10 Bbased MultiGrid Detectors as an alternative to

10 B-based Multi-Grid Detectors as an alternative to 3 He In-beam test on the IN 6 To. F spectrometer ILL Mathieu Ferraton, Jean-Claude Buffet, Je. F Clergeau, Jonathan Correa, Sylvain Cuccaro, Bruno Guérard, Francesco Pitcitelli, Patrick Van Esch ESS Carina Höglund, Richard Hall Wilton, Anton Khaplanov 14/10/2013 Special Workshop on Neutron Detection with MPGDs 10 B-based Multi-Grid Detectors as an alternative to 3 He

Outline • Basic principles and design of the IN 6 Multi-Grid prototype – mechanics – electronics • In-beam measurement on the IN 6 To. F spectrometer – – – Neutron efficiency and comparison with 3 He tubes Gamma sensitivity Background Time resolution Scattering in aluminum • Construction of an IN 5 Multi-Grid prototype 14/10/2013 Special Workshop on Neutron Detection with MPGDs 10 B-based Multi-Grid Detectors as an alternative to 3 He

Basic principles of the Multi-Grid and design of the IN 6 prototype 14/10/2013 Special Workshop on Neutron Detection with MPGDs 10 B-based Multi-Grid Detectors as an alternative to 3 He

Principle and Mechanical Design ts neutrons sio n – – 1 frame is mounted with 14 blades coated on each side with 10 B 4 C (1 µm thick) -> 15 cells in depth direction (1 cm each) 1 grid = 15 × 4 cells (2 × 1 cm) -> 60 cells grid are stacked to form 60 gas proportional counters layers (1 µm) en – Al substrate (0. 5 mm) 10 B C 4 gm Base elements are grids (1 grid = frame + blades) fra • Fis Amplification gas 8 cm neutrons 15 cm Neutron conversion in 10 B : neu tron s 2 cm The IN 6 prototype : • • 96 frames arranged as 6 stacks of 16 frames (sensitive area 0. 15 m²) 60 anode wires per stack (total 360 wires) Position Sensitive Detector -> coincidence mode : – Frames : vertical position – Wires : horizontal position and depth Gas mixture : 1 bar Ar/CO 2 (90/10) flushed 14/10/2013 Special Workshop on Neutron Detection with MPGDs ns neutro 10 B-based Multi-Grid Detectors as an alternative to 3 He

Readout Electronics : reduction of channel number • 96 frames + 360 wires = 456 channels • Reduction of channel number : – 30 wires connected together via resistive networks -> charge division allows determination of the targeted wire 2 R R R anode wires R Charge division card Charge Preamplifier • 12 resistive networks × 2 ends = 24 readout channels – 3 frames connected together horizontally • 96 / 3 = 32 readout channels -> 56 readout channels to determine position and depth (reduction by a factor 8) 14/10/2013 Special Workshop on Neutron Detection with MPGDs 10 B-based Multi-Grid Detectors as an alternative to 3 He

Readout Electronics : data acquisition Time signal (from IN 6 chopper) Anode signal (resistive networks) Charge division (or energy) card MCC i. SDN PC Cathode signal (grids) Actual position of the beam MCC (Multi Channel Controller) • • Coincidence reconstruction Position resolution improvement trough Co. G algorithm -> ½ grid (1 cm), ¼ grid (0. 5 cm) x (cm) Result of the Co. G algorithm 0 x (cm) 14/10/2013 Special Workshop on Neutron Detection with MPGDs 10 B-based Multi-Grid Detectors as an alternative to 3 He

In-beam measurement on the IN 6 time-of-flight spectrometer at ILL 14/10/2013 Special Workshop on Neutron Detection with MPGDs 10 B-based Multi-Grid Detectors as an alternative to 3 He

Interest of this measurement • Direct comparison between 10 B Multi-Grid detector and 3 He tubes performances • More observables available thanks to the timing information from the IN 6 chopper • Low background instrument 14/10/2013 Special Workshop on Neutron Detection with MPGDs 10 B-based Multi-Grid Detectors as an alternative to 3 He

The IN 6 instrument • • To. F spectrometer in the range of thermal neutrons Available incident wavelengths : 4. 1, 4. 6, 5. 1, 5. 6 Å Detection system : 337 3 He tubes (sensitive area 4 m²) Total background : 4. 3 Hz • • 3 He tubes (3 bar, diameter 3. 2 cm, length 30 cm) 3 weeks measurement @5. 1 Å with users’ samples 24 h dedicated beam time @4. 1 Å and 4. 6 Å 14/10/2013 Special Workshop on Neutron Detection with MPGDs 10 B-based Multi-Grid Detectors as an alternative to 3 He

Neutron efficiency : comparison with IN 6 53% efficiency was measured @2. 5 Å YGarnet @4. 1 Å Si @4. 6 Å Bragg peaks in the detector -> position spectra match 3 He tubes’ (average on top and bottom 3 He tubes rows) -> better position resolution in the prototype (higher granularity) Ratio of integrated rates in Bragg peaks : - 4. 1 Å : rate(10 B) / rate(3 He) = 1. 08 - 4. 6 Å : rate(10 B) / rate(3 He) = 0. 97 • • 3 He tubes : higher intrinsic efficiency (see theoretical curves) 10 B Multi-Grid : less dead spaces thanks to optimized geometry -> measured efficiencies are similar in both detectors @4. 1 and 4. 6 Å !! 14/10/2013 Special Workshop on Neutron Detection with MPGDs 10 B-based Multi-Grid Detectors as an alternative to 3 He

Gamma sensitivity 3 He (gas) gammas and fission fragments well separated 10 B (solid) plateau measurement gamma and fission fragment spectra widely overlapping Time spectrum Na. I scintillator : -> Strong gamma background from IN 6 (see spectrum) -> well defined time structure Time spectrum multigrid Multi-Grid detector : -> a similar time structure is observed for large values of the high voltage (above 900 V) -> no sign of this structure down from 900 V 14/10/2013 Special Workshop on Neutron Detection with MPGDs 10 B-based Multi-Grid Detectors as an alternative to 3 He

Background measurement • 4. 4 Hz flat background (30 times higher than IN 6’s) was observed (no time structure) -> independent of the IN 6 instrument Zn. O@5. 1 Å • Energy structure of the background (Pulse Height Spectrum measured on wires) : PHS measured on wires – significant rate up to more than 3 Me. V (excluding neutrons and gammas) – background energy spectrum overlaps fission fragments spectrum (no threshold discrimination possible) How do we explain this background ? 14/10/2013 Special Workshop on Neutron Detection with MPGDs 10 B-based Multi-Grid Detectors as an alternative to 3 He

Source of the background • Aluminum is known to be contaminated by alpha emitters (238 U, 232 Th and daughters) – corresponding measured rate : 0. 05 to 0. 25 cm-2. h-1 – our detector is made of 360 Al tubes, 192 cm² each -> expected total rate between 0. 96 Hz and 4. 8 Hz (whole detector) -> the measured 4. 4 Hz background rate is coherent with these values alpha energy (from MC simulation) Background PHS on wires (no B 4 C coating) • Two solutions have been investigated : - Ni layer ( > 23 µm) deposited on the Al surface - ultra-pure Al (U, Th concentration < 1 ppb) -> Background reduced by a factor of 20 14/10/2013 Special Workshop on Neutron Detection with MPGDs 10 B-based Multi-Grid Detectors as an alternative to 3 He

Time resolution : effect of time correction • • Measured To. F depends on the interaction depth in the detector To. F value of interest is at the entrance window of the detector -> To. F value has to be corrected for depth Elastic neutrons 10 B@4. 6 Wavelength (Å) 4, 1 4, 6 5, 1 FWHM (µs) 3 He 10 B 45, 3 45, 9 57, 3 50, 7 53, 0 65, 2 Å (10 B -3 He) / 3 He 12, 0% 15, 5% 13, 7% 14/10/2013 Special Workshop on Neutron Detection with MPGDs δdepth = 1 cm → δTo. F = 8. 6 µs (@4. 6 Å) 10 B-based Multi-Grid Detectors as an alternative to 3 He

Time resolution : effect of scattering in Al YGarnet@4. 1 Å • Base of the elastic peak is widening toward low energy for 4. 1 Å and 4. 6 Å data • No such effect @5. 1 Å Si@4. 6 Å -> consequence of scattering in aluminum (Bragg cutoff @4. 67 Å) Zn. O@5. 1 Å 14/10/2013 Special Workshop on Neutron Detection with MPGDs 10 B-based Multi-Grid Detectors as an alternative to 3 He

Neutron scattering in aluminum • Cd shielding Dedicated experiment (24 h beamtime), Bragg peaks in the detector (higher rate and peak/background ratio, well defined angular position) – 2 wavelengths and 2 samples (YGarnet@4. 1 Å, Si@4. 6 Å) – Bragg scattering angles : θ • 4. 1 Å : θ = 122° • 4. 6 Å : θ = 160° Some neutrons have negative speed (traveling from the back to the front of the detector) -> Bragg scattering at the back of the detector (thick exit Al window to cross) 4. 6 Å z = 12 4. 6 Å z=6 • • 14/10/2013 Special Workshop on Neutron Detection with MPGDs Only neutrons with λ < 4. 67 Å (Bragg cutoff) induce coherent Bragg-scattering (σincoherent << σcoherent) Shielding the back of the detector will suppress the observed bump in time-of-flight spectra 10 B-based Multi-Grid Detectors as an alternative to 3 He

Summary of the results • The Multi-Grid concept has confirmed the good expected performances (efficiency comparable with IN 6’s, low gamma-sensitivity, good time-of-flight resolution) • Scattering in aluminum was observed • The question of alpha emission in aluminum was raised -> It is now time to go to the next step! 14/10/2013 Special Workshop on Neutron Detection with MPGDs 10 B-based Multi-Grid Detectors as an alternative to 3 He

The IN 5 Multi-Grid prototype • The construction phase of a much larger prototype has started (size of an IN 5 module, 1/12 of the instrument’s detector) – Sensitive area will be 3 * 0. 8 m² • 1024 grids (8 stacks of 128 grids), ~17500 blades • 480 wires , 3 m long (~1. 5 km of wire) – 1500 readout channel (to be reduced to 288) 14/10/2013 Special Workshop on Neutron Detection with MPGDs 10 B-based Multi-Grid Detectors as an alternative to 3 He

The IN 5 Multi-Grid prototype • Design, inner mechanics and assembly at ILL – Final design now settled on – Vessel under fabrication by the German company Pro. Beam (electron-beam welding) • Detector’s components supplied by ESS and Linkoping University – 1024 Ni-plated frames – 17500 two-side 10 B 4 C-coated blades (35 m²) -> Assembly will start in January 2014 14/10/2013 Special Workshop on Neutron Detection with MPGDs 10 B-based Multi-Grid Detectors as an alternative to 3 He

Thank you for attention !! 14/10/2013 Special Workshop on Neutron Detection with MPGDs 10 B-based Multi-Grid Detectors as an alternative to 3 He