Applications of the GEM at high pressure for neutrons and X-rays T.L. van Vuure , R. Kreuger , C.W.E. van Eijk  and R.W. Hollander , L. M. S. Margato , F. A. F. Fraga *, M. M. F. R. Fraga *, S. T. G. Fetal *, R. Ferreira Marques *, A. J. P. L. Policarpo *  Radiation Technology Group TU Delft  LIP Coimbra Universidade de Coimbra

Why the GEM? New spallation sources make new demands: higher flux density: order of magnitude 1 mm position resolution high efficiency for thermal neutrons good time resolution (us)

Electric field near holes in the GEM

% transparency Real gain 200 Effective gain 80 50% yield

3 He thermal neutron capture Thermal neutron detection based on 3 He + n  3 T + p MeV Centroid charge distribution does not correspond with interaction position n 3T3T p 3 He Position error (FWHM) ~ 80% proton range Add high pressure stopping gas

High pressure test vessel CF40 flange (4 total) CF160 flange  200 mm 150 mm 6 mm exposed Be Be 23 mm

Gain curves for a GEM in Xe/TMA (4.0 bar necessary) ~ position of 1 bar pure Xe

Comparison between gases (2)

Gain curves for a GEM in 3 bar Xe/TMA with He He partial pressure

Electronics prototype A strip readout will be used: 50 strips of 1 mm wide. For 3 mm gap between GEM and strips, pulses have been shown to be ~400 ns This is reasonably matched with the available preamplifiers, IDE AS VA-TAN

CCD readout of GEM scintillation Radiation source

Radiography of a small dog-whelk double GEM, 5mm absorption space, Xe-2.5%TMA at 5bar, molybdenum X-ray tube at 40 kV

Radiography of a small snail (~8 mm) double GEM, 5mm absorption space, Xe-2.5%TMA at 5 bar, molybdenum X-ray tube at 30 and 40 kV The width of the shell fissure is similar to the GEM pitch

Current status Manufacturing prototype neutron counter Investigating electron diffusion in Xe/TMA