Editing Beta decay (section)

===Double beta decay===
{{main|Double beta decay}}
Some nuclei can undergo double beta decay (2β) where the charge of the nucleus changes by two units. Double beta decay is difficult to study, as it has an extremely long half-life. In nuclei for which both β&nbsp;decay and 2β are possible, the rarer 2β process is effectively impossible to observe. However, in nuclei where β&nbsp;decay is forbidden but 2β is allowed, the process can be seen and a half-life measured.<ref name="Bilenky">{{cite journal
 |last=Bilenky |first=S. M.
 |year=2010
 |title=Neutrinoless double beta-decay
 |volume=41 |issue=5 |pages=690–715
 |journal=[[Physics of Particles and Nuclei]]
 |arxiv=1001.1946
 |bibcode=2010PPN....41..690B
 |doi=10.1134/S1063779610050035
|hdl=10486/663891
 |s2cid=55217197
 }}</ref> Thus, 2β is usually studied only for beta stable nuclei. Like single beta decay, double beta decay does not change {{mvar|A}}; thus, at least one of the nuclides with some given {{mvar|A}} has to be stable with regard to both single and double beta decay.

"Ordinary" 2β results in the emission of two electrons and two antineutrinos. If neutrinos are [[Majorana particle]]s (i.e., they are their own antiparticles), then a decay known as [[neutrinoless double beta decay]] will occur. Most neutrino physicists believe that neutrinoless 2β has never been observed.<ref name="Bilenky" />