Determination Of Uranium, Thorium And Potassium Elemental Concentrations In Surface Soils In Suzhou

Objective: This research aims to evaluate the radiological background level of Suzhou city by detecting and analyzing the elemental concentrations of thorium, uranium and potassium in surface soils respectively and hence provide the radiological environmental background information for further researches.Methods: Natural radionuclide activity concentrations in surface soils of Suzhou Municipal was measured by using a portable FD-3022 NaI(Tl) detector. The pre-arranged observation points cover Suzhou urban area,industrial park zone and the district of Wuzhong with a total number of 349. Soil samples collected from representative points was analyzed with a high-resolution HP-Geγ-ray spectrometry to judge the measurement quality of the portable NaI(Tl) detector. Radionuclide activity was calculated by using relative comparing method.Result: The arithmetic means (A.M.±S.D.) of surface soils of Suzhou are (4.31±1.26)μg g-1,(1.51±0.36)% and(12.45±3.02)μg g^-1 for uranium,potassium and thorium respectively. Apparent linear relationships among the concentrations of Th,U and K versus each other are achieved with correlation coefficients of 0.61(Th/U), 0.60(K/U) and 0.72(K/Th)respectively. Ratios of eTh/eU,K/eU and K/eTh are 3.0±0.80,(3.6±0.85)×10³ and (1.2±0.23)×10³ respectively . The average activities are measured as 53.23 Bq Kg^-1,50.55 Bq Kg^-1 and 472.63 Bq Kg^-1 for the natural radionuclide 238U,232Th and 40K,respectively. The average air absorbed dose ratio in working areas is 74.89 nGy/h(converting to an effective dose of 92.13μSv/a for local residents).Conclusion:1 Comparing with the research data of other regions sharing the same geological patterns and of nearby areas,soil radioactivity measured in this study indicates a background radiation level that falls within the natural limitation but is higher than the average. Due to Suzhou city's specific geological characteristics,the abundant kaolin and granite in the city influence the component of soil and thus the relatively higher level of radioactivity is anticipated.2 Relatively sound outcomes will be secured by applying the in-situγ-ray spectrometry detector in environmental radiological evaluation. The data gained can be used to study the geology background and condition for mine-forming in a region. The data gained in search for uranium mine by usingγ-ray spectrometry are available to be applied to evaluating environment quality of natural radiation.Consequently considerable labor forces and material devices can be saved.3 It is critical to collect soil samples and then measure them with a high-resolution HP-Geγ-ray spectrometry in the laboratory,while survey is conducted in an approach of in-situγ-ray spectrometry by using NaI(Tl) detector.There is no significant difference between the measurements by HP-Geγ-ray spectrometry and NaI(Tl) detector.4 The average absorbed dose ratio of suzhou city in this study fallen within the range of 18-93 nGy/h reported in the UNSCEAR Publication of 2000. Using the data in this study,the average annual effective dose equivalent caused by outdoorγ-ray for a permanent Suzhou resident is estimated to be about 92.13μSv,higher than the global average level of 70μSv.