1. Status report FRM2 In-Kind Contribution: a 10 B-based gas detector with macrostructured multilayers Irina Stefanescu, Yasin Abdullahi, Ilario Defendi, Machiel Zee, Karl Zeitelhack FRM-II, Technische Universität München, Germany Carina Höglund, Richard Hall-Wilton European Spallation Source, Lund, Sweden Jens Birch, Lars Hultman Thin Film Physics Division, Linköping University, Sweden

2. Concept Traditional MWPC with several layers of Boron-lined flat parallel plates MWPC with several layers of Boron-lined grooved cathodes 3D regular pattern consisting of grooves that can be created in the cathode material by milling, extrusion, forming, etc.  mm α=45° Sense wires

3. Concept

4.  MWPC with Boron-lined grooved cathodes is expected to have an efficiency superior to that of a counter incorporating the traditional flat plates.

5.  chosen design consists of 45° grooves separated by small, flat portions;  fabricated by milling with a 45° milling cutter. Selecting the geometry of the 3D pattern h = 1  5 mm Shape parameters optimized in Geant4: height of the groove, h; length of the flat top, f; thickness of the Al-substrate at the bottom (top) of the groove, l. GOALS: - Lightweight cathode, but robust and easy to handle; - maximum conversion efficiency when coated with 10 Boron.

6. Optimization of the design in GEANT4 Geant4 optimization analysis performed for both coating scenarios.

7. Optimization of the design in GEANT4 Ɛ Geant4 = Integral energy spectrum > threshold number of incident neutrons Generation of low-energy electrons along a particle track and the precise tracking of the drift electrons in the presence of the an electric field are beyond the current capabilities of GEANT4  efficiency extracted from the energy deposition spectra. Ar/CO 2 (70/30) 10 B(n,α) 7 Li ε detection = ε conversion x ε charge collection ε Geant4  ε conversion Record histograms with the energy deposited in gas by the reaction products ( 7 Li and α)

8. Conversion efficiencies calculated with GEANT4 = 4.7 Å t side = t top · sin(22.5°) t side = t top · x/h t top = t flat = 3 μm

9. Proof-of-concept measurements cathodes with grooves with heights 1.1, 2.1, 3.5, 4.5, and 5 mm manufactured with the 45° milling cutter ; coated on one side with 3  m enriched 10 B 4 C by DC magnetron sputtering in the Thin Film Physics Division at the University of Linköping, Sweden. C. Höglund et al., Journal of Applied Physics, 111 (2012) 104908. Cathodes mounted in a test detector placed on a X-Y moving table. Efficiencies determined by normalizing the number of counts observed in the PHS to the integral of the spectrum measured with a calibrated 3 He tube mounted in the detector position. n y +x - x In-beam measurements at TREFF, FRM-II

10. Proof-of-concept results; comparison with GEANT4 Groove with h = 2.1 mm Scans with collimated beam (0.3 mm 2 ) top bottom side I. Stefanescu et al., submitted to NIMA.

11. Predictions for multilayer configurations = 1.8 Å The number of layers in the stack refers to 2-sided coated layers. Goal: ε > 50% at 1.8 Å

12. Garfield calculations MWPC with flat cathodes Ar-CO 2 gas (70-30), 1 atm, 300 K A-C distance = 3.7 mm Wire pitch = 5 mm α track, 1.47 MeV Cathode planes, V=0 Wires, V= 1.2 kV Drift time  0.4 μs p track, 570 keV Drift time  4.5 μs 1´´ 3 He tube @ 6 atm Wires

13. Garfield calculations MWPC with grooved cathodes Drift time  0.7 μs Groove height = 3.5 mm

14. The FRM2 demonstrator 40 cm - first version will incorporate 5 independent MWPCs (10 Boron layers); - will operate in continuous gas flow; - will have resistive readout, wire pitch = 5 mm; - will simultaneously demonstrate the performance of both macrostructured-cathode MWPC concept, as well as the flat-cathode multi-layer MWPC. n

15. The Boron-coated cathodes 28 plates, 5x40 cm 2, groove depth = 2.1 mm, 1.4 μm 10 B 4 C, 2- sided. 11 plates, 10x40 cm 2, 1 μm 10 B 4 C, 2-sided. Coatings for the demonstrator from U. Linköping, Sweden Support structures for the cathodes and wires.

16. The FRM2 demonstrator (2) The winding machine The ZWICK machine The Mesytec electronics

17. The test detector (1) Measurements of efficiencies for multilayer configurations and position resolution planned for the next beamtime (to begin on 18.02.2013). Old test detector can accomodate 3 independent MWPCs Old detector pot Extension ring7 cm 20 cm

18. The test detector (2) The 13x13 cm 2 cathodes for the test detector were made with the “chop and glue” technique. C. Höglund et al., Journal of Applied Physics, 111 (2012) 104908. K. Andersen et al., arXiv:1209.0566v1, 2012. Possible to compensate the non-uniformity in layer thickness by assembling the layers such that the F-B coatings in a counter compensate each other‘s gradient. 1 μm  - 20% 1.4 μm  - 20% ….but the plates mounted randomly

19. Multilayer configurations, 4.7 Å

20. Perspectives Short term plans (current + 1 yr) - further measurements to address key parameters like position and time resolution, efficiency multilayers (small test detector  ``physics prototype”); - measurements with the demonstrator  ``technical prototype”. Need to asses performance on existing instruments in real conditions. Long term plans - optimization of the geometry of the macrostructured cathode (Geant4 + extrusion or forming); - concept adequate for applications that require several m 2 of active area, ε  50% at 1.8 Å, position resolution better than 1x1 cm 2, time resolution better than 5 μs (use single coatings); - optimizations to meet the requirements of a specific instrument (e.g., Chopper Spectrometer).

21. Garfield calculations

22. h > 2 mm n  - threshold h  0.5 mm n  - threshold Calculations performed with a parallel neutron beam of 4.7 Å striking the cathode at normal incidence. Boron layer: enriched 10 B 4 C ; t top = 3 μm = t flat ; t side = t top · sin(α/2)  1.15  m for the uniform coating scenario t side = t top · x/h  0…3  m for the non-uniform coating scenario Conversion efficiencies calculated with GEANT4 = 4.7 Å

23. Theoretical efficiency scans were performed with a 0.3 mm wide, parallel neutron beam of 4.7 Å. n 7 Li α Top Side Bottom Conversion efficiencies calculated with GEANT4  9%  9-15%  2-5% h = 2.1 mm 2.5 mm h = 5 mm 5.9 mm