1. EXPRESS DETERMINATION OF SR-90 IN DIFFERENT OBJECTS WITH DICYCLOHEXYL-18-CROWN-6 (DCH18C6) EXPRESS DETERMINATION OF SR-90 IN DIFFERENT OBJECTS WITH DICYCLOHEXYL-18-CROWN-6 (DCH18C6) A. Burak 1, H. Fischer 1, O. Bilan 2, E. Rudak 2, O. Yachnik 2 1 University of Bremen, Institute of Environmental Physics, Bremen, Germany 2 Institute of Physic of the National Academy of Sciences of Belarus, Minsk, Belarus The present method is worked out for Sr-90 determination in objects of different origin, especially in agricultural production, cattle production, and food. The scientific bases of the most exact and express method of definition of the Sr-90 contents in the objects of environment were developed in GEOHI of the Russian Academy of Science (Moscow) at once after the accident on the Chernobyl NPP. This method was later adapted at the Institute of Physic NAS of Belarus. Now the method is being tested and modernized in the Institute of Environmental Physics, University of Bremen. During this work optimum parameters for the given method will be determined. Also the procedure will be tested for low activities (less than 1 Bq). Introduction Methods The principle of the method is based on chromatographic extraction of strontium from nitrate solutions followed by radiometric determination in the liquid phase of Sr-90 activity. The main element of the method is Sr-90 extraction from the investigated sample by dicyclohexyl-18-crown-6 in tetrachlorethane. Dicyclohexyl-18-crown-6 belongs to synthetic macrocyclic polyethers (so-called crown ethers) and has the ability to bind Sr-90 with high selectivity so that Sr-90 is extracted with 92 – 97 % efficiency. Crown ethers are available in a variety of sizes and are named according to the number of atoms in the ring. For example, 18-crown-6 derives its name from the 6 oxygen atoms in the 18-membered ring. The other 12 atoms in the ring are carbon atoms. Dicyclohexyl-18-crown-6 has complexed a strontium ion in the image below. 1.M. Hiraoka. Crown Compounds. Their characteristics and applications. Elsevier, New York (1992) 2.N.Yu. Kremlyakova. The Determination of Radiostrontium in Environmental Objects by Extraction Chromatography Using TVEX-DCH18C6.//J.Radional. Nucl Chem. Articles, V.170, 186-194 (1993) 3.S. Zablotsky, E. Rudak, L. Stopolyanskaya, J. Wiley. Improvements in the method of Sr-90 extraction from environmental samples with dicyclohexyl-18-crown-6. Kerntechnik, V.60, 262-264 (1995). Desorption temperature, 0 C 30 405060708090 Yield, % 63677092969792 Conclusions Multiple use of the chromatography column Determination of optimal desorption temperature Results Chemicals consumption per chromatographic column Discussion References A highly porous matrix of styrene-divinylbenzene copolymer is used as a substrate to support the extractant, dicyclohexyl-18-crown-6 (DCH18K6) in tetrachloroethane, which is in the liquid state deep in the pores of the matrix. Matrix of styrene-divinylbenzene copolymer (TVEX) Pore Diameter 50-500 x 10 -9 m Spheres Diameter 0.2-0.5 mm 1.Sample preparation. The method of wet combustion of the samples by aquafortis, filtering and final correction of the nitric acid concentration to 1.5 M of obtained solutions are used. 2.Preparation of selective sorbent, extract eluation trough a column, strontium desorption. 3.Radiometric measurement is performed in the liquid phase using liquid scintillators. The short-scheme of the method To determine strontium losses and a chemical yield, tests were made using the radionuclide Sr-85 as a tracer. Sr-85 was registered by gamma spectroscopy, using a HPGe detector of 50% relative efficiency and having resolution of 2.4keV at 1.33MeV.For registration of Sr-90 a Liquid Scintillation Analyzer (Tri-Carb 2800TR) was used. Results of these investigations are given below. Eluation curves at various temperatures The present method provides considerable reduction of time needed for measurement of a sample (5-7 hours) in comparison to traditional radiochemical method (up to 2 weeks). The method may be applied to determine the Sr- 90 contamination of objects and territories, which were exposed to accidents at nuclear facilities, buffer areas of NPP, and possible use of so called «dirty» bombs. The stepwise investigation of the overall method showed that significant strontium losses occur only in acid leaching of the prepared samples and in desorption from the chromatographic column. Losses are considerably reduced by use of the method "wet combustion". Based on the results, re-use of the chromatographic column can be recommended only if it is known that the measured activities of all samples in the series are virtually equal. Detection limits depend both on the chemical steps and the quality of the radiometer. The basic technical parameters of the method are presented in the table. ParameterValue Time of one analysis, h 5-7 Desorption temperature, 0 C70-80 Crown ether in tetraclorethane concentration, % 5 Chemical yield, % max 97 Multiplicity of one column 6-8 Measurement error, % 1-3 Bq (radiometer Beta-2) 3-10 Bq 10-1000 Bq 30 20 15 Chemical substanceConsumption, g Price, € Styrene- divinylbenzene copolymer 8 1.5 Crown ether (DCH18C6) 112 Tetraclorethane120.5 The main stages of the method are: