A high speed disintegration electron (i.e., negatron or positron) spontaneously emitted from an atomic nucleus as a form of [[radiation]]. Electrons (negative or positive) do not exist in nuclei; they are created at the moment of emission and are accompanied by the transition of a [[neutron]] into a [[proton]], or a proton into a neutron. The [[atomic number]] of the [[nuclide]] is changed by a +1 or a –1 with no significant change in [[atomic weight]]. A beta particle can penetrate only a few millimeters of rock.