for beta particles by the method of J. J. Thomson used to study cathode rays and identify the electron. He found that for a beta particle is the same as for Thomson's electron, and therefore suggested that the beta particle is in fact an electron. Health Beta particles are moderately penetrating in living tissue, and can cause spontaneous mutation in DNA. Beta sources can be used in radiation therapy to kill cancer cells. See also Common beta emitters Electron irradiation Particle physics n (neutron) rays δ (delta) rays References Further reading Radioactivity and alpha, beta, gamma and X­rays Rays and Particles University of Virginia Lecture History of Radiation at Idaho State University Basic Nuclear Science Information at the Lawrence Berkeley National Laboratory Ionizing radiation Radioactivity