Cheol-Su Kim

Determination of Pu isotope concentrations and isotope ratio by inductively coupled plasma mass spectrometry: a review of analytical methodology

A number of analytical methods for Pu isotopes based on ICP-MS measurement have been developed and applied to the measurement of ultra-trace levels of Pu in nuclear fuel samples and environmental samples. The endeavour to improve the detection limit to sub-10−18 g (ag) mL−1 has been continued by using efficient sample introduction systems. This review summarizes and critically discusses various types of ICP-MS, sample introduction systems and separation methods applied to the determination of Pu in many sample types. Together with the separation method, the adjustment of the Pu oxidation state in the loading solution preparation step and Pu elution step is summarized. The interference problem from polyatomic ions in ICP-MS coupled with various sample introduction systems is described, especially focused on the UH+ interference. Several factors affecting the trueness and precision of Pu results are discussed.

Simultaneous analysis of 237Np and Pu isotopes in environmental samples by ICP-SF-MS coupled with automated sequential injection system

A simultaneous analytical method for 237Np, 239Pu and 240Pu has been developed using sector field inductively coupled plasma mass spectrometry (ICP-SF-MS) detection combined with an automated sequential injection (SI) separation system. The chemical purification of these actinides was carried out on an actinide-specific extraction chromatographic resin, TEVA-Spec, in an automated SI system. The similar chemical behaviors of Np and Pu on TEVA-Spec was confirmed by recovery test after treating with ascorbic acid in 5 M HNO3. TEVA-Spec maintained its re-usability, giving high and consistent chemical recovery, and showed good selectivity for Np and Pu and a low memory effect during the consecutive analysis of nine replicate samples. The high chemical recovery (>90%), reliable accuracy and repeatability of 237Np and Pu isotope purification using the SI system were proved using standard reference materials. Low detection limits of 2.5, 2.1 and 0.42 fg ml−1 were obtained for 237Np, 239Pu and 240Pu, respectively, which make it possible to analyze these nuclides in samples of soil and sediment as low as 1 g. With the exception of the preparation process required prior to loading a sample, all chemical purifications were carried out automatically by the programmed SI system, and were completed within 1 hour, which included measurement by ICP-SF-MS. This method was successfully applied to the analysis of the environmental levels of 237Np and Pu in soil, sediment and in biological samples.

Plutonium isotopes in seas around the Korean Peninsula

239+240Pu concentrations and 240Pu/239Pu atom ratios in coastal seas adjacent to the Korean Peninsula were determined, during the period 1999 to 2002, to assess the current distribution and to identify sources of Pu isotopes. 239+240Pu concentrations in surface waters ranged from 3.1 to 22.3 mBq m(-3) with higher concentrations in winter than in summer. 239+240Pu concentrations in seawaters around the Korean Peninsula are greater than that in the western North Pacific. 240Pu/239Pu atom ratios ranged from 0.18 to 0.33 with an average value of 0.25+/-0.03, which is significantly higher than the global fallout average. The 240Pu/239Pu atom ratios of the 2000 m deep entire water column in the south western part of the East Sea (Sea of Japan) was comparable to that observed in waters near Bikini Atoll. The higher 240Pu/239Pu atom ratios than that of global fallout may be explained by the hypothesis that the earlier input signal of low 240Pu/239Pu atom ratio (0.18-0.19) of global fallout plutonium in seas adjacent to the Korean Peninsula is being gradually diluted by the high 240Pu/239Pu atom ratio plutonium transported from the tropical Pacific Proving Grounds via prevailing ocean current.

Rapid determination of 99Tc in environmental samples by high resolution ICP-MS coupled with on-line flow injection system

High resolution inductively coupled plasma mass spectrometry coupled with an on-line flow injection system (FI-HR-ICP-MS) was applied to determine the ultra-trace level 99Tc in soil. The flow injection system (PrepLab™) was composed of two TEVA-SpecÒresins, reduced remarkably the sample amounts and the analysis time, compared to the conventional analytical methods. In the flow injection system, Mo and Ru were sufficiently eliminated by using the flow injection system, with the decontamination factors of 1.6.104 and 9.9.105, respectively. With the present method, it was possible to determine ultra-low level of 99Tc in 3-6 g soil at 3–5 hours of analysis time per sample. The relative standard deviation for each sample was less than 4%. The detection limits for 99Tc was 85 fg.ml–1 (0.05 mBq.ml–1), which was calculated from the three times standard deviation of the count rate of the blank.

240Pu/239Pu atom ratios in the bottom sediments of the NW Pacific Ocean

Abstract239+240Pu concentrations and 240Pu/239Pu atom ratios in bottom sediments of the Yellow Sea, Korea Strait, East Sea (Sea of Japan), Sea of Okhotsk, and Northwest Pacific Ocean were determined. In coastal sediments near the Korean Peninsula, 239+240Pu concentrations varied from 0.02 to 1.72 Bq.kg-1, and their 240Pu/239Pu atom ratios from 0.15 to 0.24, with an average of 0.20±0.03. 240Pu/239Pu atom ratios of bottom sediments in the deep NW Pacific Ocean and its marginal seas (East, Okhotsk seas) were in the range of 0.15-0.23. A little elevated 240Pu/239Pu atom ratios in the bottom layer sediment may be due to Pu released into the environment during the pre-moratorium period, having high 240Pu/239Pu atom ratios and low 238Pu/239+240Pu activity ratios.

Determination of226Ra in environmental samples using high-resolution inductively coupled plasma mass spectrometry

A time-saving and accurate technique for determining226Ra in groundwater and soil was examined, using high-resolution inductively coupled plasma-mass spectrometry (HR-ICP-MS). The technique was applied to the determination of226Ra in groundwater and soil samples and compared with the conventional liquid scintillation counting method. This technique was capable of completing226Ra counting within 3 minutes, without the in-growth period to allow radon and its progeny to achieve secular equilibrium with the parent226Ra. The detection limits of HR-ICP-MS for226Ra in groundwater and soil were 0.19 mBq·1−1 and 0.75 Bq·kg−1, respectively, which were about 10 times lower than that of the liquid scintillation counter. The results obtained from HR-ICP-MS in groundwater and soil were in accordance with those of LSC within a relative error of about 13%.

Distribution of3H,137Cs and239,240Pu in the surface seawater around Korea

The concentrations of3H,137Cs and239,240Pu were determined in surface seawaters collected at 21 sampling stations around Korea from October of 1994 to May of 1995. The results were consistent with the past data observed in the North Pacific. The concentrations of3H and137Cs did not show much difference no matter where the samples were taken. Due to the limited distribution of sampling points, no systematic change in3H and137Cs levels with latitude was observed. On the other hand,239,240Pu concentration in the East Sea (Japan Sea) was somewhat higher than that in the South and the Yellow Seas, although the data on239,240Pu concentration were not enough to explain the reason. The activity ratios of239,240Pu/137Cs in surface seawater ranged from 0.13% to 0.44% with a mean of 0.25±0.08%. The activity ratios were lower than those of the global fall-out level, 1.1%. This result presumably arose from the different behavior of the two radionuclides in seawater.