| 释义 |
positron Physics.|ˈpɒzɪtrɒn|
[f. positive a. and n. + electron2.]
The anti-particle of the ordinary (negative) electron, having the same mass and a numerically equal but positive charge.
1933C. D. Anderson in Science 5 May 432/2 Experiments have been carried out which gave conclusive evidence that positrons are ejected from lead by the γ-radiation of ThC{pp}. [Note] The contraction positron is here used to denote the free positive electron. 1933Times 9 Dec. 9/3 The unit of heavy hydrogen, the deuteron, or deuton, as it has been called, bids fair to rival in interest its recently found cousins, the neutron and positron. 1934Discovery May 123/2 It appears from investigations that the earth is being bombarded by streams of positrons and electrons of very high energy. 1946Ann. Reg. 1945 356 The Bethe carbon cycle (in which carbon acts as a catalyst for the conversion of hydrogen into helium and positrons). 1958Spectator 13 June 778/3 When the electron and the positron meet they annihilate each other. 1960Chalmers & Quarrell Physical Examination of Metals (ed. 2) xvi. 765 Positrons, sometimes called ‘positive electrons’, result from proton–neutron transitions. 1968C. G. Kuper Introd. Theory Superconductivity xii. 193 The conduction electrons and holes of semiconductor theory are closely analogous to the electrons and positrons of the Dirac theory. 1974G. Reece tr. Hund's Hist. Quantum Theory xv. 203 Not until the experimental observation of the positron..was the Dirac ‘hole’ theory generally believed.
Hence posiˈtronic a.
1948I. Asimov in Astounding Sci. Fiction Feb. 44/2 If the field were a trifle stronger, the robot would never reach the technician concerned, since its positronic brain would collapse under gamma radiations—and then we would be out one expensive and hard-to-replace robot. 1957― Naked Sun (1958) ii. 32 He knew a positronic brain..nestled in the hollow of the skull. He knew that Daniel's ‘thoughts’ were only short-lived positronic currents. 1968Punch 23 Oct. 592/2 Barbarella (Jane Fonda), a respected astronaut in 40,000 AD, is being briefed for her mission to find an important scientist from Earth who has disappeared among the planets with his great invention the positronic ray. 1974I. Asimov in George & Humphries Robots are Coming 5 My positronic robot stories.
Add:2. Special Comb. positron emission tomography Med., a form of tomography which employs positron-emitting isotopes introduced into the body as a source of radiation instead of applying X-rays externally; abbrev. PET.
1976Jrnl. Nuclear Med. XVII. 546/1 (heading) Evaluation of *positron emission tomography for study of cerebral hemodynamics in a cross section of the head using positron emitting gallium 68-EDTA and Krypton-77. 1992Economist 26 Dec. 116/2 Positron emission tomography (PET) enables researchers to watch people think. |