Editing Beta decay (section)

===Discovery and initial characterization===
Radioactivity was discovered in 1896 by [[Henri Becquerel]] in [[uranium]], and subsequently observed by [[Marie Curie|Marie]] and [[Pierre Curie]] in [[thorium]] and in the newly discovered elements [[polonium]] and [[radium]]. In 1899, [[Ernest Rutherford]] separated radioactive emissions into two types: alpha and beta (now beta minus), based on penetration of objects and ability to cause ionization. [[Alpha rays]] could be stopped by thin sheets of paper or aluminium, whereas beta rays could penetrate several millimetres of aluminium. In 1900, [[Paul Villard]] identified a still more penetrating type of radiation, which Rutherford identified as a fundamentally new type in 1903 and termed [[gamma ray]]s. Alpha, beta, and gamma are the first three letters of the [[Greek alphabet]].

In 1900, Becquerel measured the [[mass-to-charge ratio]] ({{math|''m''/''e''}}) for beta particles by the method of [[J.J.&nbsp;Thomson]] used to study cathode rays and identify the electron. He found that {{math|''m''/''e''}} for a beta particle is the same as for Thomson's electron, and therefore suggested that the beta particle is in fact an electron.<ref name="Handbook">{{cite book|last1=L'Annunziata|first1=Michael|title=Handbook of Radioactivity Analysis|date=2012|publisher=Elsevier Inc.|page=3|edition=Third|url=https://books.google.com/books?id=S4FrejzJy0cC&pg=PA3|access-date=4 October 2017|isbn=978-0-12-384874-1}}</ref>

In 1901, Rutherford and [[Frederick Soddy]] showed that alpha and beta radioactivity involves the [[Nuclear transmutation|transmutation]] of atoms into atoms of other chemical elements. In 1913, after the products of more radioactive decays were known, Soddy and [[Kazimierz Fajans]] independently proposed their [[Radioactive displacement law of Fajans and Soddy|radioactive displacement law]], which states that beta (i.e., {{SubatomicParticle|Beta-}})&nbsp;emission from one element produces another element one place to the right in the [[periodic table]], while alpha emission produces an element two places to the left.