Radioactivity

Radioactivity :-

Henry Becquerel discovered the phenomenon of radioactivity in 1896.Once,in a dark room he left a uranium salt placed on a photographic plate wrapped in a black paper. After few days he saw the plate was affected. From this ,he concluded that uranium and it's salts emit some kind of radiations which can pass through the cover.This radiations were called Becquerel rays.

The substances which decay or disintegrate by spontaneous emissions of radiations are called radioactive substances. E.g radium,aluminium etc.

Important points to remember :-

• Any physical change(pressure and temperature )does not change the nature of radiation emitted by the substances and it's rate.
• Radioactivity is a nuclear phenomenon. 
• It's also a random phenomenon. 
• Exposureto radiations may be harmful.

Terms to Remember :-

• Isotops:- The atoms of same elements with different mass number. 
• Isobars:-The atoms of different elements which have same mass number but different atomic number. 

Isotones:-The atoms having different number of protons but same number of neurons also different number of electrons. 

    

Types of radiations :-

• Alpha rays:- consists of  2 protons and 2 neutons (doubly ionised helium atom). Their speed is 10^7 m/s. (ten to the power 7). These are positively charged.
• Beta particles:- fast moving electrons,mass is 9.1×10^-31 kg. 90% of the speed of light. Negative charge. Causes more harm and damage .
• Gamma particles:- no charge,same as speed of light (3×10^8 m/s).Causes serious damage. They can easily pass through human body.