Positron

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Die Kreisbogenartige Spur eines Positrons in einer Nebelkammer: die Länge und die Krümmung der Spur geben Rückschlüsse auf das Teilchen selbst. Die Krümmung kommt durch ein von außen angelegtes Magnetfeld zustande. Infolge der magnetischen Komponente der Lorentzkraft wird eine bewegte Ladung dort von ihrer Bahn abgelenkt.

Cloud chamber photograph of the first positron ever observed. The thick horizontal line is a lead plate. The positron entered the cloud chamber in the lower left, was slowed down by the lead plane, and curved to the upper left. The curvature of the path is caused by an applied magnetic field that acts perpendicular to the image plane. The higher energy of the entering positron resulted in lower curvature of its path.

Original caption: A 63 million volt positron (Hρ = 2.1×105 gauss-cm) passing through a 6 mm lead plate and emerging as a 23 million volt positron (Hρ = 7.5×104 gauss-cm). The length of this latter path is at least ten times greater than the possible length of a proton path of this curvature.

Original publication: Anderson, Carl D. (1933). "The Positive Electron". Physical Review 43 (6): 491–494. DOI:10.1103/PhysRev.43.491

No copyright: Obtained from American Physical Society, March 5, 2008. The copyright for the periodical containing this picture, if renewed, would have had to be renewed in 1960 or 1961. I (Wikimedia) checked the Catalog of copyright entries for Periodicals in 1960 and 1961, http://onlinebooks.library.upenn.edu/cce/, but The Physical Review is not listed there. Therefore, the copyright on the entire issue of The Physical Review, including this picture, has expired.

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