Editing Exotic atom (section)

=== Muonic hydrogen ===
Muonic hydrogen is like normal hydrogen with the electron replaced by a negative muon—that is, a proton orbited by a muon.  It is important in addressing the [[proton radius puzzle]].

Muonic hydrogen atoms can form muonic hydrogen molecules. The spacing between the nuclei in such a molecule is hundreds of times smaller than in a normal hydrogen molecule – so close that the nuclei can spontaneously fuse together. This is known as ''[[muon-catalyzed fusion]]'', and was first observed between hydrogen-1 and deuterium nuclei in 1957.<ref name="Alvarez">{{cite journal | last1= Alvarez |first1=L.W. | year = 1957 | title = Catalysis of Nuclear Reactions by μ Mesons | journal = Physical Review | volume = 105 | issue = 3| page = 1127 |doi= 10.1103/PhysRev.105.1127 |bibcode = 1957PhRv..105.1127A | display-authors = 1 | last2 = Bradner | first2 = H. | last3 = Crawford | first3 = F. | last4 = Crawford | first4 = J. | last5 = Falk-Vairant | first5 = P. | last6 = Good | first6 = M. | last7 = Gow | first7 = J. | last8 = Rosenfeld | first8 = A. | last9 = Solmitz | first9 = F. |s2cid=123886206 }}</ref> Muon-catalyzed fusion has been proposed as a means of generating energy using fusion reactions in a room-temperature reactor.