Why are alpha particles repelled by the atomic nucleus?
Alpha particles (named after and denoted by the first letter in the Greek alphabet, α) consist of two protons and two neutrons bound together into a particle identical to a helium nucleus; They have a net spin of zero, and normally a total energy of about 5 MeV. They are a highly ionizing form of particle radiation, and have low penetration.
Alpha particles consist of two protons and two neutrons, so they have a net charge of +2e, or +3.204 x 10^-19 C. Atomic nucleus consist of a number of protons and neutrons, giving them a positive charge. Since like charges repel, this causes the positively charged alpha particles and the positively charged atomic nucleus to experience electrostatic repulsion.
