GEANT4 simulation of the 10 B-based Jalousie detector for neutron diffractometers

Transcription

1 GEANT4 simulation of the 10 B-based Jalousie detector for neutron diffractometers Irina Stefanescu 1, R. Hall-Wilton 1, G. Kemmerling 2, M. Klein 3, C.J. Schmidt 3,4, W. Schweika 1,2 1 European Spallation Source ERIC, S Lund, Sweden 2 Forschungszentrum Jülich GmbH, D Jülich, Germany 3 CDT CASCADE Detector Technologies GmbH, D Heidelberg, Germany 4 GSI Detector Laboratory, D Darmstadt, Germany

2 Inter-Planar Spacing, d hkl, and Miller Indices ter-planar spacing (d hkl ) between crystallographic planes belonging same family (h,k,l) is denoted (d hkl ) Neutron diffraction the bare essentials ces between planes defined by the same set of Miller indices are for each material Neutron diffraction is used to study samples that are composed of single or many different crystals (polycrystals). 2D d' h k l d hkl d h k l Debye-Scherrer diffraction cones according to Bragg s law: λ i = 2 d hkl sinθ hkl (λ wavelength neutron, d hkl lattice distance, θ hkl scattering angle) planar spacings can be measured by x-ray diffraction d hkl (Bragg s Law) d h k l detector 2

3 Inter-Planar Spacing, d hkl, and Miller Indices ter-planar spacing (d hkl ) between crystallographic planes belonging same family (h,k,l) is denoted (d hkl ) Neutron diffraction the bare essentials ces between planes defined by the same set of Miller indices are for each material Neutron diffraction is used to study samples that are composed of single or many different crystals (polycrystals). 2D d' h k l d hkl d h k l Debye-Scherrer diffraction cones according to Bragg s law: λ i = 2 d hkl sinθ hkl (λ wavelength neutron, d hkl lattice distance, θ hkl scattering angle) planar spacings can be measured by x-ray diffraction d hkl (Bragg s Law) d h k l detector 3

4 Neutron diffraction at ESS ESS Lund At ESS three diffraction instruments (DREAM, MAGIC, HEIMDAL) are about to finalize the detailed design. DREAM, powder diffractometer MAGIC, single-crystal diffractometer HEIMDAL, thermal powder diffractometer Requirements for detectors for the ESS instruments: able to handle rates as large as 4 khz/cm 2 2θ-resolution < 0.29 (< 6 mm x 6 mm pixel size) neutron detection efficiency > 50% at 1 Å γ-sensitivity < 10-6

5 Neutron diffraction at ESS ESS Lund At ESS three diffraction instruments (DREAM, MAGIC, HEIMDAL) are about to finalize the detailed design. DREAM, powder diffractometer MAGIC, single-crystal diffractometer HEIMDAL, thermal powder diffractometer Requirements for detectors for the ESS instruments: able to handle rates as large as 4 khz/cm 2 2θ-resolution < 0.29 (< 6 mm x 6 mm pixel size) neutron detection efficiency > 50% at 1 Å γ-sensitivity < 10-6 I. Stefanescu et al., Neutron detectors for the ESS diffractometers, JINST 12, P01019(2017).

6 The Jalousie detector The Jalousie detector designed to fulfil the requirements of the new generation of neutron diffractometers. Developed by the company CDT in Heidelberg, Germany. Jalousie utilizes the 10 B-technology. Mantel detector The POWTEX-Jalousie mantel detector currently under construction and testing. n The design and construction of the DREAM- Jalousie mantel detector planned to start in The results of the simulation for the POWTEX-Jalousie detector are also valid for the DREAM-Jalousie detector. Jalousie detector for POWTEX (FRM2) and DREAM (ESS)

7 O N M L K J I H G F E D C B A cathode strips The POWTEX-Jalousie detector 2.3 m segment sample 45 Δθ= n 0.8 m 3D matrix of 16 (wires) x 192 (cathode strips) = non-identical sensitive elements per counter (voxels). 4 5

8 The POWTEX-Jalousie detector The Jalousie segments are mounted in modules of detector modules to cover 2π around the sample. M. Henske et al., The 10 B-based Jalousie neutron detector An alternative for 3 He-filled position sensitive counter tubes, NIMA 686 (2012) 151. s: he n the of e hest Module with 8 segments at 10 Depth of the segment (~25 cm) chosen to allow for the interaction of each incoming neutron with up to 8 Boron-layers. Counting gas: Ar-CO 2 (80-20) in continuous flow. Neutron beam ε 50% at 1 Å 8

9 GEANT4 simulations for the Jalousie detector Info needed on the creation and propagation of the electron avalanches and their collection by the anode wire. Simulation strategy: model the readout voxels as trapezoids made of Ar-CO 2 gas n + 10 B 7 Li + α voxel i+1 E i+1 ~8 mm x 7 mm x 15.6 mm tof E i voxel i info on the energy deposited, tof, voxel ID ( voxel center) saved on file for each detected neutron. 9

10 Validation of the GEANT4 model for Jalousie Experimental results obtained in measurements with collimated beams FWHM =7.85 mm (wire pitch = 12.6 mm) G. Modzel, PhD thesis, Univ. of Heidelberg, strip with width 7.22 mm FWHM = 12.8 mm GEANT4 FWHM = 8.1 mm FWHM = 12.5 mm 10

11 Efficiency (%) GEANT4 simulations for the Jalousie detector 80,00 70,00 60,00 50,00 CAD design for the POWTEX/DREAM Jalousie detector 40,00 30,00 20,00 eff, all events eff, threshold = 100 kev 10,00 GEANT4 0, Wavelength (Å) simulated efficiency for the POWTEX-Jalousie mantel detector > 50% at 1 Å 11

12 GEANT4 simulations for the Jalousie detector experimental, NaCaAlF sample Δd/d = instrumental resolution (resolution function) Δd/d At spallation sources: Δd/d = Sample Instrumentation moderator, beamline components, detector

13 GEANT4 simulations for the Jalousie detector study the detector contribution to the resolution function by comparison to a reference detector

14 GEANT4 simulations for the Jalousie detector study the detector contribution to the resolution function by comparison to a reference detector

15 GEANT4 simulations for the Jalousie detector study the detector contribution to the resolution function by comparison to a reference detector Use the Vitess neutron trajectories as input for the GEANT4 ParticleGenerator.

16 *WISH: world-class powder diffractometer operational at the ISIS (UK) spallation source. GEANT4 simulations for the Jalousie detector study the detector contribution to the resolution function by comparison to a reference detector GEANT4 Jalousie detector Use the Vitess neutron trajectories as input for the GEANT4 ParticleGenerator. WISH-like detector* ( 3 He-tubes)

17 Counts Counts GEANT4 simulations for the Jalousie detector POWTEX-Jalousie detector, GEANT WISH-like detector, GEANT d_spacing (Å) d-spacing (Å) Main diffraction peaks and their relative intensities well reproduced by the model. WISH, experimental 17

18 Conclusions and outlook The implementation and validation of the GEANT4 model for the Jalousie mantel detector (POWTEX/DREAM version) almost completed. Focus is now on using the detector model to predict the physics performance in real experiments. The Jalousie detector is the baseline technology for the single-crystal diffractometer (MAGIC) and the thermal powder diffractometer (HEIMDAL) at the European Spallation Source. Both detector designs will be optimized in GEANT4. 18

19 GEANT4 simulations for the Jalousie detector POWTEX-Jalousie detector, GEANT4 WISH-like detector, GEANT4 19

20 FWHM TOF through detector (μs) GEANT4 simulations for the Jalousie detector 10 B 4 C layers 40 Δtof det 35 POWTEX-Jalousie d ~ 15 mm WISH, 3He tubes, 8 mm diameter, 15 bar ~8 mm 10 d 8 mm in current tof detectors used for power diffraction studies (e.g., thin ZnS scintillators or 3 He-based gas counters) Wavelength (Å) Δd d = Δtof res chopper or moderator pulse width + Δtof detector tof 2 + ΔL L 2 + Δθ cot θ 2 For POWTEX (L = 20 m), Δtof res-chopper = 10 μs Δtof/tof 0.15%. ESS: DREAM: L = 76 m, MAGIC = 171 m, HEIMDAL = 168 m. 20