Radioactivity

What is Radio activity?

In 1 March, 1896 Henry Bacquerel (French) was accidentally found that certain substances (Urnanium containing minerals) spontaneously emitting the invisible  light radiation and effect on photographic plate. This activity of substance was termed as radioactivity.

Radioactivity-

The phenomenon of spontaneous emission of certain invisible radiation by some elements are called radioactivity.

The elements which have radioactivity properties are called radioactive elements and the emitted radiation is called radioactive radiation.

The radioactivity are classified as two types

1. Natural Radio activity- The substance which emits radiation by itself without the help of external agency.

2Artificial Radioactivity- The substance which does not emit radiation by itself but emits radiation           with the help of external agency.

Types of Radioactive radiation

1897 Ernest Rutherford (Newzeland) was conducted an experiment and found  that the radio active substance posses  three type of  Rays (radiation) and named them as greek alphabate alpha,beta and gamma.

One type of radiation deflected towards negatively charged electrode , it consists of negatively charged particles called α particle.

Second type of radiation deflected towards positively charged electrode ,it consists of negatively charged particles called β particle

Third type of radiation was undeflected and strike the photographic plate straight. It consists of particle having no charge and called γ particle.

Proerties of α ,β , γ Rays(Radiations).

α rays:

• It carries two unit positively charge particle and has mass equal to 4 times of hydrogen atom. So,it can be reprent as He²⁺
• It moves with 1/10 th velocity of light.
• Due to large mass this particle ,it has large kinetic energy
• Its penetration power is lower than other two particle.it can be stopped by an aluminium foil less than 0.1mm of thickness.
• It has ionisation power as compared other two rays.
• It affects on photographic plate

β rays:

• It carries one unit negatively charge particle and has mass equal  to 1/1835th  the mass of a hydrogen atom.
• Velocity is same as that of light.
• Due to high velocity and small mass,it has high penetration power than alpha particle.it can be stopped by an aluminium foil about 5 mm thick.
• Due to small mass its kinetic energy will be lesser and ionising power will less as compared to alpha particle.
• It affects on photographic plate lesser than alpha particle

γ Rays:

• The gamma particle has no charge and no mass.
• It travels with the light velocity
• Due to short wavelength or high frequency they have high  penetrating power.it can be able to penetrate 25cm of iron sheet
• Weak ionisation power
  • Very little effect on photo graphic plate.

    Unit of Radioactivity

The SI unit of radioactivity is the becquerel (Bq). One becquerel is defined as one radioactive decay (or disintegration) per second.

Other units of radioactivity include:

• Curie (Ci): A non-SI unit, originally based on the activity of one gram of radium-226. 1 Curie = 3.7 × 10¹⁰ disintegrations per second (dps).

• Rutherford (Rd): 1 Rutherford = 10⁶ disintegrations per second.

• Older units: Millicurie (mCi), microcurie (μCi), and picocurie (pCi) are smaller divisions of the curie and often used in practical settings.

• SI unit: Becquerel (Bq) = 1 decay per second

• Common practical unit: Curie (Ci) = 3.7 × 10¹⁰ decays per second

Dr.Dash Srimanta

Hi…! Currently, I am working as an  Professor at Department of Pharmaceutical Chemistry(H.O.D),The Pharmaceutical College, Barpali, Odisha. I have more than 19 years of teaching & research experience in the field of Chemistry & Pharmaceutical sciences.