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Spark chamber discussion


My first publication as a physicist was “Properties of a Spark Chamber,” Nuovo Cimento 20 (1961) 502-8, with B. Cork, P. G. Murphy, and W. A. Wenzel.  Its background was as follows:

A variety of instruments can be used to show the “track” of an electrically charged elementary particle traveling through a transparent medium.  They all operate on the principle that the particle ionizes molecules of the medium, but beyond that the process depends on the instrument.  At least in the days when this article was written, the most well known such device was the bubble chamber.  It worked by having a liquid medium compressed just before a beam of particles was expected to go through it, and promptly releasing the pressure just after it did so.  The release would cause tiny bubbles of vapor (localized boiling of the liquid) to form around any ions that had been created, which were then photographed.  Technicians could then scan the photographs produced in successive beam pulses for tracks.

However, while typical bubble chambers produced images of fine resolution, they were limited by the compression-decompression cycle, in that such mechanical processes are slow in comparison with electronic ones.  Thus a number of people worked to develop a device which could show tracks but recover within about a millionth of a second.  Such an instrument, called a spark chamber, worked by applying a high voltage pulse to alternate metal plates immersed in a noble gas such as neon or argon.  The pulse would be applied immediately after an electronic signal indicated that an electrically-charged particle had traversed the device.  Any ions the particle produced in the gas would then create a conduit for an electrical discharge (the spark) at the location of its path, which could then be photographed.

As a graduate student I worked with the first group to develop spark chambers for actual use in performing laboratory experiments with unstable elementary particles.  (My PhD thesis was based on one such experiment.)  This particular article describes the prototype of the devices the other authors cited and I built for the purpose (Cork and Wenzel were my mentors and Murphy was a visitor).