Progress with the nRPC-4D detector concept for neutron scattering applications: assessment of XYZ-position and nTOF readout capability in beam tests

Progress with the nRPC-4D detector concept for neutron scattering applications: assessment of XYZ-position and nTOF readout capability in beam tests Luís Margato, A. Morozov, A. Blanco, J. Saraiva, L. Lopes, P. Fonte Chung Chuan Lai, Per-Olof Svensson B. Guerard and J. Marchal [email protected] | XVII international Conference on Resistive Plate Chambers and Related Detectors 9 -13th September 2024, Santiago de Compostela Outline ●Introduction ●nRPC-4D detector design ●Detector prototype ●Experimental results ●Summary 2 Introduction 3 Motivation The RPC detectors, introduced in the 80s by R. Santonico, R.Cardarelli (1981) [1] shows a strong potential for applications in Neutron Scattering Science (NSS) and Beyond. The European Spallation Source is currently driving the development of new types of neutron detectors. Main goal Develop RPC-based neutron detectors able to satisfy modern NSS instrument requirements, such as: ●High (> 50 %) neutron detection efficiency ●Low gamma sensitivity ●High spatial resolution and nTOF capability ●High counting rate ●Affordable costs Previous work [1] https://doi.org/10.1016/0029-554X(81)90363-3 10 Double gap RPCs ●Active area: 8 cm x 8 cm ●Anodes: 0.5 mm thick float glass ●Cathodes: 0.5 mm thick Al ●Gas gap width: 0.35 mm ●10B4C layer: 1.15 μm ●Detection Efficiency: 62.1% (λ = 4.73 Å) ●Spatial resolution (x and y): ~ 0.25 mm FWHM ●Gamma sensitivity (0.511 MeV) < 10-6 L.M.S. Margato et al 2020 JINST 15 P06007 Detector tested at FRM II (MLZ) nRPC-4D detector design 4 ●Standalone neutron detection modules: Double gap RPCs coated with 10B4C to enable sensitivity to cold/thermal neutrons nRPC-4D detector design 5 Thin film PBCs ●25 μm thick polyamide ●2 arrays of parallel mutually-orthogonal Cu strips: Pitch = 1mm; Width = 0.3 mm ●Standalone neutron detection modules: Double gap RPCs coated with 10B4C to enable sensitivity to cold/thermal neutrons ●Signal pickup: Thin film PCBs with parallel Cu strips for XY position readout nRPC-4D detector design 6 ●Standalone neutron detection modules: Double gap RPCs coated with 10B4C to enable sensitivity to cold/thermal neutrons ●Signal pickup: Thin film PCBs with parallel Cu strips for XY position readout ●Multilayer structure for high neutron detection efficiency: Stack of 10 nRPC modules Optimization of the 10B4C layers thickness 7 All 10B4C layer with the same thickness (1.15 μm) The sum of all contributions adds up to 59.8% total detection efficiency. Simulations in Geant4 (v10.7.2) Detection Efficiency optimized by setting only 3 different possible thicknesses for the 10B4C Primary neutrons (4.7 Å) generated as a pencil beam with normal incidence at the center of the detector. Optimized thicknesses for (λn = 4.5 Å) ●0.4 μm for RPC 1 to 3 ●0.6 μm for RPC 4 to 7 ●2.2 μm for RPC 8 to 10 https://doi.org/10.1016/j.nima.2023.168267 Identify the 10B4C layer where a neutron is captured 8 A. Morozov et al 2021 JINST 16 P08032 ~ 0.2 mm Observed shift in the reconstructed position, most likely due to a misalignment between the strip arrays for the Ycoordinate. Xi (Yj) strips, from each array, with the same index are interconnected and read by the same electronic channel Ambiguity in the 10B4C layer where a neutron is captured One possible solution: Pair of arrays of parallel Cu strips, mutually orthogonal. x1 x1 RPC RPC Timing and XYZ coordinates 9 Cathode signal (serves two purposes) ●Event timing → nTOF ●Identification of the nRPC where a neutron is captured Arrays of parallel Cu strips mutually orthogonal ●XYcoordinates Triggered cathode + Difference in signal sum on strips x and y, Xsum signal > Ysum signal Neutron capture in the top 10B4C layer of a nRPC Xsum signal < Ysum signal Neutron capture in the bottom 10B4C layer of a nRPC ●Z-coordinate 16 Results: PHS of cathode signals RPC gas gap Index 1h 2h 3h 4h 5h 6h 7h 8h 9h 1l 2l 3l 4l 5l 6l 7l 8l 9l h: upper gas gap l: lower gas gap PHS are almost identical for all nRPCs gas gaps → Good uniformity of the gas-gap width Flood dataset: HV=-2050 V; Att. Thickness: 4 x 2 mm + 1.8 mm 1h 9h 1l 9h 17 Results: Detection efficiency Measured relative DEs DE ~ 42 % @ 2050 V Plateau knee at lower voltage than for 0.35 mm gas gap nRPCs but shorter Simulation results (GEANT4 /ANTS3) Total Detection Efficiency (DE) ●41.5% for λn=2.5 Å 0.4 μm 0.6 μm 2.2 μm DEs follow the trend predicted by the simulation. 10B4C layers thickness may differ slightly from the theoretical ones 18 Results: Uniformity # 6 XProfiles 21.2mm # 5 YProfiles ●#5 (red); ●#6 (blue) 21.2 mm Images recorded with the detector irradiated at different locations ●Beam collimation: 21 mm x 21 mm opening on a B4C sheet ●RPC 1-9 at -2050 V Misalignment between the beam and the collimator opening is evident. Almost the same response in both areas (profile overlap) PHS (all 9 RPC cathodes) Detector irradiated in 7 different locations Max. peak deviation from its average ~2% 19 Results: Z-coordinate - nRPC gas gap identification Identification of the 10B4C layer along the stack (Z-direction) where neutron capture occurs ●To correct the of offsets between the XY arrays of strips ●To suppress the uncertainty in time caused by the neutron ToF through the Al cathode ( ~ 760 ns for λn = 10 Å) Enables 20 Results: Offset between arrays of strips (thin-film PCBs) To determine the offset, the x and y position for the neutron events in the lower gas gap of the nRPC1 was taken as a reference (zero on the plots). X-coordinate Y-coordinate 21 Results: Spatial resolution ●Cd slit in contact with the detector window ●Attenuators: 3 glass plates (2 mm thick each) ●RPC1-9 at HV= -2050 V; Th=35 mV ●Count rate ~ 19 kHz/cm2 Cd slit 0.2 mm width Run 118 Spatial resolution performance as in the 1st small nRPC detector prototype: FWHM < 0.3 mm 22 Results: Spatial resolution x z yRPC 1: Upper gas gap RPC 1: Lower gas gap RPC 9: Lower gas gap Image corrected for the offset in the position of the XY strip arrays ●Cd mask: 1 mm thick ●Letter grooves: 0.4 mm wide ●Diagonal groove: 0.3 mm wide Cd mask Excellent fidelity is observed in the reproduction of all Cd mask details Images reconstructed for each individual 10B4C layer 23 Results: Counting rate for nRPC 1 - 9 (float glass) Local counting rate is linear with beam intensity up to ~ 70 kHz/cm2 (~15% deviation @ ~120 kHz/cm2) ●0.2 mm wide Cd slit (@BMonitor) ●RPC1-9: HV= -2050 V 24 Results: Counting rate for nRPC 1 - 9 (float glass) Attenuation: 2x2 mm C. rate ~ 36 kHz/cm2 FWHM ~ 0.39 mm Attenuation: 3x2 mm C. rate ~ 19 kHz/cm2 FWHM ~0.36 mm Attenuation: 1x2 mm C. rate ~ 70 kHz/cm2 FWHM ~ 0.42 mm 25 Results: Counting rate for nRPC 10 (LRglass) RPC10 (Low resistivity glass) (ρ ~ 1.5 x 109 ῼ cm) Measurement performed with a wider Cd slit: 0.5 mm Integral of histograms normalized to unity No significant change is observed in the profile of the slit image with the nº of attenuators in the beam Rate vs neutron flux (beam test at HZB) L.M.S. Margato et al 2021 JINST 16 P07009 nRPC with low resistivity electrodes Vap: Applied voltage Vef f: Effective voltage applied across the gap I: Counting current drawn by the detector in area A R: Electrical resistance seen by this current Ρ: DC bulk resistivity of the electrode resistive material 32 [email protected] BkUp slide