The hunt for an elusive particle critical to physics once saw Holborn tube station used for a revolutionary science experiment.
Neutrinos are high-energy particles that almost never interact with normal matter. We are bombarded by them, yet barely a trace of their existence can be found. They are as slippery as a politician.
In fact, calculations at Cambridge University in the 1930s by James Chadwick and DE Lea predicted — optimistically as it later turned out — that a neutrino could travel through more than 90 miles of air before hitting anything.
One way to detect them is to look for the tiny flashes of energy that are released on the rare times they do hit something, but to do so on the surface in a building is impossible because all the noise from other sources of particles and cosmic radiation drowns out the few hits that are caused by neutrinos.
So, go underground and hope that the depth will absorb the noise. And in 1943 that’s exactly what the British physicist, Maurice Nahmias did.
Not offered a deep mine to use, he found that he was able to set up an experiment inside Holborn tube station — some 100 meters below ground. The aim being to reduce interference from cosmic radiation, and other sources that could interfere with the experiment.
Sadly, as it turned out 100 feet under London is simply not good enough to clean out the noise so that if a flash does occur, the scientists can be pretty certain that it was a neutrino, and not some other particle banging into something.
Although the experiment failed to detect neutrinos, the drop in noise it did provide showed other scientist the direction to follow… downwards, and down they have gone ever since. Some of the largest neutrino detectors in the world are deep underground often in disused mines.
If you ever sigh at the slow lifts in tube stations that still use them, then think about neutrino hunters, who can have a lift journey of several minutes to get down to their experiment.
And all thanks to a small box once installed in a corner of Holborn tube station.
After that initial experiment showed the potential for carrying out studies underground, in the 1960s, Holborn was often used for science of this nature.
A spare platform at Holborn had been converted to offices during the war. Immediately after the war it was used as a staff hostel, and later many of the rooms were used by physicists for experiments needing a deep location.
These were usually lead by John Barton, one of the founders of particle astrophysics, who was based in London at the Birkbeck College Physics Department, just up the road from the tube stattion.
The laboratory rooms were reached through a service door on one of the Piccadilly Line platforms. They were linked by an extremely narrow corridor, only wide enough for a single person, running along the edge of what had once been the platform. It was a dry and dusty environment and there were occasional problems caused by rodents chewing cables, but for scientists based in London, it was none the less an extraordinarily convenient site to work.
In fact, Holborn was reused for science as recently as the 1990s, when a low background HPGe detector was installed in the tube station from May 1990 to July 1993.
Most of the materials studied were those being considered for use in the Solar Neutrino Observatory, which was a detector some 2km deep under Canada, or in the UK Dark Matter programme.
Holborn tube station is a veritable hot bed of science of the most exotic sort. Something to think about the next time you use it.
“100 meters”?