Design Of The SANS Spectrometer For CPHS And Prototypical Research On Detector System

Neutron scattering is an important means to study material microstructure. Withyears of development, it has grown into an independent discipline in foreign countries.However, domestic progress in this area is relatively behind. Researchers are workingvery hard to close the gap. Small angle neutron scattering （SANS）, as an importantbranch of neutron scattering, is widely used in material science, biology, chemistry andother fields. SANS can measure the shape and size of the scattering cluster and theposition information of some specific component in the particle, with measurementscale ranging from a few angstroms to several hundred nanometers.Compact Pulsed Hadron Source （CPHS）, as one of the domestic neutron scatteringfacilities under construction, is a low-energy accelerator-driven neutron source inTsinghua University. Based on the CPHS project, this dissertation completes theinstrumental design of the SANS spectrometer for CPHS, and conducts the prototypicalresearches aiming to solve key technical problems in engineering construction of theSANS spectrometer.Firstly, design of the SANS spectrometer for CPHS is analyzed in detailbased on full investigation of similar spectrometers abroad, with specialconsideration on the long pulse characteristics of CPHS. By shortening thelength of the spectrometer and using wide neutron wavelength range, the SANSspectrometer can cover a Q-range of0.007¹A^-1without changing theinstrument setting under the help of large area detector. It can greatly diminishthe engineering difficulty without moving the detector.Secondly, related prototypical researches are carried out based on the physicaldesign of the SANS spectrometer. Detector system is the key component of the SANSspectrometer, and thus the main content of this thesis. An array of linear positionsensitive³He tube detectors （LPSD） is chosen according to the requirements of theSANS spectrometer and domestic technological status. Two prototypical³He tubedetectors （L=1m, Φ=12mm） are made in cooperation with domestic manufacturer,while the signal position of LPSD is calculated using charge division method. Thisresearch systematically studies the design of the front-end electronics for LPSD withPSPICE simulation tool. Detail analyses are made on circuit noises as well as the impacts of different circuit components on position measurement. Data acquisitionsystem is designed based on VME architecture and FMC board interconnect standard.With a high degree of flexibility and scalability, it can apply to various spectrometers.In the end, this research builds an experimental platform to test the detector system.Characteristics of the³He tube detector are tested and analyzed in detail, including theamplitude spectrum, detection efficiency, position resolution and other factors. Underappropriate working conditions, optimal position resolution of8mm （FWHM） can beobtained, reaching the advanced level of similar researches abroad.This dissertation completes the instrumental design of the SANS spectrometer forCPHS and prototypical researches on detector system, solving key technical issues ofengineering construction. Preliminary experimental results achieve the designedspecifications, laying sound foundation for project construction in the next phase. Thiswork will promote domestic development of neutron scattering technology. Moreover,the successful development of the detector system will help realize independent R&D ofrelated technologies in China.