Riki Seki

Application of a high resolution inductively coupled plasma mass spectrometer to the measurement of long-lived radionuclides

Some long-lived radionuclides, such as 99Tc, 226Ra, 232Th, 237Np, 238U, 239Pu and 240Pu were measured using high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS). By using HR-ICP-MS with an ultrasonic nebulizer, the detection limits of these nuclides were 0.002–0.02 pg ml–1 and the sensitivities were 10 times better than those obtained using HR-ICP-MS without the ultrasonic nebulizer. More accurate isotopic data were also obtained using HR-ICP-MS than with quadrupole ICP-MS at lower concentrations of the analyte because of the improvement in counting statistics that can be obtained with HR-ICP-MS due to the greater efficiency of ion transmission. A comparison of the measurement of the 240Pu to 239Pu ratio is shown.

Determination of technetium-99 in environmental samples by inductively coupled plasma mass spectrometry

Abstract A new analytical technique using inductively coupled plasma mass spectrometry (ICP-MS) was applied to the determination of 99Tc in some environmental samples. The accuracy and precision of the new method were assessed by comparison with those of the liquid scintillation counting method. The results obtained by ICP-MS were in good agreement with those by liquid scintillation counting at a relative deviation of 3%. The detection limit is 1.1 mBq/mL (1.73 pg/mL).

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.

Determination of U in Japanese human tissues by the fission track method.

Uranium in several human tissues (lung, liver, kidney, muscle, spleen, heart, cerebrum and bones) from Japanese in the Tokyo area was determined by the fission track method. The average U content was the highest in lung with 1.70 ppb wet, and decreased in the order of lung greater than bones greater than heart and muscle greater than kidney greater than liver and spleen, showing markedly different tendencies from the description in the 1982 UNSCEAR Report (UNSCEAR82). Correlations were observed between U content in lung and in other tissues. These data suggest that the contribution of inhalation of U to its total intake is not negligible. The total body burden of U for the ICRP Reference Man (ICRP74) was estimated to be about 40 micrograms, which is rather small compared with the average normal burden of 90 micrograms currently accepted by the International Commission on Radiological Protection (ICRP79).

Distribution and behavior of long-lived radioiodine in soil

The concentration of129I in soil in Japan was determined by neutron activation analysis. For the activation analysis, pre-irradiation chemical separation of the iodine was carried out by acid decomposition and distillation and post-irradiation treatment was performed by ion exchange and solvent extraction. The concentration of stable iodine and137Cs were also determined and compared with the behavior of129I in soil.Soil samples from Ibaraki, Fukui, Fukushima, and Nagasaki Prefectures were analyzed and129I was detected in amounts ranging from 10−7 to 10−5 Bq/g soil in uncultivated surface soil. There are apparently small variations in the129I concentrations in each of the regions analyzed.From depth profile studies in sandy soil, the iodide form of129I was found to migrate downward at a relatively rapid rate while other species remain longer in the surface soil.

Distribution and behaviour of99Tc,237Np,239,240Pu, and241Am in the coastal and estuarine sediments of the Irish Sea

Intertidal coastal and estuarine sediments from 24 sites in the Irish Sea have been analyzed for99Tc,237Np,238Pu,239,240Pu and241Am. The237Np activity and239Pu/240Pu ratio were measured simultaneously by ICP-MS, and99Tc was determined by HR-ICP-MS which is ten times more sensitive than Q-ICP-MS.The activities of99Tc,237Np,239,240Pu and241Am were distributed over a wide range of 1.5–70.5, 0.01–13.3, 2.3–1589, 2.6–1894 Bq/kg, respectively. Activities of these radionuclides decreased exponentially with distance from the Sellafield source. The241Am/239,240Pu and237Np/239,240Pu ratios were almost constant with distance from the Sellafield. This result suggests that the distribution and behavior of Np and Pu are controlled by complicated factors such as the influence of transport, the variation with time of Np/Pu ratio in the Sellafield discharges and sedimentary mixing processes in the Irish Sea.

Particle-size distribution of fission products in airborne dust collected at Tsukuba from April to June 1986

Abstract The radioactivity released by the reactor accident at Chernobyl was detected in surface air at Tsukuba, Japan. Gamma-spectrometry of airborne dust collected using aerodynamic separation showed higher concentrations of radionuclides in fine particles. The particle-size distribution of radionuclides changed with time.

Status of the 36Cl AMS system at the University of Tsukuba

Abstract The current status of the 36Cl AMS system at the University of Tsukuba is reported. A “tri-molecular pilot beam” method is used to stabilize the terminal voltage of a 12UD tandem instead of an ordinary GVM stabilizer. The terminal voltage is kept stable within 0.1%. The capabilities of the ion source have been tremendously improved. Both Cl− negative ions and a 12 C 3 − tri-molecular pilot beam can be produced simultaneously with reasonable stability and intensity. The 36Cl/35Cl ratio can be measured with a precision of ±2% for a 15 μA Cl− beam current. A high sulfur reduction is achieved by introducing two independent chemical procedures, so that the background reaches up to 2×10−14. This sensitivity is still insufficient. Therefore, our current effort is focused on improving it.

1H and 19F NMR studies on molecular motions and phase transitions in solid triethylammonium tetrafluoroborate

Abstract Measurements by differential thermal analysis and differential scanning calorimetry and of the spin-lattice relaxation time (T1), the spin-spin relaxation time (T2), and the second moment (M2) of 1H and 19F NMR were carried out in the three solid phases of (CH3CH2)3NHBF4. X-ray powder patterns were taken in the highest-temperature phase (Phase I) existing above 367 K and the room-temperature phase (Phase II) stable between 220 and 367 K. Phase I formed a NaCl-type cubic structure with a = 11.65(3) A , Z = 4, V = 1581(13) A 3 , and Dx = 0.794 g cm−3, and was expected to be an ionic plastic phase. In this phase, the self-diffusion of anions and the isotropic reorientation of cations were observed. Phase II formed a tetragonal structure with a = 12.47(1) and c = 9.47(3) A , Z = 4, V = 1473(6) A 3 , and Dx = 0.852 g cm−3. From the present DSC and NMR results in this phase, the cations and/or anions were considered to be dynamically disordered states. The C3 reorientation of the cation about the NH bond axis was detected and, in addition, the onset of nutation of the cations and local diffusion of the anions was suggested. In the low-temperature phase (Phase III) stable below 219 K, the C3 reorientations of the three methyl groups of cations and the isotropic reorientation of anions were observed. The motional parameters for these modes were evaluated.

Neptunium in intertidal coastal and estuarine sediments in the Irish Sea

Abstract A survey has been carried out of 237 Np activities in sediments of the Irish Sea. Two independent methods of analysis were used (ICP-MS and alpha-spectrometry) to enable the intercomparison of the results produced. The 237 Np content of the samples ranged from 0·.01–4·5 Bq/kg for all areas apart from the Ribble Estuary. In the Ribble, a source of 237 Np other than Sellafield has been found which supports 237 Np activities in sediments up to 13·.3 Bq/kg. This anomaly is verified by comparing 237 Np with the 239.240 Pu content of the sediments. These are believed to be the highest environmental 237 Np values yet recorded.