^Binding energy per nucleon

1. is low for both heavy & light nuclei.

2. increases rapidly up to A = 20 & have peaks for ₂He⁴, ₆C¹² & ₈ O¹⁶ .

3. increases gradually after A = 20.

4. becomes less or more flat between A = 40 to 120.

Also it has average value in this region is 8.5 MeV.

5. has maximum value 8.8 MeV for the ₂₆Fe⁵⁶.

6. decrease after A =120 & drops to 7.6Mev for ₉₂U²³⁸.

In order to increases the values of binding energies light nuclei undergo fusion while heavy nuclei undergo fission reactions i.e. heavy nuclei become more stable after fission & light nuclei become more stable after fusion.

^Nuclear Force

It binds the nucleons together protons and neutrons together in the nucleus of an atom against the repulsion of positively charged protons. It is a is short range force & believed to be due to the exchange of pions (also called π – mesons) between the nucleons. It is the strongest (as F_g: F _e: F_n   = 1: 10³⁶: 10³⁸) of the fundamental forces. Also it is Short range, Non central, Saturated, Attractive as well as repulsive.

^Nucleus

Scattering experiments using fast electrons (instead of α – particles) as projectiles on targets of various elements, the sizes of nuclei of various elements have been accurately measured to be R = R₀ A^1/3

Here R₀ = 1.2 × 10 ^-15 m known as nuclear unit.

^Nucleus of an atom

Large angle scattering of α-particles by thin metal foils in Rutherford’s experiment revealed

1. Nuclear size is found to be of the order of 10^–14 m whereas the diameter of an atom is of the order of 10^–10 Hence most of the atom is empty or nucleus of an atom is a very tiny central region.

2. Charge of a nucleus of atomic number Z = +

3. More than 99.9% of the mass of an atom is concentrated in the nucleus.

^Facts

1. In an H-atom the energy gap of any transition is not enough to emit X- Electronic transitions in an H-atom can produce IR, UV & visible radiations only.
2. Production of the X-rays is an atomic phenomenon whereas the production of γ-rays is a nuclear