1. NMX STAP REVIEW: DETECTORS FOR NMX Dorothea Pfeiffer on behalf of the ESS detector group 10.09.2014

2. Content 2  Collaboration  NMX instrument and requirements  Principle of GEM detectors  Neutron converters  Gd-Neutron GEM simulations and prototypes  Schedule and cost Dorothea Pfeiffer – NMX STAP Review 10.09.2014

3. Collaborations and People involved 3  ESS detector group  Dorothea Pfeiffer (CERN) – Coordinator (1yr)  Filippo Resnati (CERN) – Detector R&D (March)  Thomas Kittelmann (Lund) – Computing and Simulations  Scott Kolya (Lund) - Electronics  Carina Hoeglund (Linkoping) - Coatings  Linda Robinson (Linkoping) - Coatings  ESS joined RD51 in 2013 as only external institute financially supporting the MPGD R&D and detector lab  CERN MPGD group world wide leading in R&D  Superb track record in delivering high performance detectors (took on message from STAP)  Support from CERN thin film experts from TE-VSC Dorothea Pfeiffer – NMX STAP Review 10.09.2014

4. Neutron Macromolecular Crystallography 0.2mm Resolution 60x60cm modules? Good time resolution > 30% efficiency Gamma rejection not particularly important E. Oksanen

5. Challenges and History 5  200 um beyond state of art for time resolved detector  Rate requirements to be evaluated, but may be relatively high  Gd-MSGC was obvious choice, HZB was a strong and certain in-kind partner with a10 yr history  Ca. 18 months ago: HZB ordered to cease development  ESS detector group prioritized this development  Employed Dorothea, funded Filippo as CERN fellow  Engaged with CERN as strong, stable, long term collaborative partner  Joined RD51, Strong R&D collaboration and community (ca. 500 people, 100 institutes)  No problem to find in-kind partners once R&D is proven Dorothea Pfeiffer – NMX STAP Review 10.09.2014

6. Gd-Based MSGC/GEM Detector HZB in-kind contribution to ESS originally developed within context of DETNI /NMI3 Substitute MSGC with GEMs: now a collaboration CERN-HZB- ESS

7. GEM detector principle 7 Dorothea Pfeiffer – NMX STAP Review 10.09.2014 Courtesy: F. Sauli

8. GEM Foil Amplification Principle 8 Dorothea Pfeiffer – NMX STAP Review 10.09.2014 Courtesy: F. Sauli

9. GEM Foil 9 Dorothea Pfeiffer – NMX STAP Review 10.09.2014 Courtesy: F. Sauli

10. Neutron converters  Good neutron converters have a high cross section for thermal neutrons  The neutron capture creates a charged particle that can be easily detected  The converter has to have the correct thickness so that a maximum of the charged particles can escape and reach the gas volume 10 Dorothea Pfeiffer – NMX STAP Review 10.09.2014

11. Thermal neutron cross sections 11 Cross sections, especially for Gd, vary considerably in the literature Dorothea Pfeiffer – NMX STAP Review 10.09.2014

12. Geant4 Gadolinium Simulations 12 Converter Drift backwards 0.25 – 50 um 25 meV neutrons Scoring of electrons that cross boundary between converter and drift Drift forwards  Geant4 simulations to evaluate different converter materials and thicknesses  Natural Gd, 155 Gd, 157 Gd, Gd2O3 and enriched Gd2O3 were simulated Dorothea Pfeiffer – NMX STAP Review 10.09.2014

13. Neutron capture and conversion electrons 13

14. Conversion electrons in drift space 14

15. Electron spectra of natural Gd and 157 Gd 15 conversion electrons (in converter) Electrons arrived in drift natural Gd 157 Gd MeV Mean: 67 keV Mean: 69 keV Mean: 60 keV Mean: 54 keV

16. Gd GEM – first simulation results  Oxides lead to comparable results for number of captured neutrons and conversion electrons created, but are not conductive. Need to have conductive layer added if they are used in forwards and backwards direction  Contrary to what is found in the literature, 155 Gd has a higher percentage of conversion electrons per captured neutron than 157 Gd  The capture cross section of 155 Gd is smaller than that of 157 Gd, therefore a thicker converter is needed. But since the spectrum of 155Gd (mean 83 keV) is considerably harder than that of 157 Gd (mean 61 keV), the conversion electrons can exit the converter  Assuming the simulations are correct, the upper threshold for the detection efficiency lies at 45 %  Needs to be verified by measurements! 16 Dorothea Pfeiffer – NMX STAP Review 10.09.2014

17. Gd2O3  Gd2O3 coated Al foil can be bought from companies like Euro Collimator  The coating is created by spraying a paint consisting of Gd2O3 and acrylic resin onto the foil  The highest density that can be reached at the moment is 47% of Gd2O3  Enriched Gd2O3 is available e.g. from STB Isotope GmBH for the following prices:  For 1g of 90.2 % Gd 155 in Gd2O3: 10.10 per mg  For 1g of 87.5 % Gd 157 in Gd2O3: 7.33 per mg  The enriched Gd2O3 only leads to considerably better results than the natural Gd in metal form if the paint consisted of >= 80% Gd2O3 17 Dorothea Pfeiffer – NMX STAP Review 10.09.2014

18. Enriched Gadolinium in metal form  100 um sheets of enriched Gd can be obtained from the Swedish company Buyisotope.com:  Gd-155 isotope in metallic chemical form with isotopic enrichment 90.4% in form of metal foils with following dimensions (approx.): 1) 50 mm*100 mm*0.1 mm, total mass of one foil is approx. 3900 mg at price of 8.96 Euro per mg.  Gd-157 isotope in metallic chemical form with isotopic enrichment 88.4% 3) 50 mm*100 mm*0.1 mm, total mass of one foil is approx. 3900 mg at price of 6.49 Euro per mg.  Very expensive, 70000 Euros for two small sheets! We will verify this once we know rest of concept is proven.  On the phone I was told that the production of the sheets starts out with enriched Gd2O3  In collaboration with the CERN surface treatment group we are now investigating possibilities to create thin films also starting with the oxide 18 Dorothea Pfeiffer – NMX STAP Review 10.09.2014

19. Natural Gadolinium in metal form  Obtained 10 cm x 10 cm and 10 cm x 5 cm Gd sheets from ESPI metals in 0.01‘’ thickness  Will be tested in backwards configuration with new triple GEM (arrival of detector: October 3 rd )  Efficiency of natural Gd not sufficient for NMX, but basic principles of the detector can be evaluated 19 Dorothea Pfeiffer – NMX STAP Review 10.09.2014

20. Neutron GEM in backwards configuration 20 Dorothea Pfeiffer – NMX STAP Review 10.09.2014

21. Geant4-Garfield Simulation Setup 21 Converter Drift (3mm – 10 mm) 50 um of natural Gd 25 meV neutrons  To simulation the position resolution, the deposited energy of the conversion electrons and the sensitivity to gamma background, a Geant4/Garfield++ interface was created  As a first step of a complete detector simulation, the primary ionization clusters in the drift were simulated 100 keV – 1GeV gamma (forwards) electrons 100 keV – 1GeV gamma (backwards) Dorothea Pfeiffer – NMX STAP Review 10.09.2014

22. Tracks left by conversion electrons in ArCO 2 22 50 um natural Gadolinium 10 6 thermal neutrons simulated, of which 16% had conversion electrons create a track in the drift Simulated with Heed, which assumes a thin absorber and does not include multiple scattering

23. Projection of tracks in xy plane at start of drift (z=-0.5 cm) 23 10 6 thermal neutrons simulated, of which 16% had conversion electrons create a track in the drift eV

24. Projection of tracks in xy plane at end of drift (z=0.5 cm) 24 10 6 thermal neutrons simulated, of which 16% had conversion electrons create a track in the drift eV

25. Position resolution  The conversion electrons leave long straight tracks in the drift space  The majority of tracks start with an angle close to the surface normal of the converter  But still the endpoints of the track show a large spread  Centroid calculation not sufficient to determine position  Tracking method is needed to determine the start point of the track, or an additional CsI layer that converts the conversion electrons into very low energy secondary electrons (a few eV) 25 Dorothea Pfeiffer – NMX STAP Review 10.09.2014

26. uTPC analysis  As already shown with data acquire with the Boron GEM, the uTPC analysis has the capability to determine the start of a track which leads to a position resolution of ~100 um  Also has the capabilities to distinguish between electrons and gammas  The Boron GEM prototype is ready to validate general neutron performance of GEM 26 Drift time [25 ns bin] alphagamma

27. Tracks created by prompt gammasin ArCO 2 27 10 6 thermal neutrons simulated, of which 0.06 % had prompt gammas create a track in the drift

28. Conversion electrons - Primary ionization spectrum 28

29. Primary ionization in 10 mm ArCO 2 by electrons caused by gamma background 29 - No clear discrimination between conversion electrons and secondary electrons created by gammas - Pulse height spectrum depends on the energy of the incoming gamma - However difference in distribution similar to that from ZnS scintillators - Future study will evaluate rejection power

30. Signal height and gamma discrimination  The amount of deposited energy and thus the signal height (independent of amplification by the GEMs) depends on the size of the drift space  Ionization spectrum of conversion electrons is a Landau distribution  Drift thickness, gain of detector and electronics have to be chosen in such a fashion that all signals created by conversion electrons are correctly detected (dynamic range)  Gamma background deposits different amounts of energy depending on the energy of the incoming gamma and the thickness of the converter, but on average more than the conversion electrons  Upper discriminator threshold to reduce background? 30 Dorothea Pfeiffer – NMX STAP Review 10.09.2014

31. Sensitivity to gamma background 31 Gamma background creates secondary electrons in the Gd and other detector parts, which then ionize the gas in similar fashion as the conversion electrons Dorothea Pfeiffer – NMX STAP Review 10.09.2014

32. Shortterm R&D Schedule  Fall/winter 2014: Characterize Gd2O3 and Gd GEM, investigate CsI option. Simulate complete detector with Geant4/Garfield++ interface, develop first test prototype (prototype 1)  End 2014: Have Boron GEM and Gd GEM plus crate ready to take to test beam. a) IFE or Berlin - definitely. b) Los Alamos if possible? NMX line would be very helpful.  Q1/2 2015: Verify simulations, determine in which ways the detector has to be improved, decide whether Gd is feasible  Late 2015: Refined prototype  2016: Test samples Gd-155, 157  2017: Decision on technology  2017: Technology demonstrator  Late 2017: Start of construction 32 05.05.2014 Dorothea Pfeiffer – NMX STAP Review 10.09.2014

33. Electronics - ASICs 33 Dorothea Pfeiffer – NMX STAP Review 10.09.2014 Courtesy: S. Kolya Being evaluated ASIC used for R&D

34. Electronics – Readout Model 34 Dorothea Pfeiffer – NMX STAP Review 10.09.2014 existing ASIC, no development needed Developed by ISIS ICS DMSC Courtesy: S. Kolya

35. 35 Schedule

36. Present costing of options  Gd GEM, Plan A  Coatings: 3 M€ max.  Electronics: 750 k€ Frontend: 500 k€ Backend: 200 k€ HV/LV: 50 k€  Mechanics: 100 k€  Labor: 1 M€  Conservative Total: 4.85 M€  Big opportunity: Coating cost  Anger cameras, Plan B  (-) 108 modules: high cost Guestimate 2017: 20% less ??  (-) Resolution: severely degraded  (-) Rate requirement needs evaluation  (+) Known technology  (+) Experts in Europe (Juelich)  (+) Possible commercial supply 36 Dorothea Pfeiffer – NMX STAP Review 10.09.2014