How is Neutron discovered?

In 1930, Bothe & Becker bombarded Lithium, Beryllium and Boron with alpha particles from Polonium and found a very penetrating but non-ionizing radiation, they assumed that the radaition was of gamma rays type because of its high penetration.

While repeating these experiments in 1932, Dr. F. Joliot and his wife, Dr. Irene Curie Joliot found that when a sheet of Hydrogen containing material, particularly paraffin, was interposed in the path of these radiations, Protons were ejected with a considerable velocity.

From the ranges of these recoil protons, the maximum proton energy 'E' proved to be about 5.3 MeV. Assuming that the protons were produced as the result of elastic collisions with the gamma ray photons, calculations showed that each photon must have possessed an amount of energy about 52MeV. These results were entirely inconsistent with the results from experiments on absorption of these in lead(about 7 MeV).

Chadwick, in England in 1932, after performing a series of measurements of energies of recoil of Protons ejected from thin targets by the penetrating "Be-radiation", with a pulse ionizing chamber and amplifier. He said, "these results are very difficult to explain on the assumption that the radiation from Beryllium is a quantum radiation, if energy and momentum are to be conserved in the collisions. These difficulties disappear, however, if it be assumed that the radiation consists of particles of mass 1 and charge 0 later named as Neutrons.          

These neutrons were formed as a result of highly exoergic nuclear reactions.

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