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[en] In this paper two samples of shielding concrete around target of BX2 of the accelerator facilities of Paul Scherrer Institute were analysed. First sample was located in beam direction, 11 cm from target, behind 8 cm copper and 3 cm lead shielding. The second sample was a 20 cm long boring column of 5 cm diameter, taken 4 cm beside the beam direction, but shielded by 8 cm copper only. Its distance to the target was 12 cm. From this boring column, five samples were taken in distances of 5 cm each, vertically from the surface. First, the gamma-Spectra of all samples were taken by a Ge(Li) Detector. The radionuclides in shielding concrete are formed mainly by impurities: the europium nuclides Eu-152 and Eu-154 and Sc-46 as well from rare earths and their homologues, Co-60 and Mn-54 from iron, Na-22 possibly from magnesium and Cs-134 and Ba-133 from barium. The amount of Eu-152 is far beyond the exemption limit; the shielding blocks must be generally handled as radioactive materials. For the determination of U-238 and Pu-239, the concrete was fine powdered in a mill. In order to detect the chemical yield, defined amounts of 3.75·105 Pu-242 and 68.9 U-232 carriers were added. The powder (∼ 1 g) was disintegrated with 3-5 ml 40 % HF/4-5 ml 7N HNO3. The solution was oxidized by H2O2, and plutonium and uranium were separated by two consecutive columns, BIORAD 1-X2 and UTEVA, respectively. The measuring samples were prepared by electrodeposition. The four nuclides, Pu-239,240, Pu-242, U-238 and U-232 were measured by alpha-spectrometry in the respective fractions. The purity of each fraction was checked by gamma-spectrometry using a Ge(Li) detector. Despite the remarkable differences in the contents of U-238 and Pu-239 in the concrete samples, the quotient of them shows a closed line, nearly a straight one. This indicates a formation of plutonium from the uranium impurities (1-2 ppm) by only one main reaction, probably by thermalized or resonance neutrons, but it shows also strong inhomogeneities of the uranium content in the sample. (authors)
Source
Kuruc, J.; Kufcakova, J.; Macasek, F. (Dept. of Nuclear Chemistry, Comenius University, Bratislava (Slovakia)) (eds.); Foundation Curie, Bratislava (Slovakia); Department of Nuclear Chemistry, Comenius University, Bratislava (Slovakia); 161 p; ISBN 80-223-1877-9; 
; Aug 2003; p. 123; 10. international conference on Separation of Ionic Solutes (SIS'03); Podbanske, High-Tatras (Slovakia); 6-11 Sep 2003; Also available from Foundation Curie, Mlynska dolina CH-1, 84215 Bratislava, Slovakia
; Aug 2003; p. 123; 10. international conference on Separation of Ionic Solutes (SIS'03); Podbanske, High-Tatras (Slovakia); 6-11 Sep 2003; Also available from Foundation Curie, Mlynska dolina CH-1, 84215 Bratislava, Slovakia