A simulation study of a high-resolution fast neutron imaging detector based on liquid scintillator loaded capillaries

Background At present,the highest spatial resolution of a fast neutron imaging detector,mainly determined by the range of secondary particles generated by fast neutrons,is about hundreds of microns.In view of the above inherent spatial resolution limitation,a capillary-based scintillation detector that can improve the spatial resolution of fast neutron imaging by recording and reconstructing the recoil proton track was developed.Purpose The purpose of this paper is to develop a detector for recognizing recoil proton events,reconstructing particle track and improving the position resolution with track reconstruction method to reconstruct the position of interaction.Methods The proposed detector consists of a 1000×1000 array of glass capillaries loaded with a high refractive index liquid scintillator.Each glass capillary was 10μm in diameter and 5 cm in length.The recoil protons generated by the incident neutrons move within the detector and produce scintillation light within each capillary that they traverse.The light emitted from the capillary array can be recorded by employing an intensified CCD camera.We used Geant4 to simulate the detector performance and CERN ROOT analysis framework to record physical information of recoil proton,including position,energy deposition in each capillary and track length.Based on Hough transform,a rapid,computerized and efficient proton track reconstruction procedure was developed.Conclusion The recoil proton events display a continuous extended structure.The track reconstruction algorithms can reconstruct individual track precisely,and when the counting rate was relatively low,the track reconstruction results were in good agreement with simulation data.Moreover,for intensive overlap conditions,this algorithm also reconstructs periphery tracks with high rate of accuracy.

Compact MPPC-based coded aperture imaging camera for dual-particle detection

Purpose Fast neutrons and gamma-ray imaging detection is an effective way to detect and identify radioactive material in the field of nuclear security.A compact coded aperture imaging(CAI)camera was designed to be sensitive to both gamma and neutron radiation based on plastic scintillators and multi-pixel photon counters(MPPC).Methods MPPCs coupling with the 13×13 pixelated plastic scintillators one-to-one were utilized to reduce the scale of the CAI system while maintaining good positional performance.The symmetric charge division(SCD)circuit was adopted to reduce the 169 signals output from the MPPC array to 26.Each waveform was collected and processed with four Domino Ring Sampler 4(DRS4)chips and two 16-channel analog-to-digital converter(ADC)modules.As the pulse shapes of fast neutrons would be broadened after elastic scattering multiple times in the scintillators,the Anger-Logic method was applied to eliminate multiple elastic scattering events so that good pulse shape discrimination(PSD)performance can be achieved.Results The imaging and detection ability of the camerawas evaluated using the 241Am-Be(5.9×10^(5) n/s)neutron source and 137Cs(370 MBq)gammasource.The camera can be used to detect fast neutrons(0.5–10 MeV)and gammarays(0.2–2.5MeV).Furthermore,it can implement efficient neutron/gamma PSD capabilities in the mixed-field environment.The figure of merit(FOM)of the camera calculated at 400keVee energy cut is 0.93.Conclusion A compact MPPC-based CAI camera was designed to detect and discriminate fast neutrons and gamma rays.Its good PSD performance was well suited to distinguish fast neutrons from gamma rays in a dual-particle environment.The portable design makes it promising for complex monitoring scenarios in nuclear security.