N. Genova

Neutron Activation Analysis: a Powerful Tool for Assay of Rare-Earth Elements in Terrestrial Materials

Abstract Neutron activation analysis methods for determination of rare-earth elements in different matrices have been developed at the University of Pavia using the 250 Kw TRIGA Mark II reactor. A critical review of both instrumental and destructive methods is presented, as well as the indication of the best working conditions for irradiation, counting and radiochemical separations. The optimized procedures were utilized in the determination of rare-earth elements in standard reference materials of both mineral and biological origin. The adopted radiochemical procedure is based on the separation of the rare-earth element group by fluoride precipitation. Results, given as the average of six independent determinations and relative standard deviations, are reported and discussed. Precision of the methods can be deduced from the reproducibility of data, whereas accuracy is evaluated by comparison with existing values in the literature. Sensitivity limits under the described operational conditions are also reported, as are trends and correlations among data.

Trace elements distribution in Antarctic sediments by neutron activation analysis

In the present investigation iron and trace elements were determined by instrumental neutron activation analysis in a number of sea bottom sediment samples, collected in the Ross Sea and close to the Italian Station at Terra Nova Bay in Antarctica. Full listing of results is presented and discussed as well as the evaluation of precision and accuracy. In order to find correlations and similarities among the sediment samples, the analytical data were submitted to statistical treatment. In addition rare earth element patterns were obtained. Typical trends were observed with no evident Eu negative anomaly and a depletion of heavy rare earth elements.

Rare-earth elements in the NBS standard reference materials spinach, orchard leaves, pine needles and bovine liver

A highly sensitive radiochemical neutron activation method for the determination of all rare-earth elements (REE) in NBS biological reference materials is described. The materials are irradiated, dissolved in HF/HCl solutions, mixed with scandium and REE carriers (except La, Pr, Nd, Dy, Er), and the resulting solutions evaporated to dryness. The residues are dissolved in HCl and the REE precipitated as fluorides on addition of HF/NH4F solutions. The REE fluorides were collected, dissolved in a nitric/boric acid solution and the radioactivity of the resulting solutions determined by gamma spectrometry. The concentrations of REE in the NBS SRM Spinach, Orchard Leaves, Pine Needles, and Bovine Liver were found to be in the ng/g to microgram/g range. The relative standard deviations are approximately 8%. The results agreed, within experimental errors, with literature values. The distribution patterns of REE in the NBS materials relative to chondritic meteorites resemble the patterns for geological materials.

Rare-earth elements abundance and distribution in pelagic sediments by instrumental neutron activation analysis

The geochemical behavior of REE has been tested in the Umbro-Marchean (Italy) pelagic sequences of Cretaceous-Paleocene age. REE were determined by INAA in a number of limestone, marl and clay samples. Both chondrite and shale normalized patterns are discussed: the observed REE amounts and distributions are mainly attributed to highly complex diagenetic processes.

AN ACCURATE PROCEDURE FOR THE DETERMINATION OF LOW LEVELS OF IRIDIUM IN STANDARD REFERENCE MATERIALS BY NEUTRON ACTIVATION ANALYSIS

The paper describes a destructive neutron activation procedure especially set up for the determination of low levels of iridium. Only a few steps are required after irradiation, namely sample dissolution, noble metals adsorption on an ion-exchange column, removal of interfering radionuclides and counting. Successively iridium is removed from the column and the chemical yield evaluated. The method has been used for the determination of iridium in a large variety of standard reference materials, including materials of geological, biological and technological origin, with iridium levels ranging from about 0.005 to 18 ng/g. Results, given as the average of three or more independent analyses, and relative standard deviations, are reported and discussed. Average precision is about 8%, and the sensitivity is 0.004 ng.

Multielement trace analysis by atomic absorption spectrometry and neutron activation analysis in biological matrices

The following elements: Cr, Zn, Co, Cd, Mn, V are determined in a sample of NBS (spinach) which has to be certified as a new standard. Both neutron activation analysis and atomic absorption spectrometry are used; a good agreement is foudn among the different techniques. Different procedures of samples chemical dissolution are compared.

Plasma and tissue levels of some lanthanide elements in human colorectal lesions

Lanthanide (Ln) levels in plasma and tissues from colorectal patients and healthy subjects were determined by radiochemical neutron activation analysis. Results, precision, accuracy and sensitivity are presented and discussed. Mean plasma levels of La, Ce, Nd, Eu and Yb were significantly higher (p<0.01) in adenoma and adenocarcinoma patients compared to control subjects. Increasing concentrations of plasmatic La, Eu and Yb as well as Ln levels in tissue from healthy subjects, adenomatous polyps, and adenocarcinoma (ADK) patients were observed. Measured tissue levels of Ln were constantly higher in ADK and adenomatous polyps than in the adjacent normal tissues. These findings may reflect impaired calcium metabolism possibly involved in the early process of carcinogenesis leading to the development of ADK.

A rapid radiochemical procedure for uranium determination in natural waters

A neutron activation analysis method for the determination of uranium in natural fresh waters is described. The method is based on a preconcentration step by precipitation of the metal oxinate on a phenolphtalein bed followed by instrumental neutron activation analysis. Preliminary investigations with239U radiotracer were carried cut to set up the best working conditions and to evaluate the chemical yield. The whole procedure has been applied to the determination of uranium in river water.

Provenance studies of ancient Etruscan marble monuments and Sardinian pottery by neutron activation analysis and data reduction

The development of a trace element “fingerprint” as obtained by trace element determination and data reduction has been successfully applied to clear out correlations and similarities among objects of archaeological interest. In the present paper instrumental neutron activation analysis and statistical data treatment were used to solve two archaeological question: (1) the search of white marble quarries which Etruscans were used to exploit to manufacture monuments and sculptures; (2) the search of similarity, and possibly of provenence, among pottery fragemets excavated in Sardinia and belonging to the eneolithic period. Trace element matrices are presented and discussed. Data treament, such as rare-earth element pattern and pattern recognition procedures, is reported and discussed.

Radioisotope-induced X-ray fluorescence in the analysis of atmospheric particulates: Quantitative determination of zinc and lead

Multielemental analysis of atmospheric particulates collected on filter paper has been investigated using different radioisotopic exciting sources. Quantitative determinations for zinc and lead during a one year period are reported.