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

Available techniques Phase, structure texture analysis: –Neutron diffraction. Element analysis: –Delayed Gamma Activation Analysis (DGAA) –Prompt Gamma Activation Analysis (PGAA) –Neutron Resonant Capture Analysis (NRCA) Introduction

Imaging techniques: –Neutron tomography (NT) –Neutron diffraction tomography (NDT) –Prompt Gamma Neutron Activation Imaging (PGAI) –Neutron Resonance Capture Imaging (NRCI) –Neutron Resonance Transmission (NRT) Our detector transmission neutron detector NRT

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.

Construction Photos

Construction

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

The end THANK YOU