Study Of A Fast Neutron Spectrometer Based On GEM-TPC

Fast neutron spectrometer will play an important role in the future nuclear industry,nuclear physics experiment and homeland security field.It is expected to be used in the following applications: fast neutron reactor monitoring,special nuclear material detection,thermo-nuclear fusion plasma diagnostics and so on.However,it's difficult for traditional fast neutron spectrometers to achieve high energy resolution and high detection efficiency at the same time,or there are some special requirements for the detector's medium material,neutron source,and neutron beam.These factors have limited the wide application of the traditional fast neutron spectrometers.Therefore,a new type of fast neutron spectrometer is needed,which has a high energy resolution,a high detection efficiency,an excellent n/? suppression ratio,easy access to medium material,and a wide range of application.The dissertation presents the notion of a fast neutron spectrometer based on a GEM-TPC(Time Projection Chamber with Gas Electron Multiplier amplification)named neutron-TPC,trying to overcome the difficulty faced by the traditional fast neutron spectrometers.By comparing the performance parameters of traditional neutron spectrometers,and considering the characteristics of the neutron-TPC,an expected performance of the neutron-TPC is proposed: 1)for 5MeV neutron,energy resolution(FWHM)?5%,and detection efficiency ?10-5;2)for 2.5MeV neutron,energy resolution(FWHM)?7%,and detection efficiency ?10-5.The dissertation has completed the simulation,theoretical analysis,design and experimental study of the neutron-TPC system.The specific research contents include: 1)A Monte-Carlo simulation of the neutron-TPC's performance based on Geant4,Garfield and ROOT software was carried out.From the simulation results,the neutron-TPC's performance for 5MeV and 2.5MeV neutron could meet the expected requirement.2)To find the theoretical direction of optimising the neutron-TPC,a mathematical analytical model of the neutron-TPC was established.All the important factors affecting the performance of the neutron-TPC were analyzed.3)The neutron-TPC was designed,built and tested.And a correction method of channel gain inconsistency of the neutron-TPC based on measurement of cosmic rays was applied,realizing the calibration and correction of the channel gain of the arc shaped readout pads.4)The neutron beam experiment of the neutron-TPC system was completed,with the data processing program written independently.The following issues were analyzed and solved: by using the integral area and time gravity of the signal waveform to characterize the energy and time information of the signal,the influence of the ballistic deficit on the signal's energy and time information was eliminated;an correction method based on the mathematical formula and the experimental data was adopted to correct the electron drift velocity;during the track reconstruction,Hough transformation was used,excluding the interference signals around the proton track effectively;by comparing the starting positions and average ionization energy loss rate of particles,the influence of the background particles on the true proton events was eliminated.Finally,the result of the neutron beam experiment shows that,for the 1.2MeV,1.81 MeV and 2.5MeV neutron,the energy resolution(FWHM)of the neutron-TPC reaches 15.7%,10.3% and 7.0% respectively,with the detection efficiency over 10-5.Such performance meets the expectation well.