Characteristics of artificial radionuclides in sedimentary soil cores from a volcanic crater lake.

The distributions of 137Cs, 237Np, and 239+240Pu activity concentrations in sedimentary soil cores of the volcanic crater-lake have been studied. The 240Pu/239Pu atom ratios measured by MC-ICP-MS and mutual activity ratios were examined. These results were used to evaluate the sedimentation characteristics of the crater-lake (Baengnokdam of Mt. Halla, Korea). The 137Cs, 237Np, and 239+240Pu activity concentrations showed similar distribution patterns and one maximum peak was observed in each sediment core, except at St.10. For all sediment cores, the activity concentrations were in the range 1.03 × 100-1.92 × 102 Bq·kg-1 dw for 137Cs, 7.56 × 10-3 - 7.15 × 100 mBq·kg-1 dw for 237Np, and 5.20 × 10-3 - 5.13 × 100 Bq·kg-1 dw for 239+240Pu, respectively. The averaged 240Pu/239Pu atomic ratio (0.159) was slightly less than the global fallout ratio (0.176). The averaged inventories were estimated to be 9.21 × 103±5.34 × 103 Bq·m-2 for 137Cs, 2.27 × 102±1.58 × 102 Bq·m-2 for 239+240Pu, and 3.22 × 10-1±1.78 × 10-1 Bq·m-2 for 237Np. The averaged 239+240Pu/137Cs and 237Np/239+240Pu activity ratios were 2.21 × 10-2 and 2.21 × 10-3, respectively. The mean sedimentation rates calculated using 239+240Pu activity concentrations at the central area (St.30 - St.45) and at all stations (St.5 - St.75) were estimated to be 0.844 cm yr-1, and 0.767 cm yr-1, respectively. In addition, the sedimentation rates calculated using 210Pb and 226Ra were 0.856 cm yr-1 at depths of 0-35 cm and 0.204 cm yr-1 at depths of 35-55 cm. These results imply that the sedimentation in Baengnokdam was relatively slow (0.204 cm yr-1) until about 44 years ago and then became faster (0.856 cm yr-1) to the present. The excess 210Pb dating is consistent with the sedimentation rate calculated from the vertical 239+240Pu profile.

Direct determination of gold in rock samples using collision cell quadrupole ICP-MS.

This study investigated the determination of Au in rock samples using collision cell quadrupole inductively coupled plasma mass spectrometry (ICP-MS). It is essential to remove various interferents using a collision cell because polyatomic ions such as (181)Ta(16)O(+) and (180)Hf(16)O(1)H(+) can interfere with the direct determination of monoisotopic (197)Au when using ICP-MS. The addition of oxygen as a reaction gas removed isobaric interferents by transforming TaO(+) and HfOH(+) to TaO(2)(+), TaO(3)(+), and HfO(2)H(+), HfO(3)H(+), respectively, in the cell without significant Au(+) loss. The ion kinetic energy effect (IKEE) due to the potential difference between the plasma and the hexapole affected the reactions in the cell. Au and interfering ions were very sensitive to cell bias voltage (Vc) at constant plasma potential (Vp) and quadrupole bias voltage (Vq). Under the condition of hot plasma, the transmission of ions was promoted, and the maximum Au signal intensity was 50% greater than under normal conditions. At Vc > 7 V, TaO(+) ions were removed to background level. Optimized conditions for real sample analysis were obtained by introducing He as an additional collision gas in hot plasma. TaO(+) ions were removed to background level at He flow rates above 0.6 mL min(-1), and the Au signal remained high. The detection limit (three times the standard deviation of the blank) of this method was 3.06 pg g(-1). The results for reference materials (STM-1 and DGPM-1) and spiked samples showed good agreement between specified and measured concentrations.

Radiological impact in Korea following the Fukushima nuclear accident.

The pathway and radiological impact of the radioactive plume released at the Fukushima nuclear accident site on the Korean Peninsula has been studied. On March 28, 2011, only (131)I was first observed at all 12 regional monitoring stations in Korea, and the highest activity concentrations in aerosol were 3.12 mBq/m(3) for (131)I at Gunsan, 1.19 mBq/m(3) for (134)Cs and 1.25 mBq/m(3) for (137)Cs at Busan on April 7, 2011. These radionuclides were also detected in dry and wet deposition samples, while the significant increase of (131)I, (134)Cs and (137)Cs activity concentrations were not observed in seawater and marine biota samples.

7Be in ground level air in Daejeon, Korea.

(7)Be concentrations in the ground level air in Daejeon, Korea were determined during the period of January 1998 to December 2009 by gamma-ray spectrometric analysis of particulate samples collected on filter paper with a high-volume air sampler. The monthly concentrations of (7)Be in the ground level air were in the range of 1.3-7.7 mBq m(-3) with strong seasonal trends of low values in the summer and high values in the spring and autumn. The annual mean values of (7)Be concentrations showed weak reverse correlation with the annual average sunspot number.