Research Of Dose Evaluation Methods Of High Energy Neutron Survey Meter

Methods of dose evaluation for neutron radiation fields to a kind of Survey meter withsingle moderator and multiple detectors have been studied in this work. The Survey meterconsists of two kinds of neutron detectors. At the center of the Survey meter there is located a3He proportional detector and six BF3proportional detectors are embedded in the surface ofthe moderator. In addition，there is a lead layer embedded in the center of the moderator, andit can improve the response to high energy neutron via （n，xn） reaction. Neutron responseswere calculated using MCNP and FLUKA based on the broad neutron spectra which werecollected in IAEA of Technical Reports Series No.318and other references.Energy responses were calculated by MCNP and FLUKA using broad neutron spectradata collected in IAEA of Technical Reports Series No.318and other references。The resultsshowed that there is a trend of monotonic increasing between ratio of inner and outerdetector’s count rate and neutron energy.Two methods for neutron dose evaluation were studied according to the results ofneutron responses. First method which called “correction factor” was that there is a monotonerelation between ratio of inner and outer detector’s count rate and neutron fluence meanenergy, so the correction factors can be determined to obtain final dose according to the ratio.Deviation of Corrected ambient dose equivalent within±60%. Design of the survey metercan improve the response of neutron fields which contain composition above10MeV.Responses to other particles were taken into consideration and calculated in this sdudyAs a section of this work, the few-channel unfolding program of MXD-FC31was usedto try to solve the neutron dose analysis. Because of the complexity for the neutron spectrathat collected in IAEA of Technical Reports Series No.318, so，three different default spectrawere determined according to the different ratio for these neutron spectra fields. Dosedeviation for unfolding method is within50%except for two data points with deviation above100%.As the experiment test of our Survey meter, Neutron radiation produced by cosmic raysfor Harbin of China were measured and analysed with two dose evaluation methods. The doserate for “correction factor” method and Few-channel unfolding method is8682.58pSv/h and11600pSv/h respectively.