|
|
Rapid determination of gross alpha activity in field conditions.
BOSÁK, Adam
The emergence of a radiological emergency as a result of radiological incident has a significant impact on a military operation. Details about the radiological situation are necessary for making timely informed decisions concerning the operating posture and for radiation exposure management. The initial information about identifying what radioactive materials are presented and the level of radioactive contamination of the environment, especially during the immediate and urgent phases of monitoring of radiation situation, are provided by field deployed laboratories. Their tasks are related to gross alpha/beta activity determination of air filters, swipes and water samples. The thesis deals with rapid determination of gross alpha activity (GAA) in field conditions. The thesis is focused mainly on increasing the capability and efficiency of measurements using the radiochemical separation method for sample preparation. The aim of this thesis is formation of an analytical method for rapid determination of GAA using liquid scintillation counting (LSC). The first part is focused on the current state of monitoring in a radiological emergency, then describes the capabilities of field deployed and stationary laboratories, especially in relation to alpha activity measurements, and introduces the gross activity and its determination. Subsequently it characterizes fundamentals of alpha decay and radiation and deals with current possibilities of detection. The principles and applications of detectors suitable for the alpha measurement and counting, i.e. Gas-Filled detectors, Semiconductor detectors and Scintillation detectors, are also mentioned. The last part of the theoretical part describes in details LSC and extraction chromatography, which are used in research. In the empirical part of the bachelor thesis the possibility of using Eichrom's Actinide Resin for rapid preconcentration of alpha particle emitters out of aqueous samples was investigated and then counted directly by LSC. The resin shows a strong affinity for actinides, and is very effective in accordance with long extracting and counting times. Based on that, kinetics of extraction was investigated by using short extracting and counting times in three observed levels of GAA in water - 1000 Bq/L, 100 Bq/L and 20 Bq/L. The results were compared with the rapid methods of measurements using the sample without modification by using the solid-state and LSC detector. Then factors possibly affecting the extraction of alpha radionuclides into the Actinide Resin were monitored. The first factor was the influence of pH of the appointed solution and the presence of beta radionuclide as the second factor. The measurements were realized by using Solid-state Scintillation Counter HandECount and Liquid Scintillation Counter TriathlerTM with 20 ml HDPE scintillation vials. AquaLight was used as LSC cocktail. 241Am, 238Pu and 90Sr were selected as radionuclides for their military significance. The results showed that even after 30 minutes' extraction time, as in the case of 241Am and 238Pu, recovery was more than 90% in all observed levels of GAA in water. The best results were achieved at lower activities (100 and 20 Bq/L), when after 30 minutes' recovery was 94 - 95 % for 241Am and 95 - 96 % for 238Pu. In the context of the pH effect of solution, it was found that a very acidic pH substantially disrupts extraction properties of the Actinide Resin. During the extraction of radionuclides in the high acidic environment, the efficacy was reduced up to 20 %. The effect of the presence of beta particle emitter was also observed. The resin showed affinity for 90Sr. After 60 minutes' approximately 36 % of 90Sr was extracted. Based on the results it can be stated that the LSC combined with sample preparation by resin is a suitable method for rapid determination of gross alpha activity in field conditions. Analytical method for the rapid determination of GAA is included in Annex of the thesis.
|
guest ::
