Kazuhisa Komura

Polonium-210 and lead-210 in marine organisms: Intake levels for Japanese

The concentrations of210Po and210Pb were determined in about 30 species of marine organisms collected mainly from the north-easterm region of Japan to know the levels and distributions of these radionuclides and to estimate their intake levels from marine foods.210Po and210Pb showed a wide range of concentration in species: 0.6–26 and 0.04–0.54 Bq/kg (wet wt) in fishes, 0.5–220 and 0.2–43 Bq/kg (wet wt) in molluscs, echinoderms and chordatas, and 2.8–4.3 and 0.4–1.3 Bq/kg (wet wt) in algae, respectively. Higher accumulation of210Po relative to210Pb was found in all of the samples analyzed. The intake levels of210Po and210Pb by marine foods consumption were roughly estimated to be 0.48–0.69 and 0.022–0.042 Bq/d per person, respectively, on the basis of the statistical data on the consumption of seafood and/or production rates of marine foods.

Cosmogenic nuclides in the Kirin chondrite

Abstract Radioactive and stable cosmogenic nuclides have been determined in the various fragments of the Kirin chondrite (H5). Experimental results obtained from our samples are described and compared with similar data obtained in other laboratories. Cosmogenic 54 Mn, 22 Na, 60 Co, 26 Al, 53 Mn, 40 K (in the metal phase), and light noble gases were measured. Based on these data, the irradiation history of this meteorite can be explained in terms of (1) a multi-stage exposure which involves a first-stage irradiation for 10 7 years and a second stage for about 4×10 5 years, and (2) depth effects in the productions of the nuclides in 4π(second stage) and 2π(first stage) geometries. These conclusions are consistent with those of our previous work which was based on a limited number of samples.

Determination of 240Pu/239Pu ratio in environmental samples based on the measurement of Lx/alpha-ray activity ratio.

The determination of the 240Pu /239Pu isotopic ratio in environmental samples has been attempted by the measurement of the Lx/alpha-ray activity ratio using a Ge- LEPS (low-energy photon spectrometer) and a surface-barrier Si detector. By this method, interesting data were obtained for various samples collected from Thule , Greenland, Bikini Atoll and Nagasaki, as well as for some soils collected from near and off-site locations of atomic power stations.

Radioisotopes of Thirteen Elements in Intertidal Coastal and Estuarine Sediments in the Irish Sea

A survey has been carried out of40K,60Co,99Tc,106Ru,125Sb,129I,134Cs,137Cs,154Eu,226Ra,228Ra,237Np,238Pu,239,240Pu,241Pu,241Am,242Cm, and243,244Cm activities in sediments from the Irish Sea. Several of these radionuclides were measured independently at two separate laboratories to enable the intercomparison of the results produced. The comprehensive data set generated allows the present spatial distributions of these radionuclides in coastal sediments to be examined in relation to sediment textural characteristics and by comparison with earlier survey, enables the temporal trends in their activities to be determined. In general all artificial radionuclides showed lower activities in sediments in response to falling discharges from Sellafield and relationships with either grain size, distance from Sellafield or both. Isotope ratios were similar to cumulative weighted activity ratios rather than present day values due to sediment mixing. Pu levels supplied evidence for the lag in response of sediment deposits with increasing distance from Sellafield due to sediment transport.

239,240Pu,241Am and137Cs in soils from several areas in China

This paper gives the first data on239,240Pu and241Am in Chinese soils. Surface soil samples with a set of 0–5 cm and 5–20 cm depth were collected from Beijing, Taiyuan, Shijiazhuang and Jinang of China in 1990, and239,240Pu,241Am and137Cs, including naturally occurring radionuclides, in these samples were measured to evaluate their present levels and distributions. From these results, the average accumulated depositions were estimated roughly to be 24±13 MBq/km2 for239,240Pu, 10±5 MBq/km2 for241Am and 1.2±0.7 GBq/km2 for137Cs. The activity ratios of239,240Pu/137Cs and241Am/239,240Pu ranged from 0.016 to 0.026 with a mean value of 0.020±0.004 and 0.35 to 0.49 with a mean value of 0.43±0.05, respectively.

Determination of237Np and241Pu in environmental samples: In soil and sediment

This paper describes the analytical methods for the determination of237Np, Pu isotopes, and241Am, with particular emphasis on237Np by alpha-ray spectrometry and241Pu by liquid scintillation technique. Results are also presented for the sediment cores collected from Mikata Five Lakes in Fukui Prefecture, Japan.

Determination of low-level99Tc in environmental samples by high resolution ICP-MS

An analytical method has been developed for the determination of low-level99Tc in environmental samples by High Resolution ICP-MS. The method consists of leaching of99Tc by HNO3 and separation by three different solvent extractions with 30% TOA-xylene, MEK, and cyclohexanone. Finally, purification of99Tc was made by using an anion exchange resin column to reduce dissolved solids content. The final solution was adjusted to 1M HNO3 for introducing into the HR-ICP-MS. The accuracy and precision of the method was confirmed to be satisfactory by applying this technique to the determination of99Tc in IAEA marine algae sample (AG-B-1). Measurements of99Tc using 0.5–2.5 g of sediment samples from the Irish Sea, UK, were successfully performed by the present method.

237Np in hemp-palm leaves of Bontenchiku for fishing gear used by the Fifth Fukuryu-Maru: 40 years after "Bravo".

The alpha radioactive components in the Hemp-palm of Bontenchiku were determined with emphasis on the measurement low-level 237Np by alpha-ray spectrometry after chemical separation. Bontenchiku is a kind of fishing gear for long-line fishing used by the Fifth Fukuryu-Maru (Lucky Dragon). This gear was exposed to fallout from the second thermonuclear test explosion (Bravo) at Bikini Atoll in March 1954. The 237Np content in the Bontenchiku sample was determined to be 11.5 +/- 0.8 mBq g(-1), with an activity ratio of 237Np:239,240Pu and an atom ratio of 237Np:239Pu estimated to be (2.2 +/- 0.2) x 10(-3) and 0.42 +/- 0.04, respectively. The data showed the existence of a chain reaction of 238U and its ratio to be 237Np:239Pu, as well as the presence of 237U at the time of fallout from Bravo event in March 1954.

Determination of Low-Level 226Ra in Environmental Water Samples by Alpha-Ray Spectrometry

A method is described for the determination of low-level 2 2 6 Ra in environmental water samples by alpha-ray spectrometry. The procedure has been developed with emphasis on the use of 2 2 5 Ra as a yield tracer, the cation-exchange separation of barium from radium using CyDTA as eluant, and the purification of barium free from 2 2 6 Ra contamination. The chemical yield ranged from 72% to 92% with a mean value of 85%. The minimum detectable activity of 2 2 6 Ra in the water samples was about 0.01 dpm (0.2 mBq) at the 95% confidence level for a 5000-min counting period.

Fallout 237Np, Pu Isotopes and 241Am in Lake and Sea Sediments from the Coastal Area of the Sea of Japan

Depth profile and inventory of fallout 2 3 7 N p in sediment cores from the Mikata Five Lakes and Nyu Bay located in the coastal area of the Sea of Japan have been studied together with those of Pu isotopes ( 3 Pu, -°Pu and 2 4 Pu), 2 4 Am and Cs to understand the sedimentation behaviors of these elements under different aquatic environments. Mikata Five Lakes has different water salinity levels in a narrow area: fresh water (Lake Mikata), brackish water (Lakes Kugushi, Suigetsu and Suga) and sea water (Lake Hiruga). The inventory of 2 3 9 , 2 4 0 Pu estimated from measured depth profiles ranged from 109 to 347 MBq/km . The depth profiles of 2 3 7 Np and 2 4 1 Am in sediment cores were similar to that of 239,240pu G n t h e b a s i s of a comparison of the 2 3 Np/ 2 3 9 2 4 Pu inventory ratio obtained in sediment cores with that in surface soils, Np is considered to be more soluble than Pu in an aquatic environment. The 2 4 Am depth profile observed can well be explained by the ingrowth from parent 2 4 1 Pu by assuming the USA nuclear tests during the late 1950s as a substantial source of this nuclide and the immobilization of Pu and Am in the sediment. The 2 3 9 , 2 4 0 Pu/ 1 3 7 Cs inventory increased from 0.027 to 0.38 with the increase of salinity of the water.