加熱回収法によるコンクリート試料中放射性炭素分離法の検討 Separation methods of radioactive carbon from concrete samples by thermal combustion methods
In order to determine the activity of ^<14>C induced in the concrete obtained from various accelerator facilities, we studied the oxidative combustion method for extraction of ^<14>C from concrete samples quantitatively. Separation conditions, such as maximum heating temperature and time were examined using ^<11>C produced by the ^<12>C (γ, n) ^<11>C reaction as a radioactive tracer instead of ^<14>C. Samples were irradiated with 30MeV-bremsstrahlung at Laboratory of Nuclear Science, Tohoku University. In this study, several types of standard rocks were combusted, because the thermal decomposition of such rocks contained in a concrete might be difficult. After irradiation, samples were heated in an IR-furnace under O_2 stream (flow rate; 100ml/min). After the decomposition of sample, the gas was sequentially guided to another furnace (catalyst; CuO, temperature; 1073K) for oxidation of CO to CO_2. Radioactive carbon dioxide was collected in 2-amino-ethanol solution of an alkali trap. As a result, the addition of oxidants was effective to improve ^<11>C yields and yields of ^<11>C from standard rock samples were over than 70% heated at 1373K for 20 minutes. It was concluded that the yields of ^<14>C from concrete samples were also more than 70%. In case of steel samples, yields of ^<11>C were about 100%. It was concluded that the separation by the thermal combustion method was useful to separate radioactive carbon, such as ^<11>C and ^<14>C, from concrete samples.
核理研研究報告 39, 47-53, 2006