As part of an ongoing Great Lakes deposition study, we have determined a series of heavy metals in air filter samples collected near Lake Ontario. To decrease our detection limits for key elements used in our receptor modeling, we have employed instrumental epithermal neutron activation analysis (NAA) and Compton suppression techniques. Our detection limits were much better than those with thermal NAA, typically, 0.3 ng for Sb, 0.7 ng for As, 8 ng for Cd, 0.2 ng for In, 14 ng for I, 5 ng for Mo and 2 ng for U. Silicon, which is usually not reported in conventional NAA results for air filters, was routinely determined at the 60 g level. Accuracy was corroborated by analyzing the certified reference material concurrently.
Authors:B. Smodiš, R. Jaćimović, G. Medin, and S. Jovanović
The k0-standardization method of INAA (instrumental neutron activation analysis) was applied to three reference materials: NIST (National Institute for Standards and Technology, Washington, D.C., USA) SRM (Standard Reference Material) 1646 Estuarine Sediment, NIST SRM 2704 Buffalo River Sediment and IAEA (International Atomic Energy Agency) CRM (Certified Reference Material) SL-1 Lake Sediment. Among the 50 elements sought yielding long-lived radioisotopes after (n, ) activation, for 32 elements numerical values were obtained, and for the remaining 18, only detection limits were estimated. When comparing the results obtained in this work to certified, recommended or other literature values, good agreement was found, proving that the same analytical procedure can be applied with confidence for analysis of environmental sediment samples.
A new approach for the determination of elemental uranium in uranium bearing ore, using high resolution -ray spectrometry, was applied. Using a variant of the enrichment technique an agreement of better than 1% has been obtained between -ray measurement results and a certified value obtained by other analytical methods. For the calibration of the -ray spectrometer uranium reference samples have been used which are made available jointly in Europe and the USA as Certified Reference Materials for Gamma-Ray Spectrometry (EC NRM 171 and NBS SRM 969, respectively). The measured ore has been put in a special designed container which ensured in all directions seen from the radiation window an uniform degree of infinite thickness of about 95%. The results can be taken as an example for the applicability of -ray spectrometry when high accuracy is required and under conditions were homogeneously distributed elemental uranium is embedded in larger amount of matrix material.
Multielement determinations in the certified reference materials of soils (IAEA soil-5 and 7) have been studied fundamentally by instrumental photon activation analysis using the internal standard method coupled with the standard addition method. For the soil-5 sample, in the first place, the qualities of the comparative standards prepared by two processing methods were compared with each other. As a result, it was demonstrated that a highly accurate and precise multielement determination can be achieved easily by minor improvement in the processing method of the comparative standard to ensure homogeneity. The utility of this processing method for soil samples was proved further through a similar analysis in another soil sample (IAEA soil-7).
Neutron activation analysis (NAA) methods have been developed for the simultaneous determinations of multielement concentrations in various types of glass and their leachates. The epithermal instrumental NAA (EINAA) method involves the irradiation of samples in a Cd-shielded site for 2–5 min in order to determine levels of of up to 13 elements through their short-lived nuclides. Another 15 elements can be measured via their long-lived nuclides using conventional instrumental NAA (INAA). Accuracy of the methods have been evaluated by analyzing certified reference materials. The limits of detection for all elements are reported. The methods have been applied to sodium borosilicate and sodium calcium aluminosilicate glass samples in order evaluate their suitability as a host matrix for immobilizing high level radioactive waste.
Authors:R. Dybczyński, M. Wasek, and H. Maleszewska
A highly accurate and precise procedure deserving the name of definitive method has been devised for the determination of copper in biological materials. The method is based on combination of neutron activation and very selective and quantitative post-irradiation separation of copper from other radionuclides by extraction chromatography, using columns with LIX 70 on Bio-Beads SM-1, followed by gamma-ray spectrometric measurement. All potential sources of errors were carefully examined and eliminated or appropriate corrections were introduced into the procedure. The method contains several warning mechanisms safeguarding against making gross errors. Limit of detection for rather short irradiation time (tir
1 h) (which enables radiochemical work without sophisticated shielding) amounts to 15 g/kg. Results for copper concentration in several NBS, IAEA and other certified reference materials are presented and a new recommended value for IAEA's Milk Powder (A-11) is proposed.
A new method for the selective radiochemical separation of cadmium from other elements, present in biological materials, using amphoteric ion exchange resin Retardion 11A8 has been elaborated. Cadmium can be taken up by the resin either as anionic chloride complexes or cationic ammine complexes, depending on the composition of the eluent, exploiting both cation and anion exchange functions of the ion exchanger. The conditions in which Cd is quantitatively retained and eluted from Retardion 11A8 were established. The method of selective isolation of cadmium was further used for the determination of Cd in three biological certified reference materials by neutron activation analysis. Analytical results obtained with the use of the proposed separation procedure show good agreement with the certified values.
Authors:M. Carmo Freitas, L. Moens, P. De Paepe, and J. Seabra E Barros
A 7 kg stone of a Carrara marble was reduced to grains smaller than 100 m, mixed and homogeneized in order to prepare a marble reference material. The homogeneity was tested for 16 elements by instrumental neutron activation analysis (INAA). Through a one-way analysis of variance based on several analyses of each of 15 bottles and within the same bottle, it was concluded that the inter-bottle heterogeneity is not greater than the intra-bottle heterogeneity. Results on the concentration of major and trace elements in the marble reference material, obtained by different laboratories and different techniques, are given. The limestone certified reference material KALKSTEIN KH was used to evaluate measurement accuracy, to intercalibrate laboratories, and to provide compatibility of measurement data.
Chromium is one of the most difficult elements to accurately determine at the naturally occuring, ultratrace levels normally found in uncontaminated biological samples. In view of the importance of Cr, both as an essential and as a toxic element, efforts have focused on developing a simple, yet reliable, radiochemical procedure for Cr determination using neutron activation analysis. A number of problem areas have been identified in earlier methods, and an improved radiochemical separation procedure, based upon the liquid/liquid extraction of Cr(VI) into a solution of tribenzylamine/chloroform, has been developed. The fast neutron interference from Fe has been evaluated for the highly thermal RT-4 facility of the NBS Research Reactor, and Cr concentrations have been determined in samples of whole human blood collected under clean conditions and in two certified reference materials.
A new assembly dedicated for the low-level ψ-ray spectrometric measurements of environmental samples have been installed recently
at the International Atomic Energy Agency's Laboratories, Seibersdorf. Calibration of the detection efficiency was performed
by a set of 14 IAEA Certified Reference Materials, a standardized solution of134Cs, solutions of 2 pure potassium salts, and 2 mixed radionuclide gamma reference standard solutions. These materials, in
1.3 liter Marinelli beakers, were measured by a large HPGe detector. The high precision and accuracy of the calibration procedure
is shown by the high significance achieved in the linear fits of the efficiency results, which are traceable to certified
and standard reference materials. Small biases between some calibrands were detected. A new corrected result is the 1.37±0.05
Bq/kg activity concentration of137Cs in IAEA-A-14 Milk Powder.