ESS NMX: neutron detection with GEMs

In the framework of the BrightnESS grant, the prototype of a time resolved high resolution neutron detector has been developed for the NMX instrument at European Spallation Source ERIC (ESS). The triple GEM detector with a Gadolinium neutron converter has an active area of 50 x 50 cm2 and an x/y strip readout with 400 μm pitch, which is read out with RD51 VMM3a hybrids and the Scalable Readout System (SRS).

Cross section of the final detector design for the NMX prototype (left): The neutrons enter the detector through a thin readout foil and passes the triple GEM stack and drift volume, before it releases an electron in the gadolinium converter at the anode. The VMM readout is placed at the sides of the detector housing, as one of the design requirements is minimal size of the periphery.


A position resolution of better than 300 μm has been obtained with thermal neutrons. A Cadmium mask with 1.0 mm holes, diagonally separated by 1.3 mm, can be clearly resolved.

Left: photograph of the a Cadmium mask put into the neutron beam. Right: image of the cadmium mask recorded using a triple GEM detector with a Gadolinium neutron converter.


The first measurement with the full size demonstrator have been performed using a Copper X-ray beam. The 2D image of the beam is presented below.

2D image of our X-ray beam.