In recent years increased information is required about the distribution of elements at low concentration levels in the biosphere.
Neutron activation analysis can play an important role if it can supply many data at relatively low cost. As some of the concentrations
are too low for determination by non-destructive techniques, equipment for chemical separations on a routine basis is necessary.
For environmental studies a separation scheme has been developed successfully for arsenic, antimony, cadmium, copper, mercury,
selenium and zinc. It is based on a combination of distillation and ion-exchange. Special attention is paid to the prevention
of interference from bromine and sodium. Additional information about chromium, cobalt, nickel and tungsten can easily be
obtained. Experience gathered with an automated instrument for fifty samples a week is described.
The radiation-chemical processes in aqueous solutions of dichromates, isopolymolybdates and isopolytungstates have been studied.
The radiation reduction of Cr(VI) to Cr(III), Mo(VI) to Mo(V) and W(VI) to W(V) takes place. Molybdenum and tungsten blues
are the products of the last two processes in acid solutions. The yields of reduction decrease significantly with the increase
of pH. The mechanisms of the processes have been discussed. The photochemical reduction of Mo(VI) and W(VI) for the production
of corresponding 5-valent states have been used to the study of their electron scavenging efficiencies. It has been shown
that these efficiencies decrease in the order: Mo(V)>W(V)>Cr(VI)>Mo(VI)>W(VI).
Authors:I. Konstantinov, B. Zatolokin, N. Krasnov, Yu. Sevastyanov, and L. Volkova
Procedures for determining traces of calcium, titanium, vanadium, chromium, iron, copper, niobium, molybdenum and tungsten
in tantalum are described utilizing 11 MeV proton activation. The instrumental method of analysis with the use of a Ge(Li)
detector and the radiochemical separation of the corresponding fractions are described. The formula for the calculation of
the concentration of traces with the use of thick target yields is given. Experimental data on the thick target yields of
radioisotopes44Sc,52Mn,56Co,65Zn,93mMo,96Tc are presented. Based on the experimental data, the detection limits are estimated at 1–10 ppb for the above mentioned metal
traces in tantalum. The successful solution of the task of the simultaneous determination of nine elements in tantalum confirms
the wide applicability of proton activation analysis.
A method for the determination of lathanum, praseodymium, neodymium and samarium oxides in cerium dioxide has been developed.
The sample in the oxalate form is mixed with the binding material (boric acid) in the ratio 1∶1 pressed to form a double layer
pellet over a boric acid backing pellet and irradiated by X-rays from a tungsten tube. The secondary X-rays are dispersed
with a LiF (200) crystal in a Philips PW 1220 semiautomatic X-ray fluorescence spectrometer. The intensity of fluorescent
X-rays is measured by a flow proportional counter. The minimum determination limit is 0.01% for lanthanum and samarium oxides
and 0.02% for praseodymium and neodymium oxides. The precision at each concentration of the standards and theoretical minimum
determination limit for each element have been calculated.
The complexes formed by photosubstitution of pyrazine (Pz) in octacyanomolybdate(IV) and -tungstate(IV) with 8-hydroxyquinoline have been assigned the formulae [Mo(CN)2(OH)2(Pz)2(OX)] and [W(CN)2(OH)2(Pz)2(OX)·1.5H2O]. Coordination of Pz as an unidentate ligand by donating a lone pair of electron from nitrogen is shown by an absorption peak between 8–11 µ. Mechanism for the thermal decomposition of the complexes has been given. The formation of tungsten metal as residue in case of II has been confirmed by XRD analysis. The kinetic and thermodynamic parameters like activation energy (Ea), pre-exponential factor (A) and entropy of activation (
S#) were calculated employing different integral methods of Doyle, Coats and Redfern and Arrhenius.
H for each stage of decomposition was obtained from DSC.
The chlorination kinetics of alkali-added (K and Li) tungsten trioxide were studied by thermogravimetry, using gaseous CCl4 as chlorinating agent. The reactivity of the modified samples was compared to the results on the chlorination of pure WO3. Similar apparent activation energies were found for the pure and alkali-added samples. However, potassium additive resulted in a strong decrease of the initial reaction rate, while surface lithium has no influence on it.
Authors:E. Iller, H. Polkowska-Motrenko, W. Łada, D. Wawszczak, M. Sypuła, K. Doner, M. Konior, J. Milczarek, J. Żołądek, and J. Ráliš
Studies of zirconium tungstate gels for production of 188W/188Re generators using tungsten of natural isotopic abundance irradiated in a moderate flux nuclear reactor have been carried
out. Composites of WO3–ZrO2 have been synthesized by Complex Sol–Gel Process developed in INCT and other techniques. Different proportions of metal oxides
and temperature were applied. Elution profiles of columns filled with gel samples irradiated in nuclear reactor have been
studied using as an eluent 0.9% NaCl solution. Purity of 188Re fraction and efficiency of elution were determined. Ageing effect on elution efficiency was also examined. It was found
that the best elution performance showed zirconium tungstate gel prepared in 110 °C or 500 °C in which molar ratio of metal
oxides was 1:2.
Authors:José Hidalgo, Antonio Pineda, Rick Arancon, Radek Černý, Maria Climent, Antonio Romero, and Rafael Luque
SBA-15 materials exhibit important properties including large surface area, highly ordered mesopores, and high stability in a variety of catalytic reactions. In this study, Al and Zr-loaded SBA-15 materials (Si/Zr = 30, Si/Al = 30), 50 molar ratio with Pd (1, 2, and 4% (w/w)) and Pt (0.5 and 1% (w/w)) were tested in the isomerization of C5–C7 linear alkanes. These solids were characterized using thermal gravimetric analysis–differential thermal analysis (TGA–DTA), nitrogen physisorption, and energy dispersive X-ray (EDX). Interestingly, the low porosity SBA-15 materials loaded with 2% (w/w) Pd were most active catalysts for n-heptane isomerization. The mechanochemical addition of tungsten also resulted in the increase of catalytic activity for the reaction. The results herein demonstrate the possibilities of SBA-15 catalysts as a commercial catalyst alternative in the catalytic isomerization of hydrocarbons.
Some trace elements exist in cosmetics due to the mineral origin of their raw materials and there is no information about their concentration levels in these products. Other trace elements must not be contained in cosmetics according to the list of European Communities. Instrumental neutron activation analysis has been applied to determine the elements: cerium, cesium, europium, hafnium, lanthanum, lutetium, potassium, rubidium, samarium, scandium, sodium, tantalum, terbium, tungsten and ytterbium in eyeshadow, face powder and rouge make up cosmetic products from the Greek market. According to our results, a wide range of values was found between the three examined cosmetics as well as between the different samples belong to the same kind of cosmetics. This probably could be attributed to the various manufacturers of the analyzed samples. Moreover the use of neutron activation analysis as a suitable routine method is discussed for the control of some elements which must not be contained in cosmetics.
We are seeking to extend the capabilities of an in vivo XRF system which was originally designed for the exclusive detection of Fe in skin. Our interest concerns development of a more versatile in vivo XRF diagnostic facility for measurement of Fe and Zn. Elevations of these two elements have been noted to occur in a number of skin disorders and ailments. The XRF system comprises a high-output tungsten anode X-ray tube, the collimated exit beam of which is made to impinge on an appropriate choice of filter. The present study makes use of a beam hardening filter in place of our previous use of a K-edge filter. Operating at 15 kVp, 23 mA, and using a Mo beam hardening filter of 0.2 mm thickness, we have obtained a quasi-monoenergetic output of approximately 13 keV and full-width at tenth maximum (FWTM) of 1.4 keV. Preliminary measurements on simulated skin indicate that we are able to detect Fe, Zn and Cu, at levels of the order of 20-, 10- and 5 g (g skin tissue)–1, respectively, using monitoring periods of the order of 2000 seconds, and skin entrance doses of less than 16 mSv.