V. P. Kolotov

An electronic database with a compilation of k0 and related data for NAA

An electronic data base (DB) containing recently evaluated k0 and related data has been developed. The tables composing the DB are relationally linked to support data integrity. The purpose of the DB development is to make an official source of data used for electronic synchronization of the input parameters needed for the k0 methodology, which is developing in numerous laboratories. Such solution saves time when updating, ensures the quality of the primary data and hence of the analysis results, and due to the recording of the updating history preserves traceability of the data in time.

Compilation of k 0 and related data for NAA in the form of electronic database (IUPAC Technical Report)

This report describes the principles underlying a comprehensive electronic database that contains data essential for calculation of analytical results from neutron-activation analysis (NAA) and that is available through IUPAC. The method used is a comparator method called the k0 method, where k0 is a dimensionless factor which is experimentally measured with high accuracy for more than 130 isotopes and which makes use of the gamma spectroscopic line for an analyte isotope relative to a gold comparator. The database contains recommended values for k0 and other relevant nuclear data.

Estimation of true coincidence corrections for voluminous sources

To analyze a voluminous radioactive source with the highest possible sensitivity, it is necessary to use both a high efficiency detector and an optimal measurement geometry. The “optimal” geometry implies positioning the source as close to the detector as possible. It also implies selection of the shape of the source in order to reach the highest efficiency possible (e.g., Marinelli beaker). Under such conditions of measurements, true coincidences may cause systematic errors that can reach levels of more than ten percent for some radionuclides. A method for estimation of the effect of these coincidences was developed. It is based on direct computation of the effect by means of integration of a function which involves the experimentally obtained detection efficiency for the place around the detector. It was found that for the tested detector with a relative efficiency of 15%, the so-called intrinsic peak-to-total calibration may be used in the course of such an integration: It has been shown that theP/T-ratio for the given energy in the working space around the detector may be considered a constant value. Some results from a peak-to-total calibration study in the presence of scattering material are also given.

SOFTWARE ASPRO-NUC: GAMMA-RAY SPECTROMETRY, ROUTINE NAA, ISOTOPE IDENTIFICATION AND DATA MANAGEMENT

The software ASPRO-NUC is based on new improved algorithms suggested and tested in the laboratory and intended for routine analysis. The package consists of the program ASPRO for gammaray spectra processing (peak search, multiplets deconvolution by means of method of moments, computation of correction coefficient for geometry and material of radioactive source), a program for isotope identification and a program for NAA by means of relative standardization. All output information is loaded into a data base (Paradox v.3.5 format) for supporting of queries, creation of reports, planning of routine analysis, estimation of expenses, supporting of network of analytical survey, etc. The ASPRO-NUC package also includes a vast nuclear data base containing evaluated decay and activation data (reactor, generator of fast neutrons, Cf-252 source). The data base environment allows for easy integration of a gamma spectrometer into a flexible information shell and the creation of a logical system for information management.

Testing of different true coincidence correction approaches for gamma-ray spectrometry of voluminous sources

To achieve the highest possible sensitivity of analysis for environmental samples it is common practice to use both a high efficiency detector and a close measurement geometry with a large sample size (e.g. Marinelli beaker). Under such conditions, the typical efficiency calibration procedure results in a biased activity value for many nuclides due to the true coincidence summing effect. While there are a few methods to correct for this effect with special calibration standards, such calibrations can be both time consuming and expensive. Due to these calibration difficulties, the true coincidence summing effect is often simply ignored. Recently, it has been demonstrated that the coincidence summing correction can be performed mathematically even for voluminous sources. This new method consists of an integration of the coincidence correction factor over the sample volume while taking into account its chemical composition and the container. In this paper, we will discuss the latest approaches for establishing the peak efficiency and peak-to-total efficiency curves, which are required for this method. These approaches have been tested for HPGe detectors of two different relative efficiencies.

Enhancement of digital gamma activation autoradiography capabilities by means of computer analysis of the time series images

It has been demonstrated that pixel-by pixel processing of series of autoradiography images for revealing the dynamics of decay of the induced radionuclides is an efficient approach for mapping of radionuclides in the sample in activation autoradiography. Concepts of virtual scanner and corresponding software for linearization of dependence of optical density on scanner response (luminosity) have been introduced. The concept provides unification of the subsequent processing of autoradiograms, irrespective of the method as to how the digital image has been obtained. Algorithms and the software for estimation of decay parameters of a radionuclide mixture for each pixel using a series of coaxially positioned images have been developed. The software is able generate a set of the derivative meta-images allowing a conclusion to be made about the presence of the inclusions in question. To increase the reliability of radionuclide mapping it is suggested to use analysis of distribution of half-life values estimated for pixels of image zone(s) pointed by a special mask.

Development of digital autoradiography technique for the determination of the platinum-group elements in geological materials

Application of digital document scanners as a tool for 2D-densitometry of autoradiograph images is discussed. Comparison with conventional densitometry is presented. The requirements for scanners and software for digital autoradiography of geological materials are reviewed and a selective and sensitive method for the detection of platinum by means of gamma-activation autoradiography has been developed (the detection limit is about 1 ng for Pt-inclusions in spinel). The results of an interpretation of neutron-activation autoradiographs for locating an iridium-containing phase is discussed.

Quantitative digital 2D densitometry in the processing of series of autoradiographic images

Previously we have shown that, using the mathematical pixel-by-pixel processing of a series of autoradiographic images of activated samples, analyst can gain information on the distribution of elements in geochemical samples, including large ones. The level of reproducibility in 2D densitometry is the key factor determining the efficiency of such processing. A procedure is developed for obtaining a series of digital autoradiograms using both classical nuclear photodetectors and digital imaging plates; the reproducibility of the results of quantitative densitometry was no worse than 2%. The results obtained on mapping well agree with the data of scanning electron microscopy.

Coincidence summing corrections using alternative detector characterization data

We have shown that it is sufficiently accurate to use the MCNP peak-to-total calibration results to correct for cascade summing effects in a gamma-spectrum. Also, it is sufficient to use only approximate detector characterization data with empirical peak-to-total to obtain good cascade summing correction results. The intrinsic P/T-curve for detectors with the same efficiency is very similar and it may be considered a common characteristic of the whole detectors family with given efficiency.

Gamma-activation analysis of nitrogen solubility in alumosilicates at high pressure and temperature

A solubility of nitrogen in natural basalts and synthesized albite at 1250 °C and 3 kbar was studied by γ-activation method based on the reaction14N(γ,n)13N with radiochemical separation of nitrogen by high-temperature extraction at 1800 °C. Detection limit of 0.2 μg in the samples of 15–20 mg weight is obtained. The investigation originated from the study of processes of accumulation and redistribution of nitrogen in rock-forming alumosilicate melt of the Earth mantle. The dependence of nitrogen solubility on the oxygen volatility and pressure were obtained (within 1–3 kbar in the presence of IW buffer [iron(Fe)-wustite(FeO)]) and NNO (Ni−NiO), and essential effect of the composition of the initial matrix was found. Special attention was given to standards, background, interference reactions, reliability and accuracy of the results.