Presentation on theme: "ICANS-XVIII A position sensitive transmission detector for epithermal neutron imaging E. M. Schooneveld and Ancient Charm partners."— Presentation transcript:
ICANS-XVIII A position sensitive transmission detector for epithermal neutron imaging E. M. Schooneveld and Ancient Charm partners
Content Introduction Principle Construction Measurements Conclusions Future
Introduction ANCIENT CHARM EU funded FP6 project, contract Goal: 3D imaging of cultural heritage (archaeological) objects. Archaeologists want to know elemental and phase composition of object. Want to look inside object imaging
Introduction Pros: Native imaging (2D detector) no scanning pencil beam 4 solid angle coverage Elemental analysis Structural analysis ? Cons: Small dips on high baseline need good statistics + good baseline estimation Position resolution limited to ~1mm Need low beam divergence or detector close to sample
Principle Neutron Detector beam Estimated data collection time: ~1 hr per 2D image ~1 day per tomograph.
Principle Element identification by resonant neutron absorption. Need resonance in right energy range
Periodic system with indications for suitability of NRT (regions were lowest resonance occurs) Principle
Construction Detector 16 channel PMT Optical fibres (4 per pixel) GS20 glass scintillators 1.8mm * 1.8mm * 9mm Pixels: 4 * 4 array with 2.5mm pitch 10mm * 10mm active area. Made 16 pixel prototype to get experience with assembly and test performance.
Construction Monte Carlo simulations (GEANT4) Issues: Type of optical fibre + scintillator support. Cross-talk: FibresSupportTotal cross-talk (%) - Quartz Plastic Al BoronNitride Al BoronNitride Made prototype with plastic fibres and BN scintillator support.
Measurements Measurements on INES beam line at ISIS DISCLAIMER: Measurements mainly done to examine detector performance (not to demonstrate technique) Measured a few archaeological objects, but no imaging Software for composition analysis and image reconstruction not ready yet. Not enough timing resolution yet.
Measurements Basic properties Useful energy region: up to ~1 keV Count rate (per pixel): ~200 kHz (5% dead time)
Measurements Big gold foil with 2.5mm hole. No dip for pixel with hole low cross-talk As MC predicted plastic fibres no problem
Measurements Bronze sheet (90.5% Cu, 8.49% Sn, 0.088% Ag) Good agreement Missing peaks, mainly Iodine (upstream in beam)
Measurements Agreement less good. Still good for imaging
Measurements Very corroded could not measure tin with diffraction. Piece of bronze vase from Villa Giulia
Measurements No problem to see tin resonances.
Measurements ANCIENT CHARM black box Diffraction: lot of incoherent scattering Neutron radiography: low penetration lot of H } NRT : much higher penetration of high energy neutrons hydrogen moderates neutrons peaks broader
Measurements All peaks about same height thick silver (~1 cm ) Peak amplitudes << 1 background from moderated neutrons. Peak shape correct still able to identify elements Black box contains silver object, probably also hydrogen !!
Conclusion Successfully built 16 pixel prototype transmission detector. Detector performed very well: Low cross-talk, high rate capability, acceptable energy range. Successful NRT tests. We are very happy with the detector.
Future 100 pixel detector integrated with goniometer Imaging Diffraction