The Road of Radioactive Discoveries

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Following are the important contributions to radioactivity:

1. Becquerel's discovery (1896):

• Henri Becquerel accidentally discovered radioactivity while investigating the phenomenon of fluorescence. 
  
• He observed that a uranium salt emitted rays that could darken a photographic plate, even when it was covered and protected from light. 
  
• This led him to hypothesize the presence of a new kind of radiation.
  

2. Marie Curie's discovery (1898): 

• Marie Curie, along with her husband Pierre Curie, continued Becquerel's work and discovered two new radioactive elements: polonium and radium. 
• They coined the term "radioactivity" to describe the phenomenon.
  

3. Thomson's discovery of subatomic particles (1897): 

• J.J. Thomson discovered the existence of negatively charged particles called electrons, using cathode rays in a vacuum tube. 
  
• This discovery laid the foundation for understanding the structure of the atom.
  

4. Rutherford's experiments (1902-1909): 

• Ernest Rutherford conducted a series of experiments to understand the nature of radioactivity. 
  
• He established that radioactivity involves the disintegration of atoms alongwith releasing particles with positive or negative charge. 
  
• Rutherford also discovered the existence of alpha and beta particles and proposed the nuclear model of the atom, which states that the positive charge and most of the mass of an atom is concentrated in its nucleus.
  

5. Discovery of gamma rays (1900s): 

• In addition to alpha and beta particles, gamma rays were also discovered. 
  
• They are high-energy electromagnetic radiation emitted during radioactive decay. They have no mass or charge but can penetrate matter.