A Quite Extraordinary Demonstration of Quantum ElectroDynamics!

Abstract

A bubble chamber plcture of part of an ala&* magnetk shower demonatrates many lnterestlng phenomena, lndudlng the existence of antlmaner, the maleriaiizaffon of a hlgh anergy photon Into en electron-posltron pair, the em1!3slon of radlanon by accelaratlng charges, and the Compton affed. Thls alticle Introduces the subject of particle physlca, explaining In particular the role of the bubble chamber, and It carefully deacrlbes the parts of the plchlre that demonatrate the phenom ena ot interest. Some relevant kinematies Is given In an appendlx.' The bubble chamber picture to be discussed in this article has been shown to, and discussed with, hundreds of A-level students and teachers during University of Birmingham Open Days. Many expressed amazement that so many phenomena (some not easy to demonstrate on their own!) could manifest themselves in a reasonably straightforward way on one photograph.The phenomena come under the rather formidable title of Quantum ElectroDynamics or QED. Actually, the QED label is a sign of comparative simplicity, because, of the four traditional forces of nature-gravity, electromagnetism, and the weak and strong nuclear forces-QED limits itself to electromagnetic forces. (Quantum mechanics is always needed when talking about the behaviour of particles; here, all we need to know is that it is useful to describe electromagnetic radiation in terms of the flow ofphotons.)What Is parilcle physlca?

Positron annihilation in flight

“…These are high energy photons materializing, in the field of a nucleus, into a positron-electron (e + e − ) pair. (See [6] for detailed discussion. )…”

Antimatter and 20th century science

“…Obviously at a higher level (16+) there is a great deal that can be discussed, and antimatter makes for an interesting research topic [27][28][29]. (Any detailed coverage of positron emission tomography (PET) or other antimatter-related medical ideas has been omitted here for brevity.)…”