Beta Particles

Beta particles ( β ) are nuclear decay particles and one form of ionizing radiation. In the same experiments that led Ernest Rutherford to postulate his ideas about alpha particles as positively charged particles, he also discovered that beta radiation was negatively charged. Later experiments by Henri Bequerel led to evidence that beta particles have the same mass and charge (-1) as electrons.

Beta radiation ejects a high speed electron from an unstable nucleus. The electron is formed on the spot within the nucleus by the breakdown of a neutron into a proton and an electron. The electron is released from the system. The proton that is formed remains behind in the nucleus. Thus, beta particles are electrons ejected from radioactive nuclei at very high speeds.

Since beta particles (mass = 9.11 x 10^-28 g/particle) are much smaller that alpha particles (recall that an alpha particle is an entire helium nucleus, composed of 2 neutrons and 2 protons) they have a much greater penetrating power than alpha particles. They can travel a few feet in the air. It would take 1/2 cm of lead to stop a beta particle which can penetrate several millimeters of living tissue or bone. External exposure to beta particles is not as great a risk as internal exposure through ingestion or inhalation.

Most of the radioactive fission products decay by emitting beta particles. Many radioactive products are found in fallout and cause contamination of the area.