ATLAS SHIELDING

JD Shielding

Mass = 130 ton

The disc shield (JD) serves several purposes:

	it provides shielding material to protect the first layer of forward muon chambers, (EI)
	it acts as the primary support for these chambers
	it allows the muon chambers (EI) to be retracted for maintenance
	it reduces the magnetic field level at the tile calorimeter photomultiplier tube.

It comprises a steel disc 130mm thick, with a central plug of copper casting alloy extending downstream by 2.1m and with an inner bore following the line of |ή| = 4.6. This plug interlocks with the toroid shield (JT) so there are no straight paths through which particles could escape down the gap between the two. The fixed plug has a diameter of 0.82m. Further shielding is provided by the hub of the muon chamber support frame, which can be retracted over the plug to allow access to the up stream side of the muon chambers (EI). The hub is also of copper casting alloy, to which the spokes of the frame are attached.

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