Question

what is velocity of alpha,beta,gamma rays?

Answer 1

@maham.diya
They move into vacuum as quickly as the speed of light.

Answer 2

Only gamma rays goes speed of the light. Beta rays which is electron or positron goes slower than speed of the light. Its velocity depends on which nucleus emits it and also decay energy shares between electron (positron) and anti neutrino (neutrino).
Alpha ray, which is nucleus of the helium atom, goes much slower than speed of the light because it is heavier almost 1840 times than electron. Of course its velocity also depends on which nucleus emits it