Determination of ²⁴¹Am in Large Volume Water Samples Based on Manganese Dioxide Precipitation Method

Americium-241(²⁴¹Am) is an important transuranic nuclide with a half-life of 432.6 years, and is classified as a highly toxic radionuclide. Due to its rapid migration and potential for bioaccumulation along food chains in the environment, ²⁴¹Am poses potential threats to environmental radiation safety and human health. The concentration of ²⁴¹Am in environmental water samples is extremely low, necessitating the collection of large-volume water samples to enhance detection sensitivity and enable the analysis and measurement of low-level ²⁴¹Am. Pretreatment of large-volume water samples is a major challenge in chemical separation procedures. In this paper, 50 L water samples were used for ²⁴¹Am measurement, with systematic investigation of key factors such as coprecipitation methods and precipitate carrier amounts. After separation and purification, a suitable method was selected through systematic discussion. Finally, an analytical method for ²⁴¹Am determination in environmental water samples using alpha spectrometry was established. In the process of water sample pretreatment, tap water samples(50 L) were used to compare the pre-concentration efficiencies of calcium-magnesium co-precipitation and manganese dioxide(MnO₂) precipitation were compared, and the MnO₂ precipitation method was selected for pre-concentration. Approximately 2.0 g of potassium permanganate(KMnO₄) was added to form MnO₂ precipitates, thereby enriching Am from the water matrix. In the separation and purification step, extraction chromatography was used to systematically investigate the effects of key parameters(i.e., loading acidity and elution volume) on the chemical recovery yield. DGA resin was used to adsorb Am from the sample solution under 5-6 mol/L HNO₃ conditions, followed by elution with 20 mL of 0.01 mol/L HCl-0.03 mol/L NaNO₂ to achieve effective separation of Am from other interfering nuclides. For source preparation after separation and purification, 0.1 mol/L (NH₄)₂SO₄ was used as the electrolyte solution, and the pH was adjusted to approximately 2. Electrodeposition was carried out at a current density of 0.65-0.70 A/cm² for about 60 minutes to prepare the measurement source for alpha spectrometry. Thus, an analytical method for ²⁴¹Am determination in environmental water samples based on alpha spectrometry was established. The established analytical procedure was validated. The experimental results show that with a 48 h measurement time by alpha spectrometry, the overall chemical recovery yield of ²⁴³Am in the procedure is 83.4%, the decontamination factor for ²⁴²Pu exceeds 10³, and the minimum detectable activity concentration of ²⁴¹Am is determined to be 9.48×10⁻⁶ Bq/L. These results indicate that the established method is accurate and reliable. Finally, the method is applied to analyze ²⁴¹Am in various environmental water samples, including surface water, groundwater, and river water, for monitoring radiation safety in the aquatic environment, meeting the requirements for routine analysis and monitoring of low-level ²⁴¹Am in environmental water samples.