Demonstration of Gd-GEM detector design for neutron macromolecular crystallography applications

The European Spallation Source (ESS) in Lund, Sweden willbecome the world's most powerful thermal neutron source. TheMacromolecular Diffractometer (NMX) at the ESS requires three51.2 × 51.2 cm$^{2}$ detectors with reasonable detectionefficiency, sub-mm spatial resolution, a narrow point-spreadfunction (PSF), and good time resolution. This work presentsmeasurements with the improved version of the NMX detector prototypeconsisting of a Triple-GEM (Gas Electron Multiplier) detector with anatural Gd converter and a low material budget readout. The detectorwas successfully tested at the neutron reactor of the BudapestNeutron Centre (BNC) and the D16 instrument at the InstitutLaue-Langevin (ILL) in Grenoble. The measurements with Cadmium andGadolinium masks in Budapest demonstrate that the point-spreadfunction of the detector lacks long tails that could impede themeasurement of diffraction spot intensities. On the D16 instrumentat ILL, diffraction spots from Triose phosphate isomerase w/2-phosphoglycolate (PGA) inhibitor were measured both in the MILANDHelium-3 detector and the Gd-GEM. The comparison between the twodetectors shows a similar point-spread function in both detectors,and the expected efficiency ratio compared to the Helium-3detector. Both measurements together thus give good indications thatthe Gd-GEM detector fits the requirements for the NMX instrument atESS.