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

2. Fast/Thermal neutron detector6%
94%
Ionization electrons are multiplied & localized in cascaded-GEMs imaging detector.
Detection efficiency: < 0.1%(fast-n)
~ 5% (thermal-n)
GEM foil

3. 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%.

4. Multi-layer converter + GEM detectorp
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)

5. 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)

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

7. 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

8. Simulation  Incident neutron position reconstructed

9. 250um
300um
380um
400um

10. 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

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

12. THANKS