Alpha and Beta Particles

An alpha particle is a positively charged particle spontaneously emitted by some radioactive substances. It is made of two protons and two neutrons bound together, and thus resembles the nucleus of a helium atom. ^[1]

A beta particle is an electron or positron ^[2], that is ejected at a high speed from some radioactive substances.  Beta particles are 100 times more penetrating than alpha particles. ^[3]

Alpha and beta particles were discovered and named by Rutherford in 1898 ^[4], while he was studying the types of rays emitted by uranium crystals. Rutherford discovered that there were at least two types of rays emitted by uranium, which he termed alpha and beta rays. The alpha rays were absorbed by a simple piece of paper, whereas the beta rays could penetrate through at least 0.1 inches of metal. ^[5] Rutherford would use these particles in later experiments, including his famous gold foil experiment.

Rutherford later proved that alpha particles are made of helium nuclei by sealing a sample of radium in a glass tube. The alpha particles emitted by the radium could not penetrate the glass, and they thus remained in the tube. After several days, Rutherford created a discharge using electrodes in the tube and observed the spectrum of the emitted light. He found that the light emitted matched the characteristic wavelengths of helium. This led him to conclude that alpha particles were composed of helium nuclei. ^[6]

[1] http://www.britannica.com/EBchecked/topic/17152/alpha-particle
[2] http://www.britannica.com/EBchecked/topic/63280/beta-particle
[3] Knight, R.D. Physics for Scientists and Engineers a Strategic Approach.
[4] http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1908/rutherford-bio.html
[5] Knight, R.D. Physics for Scientists and Engineers a Strategic Approach.
[6] Knight, R.D. Physics for Scientists and Engineers a Strategic Approach.