Editing Radioactive decay (section)

=== Alpha, beta and gamma decay ===
{{Main|Alpha decay|Beta decay|Gamma decay}}
[[File:Alfa beta gamma radiation.svg|upright=0.8|thumb|[[Alpha particle]]s may be completely stopped by a sheet of paper, [[beta particle]]s by aluminium shielding. [[Gamma ray]]s can only be reduced by much more substantial mass, such as a very thick layer of [[lead]].]]Early researchers found that an [[Electric field|electric]] or [[magnetic field]] could split radioactive emissions into three types of beams. The rays were given the names [[Alpha particle|alpha]], [[Beta particle|beta]], and gamma, in increasing order of their ability to penetrate matter. Alpha decay is observed only in heavier elements of atomic number 52 ([[tellurium]]) and greater, with the exception of [[beryllium-8]] (which decays to two alpha particles). The other two types of decay are observed in all the elements. Lead, [[atomic number]] 82, is the heaviest element to have any isotopes stable (to the limit of measurement) to radioactive decay. Radioactive decay is seen in all isotopes of all elements of atomic number 83 ([[bismuth]]) or greater. [[Bismuth-209]], however, is only very slightly radioactive, with a half-life greater than the age of the universe; radioisotopes with extremely long half-lives are considered effectively stable for practical purposes.
[[File:Radioactive decay modes.svg|upright=0.9|thumb|Transition diagram for decay modes of a radionuclide, with neutron number ''N'' and [[atomic number]] ''Z'' (shown are [[Alpha particle|α]], [[electron|β<sup>±</sup>]], [[proton|p<sup>+</sup>]], and [[neutron|n<sup>0</sup>]] emissions, EC denotes [[electron capture]]).]]In analyzing the nature of the decay products, it was obvious from the direction of the [[electromagnetic force]]s applied to the radiations by external magnetic and electric fields that alpha particles carried a positive charge, beta particles carried a negative charge, and gamma rays were neutral. From the magnitude of deflection, it was clear that [[alpha particles]] were much more massive than [[beta particles]]. Passing alpha particles through a very thin glass window and trapping them in a [[neon lamp|discharge tube]] allowed researchers to study the [[emission spectrum]] of the captured particles, and ultimately proved that alpha particles are [[helium]] nuclei. Other experiments showed beta radiation, resulting from decay and [[cathode ray]]s, were high-speed [[electrons]]. Likewise, gamma radiation and X-rays were found to be high-energy [[electromagnetic radiation]].

The relationship between the types of decays also began to be examined: For example, gamma decay was almost always found to be associated with other types of decay, and occurred at about the same time, or afterwards. Gamma decay as a separate phenomenon, with its own half-life (now termed [[isomeric transition]]), was found in natural radioactivity to be a result of the gamma decay of excited metastable [[nuclear isomer]]s, which were in turn created from other types of decay. Although alpha, beta, and gamma radiations were most commonly found, other types of emission were eventually discovered. Shortly after the discovery of the [[positron]] in cosmic ray products, it was realized that the same process that operates in classical beta decay can also produce positrons ([[positron emission]]), along with [[neutrino]]s (classical beta decay produces antineutrinos).