GENERAL RESEARCH LINES

• development of X-Art substance element contents analyzers;
• investigation of environmental samples for the content of heavy metals and other toxic elements;
• elaboration of X-ray optics components and devices;
• estimation and measuring of spectra from X-ray sources;
• imitation of X-ray, γ-radiation and secondary electron transport in substance.

X-Art devices (at the left - provided with cooling by liquid nitrogen, at the right - with Peltie-cooler

The Laboratory for investigations by X-ray methods was organized in 2004. The main line of its activity represents the development of substance element contents analyzers on the basis of ED XRF approach. The works in this direction are realized with support of JSC "Comita" (SPb) and in cooperation with BSI-Bruker company (Riga). X-Art devices produced with the trademark of "Comita" company are used at present for examination of artworks at two leading museums of the country: the State Tretiakov Gallery and the State Russian Museum, as well as for examination of electro-technological products at Nankin Electrotechnical Institute (CPR). Laboratory's employees took participated on repeated occasions in international intercalibration experiments, particularly, related to IAEA activity and on analysis of water samples within the frameworks of the Program for certification of 20 German laboratories by Bavarian Institute for Water Problems in Muenchen. The reports of these experiments contain the results of measurements conducted, which fall into the range of allowable variations and allow to realization of quantitative analysis of various ecological samples.

Devices of X-Art type are destined for analysis of wide range samples, such as commercial process patterns (including steels and alloys, engine oils, oil products, process solutions, rubber goods, ceramics, plastics, ferrites), geological (including ore and minerals), medical and ecological (including blood, blood plasma, hair, nails, and other biological substances, water, soil, filters after air filtering), criminological (including fragments of clothes, traces of impact on various objects), fine art patterns (including colorants of paintings, works of applied art, made of various materials, archaeological patterns). X-Art devices are equipped with cooled Si(Li) detectors with high detection efficiency, produced by BSI-Bruker company, and excitation system on the basis of X-ray tubes. The cryostat for the version with cooling by liquid nitrogen contains coolant in amount from 500 to 800 ml that allows for continuous operating during 15-20 hours. Detection unit can be kept without nitrogen for any required period of time. The version assuming cooling by Peltier-cooler suggests permanent attachment of the unit to power supply system, but it can stay without supply for 15 days, switching automatically at that to built-in accumulator. Characteristics of X-Art device are given in "Projects" section of the site of JSC "Comita" (www.comita.ru/x-art).

Analysis of medical and ecological samples for the content of heavy metals and other toxic elements is realized in cooperation with SRI of Physics, SPSU, Army Medical College, and other organizations of St-Petersburg. They carry out the works ordered for analyzing of environmental conditions in various districts of the city and everywhere over the region. In these cases they investigate water from ponds, soil, plants, and atmospheric air. Sensitivity of analysis for the elements with moderate atomic numbers is usually no worse than 10^-4%. Hair and nails serve as accumulators of heavy metals, thus why their investigation is of serious interest in the view of children health in the region, as well as in the view of professional pathology. The project assuming routine testing of such samples on the level of outpatient departments has been supported by Sanitary and Hygienic Academy.

With the purpose to collimate X-ray radiation beams in the run of forming them there have been developed and currently produced mono-capillary glass diaphragms-collimators in metal casing. These devices, which mode of functioning is based on total external reflection of X-ray photons at definite angles of incidence onto internal surface of capillary, allow for increase in luminance of micro-focus sources. An application of these devices is mainly associated with realization of explorations of biological objects with the purpose to analyze the structure of micro-molecules.

Spectra of X-radiation sources are of interest in view of precise assessment of radiation doses to patients of clinics, subjected to radiological analysis, as well as in developing of programs for quantitative analysis of substance element contents on the basis of fundamental parameters method. Direct computation of X-ray tube spectra can be carried out by Monte Carlo method, using cross-sections of electron interaction with material of tube's anode. Such type computation codes have already been elaborated and they include modeling of electron tracks, excitation of target-anode, bremsstrahlung and characteristic radiation. In parallel with this, X-ray tube spectra can be measured both with the help of Si(Li) SCD - at low threshold energies and slow counting rate - and with the help of detecting unit based on NaI crystal, designed at ENP sub-faculty of SPSU. In the last case it is possible to obtain counting rates up to 5ћ10⁵ cps, and threshold energy can reach 60-80 keV for 2-mm thick crystal and 250-300 keV - for 1-cm thick crystal.

The available package of codes on the basis of Monte Carlo method is destined in principle for ?-quantum and secondary electron energy range from 1 keV to 2 MeV. This package is compiled in the way allowing individual modeling of electron elastic scattering events, using corresponding cross-sections for relatively low energies (below approximately 100 keV), and application of collision grouping method for higher initial energies. The frame of tasks to be solved with the help of this package can be very wide. By the present moment of time the most experience is accumulated in solving the problems related to analyzing and optimization of design of γ- and X-ray radiation detectors, including proportional counters, SCD, and various scintillation detectors. In particular, the works on designing of characteristics of sensors destined to detect conversion electrons in Mossbauer spectroscopy experiments have been implemented in cooperation with IAP of RAS (S.-Petersburg) and E-15 Laboratory in Max Planck Center (Germany).