▪ I. pion Nuclear Physics.
(ˈpaɪɒn)
[f. pi-meson + -on1.]
Any of a group of mesons that have masses of approximately 140 MeV (270 times that of the electron), zero spin, zero hypercharge, and isospin of 1, and on decaying usually produce a muon and a neutrino (in the case of charged pions) or two photons (in the case of the neutral pion); a pi-meson.
| 1951 Sci. News XXI. 21 The mass of π-mesons, or pions as they are called in short,..appears to be in the neighbourhood of 276 times that of the electron. 1958 Spectator 13 June 778/3 The Japanese physicist Yukawa has shown that what causes the neutrons and the protons of the atomic nucleus to cling together with such tenacity are the revolving pions that link them. 1968 M. S. Livingston Particle Physics vi. 124 The neutral pion π° can be formed through the charge-exchange process π- + p → n + π° following capture of the π- in a Bohr orbit (i.e., in liquid hydrogen). The π° decays promptly (10-16 sec) into two photons. 1971 P. E. Hodgson Nucl. Reactions ii. 37 The interaction of fast pions with nuclei can also give information on the relative extent of the neutron and proton distributions in matter. 1975 Daily Colonist (Victoria, B.C.) 26 Jan. 14/2 The new 17-foot-long generator shoots out pions or sub-atomic particles generated by a high-energy accelerator. |
Hence piˈonic a., of, pertaining to, or involving a pion, or an atom having a negative pion orbiting the nucleus.
| 1960 P. Roman Theory Elem. Particles v. 511 All pionic interactions are of the same strength. 1967 J. C. Sens in G. Alexander High Energy Physics & Nucl. Struct. ii. 117 In muonic atoms, the muon samples the distribution of charge in the nucleus; in pionic atoms the pions form in addition a probe for the nuclear mass distribution, through the strong interactions. 1970 D. F. Jackson Nucl. Reactions x. 230 Additional information about the pion-nucleus interaction can be obtained from studies of pionic atoms and pionic x-rays. |
▪ II. † ˈpion, v. Obs.
[a. OF. pion-er, piouner intr. to pick, dig, trench, excavate (1469 in Godef.), f. pion a foot-soldier: see peon, pioneer.]
trans. and intr. To dig, trench, excavate; to do the work of a pioneer. Hence ˈpioning vbl. n.
| 1590 Spenser F.Q. ii. x. 63 With painefull pyonings From sea to sea he heapt a mightie mound. 1609 Bp. W. Barlow Answ. Nameless Cath. 13 To remooue the Crime from the Iesuites, the Principall Instigators of the Pioning Traitors to the Act. 1643 T. Goodwin Van. Thoughts 27 He'll digge and fall a pioning, with his thoughts, his engins, in the night. 1656 Sir T. Browne Let. to Dugdale 10 Nov., Wks. (Bohn) III. 405 The clearing of woods and making of passages, [and] all kind of pyoning and slavish labour. |
▪ III. pion
obs. form of peon.