Volume 106, Issue 12

Online gas-solid adsorption studies with single-atom quantities of Hg, Tl, and Pb, the lighter homologs of the superheavy elements (SHE) copernicium (Cn, Z =112), nihonium (Nh, Z =113), and flerovium (Fl, Z =114), were carried out using short-lived radioisotopes. The interaction with Au and SiO 2 surfaces was studied and the overall chemical yield was determined. Suitable radioisotopes were produced in fusion-evaporation reactions, isolated in the gas-filled recoil separator TASCA, and flushed rapidly to an adjacent setup of two gas chromatography detector arrays covered with SiO 2 (first array) and Au (second array). While Tl and Pb adsorbed on the SiO 2 surface, Hg interacts only weakly and reached the Au-covered array. Our results contribute to elucidating the influence of relativistic effects on chemical properties of the heaviest elements by providing experimental data on these lighter homologs.

Technetium-99 is a high yield (~6% fission yield) fission product and long-lived (2.13×10 5 year half-life) component of nuclear waste that will be disposed of in a geological repository. Some 99 Tc has been released into the environment due to nuclear fuel and weapon production activities at sites such as Hanford, WA. Strongly complexing ligands such as ethylenediamine- N , N , N ′, N ′-tetraacetic acid (EDTA) are known to increase Tc(IV) solubility and mobility in environmental systems and an accurate quantification of the complexation of Tc(IV) with EDTA is important for predicting its behavior in a geological repository. A liquid–liquid extraction system utilizing 0.2 M TOPO in dodecane was used to measure the stability constants of Tc(IV)-EDTA in 0.50 m NaNO 3 at variable temperatures (14.0±0.1, 25.0±0.1, and 32.0±0.1°C). The acid dependence of the apparent stability constants in the p C H range of 2.00–2.70 indicated the formation of TcO(EDTA) 2− (log β 101 =17.9±0.3, 25.0±0.1°C) and a protonated complex TcO(H)(EDTA) − (log β 111 =20.5±0.1, 25.0±0.1°C). The associated thermodynamic parameters Δ r G 101 =−101.7±0.4 kJ·mol −1 , Δ r H 101 =−47±9 kJ·mol −1 , Δ r S 101 =179±36 J·mol −1 ·K −1 , Δ r G 111 =−117.2±0.3 kJ·mol −1 , Δ r H 111 =−23±5 kJ·mol −1 , and Δ r S 111 =315±63 J·mol −1 ·K −1 (0.50 m NaNO 3 , 25.0±0.1°C) were determined by van’t Hoff analysis. The formation of each Tc(IV)–EDTA complex is exothermic and present favorable entropy terms.

Montmorillonite (Mt) is the major clay mineral of bentonite, which is the candidate buffer material in the engineered barrier system for geological disposal of high level waste (HLW). The alteration of Mt due to its interaction with carbon steel (overpack) can produce Fe–Mt. In order to understand the basic properties of Fe–Mt, the sorption studies using Eu(III) are reported here. For this, Fe(III)–Mt was prepared by conventional cation exchange method using FeCl 3 with Na–Mt. The obtained Fe(III)–Mt was then reduced to Fe(II)–Mt using ascorbic acid. Both the samples were characterized based on their X-ray diffraction, Fourier transform infrared spectra, cation exchange capacity and specific surface area. The batch sorption studies of Eu(III) were conducted for both Fe(III)–Mt and Fe(II)–Mt as a function of pH (3–10), ionic strength (0.001 M–1 M) and Eu(III) concentration (10 −8 –10 −3 M). The distribution coefficient (K d ) was found to be higher for Fe(III)–Mt compared to Fe(II)–Mt and Na–Mt. The sudden increase in sorption in the pH range 4.5–6 and remaining constant beyond it indicates ion exchange mechanism at pH<4.5, with surface complexation mechanism dominating the sorption at pH>4.5. This is further corroborated by ionic strength dependent sorption data which shows decrease in sorption capacity of Fe–Mt with increasing ionic strength at low pH, but remaining more or less unchanged at higher pH. Eu(III) adsorption isotherm on Fe–Mt increased linearly with [Eu(III)] reaching saturation at 10 −5 M and 10 −4 M for Fe(III)–Mt and Fe(II)–Mt, respectively. The amount of iron released from Fe–Mt and Fe(II)/Fe total during sorption were estimated to understand the effect on Eu(III) sorption behaviour by release of interlayer iron in Fe–Mt.

A “hot particle” found 6 km west of the Chernobyl nuclear power plant 4 years after the Chernobyl severe nuclear accident was analysed by scanning electron microscopy and electron probe micro-analysis. The matrix of the particle consists of relics of partly molten UO 2 nuclear fuel and two different phases of solidified U–Zr–O melt (U 0.77 Zr 0.23 O 2 and U 0.67 Zr 0.33 O 2 ). The particle also contains a unique metallic inclusion of a size of 30×22 μm. The inclusion is non-homogeneous and in some parts shows a dendrite-like structure. It consists of about 38 wt.% Fe, about 10 wt.% U, Mo, and Nb, about 5 wt.% Ru, Zr, Ni, and Cr, and small amounts of Tc (2 wt.%) and Si (0.4 wt.%). The presence of partly molten nuclear fuel suggests a local temperature exceeding 2850 °C. The metallic inclusion most likely formed when steel, fuel, and cladding reacted together and molten steel incorporated U, Zr, Nb, Tc, Mo, and Ru from molten fuel and cladding during a very fast high-temperature process. Fast quenching of the metallic and the oxide melt left no time for Tc and Mo to evaporate. Molten Zr was partly oxidised and acted as a buffer for O which caused the reduction of a fraction of the U. The data of this study support the previously reported supercritical nature of the Chernobyl explosion.

Based on neutron activated 99 Mo, a procedure for preparation of 99 Mo/ 99m Tc radioisotope generator was developed. Batch equilibration method was used to investigate the sorption behavior of Mo (VI) (10 −4 M) in chloride and nitrate solutions on cerium (IV) molybdate gel matrix using 99 Mo radiotracer. The breakthrough sorption capacity of cerium molybdate gel matrix for 99 Mo (VI) (3×10 −2 M) were found to be 0.54 mmol/g of the sorbent [1 g column (0.6 cm i.d.)]. Elution performance of the generated 99m Tc from cerium molybdate- 99 Mo chromatographic column was investigated as a function of inside diameter of the column, amount of the bed matrix and flow rate of the eluent. Based on the obtained results, 99 Mo/ 99m Tc radioisotope generator was prepared based on adsorption of neutron activated 99 Mo (VI) of low specific activity onto chromatographic columns packed with 5 g cerium molybdate gel matrix. The radioactivity of 99m Tc is periodically eluted with 10 mL 0.9% NaCl solution at a flow rate of 1 mL/min. Elution yield of 78±5% was obtained with high chemical, radionuclidic ( 99 Mo breakthrough 1×10 −3 ±0.3×10 −3 %) and radiochemical purity (97±2%).

The present work has assessed the ability and competency of radioiodinated landiolol that is considered a potential cardio selective imaging agent. Landiolol was radiosynthesized with [ 131 I] using chloramine-T (Ch-T) as an oxidizing agent. To give high radiochemical yield of the [ 131 I]landiolol reaching values of 98% with high stability up to 48 h. The labeled compound was separated and purified using thin layer chromatography (TLC), paper electrophoresis and high performance liquid chromatography (HPLC). Biodistribution studies indicated that [ 131 I]landiolol gave high heart uptake ratio of [45.0±0.19% ID/g at 2 min post injection (p.i.)]. Therefore, [ 131 I]landiolol could be considered as a novel tracer to image heart with high heart/blood ratio within 60 min.

Gamma ray attenuation coefficients for various concrete types containing natural sepiolite mineral and B 4 C have been experimentally investigated at different gamma energies. In order to obtain the gamma rays, the four radioactive point-isotropic sources 133 Ba, 137 Cs, 60 Co and 22 Na which energies ranged from 80.9 to 1332.5 keV have been utilized. The measurements have been carried out by using HPGe detector and MCA equipped with a personal computer. The morphological structure and elemental compositions of the concretes have been measured with scanning electron microscope (SEM) and energy-dispersive X-ray (EDX) analyses. Linear attenuation coefficient ( μ ), mass attenuation coefficient ( μ m ), half value layer (HVL) and mean free path (MFP) have been calculated for all concretes. The obtained results have been compared to the other materials such as Pb and Al.

The ionization and X-ray production cross section are fundamental parameters in elemental analysis by PIXE technique. Unfortunately no exact general analytical expression exists, from which the interest of this work. In this paper, we apply the neural network technique in the evaluation of the X-ray production cross sections. The calculations are based on Mukoyama’s PWBA data. Our results are compared with experimental data for protons and alpha particles for energies ranging from hundreds KeV to tens MeV.