MS18: Optimised design for NMX

The design of the Gadolinium GEM detector for NMX has been optimized. A CAD drawing of the detector including detector support is shown in Figure 1. A drift length of 10-15mm has been determined as the optimum drift length. With two GEM foils and a low material budget readout an efficiency of 14% is reached for thermal neutrons with a 25 um thick cathode of natural Gd. Whereas a conventional PCB board is made from 1.6 mm of FR4 and causes massive scattering of the neutrons, the low material budget readout contains only a thin foil that separates the x and y strips of the readout.

Ultrasonic welding has been used successfully to weld Gd foils to Al supports. Ultrasonic welding, which is a novel technique in combination with Gadolinium foils, makes it possible to produce a large 60cm x 60 cm cathode from commercial Gd foils. This collaborative work has been carried out with the industrial partners Branson Ultrasonic (ultrasonic welding equipment) and Goodfellow (Gd foils).

Extensive tests of the detector have been carried out at the R2D2 beam line of the Institute for Energy Technology (IFE) in Kjeller, Norway, first with hybrids with the APV-25 ASIC, later with VMM-2 hybrids.

The major physical development steps for the design optimization of the detector have thus been finished. The detector behavior and factors that affect performance are understood.