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DISCOVERY OF NEUTRON

How was the Neutron discovered?


"The fundamental subatomic particles electron and proton are not only the constituents of the atom there is still something inside the atom."  ~Rutherford(1920)

Breakthrough :
Scientists started to compare masses of different atoms on the basis of protons they possessed because electron contributes negligible mass to an atom. When the masses of the two hydrogen atoms were compared with one helium atom scientist found the huge difference in the mass between them.
Generally, Helium has 2 protons so it should have mass 2 units and 2 hydrogen atom should have 2 unit mass because of 2 protons. When the mass between them was compared it was observed the mass of the single helium atom was much heavier than the mass of two hydrogen atoms. It was found that masses of 4 hydrogen atoms were equals to mass of 1 helium atom.
This discrepancy gave birth to a new idea.

pic credit-Tyler DeWitt


Again mass of lithium, boron, carbon atoms was measured and partially mass of protons of each atom were calculated. The total mass of the individual atoms and sum of the masses of each proton of the respective atoms were not the same. This observation gave a clue that something new is there inside the atom.

James Chadwick, a British physicist carried out  an experiment: He passed a  high energy alpha particles from polonium(produces high energy alpha particles) to the beryllium sheet(it produce intense radiation). The high energy alpha particle emits heavy particles from beryllium and those particles hit another target material that is paraffin again from paraffin positive particles comes out.
pic credit-large.standford.edu
When particles emit from beryllium they are passed under the influence of electric and magnetic field and found they passed deflected and concluded that they do not carry any charges. So they are named Neutron.

Some doubt questions?

  • Why not electron or proton emitted from beryllium?

        Due to the positive charge of Alpha particles.
  • Why polonium?

        It produces high energy alpha particles.
  • Why beryllium?

      It produces intense radiation?
  • Why proton emitted from paraffin?

       Neutron is bit heavier than proton so it ejects a proton.

"Some scientists believed that because of radioactivity phenomenon it gave the birth of a new particle. The quest of scientist was to block the radiation that emits from radioactive elements. May be the James Chadwick was one of them to carried out the experiment  but discovered the subatomic particle NEUTRON."

 DISCOVERY OF ELECTRON- full analysis 

DISCOVERY OF PROTONS-full analysis

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