positronium Nuclear Physics.
(pɒzɪˈtrəʊnɪəm)
[f. prec. + -ium.]
A short-lived neutral system, analogous to an atom, consisting of a positron and a negative electron bound together.
| 1945 A. E. Ruark in Physical Rev. LXVIII. 278/1 In 1937 I conceived the idea that an unstable atom composed of a positron and a negative electron may exist in quantities sufficient for spectroscopic detection. The name positronium is suggested. The spectrum of positronium would have lines at wave-lengths twice as great as the hydrogen lines. 1957 New Scientist 26 Dec. 28/3 When positronium is in free (i.e., near-vacuum) conditions, spectroscopic measurement shows that it has a lifetime of about one and a half ten-millionths of a second. 1966 McGraw-Hill Encycl. Sci. & Technol. X. 524/1 Positronium is of particular interest because it is the two-body system to which quantum electrodynamics is applicable, and its study has served as an important confirmation of the theory of quantum electrodynamics. 1970 [see hydrogenic a. b]. 1976 Science 19 Nov. 826/3 If ψ were a bound system of two spin ½ particles, there could be excited levels with a spectrum similar to that of positronium (the system of electron and positron, bound to each other by the electromagnetic force). |