Proton-Neutron Theory:
After the discovery of neutrons (Chadwick 1932) Proton neutron theory was formulated. According to this theory:
"A nucleus of atomic no. Z and mass no.A consists of Z Protons and (A-Z) neutrons. The no. of extranuclear electrons is Z so that the nuclear charge is balanced."
This theory is able to explain:
* The observed value of nuclear spin and nuclear magnetic moment.
*The existence of isotopes . Isotopes of a given element differ only in the no. of neutrons they contain.
*The β-ray emission of a radioactive element is explained as follows:
The electron does not pre exist in the nucleus.The electron is formed just at the instant of emission, caused by the transformation of a neutron into proton.
i.e. n--->p+e-
*The positron emission is due to the converse process, i.e. when a proton transfers itself into a neutron.
i.e. P--->n+e+
* α and β decay explanation: The emission of α-particles from the nucleus of radioactive elements is due to the combination of 2-protons and 2-neutrons at the instant of emission.
Thus this hypothesis explains α-decay and β-decay.
