Nuclear Structure and Nuclear Forces
According to an earlier hypothesis, the nucleus is considered as being composed of two building blocks, proton's and neutron's, which are collectively called nucleons. The forces, which hold the nucleons together means stronger proton – proton, neutron – neutron and even proton – neutron attractive forces, exist in the nucleus. These attractive forces are called nuclear forces. Nuclear forces operate only within small distance of about or 1 fermi (1 fermi = ) and drops rapidly to zero at a distance of These are referred to as short range forces. Nuclear forces are nearly times stronger than electrostatic forces.
Yukawain 1935, put forward a postulate that neutrons and protons are held together by very rapid exchange of nuclear particles called Pi-mesons (p-mesons have mass equal to 275 times of the mass of an electron and a charge equal to +1, 0 or –1. These are designated as p+p0 and p– respectively). The nuclear force which is used in rapid exchange of Pi-mesons between nucleons are also called exchange forces.
The binding forces between unlike nucleons (p and n) are explained by the oscillation of a charged p-meson (p+ or)
Binding forces between like nucleons (p - p or n - n) result from the exchange of neutral mesons (p0) as represented below.