The Quantitative Correction Method For The Effect Of Surface Medium Characteristic On The Data From In-situ Gamma-ray Spectrometry

With the establishment of 1ong-term development objectives of Nuclear powerindustry in China, The exploration and utilization of uranium resources bringsinevitably a series of problems in environmental radiation. In-situ gamma-rayspectrometry is a quick and effective method to obtain environmental radiation fieldinformation. But in actual application it is affected by many surface factors, such assoil uniformity, soil density, soil moisture, covering layer and the terrain. Therefore, theresearch of the influence of surface factors to in-situ gamma energy spectrummeasurement and the quantitative correction method has important practical value.This paper established layered homogeneous medium model and round tablemodel based on the principles ofγ-ray and substance function, studied andsimulated the effects of soil dry density, moisture, surface covering layer, steps terrain,hillside topography and round table terrain on the measurements of in-situγ-rayspectra by numerical simulation method in order to provide the theory basis for theapplication of the quantitative correction method. Field experiments verified the effectof soil moisture and steps terrain to the measurement results which. The results ofmeasurement corrected by respectively layered homogeneous medium model andmirror image principle had eliminated the main effect of soil moisture and stepsterrain. According to the results of field experiments and numerical simulation, thefollowing conclusions can be drawn:(1) The results of the long soil moisture experiments showed that soil moisturewas the layered change after the rainfall and it was negatively correlated to the grosscount rate of characteristic peaks of natural radionuclide at very significant level. Thelayered homogeneous medium mode of soil moisture used to study the quantitativecorrect for field observation data according to the measured soil moisture. The resultof research indicated that the layered mode can effectively reduce the effect of soilmoisture on in-situ gamma energy spectrum measurement.(2) The results of steps terrain experiments demonstrated that the propersimplified model according to the actual terrain can effectively reduce the influence ofthe steps terrain to the measured results.(3) The numerical simulation results of surface covering layer illustrated that,when the covering layer(take snow for example)thickness increased,there was a significant difference in the decrement of the primary photon fluence rate of bothhigh-energy gamma rays and low-energy gamma rays in the intial stage. But whencovering layer thickness increased to a certain extent, the diversity of different energygamma rays began to reduce gradually and tended to the same finally.