 disintegrations per second.

Becquerel (Bq)

SI unit of Radioactivity is Becquerel. It is the number of disintegrations per second.

Roentgen (R)

The radiation exposure of Gamma and X-Rays is measured by a unit called Roentgen. We define one Roentgen as the quantity of the radioactive substance that generates a charge of 2.58 x 10 -4 coulomb in 1 kilogram of air under a standard condition of pressure, temperature, and humidity.

What is Radioactivity?

For some elements, the Nucleus is unstable. These unstable Nuclei undergo nuclear decay to become stable nuclei.

During this process called Nuclear reaction, these elements emit harmful radiations and some elementary particles.

This phenomenon of elements that undergo a nuclear reaction to make unstable nuclei into more stable nuclei, with the emission of alpha, beta, and gamma rays is called Radioactivity.

The elements that show such Radioactive properties are called Radioactive elements.

Natural Radioactive

Some elements show radioactive properties naturally, with the human touch. We call this phenomenon Natural Radioactivity.

This element that shows natural radioactivity usually has an atomic number of 83. Example: Uranium, Radium, etc.

Only two elements below the atomic number of 83 identified so far show Natural Radioactivity. That is Technetium (Tc) with atomic number 43, and Promethium (Pm) with atomic number 61.

 As of now, we identified 29 radioactive substances, most it is rare metal and transition metals.

Artificial Radioactivity or Induced Radioactivity

The phenomenon in which lighter elements such as Boron, Aluminium is made radioactive element by induced methods or with man-made methods is called Artificial Radioactivity or Induced Radioactivity.

This kind of nuclear reaction was found by Irene Curie and F.Joliot in 1934. When radiation such as Alpha rays from Uranium allowed emitting on the lighter elements such as Aluminium. The bombarding takes place.

This makes Aluminium emit elementary particles naturally in Uranium. The nucleus that undergoes reaction and disintegration is the Parent Nucleus, and the result of disintegration is the Daughter Nucleus.

We call the practice that is used to induce or start the radioactivity in the lighter element called Projectile. Here Uranium is the projectile.

The particle that is produced because of disintegration from the parent nucleus is called the Ejected Particle.


In this post, we have discussed the Radioactivity Unit of Measurement and types of radioactivity such as Natural or Induced Radioactivity. This is useful for Upsc, Tnpsc and other state service exams.

* * All the Notes in this blog, are referred from Tamil Nadu State Board Books and Samacheer Kalvi Books. Kindly check with the original Tamil Nadu state board books and Ncert Books.