Evaluation of a position-sensitive prototype detector unit for fast neutron imaging and spectroscopy

Purpose A novel fast neutron scatter camera with capabilities of neutron imaging and spectroscopy is under development.The detection principle is based on multiple neutron–proton(n–p)elastic scattering interactions in organic scintillator.In order to improve position measurement accuracy of recoil protons,a position-sensitive prototype detector unit has been designed and characterized experimentally.Methods The presented detector unit consisted of a plastic scintillator sheet of 10 cm×10 cm×1 cm dimensions and two groups(6×2)of wavelength-shifting fibers with orthogonal directions embedded into grooves on two opposite scintillator surfaces.Scintillation signals were read out by silicon photomultipliers(SiPMs).A collimated Sr-90 radioactive source was utilized for system calibration and position resolution measurement.Results Light output of the unidimensional six fiber channels from one side of the detector unit was calibrated to be 14.45 photoelectrons per MeVee.Position resolution of the detector unit was measured to be 0.35–0.44 times fiber pitch,corresponding to 5.48 mm for proton recoil energy interval of 1.63–2.60 MeV,and 4.60 mm for proton recoil energy interval of 4.82–5.50 MeV.Energy threshold for recoil proton localization was estimated to be 1.18 MeV.Conclusion The results shown satisfy basic requirements of the scatter camera,while space exists for further improvements.The positioning performance optimization consists of three aspects.The first one is to increase the fiber diameter so as to reduce signal loss.The second one is to depress dark rate of the SiPMs.The last one is to decrease the number of channels involved in position reconstruction by narrowing the scintillation signal distribution function of the detector unit.

Study of linearity of LYSO crystal for the high energy cosmic radiation detection(HERD)facility

The high energy cosmic-radiation detection(HERD)facility is a space mission designed for detecting cosmic ray(CR)electrons,γ-rays up to tens of TeV and CR nuclei from proton to iron up to several PeV.The main instrument of HERD is a 3-D imaging calorimeter(CALO)composed of nearly ten thousand lutetium yttrium orthosilicate(LYSO,with cerium doping)crystal cubes.A large dynamic range of single HERD CALO Cell(HCC)is necessary to achieve HERD’s PeV observation objectives,which means that the response of HCC should maintain a good linearity from minimum ionizing particle(MIP)calibration to PeV shower maximum.In order to study the linearity ofHCC over such a large energy range,a beam test has been implemented at the E2 and E3 beam lines of BEPC.High intensity pulsed electron beam provided by E2 line is used for producing high energy density within HCC;π^(+)/proton provided by E3 line are used forHCCcalibration.The results showthat no saturation effect occurs and the linearity ofHCCis better than 10%from 30 MeV(1MIP)to 1.1×10^(3) TeV(energy density is 93 TeV/cm^(3)),which can meet the requirement mentioned above.