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In 1965 the Heavy Liquid Bubble Chamber at the Rutherford Laboratory, near Didcot in Oxfordshire, commenced operation after five years of construction. The chamber, 1.4m long and 50cm square, was filled with propane and surrounded by a giant electromagnet; the whole assembly weighed some 200 tons. It was meant to be the jewel in the crown of British particle physics and was a good example of the move from individual university laboratories to central “Big Science” institutions.

But a problem soon became evident; some of the photographs seemed rather washed out. In bubble chamber photographs the background is black, with any particle tracks standing out as white, illuminated by powerful lights at the top and bottom of the chamber. These washed-out photographs looked as though they had been taken during a lightning strike. Which, in a way, they had.

The supply of particles for creating the collisions the bubble chamber was intended to study came from the NIMROD proton beam, and photographs were taken every 2 seconds. The three cameras thus had to wind the film on at the same rate, and this rapid movement caused an electrostatic charge to build up; every so often there was a lightning-like discharge inside the camera when the electric field became strong enough to ionise the air.

A similar bubble chamber at CERN experienced the same problem at about the same time, and it is interesting to contrast the measures taken to resolve it by the two labs. At CERN, a special humidifier was developed to prevent static build-up. At the Rutherford Lab, the physicist in charge of the cameras achieved the same result by putting half a potato inside.

There are several directions in which this story might now take us.

We might, for instance, use it to examine the differing cultures of experimental physics in the UK and at CERN; the “official” line taken by the latter brings to mind the concept of “design by committee”, and suggests a tension between a bureacracy-laden structure on the one hand and the innovation and creativeness of the individual scientist on the other. *

Or we might recall Peter Galison’s analysis in Image & Logic of the rise of “Big Science” at around this time, and its role in gradually removing the scientist from the “coalface” of experiment. Galison points out that scientists were no longer building their own equipment, had a diminishing role in the day-to-day running of experiments, and were required to hand over the bulk of the data analysis to an army of female scanners. So was the potato solution a rearguard action by a lone scientist determined to maintain control?

Equally, scholars of the sociology of science might gleefully hold up the use of the potato as an example of “tacit knowledge”, and use it to prove that scientific practices are less objective and less transparent than commonly supposed. To be sure, the potato is unlikely to have made it into any of the research papers on experiments conducted with this bubble chamber; however I would not take that as evidence of tacit knowledge. (I have blogged about this topic here, and no doubt will do so again, so will not take up any more space on it right now).

You might, alternatively, simply be happy to observe that this is further evidence that, contrary to popular opinion, root vegetables have indeed made their mark on the pursuit of knowledge.

However, in this blog I would like to pick out a slightly different aspect of this “solanaceous humidification system” and its vital contribution to experimental culture: basically, experimental science is messy. It is meant to contain all sorts of ad-hoc quick fixes. The potato was not, after all, a permanent solution in the same way as the CERN humidifier was; potatoes will dry out, go off, begin to smell. (And any physicist who ever smelt a rotten potato would not have wanted to be the one to open up the camera and remove the film!) But then it, and a steady supply of replacement parts, could be obtained quickly, easily and cheaply from the Didcot Co-Op.

And besides, experimental physics is supposed to be like that. A few years ago I visited three synchrotrons (circular accelerators which use fast-moving electrons to generate high energy X-rays for use in diffraction experiments) within a year or two of one another. In about 2006 I went to the first open day of Diamond, the new UK synchrotron that had been built next door to the Rutherford Lab where the potato assumed its starring role some 40 years before. It was all clean, clinical and … boring. Likewise the ESRF, the French equivalent at Grenoble, which had been running for a few years when I went there in around 2004. Everything was as shiny and new as it would have been on day 1, and all in accordance with the design documentation. You could even get lost there, as each experimental station was identical to all the others.

On the other hand, the Daresbury synchrotron (the predecessor to Diamond, located near Warrington in Cheshire) had been operating for many years when I visited (and I think it eventually closed once Diamond was fully up and running). It was full of bits of Blu-Tack, wires sellotaped on, pipes that stuck out five feet above the walkway and made you duck to avoid them. Over the years, add-ons and adaptations had proliferated. It was like going into a house that has been well and truly lived in, in contrast to a new one which as yet bears no sign of human habitation. Both the physics experiments I’ve been personally involved with have had this feel about them too. As a former engineer, I have, admittedly, wondered at times whether all the add-ons and modifications were documented anywhere, and what might happen if they weren’t (which is a subject I might come back to in another blog) but, hey, that’s physics for you – the messiness is what makes it what it is.

N.B. No potatoes were needlessly murdered in order to produce the above photograph. I had it for lunch.

*Having brushed with the CERN bureaucracy in the past, albeit in a completely different context, I can testify that it is certainly a force to be reckoned with!

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