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Basic detector elements

Diagram showing polymeric damage by path of particle

The basic MoEDAL stack housing 10 plastic layers (24 cm x 24cm), including 4 CR39 layers 3 MAKROFOL layers

The basic detector unit of the MoEDAL experiment is a stack of ten sheets of plastic NTDs, consisting of 4 sheets of CR39 (polyallyl diglycol carbonate - PADC), each ∼ 0.5 mm thick, 3 sheets of MAKROFOL (lexan (each ∼0.5mm thick) with Lexan (each ∼0.2mm thick) forming the first, middle and end sheets of the stack.

The basic MoEDAL detector units are deployed in aluminium housings that hold 6 basic MoEDAL NTD stacks. The aluminium housing is 1.00 mm thick aluminium. The size of the housing is approximately 50 cm x 75 cm with a depth of approximately 2 cm. The weight of the housing when full of detectors is around 8 Kg. Commercially pure aluminium alloy (1100) is utilized throughout the MoEDAL detector in order to reduce activation.

For highly ionizing particles such as fast magnetic monopoles the Restricted Energy Loss (REL) of the incident particle will be constant along the trajectory of the monopole through the detector sheets. Thus, etch pit cones will be collinear and equally sized, throughout the NTD stack. This energy loss signature is easily distinguished from background of low energy particles which are slowed down and even absorbed inside the detector. In this case the etch-pit size changes (increases) along the trajectory as it loses energy.