Research On Key Technologies For Space Neutron Detection Based On A CLYC Detector

Space neutron is one of the secondary particles produced by the energetic charged particles from primary cosmic rays reacting with celestial bodies or spacecraft shells.During space explorations,astronauts and spacecraft have escaped from the earth's atmosphere and geomagnetic field,and their safety is threatened by long-term space radiation.As neutron presents stronger penetration capacity and higher radiation damage effects than charged particles,the contribution of space neutrons in space radiation cannot be ignored.The long-term monitoring results of the international space station in low earth orbit show that the space neutron contributes more than 30% of the effective biological radiation exposure and is also the main factor inducing the single-particle effect.Therefore,with the further development of human-crewed spaceflight in China,it is essential to monitor the space neutron in real-time.At present,the commonly used neutron detection methods(such as the moderation method,the Time-of-Flight method,and the nuclear recoil method)have problems as large space occupation,narrowed response of the energy spectrum,and poor discrimination ability,which is not suitable for use in space environment and spacecraft.Aiming to the wide energy range,multi-particle interference,and low power consumption of space neutron detection,a space neutron measurement method based on the CLYC scintillator is proposed in this work.The main research works are as follows:(1)The physical design of a space neutron detector based on a CLYC scintillator.The CLYC scintillator contains neutron sensitive nuclides such as 6Li,35 Cl,89Y,and 133 Cs,which respond to the thermal ?100 Me V region neutrons.Through the pulse shape discrimination ability of the CLYC scintillator and the anti-coincidence detector,neutron events can be distinguished from the complex space environment.A CLYC scintillator coupled with a Si PM array,can realize small volume and low power consumption.The response matrix of monoenergetic neutrons of the CLYC detector is used to reconstruct the incident neutron spectrum.The response to monoenergetic neutrons of a ? 3.81 cm x 3.81 cm CLYC scintillator are simulated by the Monte Carlo code,Geant4.The neutron spectrum reconstruction is verified by the simulated energy deposition of a continuous neutron spectrum.(2)Assembly and test of the CLYC detector.A ? 3.81 cm × 3.81 cm CLYC scintillator is coupling to a 4×4 array composed of 3×3-mm2 Sen SL J-series Si PM elements,a 4×4 Si PM array with ESR films attached,and an 8×8 Si PM array,respectively.The power supply of Si PM and trans-impedance preamplifier is designed and assembled on a ? 6.2 cm readout board.The energy calibration,energy resolution,and PSD ability are tested by ?-ray and neutron sources.The results indicate that the 8×8 array coupled detector performs better resolution of 7.83% @ 662 ke V and PSD Fo M of 2.15@ thermal region.(3)Temperature dependence of the CLYC detector's performance.The luminous efficiency of the CLYC scintillator and the breakdown voltage of Si PM is sensitive to temperature.As the temperature of the experiment chamber in China Space Station varies from-20 ? to +40 ?,the detector's performance will be modified.In this work,the equilibrium time for the CLYC detector is estimated with COMSOL Multiphysics simulation software.A temperature chamber is used,and the setting temperature varies from-40 ? to +50 ? in steps of 10 ?.After the detector's temperature is equilibrium,the variability of peak centroid,resolution,and pulse shape are investigated using two ?-ray sources and a neutron source.(4)Improvement on PSD performance of the CLYC detector.The parasitic capacitance of a single Si PM element is in n F level,as connecting in a parallel 8×8 array,the capacitance will be further increased.It integrates CLYC's current pulse to a slow charge signal along with the equivalent resistance of the readout electronics.Thus,the initial differences in the pulse shapes are decreased.In this work,the parameters of equivalent resistance and capacitance are obtained by circuit analysis,and the current pulse before integration is obtained by numerical derivation.By applying this digital shaping algorithm,the pulse width is narrowed from 20 ?s to about 2 ?s,and the PSD Fo M value of the thermal neutron energy region is significantly improved by 13.7%.(5)Experimental monoenergetic neutron responses and spectrum reconstruction.Since monoenergetic neutron has no peak response in the CLYC scintillator,this work proposes a response matrix to solve the incident neutron spectrum.The response matrix is composed of the experimental measurement responses and the calibrated simulation responses.The mixed response of an Am-Be neutron source and a 137 Cs neutron source was measured experimentally.The measured response of the neutron emitted from the Am-Be source is obtained by PSD.The neutron spectrum is reconstructed by solving the overdetermined equations,which are constituted by the response matrix and measured response.The main innovations in this work are as follows:(1)A physical scheme for space neutron spectrum measurement based on a CLYC detector is designed.The CLYC scintillator detects wide-energy neutrons by nuclear reactions,the neutron events are discriminated by "anti-coincidence +PSD",and the energy spectrum is solved by response matrix.(2)A digital shaping algorithm based on the inversed integral process is proposed to optimize the PSD capability of the charge comparison method.Meanwhile,the pulse width is narrowed to reduce the piled-up pulses.(3)The response matrix of the monoenergetic neutron is established by experiment measurement and simulation,and the energy spectrum of the Am-Be neutron source is reconstructed by the least square method.