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Page 4
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. 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). Atoms which undergo beta decay are located below the line of stable elements on the chart of the nuclides, and are typically produced in nuclear reactors and cyclotrons. When a nucleus ejects a beta particle, one of the neutrons in the nucleus is transformed into a proton. Since the number of protons in the nucleus has changed, a new daughter atom is formed which has one less neutron but one more proton than the parent. For example, when Rhenium-187 decays (which has a Z of 75) by beta decay, Osmium-187 is created (which has a Z of 76). Beta particles have a single negative charge and weigh only a small fraction of a neutron or proton. As a result, beta particles interact less readily with material than alpha particles. Depending on the beta particles energy (which depends on the radioactive atom and how much energy the antineutrino carries away), beta particles will travel up to several meters in air, and are stopped by thin layers of metal or plastic. Antineutrinos have very little mass and no charge. Its been said that a neutrino has more than a 50% chance of traveling through a light-year of solid Lead and not be stopped.


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