Abstract
Atmospheric testing of nuclear weapons and nuclear reactor accidents has resulted in widespread distribution of radioactive fission products into the environment. Determination of these radionuclides in biological and environmental samples presents serious difficulties because of interferences (90Sr with a continuous beta spectrum needs separation from other radionuclides, such as 90Y) and the poor limits of detection established by currently available counting equipment. In this project an ion exchange chromatography procedure for the separation of Cs, Sr and Y was developed. Since these radionuclides are hazardous, the method was developed using stable isotopes and inductively coupled plasma mass spectrometry (ICP-MS) as an elemental detector. In the first instance, the optimum operating conditions of the instrument for the analysis of Cs, Sr and Y were determined. These values were found to be 1.1 kW incident power and 1 1 min-1 nebuliser flow rate. The accuracy of the ICP-MS measurments was then assessed through the use of international reference materials NIST:SRM 1572 Citrus Leaves and NIST:SRM 1573 Tomato Leaves. In general a good agreement was observed for most of the elements between certified values and the results obtained in this study. The developed separation technique consisted of three stages. In the first stage ammonium molybdophosphate (AMP) and BioRad AG 50W-X8 resins were used. Caesium was separated from the other two isotopes using 2 M NH4OH. In the second stage Sr and Y were eluted from the above mentioned column using 4 M HNO3. The solution was then loaded onto a Sr-SpecRTM column where Sr is retained. In the third stage Sr was eluted from the column using deionised water. This setup provided excellent recoveries for the three stages namely: 85 % for Cs, 93 % for Y and 95 % for Sr. The analysis of Cs, Sr, and Y in foodstuffs, namely beans and milk was carried out after using the aforementioned separation procedure. Different growth media (commercial white silica sand, Lightwater garden soil, commercial garden soil, Rose Batch compost, and commercial compost) were used to assess the effect of organic content on the uptake of Cs and Sr by bean plants. These experiments involved the addition of different doses of added elemental concentration (100 to 1000 ?g ml-1) to the substrate and also various solution pH's (4 to 9). It was observed that the higher uptake of Cs and Sr by bean plants was at solution pH 7 and also for growth media with high organic content, i.e. Rose Batch compost and commercial compost. The distribution of Cs and Sr into the bean plant tissue resulting through absorption from commercial compost, showed that Cs is absorbed mostly in the stem (95 %) and with minimal levels in root and leaves (5 %). On the other hand, Sr was readily absorbed to the aboveground parts of the bean plants (36 % stem, 63 % in leaves) in contrast to other parts; 0.3 % root and 0.05 % beans. A study was undertaken to assess the uptake of Cs and Sr by bean plants in the presence of K and Ca at various solution pH's. It was found that in general, for all solution pH's, potassium inhibits the uptake of Cs. On the other hand, there appears to be a competition between Sr and Ca at high pH (7 to 9) which resulted in a rapid reduction of the Sr uptake. The addition of Ca to the substrate decreased the uptake of Sr by stems/leaves and increased the uptake of Sr by beans. As an application, solutions with different pH and radionuclide 137Cs and 90Sr) levels were added to mature bean plants. The developed ion exchange chromatography procedure was then adopted to separate 137Cs and 90Sr from these plants. In this study a Ge(Li) gamma ray spectrometer (ND 66) was used as a detector for 137Cs whilst a liquid scintillation counter was used for measuring 90Sr. Prior to the 137Cs measurements, the detection limits, resolution, absolute full energy peak and calibration of the instrument were evaluated. In general the values obtained in this work were in good agreement with the certified values. (Abstract shortened by ProQuest.).