A History of Early High Energy Physics Research at UCL
Jim Grozier
Spark Chambers
Unlike the cloud chamber and the bubble chamber, the spark chamber cannot really be identified with a single inventor. It developed in stages betwen the 1940s and 1960s, with crucial features being added by various researchers. Peter Galison, in his book Image and Logic, points out that spark chambers grew out of the "counter tradition" in high energy physics research, as opposed to the "image tradition" which was based around devices such as cloud and bubble chambers. In fact, one of Galison's main theses - reflected in the very title of the book - is the way these two "traditions" evolved in almost complete isolation, and led to research groups with very different outlooks, often competing with one another for funding [1].
The starting point in counter technology is the Geiger counter, which dated back to the first decade of the twentieth century. It simply detected the presence of an ionising particle by means of its ability to trigger electrical breakdown in a gas in a strong electric field. In 1948, Jack Warren Keuffel, at Caltech, developed the "spark counter" - essentially a "flattened Geiger counter", which used parallel plates to provide a more uniform field and hence reduce the drift time associated with the strong position-dependence of the Geiger counter. The aim at this stage was simply to build an improved timing device for detecting fast-moving particles, without any suggestion of following a particle's trajectory.
In 1954, Paul-Gerhard Henning, in West Germany, placed three spark counters on top of one another and looked for coincidences as charged particles passed through them, photographing the sparks with a camera. A year later, this idea was developed by Marcello Conversi and Adriano Gozzini in Pisa, who built "flash tubes" - glass tubes filled with neon and triggered by a microwave pulse which produced breakdown, and hence a visible spark, in tubes through which charged particles had passed. In 1956 this work was duplicated by Shuji Fukui and Sigenori Miyamoto in Kyoto, Japan; they noticed that the electrical breakdown in the tubes took place locally around the particle trajectory, rather than simply producing an unlocalised "flash" that filled the tube. This greatly simplified the job of designing a detector which could display visual particle tracks in three dimensions. In 1959, Fukui and Miyamoto published a paper on their "discharge chamber".
Fukui and Miyamoto's discovery prompted physicists around the world to start building their own spark chambers. These were relatively easy and cheap to build, in contrast to the "big science" of the large bubble chambers. Three US physicists - William Wenzel, Bruce Cork, and James Cronin - built a spark chamber at Berkeley and used it in conjunction with the Bevatron. Melvin Schwartz, Leon Lederman and Jack Steinberger then built a large spark chamber to test the "two-neutrino hypothesis" - the postulated existence of a second neutrino associated with the muon rather than the electron. This chamber was used in conjunction with the new proton accelerator at Brookhaven to show, in 1962, that such neutrinos did in fact exist [2].
Galison is keen to point out that the spark chamber arose out of the "counter tradition" as opposed to the "image tradition". But note that even "industrial-scale" spark chambers such as that of Schwartz et al. were still essentially visual devices, in that the emphasis was on the "spark" as a source of light, and the tracks still required cameras to photograph them and scanners to analyse the photographs. But the spark chamber physicists were counter people at heart - looking to electronics and computer technology to do the work rather than relying on visual images. Wenzel is quoted by Galison as follows: "I got tired of the business of scanning and reconstructing the film". In 1964 a meeting was held at CERN on "Film-less Spark Chamber Techniques and Associated Computer Use". This led to the wire spark chamber, invented by Frank Kriernen at CERN, in which the plates were replaced by wires, and the discharges could be detected by means of the resulting pulses in the wires, and these pulses logged directly into a computer, without any intervening visual stage (although of course visual representations of interactions could always be reconstructed from the computer data) [3]. This kind of chamber was the ancestor of most modern particle detectors.
At UCL, Franz Heymann began work on the development of spark chambers in 1961. He formed a Spark Chamber Group, known as Group C (the bubble chamber work being done in Group B). When Brian Anderson started at UCL as a junior technician in 1962, his first job was with a group building spark chambers [4]. Fox tells us that "in 1963, in collaboration with the Westfield College Spark Chamber Group, spark chambers and scintillation counters were used to study the production of neutral pions in collisions between ingoing 600 MeV protons and stationary protons in a liquid hydrogen target at CERN". In 1964 Eric Burhop put forward a proposal to combine spark chamber and emulsion techniques in order to locate rare neutrino interactions in an emulsion, enabling very short-lived particles to be detected. However, Fox adds that this "aroused little interest for almost ten years". In the late 1970s, Mike Esten joined the counter group, having previously worked with bubble chambers. He worked on trigger design for fixed-target counter experiments [5].
Unfortunately it has not been possible, to date, to map out the history of the UCL spark chamber group in any great detail. Hopefully this will change.
References:
- Peter Galison, Image & Logic, University of Chicago Press, 1997, pp 463-489
- Christine Sutton, Weak Interactions, in The Particle Century, ed. Gordon Fraser, IOP 1998, pp 91-92
- Frank Close, Michael Marten and Christine Sutton, The Particle Explosion, Oxford University Press, 1987, p 123
- Interview with Brian Anderson, 23.4.13
- Interview with Mike Esten, 3.11.14