Volume 109, Issue 2

Bentonite, a natural clay, is a promising candidate to be used as a buffer/backfill material in the geological disposal systems for management of high level waste (HLW). Fe released due to corrosion of canister/overpack may result in alteration of Na-montmorillonite (Na-Mt), present in bentonite, to Fe-montmorillonite (Fe-Mt) in a span of several years after the emplacement of vitrified HLW in deep geological repositories. For realistic performance assessment, it is essential to understand the sorption behavior of altered Mt with regard to the radionuclides present in HLW. Cs is one of the high-yield ( 137 Cs t 1/2  = 30.1 y, 6%) and long-lived ( 135 Cs t 1/2  = 2 × 10 6  y) fission products in spent fuels. The objective of present study is to understand the effect of various parameters, viz., time (0–48 h), pH (3.0–9.0), ionic strength (0.001–1 M) [Cs(I)] (10 −10 –10 −3  M) and Fe dissolution on sorption behavior of Cs(I) on Fe(II)-Mt through batch sorption experiments. Fe(II)-Mt was synthesized by reducing Fe(III)-Mt using ascorbic acid as reducing agent in N 2 atmosphere. The near-constancy in Cs(I) sorption on Fe(II)-Mt with pH (≥4), and decrease with increasing ionic strength, illustrate the ion exchange as dominant mode of Cs(I) sorption. Further, Cs(I) sorption isotherm on Fe(II)-Mt is found to be linear. The estimation of dissolved iron in the supernatant of Fe(II)-Mt suspensions demonstrated that dissolved Fe decreased with increase in pH and increased with increase in ionic strength. Moreover, the Fe 2+ /Fe total ratio determined in all experiments was close to unity, thereby depicting that Fe(II) did not oxidize to Fe(III), except when suspension pH was ≥ 5.5. For comparison, Cs(I) sorption was also studied on Na(I)-Mt and compared with that on Fe(III)-Mt. Surface complexation modeling of Cs(I) sorption on the three clay minerals, viz., Na-Mt, Fe(II)-Mt and Fe(III)-Mt, has been successfully carried out.

The sorption kinetics and equilibrium isotherms of zirconium, uranium, and molybdenum ions onto synthetic polyaniline/SiO 2 composite (PAn/SiO 2 ) have been studied using batch-sorption techniques. This study was carried out to examine the sorption behavior of the PAn/SiO 2 for the removal of Zr(IV), U(VI), and Mo(VI) ions from an aqueous solution. The influence of some parameters on the sorption process was also studied. The maximum sorption for Zr(IV), U(VI), and Mo(VI) ions was achieved at 60 min shaking time. Langmuir isotherm model is the most representative for discussing the sorption process with a maximum sorption capacity of 24.26, 21.82, and 13.01 mg/g for Zr(IV), U(VI), and Mo(VI) ions, respectively. Kinetic modeling revealed that the sorption of all ions follows the pseudo-second-order kinetic model. The results demonstrated that both the external and intra-particular diffusion are taken into account in determining the sorption rate. Thermodynamic parameters like Δ G °, Δ H °, and Δ S ° for the sorption process were evaluated. The synthetic composite has been successfully applied for the removal and recovery of U(VI) ions from real solution (monazite leachate) using a chromatographic column packed with PAn/SiO 2 composite with a breakthrough capacity equal to 239.70 mg/g.

Adsorption of radionuclides in no-carrier-added (NCA) amounts from liquid metals оf Rb, Pb, and Ag was investigated. 82 Sr may be recovered from metallic irradiated Rb-target via adsorption onto various surfaces. A high chemical yield is achieved at Sr-sorption from molten Rb of big mass directly onto the inner surface of the target shell at about 300 °C. The investigation showed that the formation and dissolution of oxide sol particles of rubidium oxide, where 82 Sr is initially adsorbed in SrO form, play an important role in the mechanism of adsorption. The approach is prospective for different modes in “off-line” and “on-line” 82 Sr production. Direct sorption of different NCA radionuclides from molten Pb and Ag was also investigated. Chemical nature of the surface (Ta, Ni, Ti, Mo, Al, or quartz) is very critical for sorption of 188,189 Ir, 188 Pt, 198 Au, 97 Ru, 185 Os, 182m Re, 99 Mo and 99m Tc from molten Pb, and for sorption of 100 Pd, 101m Rh, 97 Ru, 96 Tc from molten Ag.

One of the most famous techniques for stomach ulcer imaging is the nuclear imaging technique. We aim to focus on the synthesis of 125 I-cimetidine ( 125 I-cim) as an agent for peptic ulcer imaging. Cimetidine was labeled with Iodine-125 using a different oxidizing agent (Ch-T, NBS). All factors affecting the labeling yield were optimized. The radiochemical yield of 125 I-cim was 98 ± 0.22% at optimum conditions. In vitro stability, in vivo biodistribution of 125 I-cimetidine was studied in three groups: control group, pretreated group, and ulcer bearing group. In vivo biodistribution studies of 125 I-cim revealed high uptake in the stomach ulcer, reaching about 75.4 ± 1.2% ID/g at 15 min post-injection, than pretreated groups compared to the control. The results showed the suitability of using 125 I-cimetidine for stomach ulcer imaging.

Extensive interest in the development of α-emitting radionuclides astatine-211 ( 211 At) stems from the potential superiority for the treatment of smaller tumors, disseminated disease, and metastatic disease. VP2, a small molecule fusion peptide, can specifically bind to the VPAC1 receptor which is over-expressed in malignant epithelial tumors. In our recent study, we performed the preparation of 211 At labelled VP2 through a one-step method. In this work, we explored the targeted radionuclide therapy with [ 211 At]At-SPC-VP2 in vitro and in vivo . The cytotoxicity and specific cell killing of [ 211 At]At-SPC-VP2 were evaluated using the CCK-8 assay. Compared with the [ 211 At]NaAt, the VPAC1-targeted radionuclide compound [ 211 At]At-SPC-VP2 showed more effective cytotoxicity in vitro . Targeted radioactive therapy trial was carried out in non-small-cell lung cancer (NSCLC) xenograft mice. For the therapy experiment, 4 groups of mice were injected via the tail vein with 370 kBq, 550 kBq, 740 kBq, 3 × ∼246 kBq of [ 211 At]At-SPC-VP2, of which the second and third injections were given 4 and 8 days after the first injection, respectively. As controls, animals were treated with saline or 550 kBq [ 211 At]NaAt. The body weight and tumor size of mice were monitored before the administration and every 2 days thereafter. Cytotoxic radiation of partial tissue samples such as kidneys, liver and stomach of mice were assessed by immunohistochemical examination. The tumor growth was inhibited and significantly improved survival was achieved in mice treated with [ 211 At]At-SPC-VP2, two-fold prolongation of survival compared with the control group, which received normal saline or 550 kBq [ 211 At]NaAt. No renal or hepatic toxicity was observed in the mice receiving [ 211 At]At-SPC-VP2, but gastric pathological sections showed 211 At uptake in stomach resulting in later toxicity, highlighting the importance of further enhancing the stability of labelled compounds.

A sponge rubber nanocomposite based on styrene–butadiene rubber (SBR)/nanoclay (montmorillonite, MMT) or nano-calcium carbonate (CaCO 3 ) fillers with various foaming agent contents was produced by a simple technique, roll milling. The nanoparticles were examined by different techniques, such as X-ray fluorescence (XRF), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), and Fourier-transform infrared (FT–IR). The sponge rubber nanocomposites were characterized by scanning electron microscopy (SEM) image analysis before and after exposures to radiation doses, as well as by the XRD patterns for the unirradiated samples. The different properties of the obtained nanocomposites, including their foaming degree, tensile strength, elongation at break, and thermal conductivity, were also investigated. The foam composites containing nano-CaCO 3 possessed the best cell and crosslinking densities and mechanical properties among the other composites, while its foaming degree was the lowest. The results indicated that the thermal conductivity was reduced by increasing the foaming agent concentration. However, it increased as the radiation dose increased, and the optimum radiation dose was obtained at 75 kGy. The foam containing MMT exhibited an intermediate behavior while high thermal conductivity was recorded for the foam containing the CaCO 3 nanoparticles.

In this study, the fast neutron and gamma-ray absorption capacities of the new glasses have been investigated, which are obtained by doping CoO,CdWO 4 ,Bi 2 O 3 , Cr 2 O 3 , ZnO, LiF,B 2 O 3 and PbO compounds to SiO 2 based glasses. GEANT4 and FLUKA Monte Carlo simulation codes have been used in the planning of the samples. The glasses were produced using a well-known melt-quenching technique. The effective neutron removal cross-sections, mean free paths, half-value layer, and transmission numbers of the fabricated glasses have been calculated through both GEANT4 and FLUKA Monte Carlo simulation codes. Experimental neutron absorbed dose measurements have been carried out. It was found that GS4 glass has the best neutron protection capacity among the produced glasses. In addition to neutron shielding properties, the gamma-ray attenuation capacities, were calculated using newly developed Phy-X/PSD software. The gamma-ray shielding properties of GS1 and GS2 are found to be equivalent to Pb-based glass.