GEANT 4 simulation of the 10 Bbased Jalousie
GEANT 4 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-22100 Lund, Sweden 2 Forschungszentrum Jülich Gmb. H, D-52425 Jülich, Germany 3 CDT CASCADE Detector Technologies Gmb. H, D-69123 Heidelberg, Germany 4 GSI Detector Laboratory, D-64291 Darmstadt, Germany
Neutron diffraction – the bare essentials Neutron diffraction is used to study samples that are composed of single or many different crystals (polycrystals). Debye-Scherrer diffraction cones according to Bragg’s law: λi = 2∙ dhkl ∙sinθhkl d”h”k”l” (λ – wavelength neutron, dhkl – lattice distance, θhkl – scattering angle) dhkl d’h’k’l’ n detector 2
Neutron diffraction – the bare essentials Neutron diffraction is used to study samples that are composed of single or many different crystals (polycrystals). Debye-Scherrer diffraction cones according to Bragg’s law: λi = 2∙ dhkl ∙sinθhkl d”h”k”l” (λ – wavelength neutron, dhkl – lattice distance, θhkl – scattering angle) dhkl d’h’k’l’ n detector 3
Neutron diffraction at ESS Ø At ESS three diffraction instruments (DREAM, MAGIC, HEIMDAL) are about to finalize the detailed design. ESS Lund 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 k. Hz/cm 2 • 2θ-resolution < 0. 29° (< 6 mm x 6 mm pixel size) • neutron detection efficiency > 50% at 1 Å • γ-sensitivity < 10 -6
Neutron diffraction at ESS Ø At ESS three diffraction instruments (DREAM, MAGIC, HEIMDAL) are about to finalize the detailed design. ESS Lund 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 k. Hz/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, P 01019(2017).
The Jalousie detector Ø The Jalousie detector designed to fulfil the requirements of the new generation of neutron diffractometers. Ø Developed by the company CDT in Heidelberg, Germany. Ø Jalousie utilizes the 10 B-technology. “Mantel” detector • The POWTEX-Jalousie mantel detector currently under construction and testing. • The design and construction of the DREAMJalousie mantel detector planned to start in 2018. n Jalousie detector for POWTEX (FRM 2) and DREAM (ESS) • The results of the simulation for the POWTEXJalousie detector are also valid for the DREAM-Jalousie detector.
The POWTEX-Jalousie detector 2. 3 m sample Δθ=0. 47° 45° n 0. 8 m 3 D matrix of 16 (wires) x 192 (cathode strips) = 10240 non-identical sensitive elements per counter (voxels). 192 cathode strips segment
The POWTEX-Jalousie detector Ø 18 detector modules to cover 2π around the sample. The Jalousie segments are mounted in modules of 8. 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. 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. ε ≈ 50% at 1 Å 8
GEANT 4 simulations for the Jalousie detector 15. 6 m Ø Info needed on the creation and propagation of the electron avalanches and their collection by the anode wire. m Simulation strategy: model the readout voxels as trapezoids made of Ar-CO 2 gas n + 10 B 7 Li + α voxeli+1 Ei+1 ~8 mm x 7 mm x 15. 6 mm o tof Ei o o voxeli o info on the energy deposited, tof, voxel ID ( voxel center) saved on file for each detected neutron. 9
Validation of the GEANT 4 model for Jalousie Experimental results obtained in measurements with collimated beams G. Modzel, Ph. D thesis, Univ. of Heidelberg, 2014. FWHM =7. 85 mm (wire pitch = 12. 6 mm) FWHM = 12. 8 mm strip with width 7. 22 mm GEANT 4 FWHM = 8. 1 mm FWHM = 12. 5 mm 10
GEANT 4 simulations for the Jalousie detector 80 70 CAD design for the POWTEX/DREAM Jalousie detector Efficiency (%) 60 50 40 eff, all events 30 eff, threshold = 100 ke. V 20 10 GEANT 4 0 0 1 2 3 4 5 Wavelength (Å) 6 7 8 simulated efficiency for the POWTEX-Jalousie mantel detector > 50% at 1 Å 11
GEANT 4 simulations for the Jalousie detector WISH@ISIS, experimental, Na. Ca. Al. F sample Δd/d = instrumental resolution (resolution function) Δd/d At spallation sources: Δd/d = Sample ⊗ Instrumentation moderator, beamline components, detector
GEANT 4 simulations for the Jalousie detector study the detector contribution to the resolution function by comparison to a reference detector
GEANT 4 simulations for the Jalousie detector study the detector contribution to the resolution function by comparison to a reference detector
GEANT 4 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 GEANT 4 Particle. Generator.
GEANT 4 simulations for the Jalousie detector study the detector contribution to the resolution function by comparison to a reference detector GEANT 4 Jalousie detector Use the Vitess neutron trajectories as input for the GEANT 4 Particle. Generator. WISH-like detector* (3 He-tubes) *WISH: world-class powder diffractometer operational at the ISIS (UK) spallation source.
GEANT 4 simulations for the Jalousie detector POWTEX-Jalousie detector, GEANT 4 Main diffraction peaks and their relative intensities well reproduced by the model. WISH-like detector, GEANT 4 WISH, experimental 17
Conclusions and outlook • The implementation and validation of the GEANT 4 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 thermal powder diffractometer (HEIMDAL) at the European Spallation Source. Both detector designs will be optimized in GEANT 4. 18
GEANT 4 simulations for the Jalousie detector POWTEX-Jalousie detector, GEANT 4 WISH-like detector, GEANT 4 19
GEANT 4 simulations for the Jalousie detector Δtofdet d ~ 15 mm layers o o o ~8 mm 4 C o d ≤ 8 mm in current tof detectors used for power diffraction studies (e. g. , thin Zn. S scintillators or 3 He-based gas counters) FWHM TOF through detector (μs) 10 B 40 POWTEX-Jalousie 35 30 WISH, 3 He tubes, 8 mm diameter, 15 bar 25 20 15 10 5 0 0 2 4 6 8 Wavelength (Å) 10 12 For POWTEX (L = 20 m), Δtofres-chopper = 10 μs Δtof/tof ≈ 0. 15%. ESS: DREAM: L = 76 m, MAGIC = 171 m, HEIMDAL = 168 m. 20
- Slides: 20
