TABLE OF CONTENTS From the scattering of ?-particles, Rutherford concluded that the atom of any element consists of a central core called a nucleus with electrons moving around it. The entire mass of the atom and its positive charge is concentrated inside the nucleus. The mass of the electron (9.108 10 81 kg) is insignificantly small. The nucleus consists of two particles, the proton and the neutron. Their mass are nearly the same as shown below:
The proton is a positively charged particle while the neutron is a neutral particle, i.e., it carries no charge. The charge on the proton is 1.6 10 -19 coulomb. Both the proton and neutron together in the nucleus are called nucleons. The number of protons in the nucleus is called the atomic number and the sum of protons and neutrons is called the mass number. The stability of a nucleus depends on the relative number of protons and neutrons.
From natural radioactivity considerations it was established that different particles, like ? particles, ? particles as well as electromagnetic radiations in the form of ? rays, are emitted from the nucleus. In a real sense, the ? rays are not the constituents of nuclei but they are emitted when the nucleus in an excited state returns to its normal state just like the visible light. Research on artificial radioactivity has shown that many particles like ? particles, protons, neutrons, positrons, ? particles etc., enter into...
