Relation Between Atomic Mass Unit and MeV

The unit in which atomic and nuclear masses are measured is called atomic mass unit (a.m.u).

1 a.m.u is defined as 1/12^th of the mass of an atom of ₆C¹² isotope.

It can be shown that

1 a.m.u = 1.66 x 10²⁷ kg.

According to Einstein, mass energy equivalence

E = mc²

Where m = 1.66 x 10^-27 kg.

C = 3x10⁸ m/sec ,we get

E = 1.49 x 10^-10 J (1Mev = 1.6 x 10^-13 J)

E = 931.25 Mev

Hence a change in mass of 1a.m.u (called mass defect) releases an energy equal to 931 Mev.

1 amu = 931 Mev is used as a standard conversion.

Isotopes

Isotopes of an element have same atomic number (Z) but different mass numbers (A).

For example, ₁H¹, ₁H², ₁H³ are isotopes of hydrogen;

Isotopes of an element have identical chemical properties but different physical properties.

Nuclear Forces

In spite of the strong electrostatic force of repulsion between protons, nucleus of most elements are stable. This is because of the strong forces of attraction, which hold together the nucleons in that tiny volume.

These forces are short-range forces and are the strongest in nature. They are operative up to distances of the order of a few fermi. They are charge-independent, non-central and non-conservative forces.