Monte Carlo simulation of the GEM-based neutron detector 王晓冬 2012年12月13日

Fast/Thermal neutron detector 6% 94% Ionization electrons are multiplied & localized in cascaded-GEMs imaging detector. Detection efficiency: < 0.1%(fast-n) ~ 5% (thermal-n) GEM foil

A novel high efficiency neutron detector based on GEM The drift electrode is made of 50um aluminized Mylar, under which is the multi-layer HDPE converters with thickness of 1200um, length of 3mm and the interval of 500um between two converters. The chambers are filled with 95%Ar+5%CH4 gas mixture at atmospheric pressure. E_drift=3kV/cm. The 14MeV neutron source is setup isotropically and can generate 10e7 of random passages in each simulation. In our simulation, only H(n,n’)p elastic scattering is considering and the detection efficiency of gas detector for charged particles is assumed to be 100%.

Multi-layer converter + GEM detector p 2D Readout Board HDPE layer GEM1 GEM2 ΔV E Detector Concept: n scatter on H in HDPE-converter foils, p escape the foil. p induce e- in gaseous conversion gap. e- are multiplied and localized in GEM-detector. Combine several 1D radiographs  2D cross sectional tomography. Detector Design: Foils thickness (14 MeV neutron) Gas gap thickness (Deposited energy) Number of converter foils (Detector length) Detector performances: Detector efficiency(Conversion efficiency) Efficiency of transport e- in small gap(Transport) Spatial resolution (Imaging)

Simulation  Singnal Converter Thickness Impinging neutron (En) θ Scattered neutron Target Recoiled nucleus (ER) HDPE p 1200um For 14 MeV neutron impinging on HDPE layer: -) Max. Efficiency ≈ 0.37% -) Conversion thickness = 1200 μm -) Broad Spectrum (0 ~14 MeV)

Simulation  Deposited Energy in the gas gap Ar/5%CH4 (1 atm) HDPE δe- n p HDPE Tgas

Converter thickness1200um Gas gap：500um Layers ：400 14MeV Neutrons Detector Vessel Converter thickness1200um Gas gap：500um Layers ：400 Detection efficiency： 2.3% Large tolerance ： 0.7m

Simulation  Incident neutron position reconstructed

250um 300um 380um 400um

Conclusion Detection efficiency of the detector with 400 converter units can be better than 2.3%. Reconstruction accuracy of the incident neutron position can be better than 2% New ideas Length of the converter and antistatic HDPE material(ABS-ESD7). THGEM instead of GEM. 3D printing techniques

Future Plan  14MeV neutron imaging Gas fill Ar5%CH4 Detector vessel HDPE converter 14MeV neutron

THANKS