ICANS-XVIII

1. ICANS-XVIII A position sensitive transmission detector for epithermal neutron imaging E. M. Schooneveld and Ancient Charm partners

2. Content • Introduction • Principle • Construction • Measurements • Conclusions • Future

3. Introduction • ANCIENT CHARM • EU funded FP6 project, contract 015311 • Goal: 3D imaging of cultural heritage (archaeological) objects. • Archaeologists want to know elemental and phase composition of object. • Want to look inside object  imaging

4. Introduction • 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)

5. 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

6. 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 baselineestimation • Position resolution limited to ~1mm • Need low beam divergence or detector close to sample

7. Principle Neutron Detector beam • Estimated data collection time: ~1 hr per 2D image  ~1 day per tomograph.

8. Principle • Element identification by resonant neutron absorption. • Need resonance in right energy range

9. Principle • Periodic system with indications for suitability of NRT (regions were lowest resonance occurs)

10. 16 channel PMT GS20 glass scintillators 1.8mm * 1.8mm * 9mm Optical fibres (4 per pixel) Construction • Detector • Made 16 pixel prototype to get experience with assembly and test performance. • Pixels: 4 * 4 array with 2.5mm pitch  10mm * 10mm active area.

11. Construction • Monte Carlo simulations (GEANT4) • Issues: Type of optical fibre + scintillator support. • Cross-talk: • Made prototype with plastic fibres and BN scintillator support.

12. Construction • Photos

13. Construction

14. 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.

15. Measurements • Basic properties • Useful energy region: up to ~1 keV • Count rate (per pixel): ~200 kHz (5% dead time)

16. Measurements • “Big” gold foil with 2.5mm hole. • No dip for pixel with hole  low cross-talk • As MC predicted plastic fibres no problem

17. Measurements • Bronze sheet (90.5% Cu , 8.49% Sn, 0.088% Ag) • Good agreement • Missing peaks, mainly Iodine (upstream in beam)

18. Measurements • Agreement less good. • Still good for imaging

19. Measurements • Piece of bronze vase from Villa Giulia • Very corroded  could not measure tin with diffraction.

20. Measurements • No problem to see tin resonances.

21. Measurements • Diffraction: lot of incoherent scattering • Neutron radiography: low penetration }  lot of H • ANCIENT CHARM black box • NRT :  much higher penetration of high energy neutrons hydrogen moderates neutrons  peaks broader

22. 0.25 0.20 0.15 0.10 0.05 0.00 -0.05 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 !!

23. 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.

24. Future • 100 pixel detector integrated with goniometer • Imaging • Diffraction

25. The end • THANK YOU ∙