1. 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

2. 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)

3. Electric field near holes in the GEM

4. 20 80 100 8000 80% transparency Real gain 200 Effective gain 80 50% yield

5. 3 He thermal neutron capture Thermal neutron detection based on 3 He + n  3 T + p + 0.7 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

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

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

8. Comparison between gases (2)

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

10. 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

11. CCD readout of GEM scintillation Radiation source

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

13. 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

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