Question

Why in beta decay there is an increase and decrease in atimic number by release of electron or positron What causes the change?

Answer 1

The change is caused because it is happening a nuclear process that transforms neutron in proton or transforms proton in neutron.

Explanation:

The first case is the beta- process (the most frequent), that is, a neutron decays in a bonded proton plus other two particles: a free electron and a neutrino; the other two particles are necessary for respect of conservation principles.
The second case (beta+) is a more articulated nuclear process and contemplates the creation of a positron instead of electron; it is observed only during particular nuclear reactions.