Xiongxin Dai

Ultra-trace determination of plutonium in urine samples using a compact accelerator mass spectrometry system operating at 300 kV

Accelerator mass spectrometry (AMS) is a very sensitive and robust technique for analysis of long-lived radionuclides. Employment of the AMS technique can reduce the demands on sample preparation chemistry, due to its high rejection of interferences and low susceptibility to sample matrix. This is particularly of interest for ultra-trace determination of 239Pu in bioassay and environmental samples, as other mass spectrometric methods such as inductively coupled plasma mass spectrometry (ICP-MS) can suffer from isobaric mass interferences by the presence of uranium in the sample. A rapid sample preparation method for analysis of Pu at femtogram levels in large volume urine samples is described. Using the compact ETH AMS Tandy facility operating at ∼300 kV, the method was validated by analysing urine samples spiked with known amounts of 239/240/241Pu ranging from 1 to 30 fg. The detection limits for the method were estimated to be 0.38 fg for 239Pu, 0.40 fg for 240Pu and 0.08 fg for 241Pu in 1400 mL of urine.

An emergency bioassay method for actinides in urine.

A rapid bioassay method has been developed for the sequential measurements of actinides in human urine samples. The method involves actinide separation from a urine matrix by co-precipitation with hydrous titanium oxide (HTiO), followed by anion exchange and extraction chromatography column purification, and final counting by alpha spectrometry after cerium fluoride micro-precipitation. The minimal detectable activities for the method were determined to be 20 mBq L−1 or less for plutonium, uranium, americium and curium isotopes, with an 8-h sample turn-around time. Spike tests showed that this method would meet the requirements for actinide bioassay following a radiation emergency.

A bioassay method for americium and curium in feces

Fecal radiobioassay is an essential and sensitive tool to estimate the internal intake of actinides after a radiological incident. A new fecal analysis method, based on lithium metaborate fusion of fecal ash for complete sample dissolution followed by sequential column chromatography separation of actinides, has been developed for the determination of low-level Am and Cm in a large size sample. Spiked synthetic fecal samples were analyzed to evaluate method performance against the acceptance criteria for radiobioassay as defined by ANSI N13.30; both satisfactory accuracy and repeatability were achieved. This method is a promising candidate for reliable dose assessment of low level actinide exposure to meet the regulatory requirements of routine radiobioassay for nuclear workers and the public.

Five-Column Chromatography Separation for Simultaneous Determination of Hard-to-Detect Radionuclides in Water and Swipe Samples

There is a growing demand for the rapid determination of hard-to-detect radionuclides in environmental and biological samples for environmental monitoring, radiological protection, and nuclear forensic reasons. A new method using five-column chromatography separation has been developed for the simultaneous determination of Pu, Np, Th, U, Am, Cm, Pm, Y, and Sr isotopes, as well as iron-55, by inductively coupled mass spectrometry (ICPMS), α spectrometry, Čerenkov and liquid scintillation (LS) counting. Spiked swipe and water samples as well as proficient testing water standards were analyzed to validate the separation procedure, and the results are in good agreement with the expected values. The method provides quick sample turnaround time and high analysis throughput with low analysis cost. The flexibility of the method also allows for its easy adaptation to various emergency and routine radioassays.

Rapid determination of uranium isotopes in urine by inductively coupled plasma-mass spectrometry.

Following a radiological or nuclear emergency involving uranium exposure, rapid analytical methods are needed to analyze the concentration of uranium isotopes in human urine samples for early dose assessment. The inductively coupled plasma mass spectrometry (ICP-MS) technique, with its high sample throughput and high sensitivity, has advantages over alpha spectrometry for uranium urinalysis after minimum sample preparation. In this work, a rapid sample preparation method using an anion exchange chromatographic column was developed to separate uranium from the urine matrix. A high-resolution sector field ICP-MS instrument, coupled with a high sensitivity desolvation sample introduction inlet, was used to determine uranium isotopes in the samples. The method can analyze up to 24 urine samples in two hours with the limits of detection of 0.0014, 0.10, and 2.0 pg mL−1 for 234U, 235U, and 238U, respectively, which meet the requirement for isotopic analysis of uranium in a radiation emergency.

Rapid determination of 90 Sr/ 90 Y in water samples by liquid scintillation and Cherenkov counting

Strontium-90 (90Sr) is a ubiquitous contaminant at nuclear facilities, found at high concentrations in spent nuclear fuel and radioactive waste. Due to its long half-life and ability to be transported in groundwater, an accurate method for measuring 90Sr in water samples is critical to the monitoring program of any nuclear facility. To address this need, a rapid procedure for sequential separation of Sr/Y was developed and tested in groundwater samples collected from an area of riverbed affected by a 90Sr groundwater plume. Sixteen samples, plus spike and water blanks, were analyzed. Five different measurements were performed to determine the 90Sr and yttrium-90 (90Y) activities in the samples: direct triple-to-double-coincidence ratio (TDCR) Cherenkov counting of 90Y, liquid scintillation (LS) counting for 90Sr following radiochemical separation, LS counting for 90Y following radiochemical separation, Cherenkov counting for 90Y following radiochemical separation and LS counting of the Sr samples for 90Y in-growth. The counting was done using a low-level Hidex 300SL TDCR counter. Each measurement method was compared for accuracy, sensitivity and efficiency. The results following Cherenkov counting and radiochemical separation were in very good agreement with one another.

ICP-MS method for Pu and Np isotopes in population monitoring by a micro-flow injection sample introduction system

An ICP-MS method using a micro-flow injection (μ-FI) sample introduction system was developed for measuring 237Np and 239,240,241Pu in urine samples for sensitive and rapid population monitoring following a radiological or nuclear accident. Good selectivity from the chemical separation method allowed the determination of 237Np together with Pu isotopes using 242Pu as a tracer. Significant improvements in ICP-MS sensitivity and detection limit were achieved using the μ-FI sample introduction and the desolvation techniques. The method developed has been successfully applied to a set of human urine samples spiked with Pu isotopes and a set of rat urine samples with metabolized Pu isotopes from research experiments.

Rapid determination of 226Ra in urine samples

A new radiochemical separation method has been developed for rapid analysis of (226)Ra in urine samples. In this method, radium is separated from urine matrix using cation and anion exchange column chromatography. A (224)Ra tracer is added, together with its parent in the (228)Th standard, for chemical recovery correction. After separation, the sample is precipitated with hydrous titanium oxide and then prepared for counting by creating a thin-layer counting source using BaSO(4) micro-precipitation. The radium isotopes are then counted by alpha spectrometry. Replicate spike and blank samples were analysed for validation of the procedure. The detection limit was determined to be 0.22 Bq l(-1) with 4 h of counting for 20 ml of urine sample. Using this method, the results can be reported within an 8 h turn-around time. This method is suitable for quick dose assessment of (226)Ra exposure following a radiation emergency.

EURADOS intercomparison on emergency radiobioassay

Nine laboratories participated in an intercomparison exercise organised by the European Radiation Dosimetry Group (EURADOS) for emergency radiobioassay involving four high-risk radionuclides ((239)Pu, (241)Am, (90)Sr and (226)Ra). Diverse methods of analysis were used by the participating laboratories for the in vitro determination of each of the four radionuclides in urine samples. Almost all the methods used are sensitive enough to meet the requirements for emergency radiobioassay derived for this project in reference to the Clinical Decision Guide introduced by the NCRP. Results from most of the methods meet the requirements of ISO 28218 on accuracy in terms of relative bias and relative precision. However, some technical gaps have been identified. For example, some laboratories do not have the ability to assay samples containing (226)Ra, and sample turnaround time would be expected to be much shorter than that reported by many laboratories, as timely results for internal contamination and early decisions on medical intervention are highly desired. Participating laboratories are expected to learn from each other on the methods used to improve the interoperability among these laboratories.

Canada's efforts in developing capabilities in radiological population monitoring.

Population monitoring is an important component of radiological and nuclear emergency preparedness and response. Since 2002, Canada has been investing in developing national capabilities in radiological population monitoring. This paper summarizes Canadas efforts in developing methods and techniques in biological dosimetry and in vivo and in vitro bioassay techniques. There are still many gaps to fill that require further efforts. Integration of different monitoring methods and techniques in order to have the best assessment of radiation dose to support medical management and integration of Canadas efforts with international efforts are recommended.