A beta particle is really an electron. It has a -1 charge and the mass of an electron, and is therefore about 7200 times less massive than an alpha particle. A positron has exactly the same mass as an electron. In fact, the positron is an antiparticle of an electron. An antiparticle is the opposite of the particle in charge.
All particles have antiparticles.
A positron is sometimes called a positive beta particle, and an electron is sometimes called a negative beta particle. Gamma emission often accompanies other forms of radioactive decay. For example, a nuclide might emit an alpha particle and a gamma particle. E. Protons and Neutrons Protons and neutrons are also sometimes emitted in radioactive decay, although this is much less common than alpha, negative and positive beta, and gamma emission. One form of radioactive decay involves the nucleus absorbing a particle, an electron.