Study On The Measurement Method And Technology Of The Neutron Beam Parameters For China Spallation Neutron Source

During China Spallation Neutron Source(CSNS)commission and operating period,accurate measurement of neutron energy spectrum,neutron flux and neutron pulse shape of neutron beamline in target station can lay a foundation for neutron scattering technology and the construction of scattering spectrometer in future.In addition,the measurement of the neutron beam parameters of the target station can provide the basis for the rationality analysis for the design of the CSNS target-moderator-reflector,neutron guides,neutron chopper.Based on the need of the neutron beam parameters measurement in CSNS,the experimental measurement techniques and methods of neutron beam energy spectrum,neutron flux and neutron pulse shape are carried out,and the main research contents,research results and conclusions are as follows:The traditional TOF(being pulse counting mode)and CTOF(being current integral mode)neutron energy spectrum measurement principle and related theory are studied,by comparing the advantages and disadvantages of two methods,this paper puts forward the basis scheme of using CTOF method to carry out CSNS neutron parameter measurement in the initial debugging stage of CSNS.The CTOF measurement system was developed,and CTOF measurement system was tested on the neutron beamline of time-of-flight polarized neutron reflection spectrometer(TPNR)in China MianYang research reactor(CMRR).The experimental measurement of the average charge quantity of the CTOF measurement system and the neutron energy spectrum measurements of the TPNR neutron beamline were completed and the energy spectrum result was compared with the result measured with TOF method,the results showed that the energy spectrum data obtained by two methods were well matched,and the reliability of the CTOF system for neutron energy spectrum measurement was verified.According to the measured neutron energy spectrum data,the neutron flux of the TPNR beamline was calculated,which was compared with the result measured by Au foil activation method.The results showed that the neutron flux data measured by the CTOF system was higher than 10-20%,and the main reason was that the CTOF system cannot completely remove the gamma influency.Using the developed CTOF measurement system,the preliminary experimental measurements of the neutron parameters of the 6th and 20 th beamline were completed,and the neutron wavelength spectra of the 6th and 20 th beamline were obtained,in addition,neutron flux and neutron generation efficiency of two beamlines were computed by the neutron wavelength spectrum data.The analysis result showed that the data measured by the CTOF system can correctly respond to the neutron beam characteristics of the 6th and 20 th beamline,and CTOF measurement system can be used to measure neutron energy spectra,neutron flux and other neutron parameters of the CSNS neutron beamline.Neutron pulse shape measurement system is developed,and related theories and methods are studied.Preliminary experimental test of the neutron pulse shape measurement system was carried out on the TPNR beamline of CMRR,and the flight time of the net diffraction neutron were obtained.The results showed that the obtained neutron wavelength data coincided with the computed diffraction wavelength,and preliminarily verified that the developed neutron pulse measurement system can be used to measure the neutron pulse shape of the neutron beamline in the CSNS target station.