An electron or positron
by John Carl Villanueva on July 23, 2009. An alpha particle is a particle made up of two protons and two neutrons. Since this configuration is similar to that of a helium nucleus, it’s often referred to as a helium nucleus. The term is commonly used in nuclear physics, and is one of the three particles commonly emitted during a radioactive decay, i.e., alpha, beta, and gamma particles. Because this electron is from the nucleus of the atom, it is called a beta particle to distinguish it from the electrons which orbit the atom. Like alpha decay, beta decay occurs in isotopes which are neutron rich (i.e. have a lot more neutrons in their nucleus than they do protons). The Beta Particle. Beta decay is a radioactive process in which an electron is emitted from the nucleus of a radioactive atom, along with an unusual particle called an antineutrino. The neutrino is an almost massless particle that carries away some of the energy from the decay process The beta particle is a form of ionizing radiation related to other common forms of radiation, alpha particles and gamma rays. The beta particle is a high-speed electron or positron released from a degenerating radioactive nucleus. Being medium-energy and low mass, beta particles are one of the least damaging forms of radiation, but still a very significant health concern. Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus. They are generally produced in the process of alpha decay, but may also be produced in other ways. Alpha particles are named after the first letter in the Greek alphabet, α. A higher energy version of alphas than produced in alpha decay is a common product of an uncommon nuclear fission result called ternary fission. However, helium nuclei produced by particle accelerators (cyclotrons, synchrotrons, and the like) are less likely to be referred to as alpha particles. Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei, such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay. They are designated by the Greek letter beta (β). There are two forms of beta decay, β − and β + , which respectively give rise to the electron and the positron. Although the beta particles given off by different radioactive materials vary in energy, most beta particles can be stopped by a few millimeters of aluminium. Being composed of charged particles, beta radiation is more strongly ionising than gamma radiation. Alpha particles are made of 2 protons and 2 neutrons. This means that they have a charge of +2, and a mass of 4. (the mass is measured in atomic mass units, where each proton & neutron=1). We can write them as, or, because they're the same as a helium nucleus, . Alpha particles are relatively slow and heavy. 
http://www.universetoday.com/35602/alpha-particle/ http://www.physics.isu.edu/radinf/beta.htm http://www.wisegeek.com/what-is-a-beta-particle.htm https://en.wikipedia.org/wiki/Alpha_particle https://en.wikipedia.org/wiki/Beta_particle http://www.darvill.clara.net/nucrad/types.htm
what is a beta particle made up of