Volume 98, Issue 2

Liquid samples of  93 Zr were isolated from high level liquid wastes (HLLW) by means of silica gel adsorption combined with tri- N -butyl-phosphate (TBP) extraction. Thereafter its radioactivity was determined by liquid scintillation counting (LSC) and its mass concentration by multi-collector inductively coupled plasma spectrometry (MC-ICP-MS). So a new value of  93 Zr half-life was found to be (1.13±0.11)×10 6  a.

Complexation of Pu(IV) with fluoride was studied by solvent extraction at 25, 40 and 55 °C in 2.2 mol kg -1 HClO 4 . The distribution ratio of Pu(IV) between the organic and aqueous phases decreased as the concentration of fluoride was increased due to the formation of Pu(IV)-F complexes in the aqueous phase. Two complexes, PuF 3+ and PuF 2 2+ , were identified under the conditions in this work and their stability constants at 25, 40 and 55 °C and I =2.2 mol kg -1 HClO 4 were determined from the distribution data. The specific ion interaction approach (SIT) was used to extrapolate the constants to the state of infinite dilution. Data from this work indicate that the complexation of Pu(IV) with fluoride is endothermic and entropy-driven. The complexation becomes stronger at higher temperatures.

The interactions of pentavalent Np and Pu with nitrate ligands has been investigated in perchlorate/nitrate media by capillary electrophoresis-inductively coupled plasma mass spectrometry (CE-ICP-MS). The binding constant for the complex PuO 2 NO 3 , log 10 β PuO 2 NO 3 °=0.14±0.14, is established for the first time while a new value for NpO 2 NO 3 , log 10 β NpO 2 NO 3 °=0.13± 0.14, is proposed. The usual analogy applied between Np(V) and Pu(V) interactions seems to be valid for nitrates.

Three different processes have been explored to determine the ranges of U-concentration and acidity (pH-value) for nanocrystalline U 2+x precipitation from electrolytically reduced uranyl sulphate solutions. Precipitation of U 2+x nanoparticles aggregates was found to occur only in the narrow range of pH ∼ 4.5 to 5 and for U-concentrations of ∼10 -6 to 10 -7  M. The solid phase crystallized with the typical UO 2 - fcc   structure and with a crystallite size ≤3 nm. The average aggregate size was mostly ≤80 nm. At higher U-concentrations, ranging from [U]∼10 -1  M at pH∼1.5 to [U]∼5×10 -4  M at pH∼4.9, formation of microscale precipitates of a novel complex U(IV)-sulphate phase occurred, which was characterized by SEM/EDX-WDX, ICP-OES and XRD-powder diffraction. The crystal structure was identified with an orthorhombic cell (space group  Cmca ), with the following lattice parameters: a =1.9740(2) nm, b =1.3336(2) nm and c =2.0643(2) nm. Further composition analyses indicated a basic sulphate hydrate of the type Na 3 U(SO 4 ) 3 (OH)· n H 2 O.

The suitability of solvent extraction for  210 Po analysis from groundwater samples was assessed using three extractive scintillation cocktails, POLEX, TOPO and TNOA. Validation of the extraction method was carried out using both distilled water samples with some radionuclides added and real groundwater samples. Extraction of polonium from spiked waters was successful and no co-extraction of  234 U or  238 U occurred. However, the extraction results from groundwaters differed greatly from the spiked water samples. The main interfering nuclides were  234 U and  238 U, which led to incorrect results in  210 Po analysis. Due to the co-extraction of uranium from real groundwaters, validation of the method was unfeasible.

Random coincidence summing of gamma rays and dead time count losses are a potential source of errors in gamma ray spectrometry. In this work, the magnitudes of count rate losses due to the random coincidence summing and dead time effect, alongwith corresponding corrections, have been studied. Experiments were performed in two independent gamma ray spectroscopic laboratories (referred as LAB-A & LAB-B), utilizing low activity reference nuclides  65 Zn and  60 Co. The low activity reference radionuclide  65 Zn was produced by using 10 MW nuclear reactor (PARR-1) at PINSTECH for use in one Lab. The gamma ray spectra were acquired using HPGe-detector based gamma ray spectrometers at fixed shaping times of the amplifier and positions of the reference nuclides. The MCA dead times of the spectrometers were varied to incur the count rate losses to the peaks of interest. Three procedures were adopted to determine the dead time and random summing correction factors. The corrections to count rate data measured at LAB-A, which represented a maximum of 46% losses, were obtained within standard deviation figures of 2.9%, 1.3% and 0.4% and in LAB-B case the losses of 41%, were corrected to within 1.8%, 1.1% and 0.6%, respectively with the described three procedures. The best-achieved precision (difference between the measured count rate with negligible dead time and the average of corrected count rates) in the case of LAB-A and LAB-B were within 1×10 -3 and 2×10 -2 %. The new procedure on the basis of fitting function is also evolved as a result of this study, which has produced the highly consistent results. The experimental data from the literature are also incorporated in this study for comparison purposes.

The distribution of the valence states of  75 Ge and  77 Ge was studied in three neutron-activated germanium thiocompounds. Both isotopes are formed by neutron capture and decay through their isomers. Separations of the * Ge(II) and * Ge(IV) species were carried out by HV paper electrophoresis. The radiochemical yield of the Ge(IV) seemed to be related to the covalent character of Ge–S bond. Thermal annealing patterns suggest that the trapping of metastable species is determined in part also by the matrix of the compound. An isotopic effect was observed.

Buserelin was successively labeled with [ 111 In]-Indium chloride after residuation with DTPA-dianhydride. Radio-chromatography showed an overall radiochemical purity of >90% (RTLC) and >95% (HPLC) at optimized conditions after labeling (specific activity: 400−450 GBq/M). The serum stability of the tracer was determined up to 24 h. The biodistribution of the tracer was determined in normal rats showing significant breast and ovaries uptakes 60 min post injection. MCF-7 cell binding of the tracer was >98%. A significant testes uptake was demonstrated in normal male rats using SPECT studies.

Extensive use of gadolinia for different high technology applications such as infrared absorbing automotive glass, petroleum cracking catalyst, gadolinium-yttrium garnets and color TV tube phosphors requires a precise characterization of the material. A radiochemical neutron activation analysis (RNAA) procedure has been employed to investigate 16 trace impurities in high purity gadolinia. RNAA procedure enhanced the sensitivity of the technique. The concentrations of trace impurities ranged from 20 ng/g to 34 µg/g. The impurity contents were found to be low; therefore, their deleterious effects would be negligible.