N. N. Dogadkin

An 227Ac-211Pb generator for test experiments of solution chemistry of element 114

A simple and effective method has been developed for the continuous production of the short-lived isotope Pb as a homolog of element 114 on the principle of a radionuclide generator. The method is based on the initial sorption of 227Ac or 223Ra on a small cation-exchange column, with subsequent “milking” of 211Pb (36.1 m) by a mixture of HCl/CH3OH. The optimum conditions for the repeated separation of 211Pb from radionuclides strongly sorbed by the cation-exchanger (Ac, Th, Ra, Pu, TPE) have been determined. Possibilities of using the 211Pb generator for test experiments on the solution chemistry of element 114 have been shown. Advantages of aqueous alcohol HCl solutions for the isolation of 211Pb (element 114) are discussed.

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.

The application of INAA and beta autoradiography in an investigation of the speciation of iridium in silicates in the presence of carbon phases

Beta autoradiography and progressive acid leaching have been used to investigate the distribution of Ir in silicates in the presence of carbon phases as well as without these phases. Determinations of Ir by neutron activation analysis gave results for the Ir content of basaltic glasses after experiments at 1 bar of 82 ng·g−1 (NNO buffer), 30 ng·g−1 (CCO equilibrium) and 37 ng·g−1 (IW buffer). Iridium solubility in basaltic melt in the presence of graphite and (CO, CO2) fluid increased from 1.6 μg·g−1 at 0.5 kbar to 6.2 μg·g−1 at 2 kbar. These data give Ir partition coefficients between solid metal and liquid silicate in the presence of carbon phases. Discrete (Ir, Fe) rich phases were discovered in the basaltic melt at 3 kbar and 1250°C preventing the determination of solubility data. Our results provide clear evidence that the iridium solubility in a basaltic melt in the presence of carbon is higher than the solubility of iridium in melts without carbon.

Computation of correction coefficients by means of Monte-Carlo simulation on photo activation analysis of the samples irradiated in nonuniform bremsstrahlung field of microtron

The activating field of microtron bremsstrahlung is characterized by sharp recession of intensity in lateral and longitudinal directions. Therefore, the irradiation of several samples simultaneously results in their different activation which is a source of systematic error. Evaluation of correction coefficients needed for quantitative analysis by measurement of thin copper disks placed between the samples does not result in acceptable data. For these purposes a method for 3D-activating field monitoring and Monte-Carlo simulation for computation of the needed correction coefficients has been developed. The monitor represents the copper foil wrapped round the sample assembly. The autoradiogram of the irradiated monitor is used for characterization of the activating field. The Monte-Carlo simulation model involves both the field characteristics and the results obtained while making single training analysis.

Enhancing the selectivity of digital gamma-activation autoradiography by computer processing of a series of autoradiography images

Computer processing of a series of autoradiography images obtained during sample storage (cooling) is first proposed to enhance the selectivity of gamma-activation autoradiography. To retain the spatial resolution of the method, the mathematical processing of the decay data is done for the selection of coaxially arranges pixels of a set of images. To visualize the results obtained, a method is proposed for generating a series of metaimages characterizing the spatial localization of pixels in the given range of half-lives. It was found that, for sample zones characterized by stable results in determining half-lives, the sample obeys the normal distribution, which provides a criterion for the differentiation of such zones from artifacts or background. Based on this discovery a new method is proposed for generating contrast metaimages, ensuring the separation of zones with half-lives differing by 1 h and more.

Digital gamma activation autoradiography: A method for the study of inclusions and mineralogical texture of large size geological polished thin sections

The nuclear analytical method of element mapping in large-sized (several dozen cm2) polished sections of geological samples was worked out. The method includes activation of the sample by bremstrahlung of an electron accelerator using a developed device for uniform sample irradiation. The next step is to obtain a series of digital autoradiograms, which is processed by the program for estimation of the decay dynamics of induced radioactivity for each pixel of the image. The data obtained are converted into a series of metaimages characterizing the distribution of induced radionuclides (measured elements) over the surface of polished thin sections. The results of mapping are in a good agreement with the data of scanning electron microscopy. The developed method is suggested for screening detection of element distribution including distinguishing of the sample zones containing PGE inclusions.