An alpha particle is the nucleus of a helium atoms with two protons and two neutrons, so it has a positive charge. A beta particle is an electron, so it has a negative charge. A gamma ray is a photon of very short wavelength and it has no charge. The alpha particle would be attracted to a negatively charged sheet of metal since opposite charges attract. Radioactive decay is a purely natural process and cannot be controlled or influenced by any outside variables.
Beta emission is the expulsion of a high speed electron from a disintegrating nucleus.
The emission of a beta particle increases the number of protons in a nucleus. It is as if a neutron changed to a proton by emitting the electron. So, emission of a beta particle increases the number of protons by one, but the mass number remains the same. The mass of the expelled electron is so small that it is ignored. The nucleus changes from an excited state to a lower energy state and there is no change in the number of nucleons or the mass number.