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STRUCTURES/INFRASTRUCTURE
What the eye
PHOTOGRAPHY: FOUR BY THREE
CANNOT SEE
GRAEME BICKERDIKE
Dr Chris Steer and Dr Patrick Stowell check data below the ventilation shaft.
S
ome things make my brain hurt: Channel Four’s Naked Attraction, all Apple products, the cost of HS2. But, most recently, I’ve found myself befuddled by a scientist’s assertion that we are constantly being rained upon by subatomic particles which pass through anything and everything as they head deep into the Earth.
What’s even more baffling is that these particles have value in asset management terms. In fact, they have the potential to help the railway draw a line under a longstanding concern both of Network Rail and the Office of Rail and Road, by confirming the location of many-dozen hidden construction shafts, sunk when our inventory of tunnels was driven during the Victorian era but for which records no longer exist.
Science lesson Cosmic rays are produced where solar and extra-galactic particles collide with the upper atmosphere, causing a further shower of particles which fall towards the Earth’s surface. Of those that make it all the way, the majority are muons; these typically have a rate of
Rail Engineer | Issue 186 | September/October 2020
10,000 per square metre per minute - that’s the approximate equivalent of one passing through your hand every second, if held horizontally. The energy range of the particles is quite broad; a fraction hit the ground and stop, whilst the remainder penetrate the rock and can continue downwards for hundreds of metres. Their presence can be recorded by means of a detector wherein they deposit small amounts of energy which is converted into light and captured by a photosensor. If the equipment is moved through a tunnel, any low-density features within the overburden - such as a shaft - will coincide with a higher rate of penetrating muons than elsewhere, although the results have to be adjusted to take account of variations in the depth of the overburden.
