Determination of Ultra-Low Level Plutonium Isotopes in Large Volume Environmental Water Samples

Abstract

Plutonium is an important artificial element, 239 Pu and 240 Pu are two major radioisotopes of plutonium in the environment released by human nuclear activities. Due to their high radiotoxicity and bio-toxicity, the determination of these radionuclides is critical in view of radiation protection and environmental radioactivity. It is still a major challenge to accurately determine these radionuclides in environmental water samples due to their extremely low concentrations. In this work, a sensitive analytical method for determination of 239 Pu and 240 Pu in environmental water samples was reported. By co-precipitation of plutonium with Ti(OH) 3 followed by separation of plutonium using extraction chromatography with TEVA resin, a recovery of more than 80% for plutonium and decontamination factor of 1.3 × 10 5 for uranium were achieved. A triple quadrupole inductively coupled plasma mass spectrometry (ICP-MS) with dynamic collision/reaction cell was used for measurement of plutonium isotopes. By using NH 3 -He double gasses as collision/reaction gas, 238 U 1 H + polyatomic ion interference to measurement of 239 Pu was significantly suppressed and the final abundance sensitivity of 238 U to m/z 239 was reduced to < 1 × 10 –11 , and sensitivity of 239 Pu was improved to 990 cps/(pg/g). For 20 L water sample, the detection limits of the method for 239 Pu and 240 Pu reached 1.28 × 10 –7 Bq/L and 1.38 × 10 –7 Bq/L, respectively, which enabled accurate determination of 239 Pu and 240 Pu in normal environmental water samples. The developed method was successfully applied to determine 239 Pu and 240 Pu in the spiked water and real environmental water samples, and the results indicated that this method was reliable and could be practically applied. A sensitive method for determination of ultra-low level 239 Pu and 240 Pu was established by pre-concentration of plutonium from large volume water using Ti(OH) 3 co-precipitation, purification for plutonium using extraction chromatography with TEVA resin and triple quadrupole ICP-MS measurement of plutonium isotope. NH 3 -He was used as reaction gas for elimination of uranium hydride interference and increasing the measurement sensitivity using collision focusing. The method was successfully applied for analysis of environmental water samples from China.