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OPAL was one of the 4 experiments at CERN's Large Electron Positron collider (LEP) which ran from 1989 - 2000. This array of 96 lead glass bricks formed part of the OPAL electromagnetic calorimeter. In total, there were 9440 lead glass counters in the OPAL electromagnetic calorimeter, made of Schott type SF57 glass and each block weighs about 25 kg and consists of 76% PbO by weight. Each block has a Hamamatsu R2238 photomultiplier glued on to it. The complete detector was in the form of a cylinder 7m long and 6m in diameter. It was used to measure the energy of electrons and photons produced in LEP electron positron collisions.

This module was built and tested with beam to validate the ATLAS electromagnetic calorimeter design. One original design feature is the folding. 10 000 lead plates and electrodes are folded into an accordion shape and immersed in liquid argon. As they cross the folds, particles are slowed down by the lead. As they collide with the lead atoms, electrons and photons are ejected. There is a knock-on effect and as they continue on into the argon, a whole shower is produced. The electrodes collect up all the electrons and this signal gives a measurement of the energy of the initial particle. This 2 m long module dates back to the first detector studies for the LHC in the 1990’s. It was built by the R&D collaboration RD-3 to evaluate the performances of liquid argon calorimetry for the physics programme - the search for the Higgs boson decays into two photons, in particular. After the choice of that technology by the ATLAS collaboration, the design of its elements were reassessed in view of production and a new module was tested in the CERN beam lines, leading to the Technical Design Report in 1996.

Muon detectors from the outer layer of the ATLAS experiment at the Large Hadron Collider. Over a million individual detectors combine to make up the outer layer of ATLAS. All of this is exclusively to track the muons, the only detectable particles to make it out so far from the collision point. How the muon’s path curves in the magnetic field depends on how fast it is travelling. A fast muon curves only a very little, a slower one curves a lot. Together with the calorimeters, the muon detectors play an essential role in deciding which collisions to store and which to ignore. Certain signals from muons are a sure sign of exciting discoveries. To make sure the data from these collisions is not lost, some of the muon detectors react very quickly and trigger the electronics to record. The other detectors take a little longer, but are much more precise. Their job is to measure exactly where the muons have passed, calculating the curvature of their tracks in the magnetic field to the nearest five hundredths of a millimetre. Even these precision detectors are not exactly sluggish – they react within a millionth of a second. Such a fast response is essential when new collisions are occurring in the centre of ATLAS 40 million times every second! This muon detector is a drift tube - an aluminium tube with a wall thickness of some 1/10 mm that is filled with a special gas mixture. Inside the tube there is a wire that is tightened all over the length of the tube and fixed at the end caps. Particles (or ionizing radiation) that enter the tube ionize the gas molecules and liberate electrons. Since there is a high voltage between the wire and the tube wall, the released negatively charged electrons move towards the wire in the centre of the tube. On their way to the central wire, the moving electrons induce an electric signal that can be amplified and registered by further electronics.