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- Author or Editor: A. Byrne x
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Abstract
In radiochemical neutron activation analysis, standards may be measured directly or subjected to the same radiochemical processing as the sample. Some considerations in regard to processing are examined, and the advantages and disadvantages of this approach discussed. It is concluded that processing of standards is often inadvisable and can lead to errors, particularly if used as a substitute for radiochemical yield determinations.
Abstract
Tin is determined at the low nanogram level in biological samples by neutron activation using the pure β−emitter121Sn of half-life 27 hours. The method is based on the concept of extracting tin selectively into an organic phase, which, after addition of a scintillant (PPO), can be directly counted by liquid scintillation counting with near 100% efficiency. Tin is first selectively extracted as its iodide into toluene, stripped and then re-extracted selectively into a toluene solution of N-benzoyl N-phenylhydroxylamine for scintillation counting. Results are given for various biological reference materials.
Abstract
Tin has been determined in biological materials by NAA of the γ-emitting 40-min123Sn and 9,7-min125Sn isotopes at the sub-ppm level. For123Sn, samples are wet-ashed after irradiation, whereas to allow fast radiochemistry for125Sn, the samples are dry-ashed prior to the irradiation. Both separation techniques rely on selective solvent extraction of tin(IV) iodide, and NaI(TI) counting. Comparative analyses of several materials by both methods gave good agreement, indicating that tin is not lost on dry-ashing and that simple dissolution of the ash in an HCl−HI mixture is complete. Results by both techniques are presented for the standard materials Bowen's Kale and NBS Orchard Leaves, and for some other materials.
Abstract
A radiochemical procedure for simultaneous determination of lead (203Pb), thallium (202TI) and cadmium (115Cd
115mIn) after fast neutron activation, based on ion-exchange separation from bromide medium and additional purification steps for Pb and Tl is described. Radioactive tracers210Pb and109Cd were used for determination of the chemical yields of Pb and Cd; for Tl it was determined gravimetrically. Two standard reference materials, BCR CRM No. 146 Sewage Sludge and NIST SRM 1633a Coal Fly Ash were analyzed and satisfactory agreement with certified values was obtained.
Abstract
Large bodies of data on a given material from different sources appear a major advantage of intercomparison experiments and a sound basis for a straight statistical evaluation (as is the usual approach in the assignment of recommended or consensus values). On closer inspection of the results, however, it is usually found that only one or two techniques are represented in statistically significant numbers, most frequently AAS and NAA, and their distribution may not be normal. Correct results are sometimes hidden among laboratory means in the lower or upper part of the frequency distribution plots. Conventional statistics neglecting procedural details and the chemistry behind a procedure may result in incorrect assignment from the reported data, which can be affected by unidentified systematic effects. Generally, in the lowest concentration range contamination predominates as the systematic error determining the accuracy of results. Activation analysis being the least vulnerable to this type of error, it is, if applicable, in principle the most likely to give correct answers. Follow-up work was carried out in this laboratory on the IAEA reference samples of Milk Powder A-11, Muscle Tissue H-4, Fish Flesh MA-A-2 and the Soil-5, clearly demonstrating the potential of activation analysis as verification technique. By determining the same element in the destructive and nondestructive mode, and on the basis of two different isotopes, virtually independent approaches are achieved, often allowing the disclosure of different types of errors. Results are also reported for nickel by a new voltammetric technique enabling its determination at the microgram per kilogram level.
Abstract
A derivative form of NAA is proposed which is based on the use of an endogenous internal standard of already known concentration in the sample. If a comparator with a known ratio of the determinand and endogenous standard are co-irradiated with the sample, the determinand concentration is derived in terms of the endogenous standard concentration and the activity ratios of the two induced nuclides in the sample and comparator. As well as eliminating the sample mass and greatly reducing errors caused by pulse pile-up and geometrical differences, it was shown that in the radiochemical mode, if the endogenous standard is chosen so that the induced activity is radioisotopic with that from the determinand, the radiochemical yield is also eliminated and the risk of non-achievement of isotopic exchange greatly reduced. The method is demonstrated with good results on reference materials for the determination of I, Mn and Ni. The advantages and disadvantages of this approach are discussed. It is suggested that it may be of application in quality control and in extending the range of certified elements in reference materials.
Abstract
A method for the simultaneous, radiochemical neutron activation analysis of uranium and thorium at trace levels in biological materials is described, based on a technique known as LICSIR, in which a double neutron irradiation is employed. In the first, long irradiation233Pa (27.0 d) is induced by neutron capture on232Th and then the sample is cooled for several weeks. A second short irradiation to induce239U (23.5 m) is followed by a rapid sequential radiochemical separation by solvent extraction of239U with TBP and233Pa with TOPO. Chemical yields of239U and233Pa were measured for each sample aliquot using added235U and231Pa tracers from the 
-spectra of the separated fractions. The technique was validated by quality control analyses.
