تغييرپذيري محتواي سزيم - 137 در سايت مرجع شهرستان فريدن

چكيده انگليسي :

98 Variability of Cesium 137 Inventory in Reference Site of the Fereydan District Nasim Bazshoshtarizadeh n shooshtari70@yahoo com September 9 2015 Department of Soil Science Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisor S Ayoubi ayoubi@cc iut ac irAbstractCesium 137 is an artificial radionuclide with a half life of 30 2 years and strong gamma radiation that due to nuclearexplosions in the 1950s and 1960s entered the Earth s surface by the rain This element was rapidly absorbed to fineparticles of soil surface horizon and its distribution is basically accompanied by the physical changes of soil such aserosion and plowing The basis of calculating of erosion by radioactive cesium method is based on a comparisonbetween the amount of cesium 137 in soil exposed to erosion and a reference surface The values attributed to thereference inventory of cesium 137 plays an important role in converting measurements to estimates of rates of soilerosion or sediment rate Incorrect and uncertain values of Cs 137 in reference site will be caused to biased andunreliable estimates of soil erosion and sediment deposition This study was conducted to evaluate the variability ofthe content of cesium 137 regarding to the sampling program including sample size distance and sampling method This study was conducted in a reference site located in vicinity of Fereydan city located at western of Isfahanprovince Throughout two network sampling 3 8 comprising big network 35 m length and 8 m width and smallnetwork 24 m length and 6 m width 96 soil samples were collected from 0 15 cm and 15 30 cm depths Moreover for evaluation of vertical distribution of Cs 137 in two networks two profiles were dug and soil samples werecollected from 0 5 5 15 15 25 and 25 35 cm depths Gamma ray spectrometry device was used for Cesium 137analysis Magnetic susceptibility values were measured using Bartington susceptimeter at low 0 46 kHz and high 4 6 kHz frequencies and magnetic susceptibility dependent was calculated by low and high frequency values Soilcharacteristics including pH EC texture gravel organic material total nitrogen cation exchange capacity calciumcarbonate equivalent and bulk density of all the samples and the types of clay in the two soil samples weredetermined To evaluate spatial variability of Cs in two networks variography analysis was done using Variowinsoftware R software was employed for evaluating the sampling method regular network simple random andtransect and selecting the number of samples for covering the variability of the content of cesium 137 The results ofstudy showed that among the soil physicochemical and magnetic properties bulk density had the highest correlationwith cesium 137 r 0 46 p 0 01 A negative correlation was observed between the clay content and cesium 137inventory r 0 52 Clay mineralogy showed that clay minerals included illite kaolinite and chlorite were existedin the reference site and the results confirmed that nature of mineralogy is effective in absorption of cesium 137 insoil The results of multiple regression analysis indicated that bulk density clay content and magnetic susceptibility atlow frequency explained 43 of total variability of Cs 137 No significant differences were observed for the values ofsill and range of the two networks and spherical models was fitted for two studied networks The content of cesium 137 in the reference site showed relatively low variability 15 The distance of sampling and the sampling methodwas not significantly on variability of the content of cesium 137 in the studied reference site The existence ofmicrotopography in the big network resulted lower coefficient of variation of cesium 137 compared to small network The number of samples affected the variability of cesium 137 in the studied reference site Also as the variability ofthe cesium 137 content and the accuracy increased the number of samples required for a reliable estimate of averagecesi

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تغييرپذيري محتواي سزيم - 137 در سايت مرجع شهرستان فريدن

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