排序方式: 共有5条查询结果,搜索用时 15 毫秒
1
1.
Taeko Shinonaga Helmuth Aigner Dilani Klose Peter Spinder Heinz Fröschl David Donohue 《Geostandards and Geoanalytical Research》2008,32(1):93-101
The recommended concentrations of 239Pu, 240Pu and 239+240Pu in reference material IAEA‐315 (marine sediment) were estimated by three analytical methods: isotope dilution thermal ionisation mass spectrometry (TIMS), isotope dilution inductively coupled plasma‐mass spectrometry (ICP‐MS) and alpha spectrometry. The determination of 239Pu and 240Pu (239+240Pu by alpha spectrometry) was carried out with samples from randomly selected bottles using each method. Plutonium‐238 was also measured by alpha spectrometry. A plutonium‐242 reference material was used as a spike for the quantitative analysis. The influence of 242Pu in the samples was therefore calculated; however, this contribution was less than the range of uncertainty and did not influence the final results. The obtained data were statistically analysed using variance component analysis and paired comparison. The combined standard uncertainties from “method/measurement”, “bottle” and “sub‐sample” were in the order of 3 to 6%. The main contributions to the uncertainty were from the material heterogeneity and from systematic differences between methods. Based on this study with twenty‐seven analyses using 10–14 g sample mass, concentrations of (38 ± 3) Bq kg?1, (28 ± 3) Bq kg?1 and (66 ± 4) Bq kg?1 are proposed as recommended values for 239Pu, 240Pu and 239+240Pu, respectively, and (9.5 ± 0.4) Bq kg?1 for 238Pu as an information value in reference material IAEA‐315. In mass concentration units, these amount to (16.4 ± 1.2) ng kg?1, (3.3 ± 0.4) ng kg?1 and (0.015 ± 0.003) ng kg?1 for 239Pu, 240Pu and 238Pu, respectively. The certified reference materials NIST 4350B and NIST 4354 were also analysed by TIMS for quality assurance of the method used in this study. 相似文献
2.
3.
Instrumental Neutron Activation Analysis of Estuarine Sediment as a Proposed Reference Material for Environmental Studies 总被引:1,自引:0,他引:1
Shahida Waheed Mohammad Wasim Asma Rahman Shujaat Ahmad 《Geostandards and Geoanalytical Research》2001,25(1):137-143
The International Atomic Energy Agency (IAEA) Marine Environmental Studies Laboratory (MEL) organised an intercomparison exercise, through its Analytical Quality Control Services (AQCS), for the determination of trace elements in estuarine sediment IAEA-405, well suited for the characterisation of sediments. The instrumental neutron activation analysis technique (INAA) was developed using a 27 kW low power research reactor. Forty elements in the sediment were determined with a measurement precision varying from 1.8% to 12.3%. IAEA reference materials SL-1 and SD-M-2/TM were analysed throughout this work as quality assurance samples. 相似文献
4.
5.
R. J. Wilman A. C. Edge R. M. Johnstone C. S. Crawford A. C. Fabian 《Monthly notices of the Royal Astronomical Society》2000,318(4):1232-1240
We present J , H and K -band spectroscopy of Cygnus A, spanning 1.0–2.4 μm in the rest-frame and hence several rovibrational H2 , H recombination and [Fe ii ] emission lines. The lines are spatially extended by up to 6 kpc from the nucleus, but their distinct kinematics indicate that the three groups (H, H2 and [Fe ii ]) are not wholly produced in the same gas. The broadest line, [Fe ii ] λ 1.644, exhibits a non-Gaussian profile with a broad base (FWHM≃1040 km s−1 ), perhaps because of the interaction with the radio source. Extinctions to the line-emitting regions substantially exceed earlier measurements based on optical H recombination lines.
Hard X-rays from the quasar nucleus are likely to dominate the excitation of the H2 emission. The results of Maloney, Hollenbach & Tielens are thus used to infer the total mass of gas in H2 v=1–0 S(1)-emitting clouds as a function of radius, for gas densities of 103 and 105 cm−3 , and stopping column densities N H =1022 –1024 cm−2 . Assuming azimuthal symmetry, at least 2.3×108 M⊙ of such material is present within 5 kpc of the nucleus, if the line-emitting clouds see an unobscured quasar spectrum. Alternatively, if the bulk of the X-ray absorption to the nucleus inferred by Ueno et al. actually arises in a circumnuclear torus, the implied gas mass rises to ∼1010 M⊙ . The latter plausibly accounts for 109 yr of mass deposition from the cluster cooling flow, for which within this radius. 相似文献
Hard X-rays from the quasar nucleus are likely to dominate the excitation of the H
1