Volume 104, Issue 8

Abstract: The cross sections for (n,x) reactions on samarium isotopes were measured at (d-T) neutron energies of 13.5 and 14.8 MeV with the activation technique. Samples were activated along with Nb and Al monitor foils to determine the incident neutron flux. Theoretical calculations of excitation functions were performed using the nuclear model codes TALYS-1.6 and EMPIRE-3.2 Malta with default parameters, at neutron energies varying from the reaction threshold to 20 MeV. The results were discussed and compared with experimental data found in the literature. At neutron energies 13.5 and 14.8 MeV, the cross sections of the 149 Sm(n,p) 149 Pm reaction are reported for the first time. The cross sections of the 150 Sm(n,p) 150 Pm, 144 Sm(n,p) 144 Pm, 152 Sm(n, α ) 149 Nd and 144 Sm(n, α ) 141 Nd reactions at different neutron energies reported in the present work can be added as new data in the nuclear databases.

The decomposition behavior of group 6 metal hexacarbonyl complexes (M(CO) 6 ) in a tubular flow reactor is simulated. A microscopic Monte-Carlo based model is presented for assessing the first bond dissociation enthalpy of M(CO) 6 complexes. The suggested approach superimposes a microscopic model of gas adsorption chromatography with a first-order heterogeneous decomposition model. The experimental data on the decomposition of Mo(CO) 6 and W(CO) 6 are successfully simulated by introducing available thermodynamic data. Thermodynamic data predicted by relativistic density functional theory is used in our model to deduce the most probable experimental behavior of the corresponding Sg carbonyl complex. Thus, the design of a chemical experiment with Sg(CO) 6 is suggested, which is sensitive to benchmark our theoretical understanding of the bond stability in carbonyl compounds of the heaviest elements.

Irradiation of natural thorium with medium-energy protons is considered to be a prospective approach to large-scale production of 225 Ac and 223 Ra. In addition to the earlier-developed method of 225 Ac isolation, the present work focuses on the simultaneous recovery of. 223 Ra from the same thorium target. Radiochemical procedure is based on liquid-liquid extraction, cation exchange and extraction chromatography. The procedure provides separation of radium from spallation and fission products generated in the thorium target. High chemical yield (85– 90%) and radionuclide purity of 223 Ra (> 99.8% except 224 Raand 225 Ra isotopes) have been achieved.

Ordered mesoporous UO 2 with 3-D structure (for UO 2 -KIT-6) and nanowire bundles (for UO 2 -SBA-15) was synthesized for the first time by a nanocasting route using different ordered mesoporous silica (KIT-6 and SBA-15, respectively) as templates and uranyl nitrate hexahydrate as the metal precursor. The uranyl nitrate was impregnated into the mesopore of the silica template and was converted to U 3 O 8 after the first step. The synthesis of ordered UO 2 mesostructure was achieved by reducing the mesoporous U 3 O 8 with silica composites under 5% H 2 /Ar atmosphere at 700°C, followed by a template removal process. The as-prepared UO 2 -KIT-6 had a particle size of several millimeters, and was constructed with uncoupled subframework mesostructure and crystalline walls, while UO 2 -SBA-15 possessed a rope-like morphology and consisted of nanowire arrays. The surface area and pore volume of ordered UO 2 mesostructure are 47.2 m 2 g −1 and 0.23 cm 3 g −1 for the UO 2 -KIT-6, and 54.4 m 2 g −1 and 0.28 cm 3 g −1 for the UO 2 -SBA-15, respectively.

Polyaminopolycarboxylates are attractive ligands for binding cationic radionuclides for synthesis of radiopharmaceuticals with target delivery to tumor cells. Nowadays beta emitting Y−90 and Lu−177 are used as therapeutic agents, while Ac−225 and Bi−213 are considered as perspective for alpha therapy. In the present study new data on complexation of Y 3+ , Lu 3+ , Ac 3+ and Bi 3+ with 2,2’-(15-formyl-2,3,5,6,8,9,11,12-octahydrobenzo [b][1,4,10,7,13]trioxadiazacyclopentadecine-4,10- diyl)diacetic acid are presented. For ligand and complexes characterization potentiometric titration, solvent extraction, chromatography and solubility techniques were applied. The highest values of stability constants within the range of log K = 5.8 – 7.5 were found for Ac 3+ and REE. Fast complex formation is established which is beneficial for practical applications in radiopharmaceutical synthesis.

Solvent extraction of microamounts of trivalent europium and americium into nitrobenzene by using a mixture of hydrogen dicarbollylcobaltate (H + B − ) and magnesium ionophore II (L) was studied. The equilibrium data were explained assuming that the species HL + , HL2+${\rm{HL}}_2^ + $, ML23+${\rm{ML}}_2^{3 + }$, and ML33+${\rm{ML}}_3^{3 + }$ (M 3+ = Eu 3+ , Am 3+ ; L=magnesium, ionophore II) are extracted into the nitrobenzene phase. Extraction and stability constants of the cationic complex species in nitrobenzene saturated with water were determined and discussed. From the experimental results it is evident that this effective magnesium ionophore II receptor for the Eu 3+ and Am 3+ cations could be considered as a potential extraction agent for nuclear waste treatment.

In this study the sorption of cesium was investigated on four different minerals; quartz, plagioclase, potassium feldspar and biotite as well as granodiorite obtained from the Grimsel test site in Switzerland. The experiments were conducted in the presence of the weakly saline Grimsel groundwater simulant by determining the distribution coefficients using batch sorption experiments and PHREEQC-modelling across a large concentration range. In addition, the purity of the minerals was measured byXRDand the specific surface areas by BET method using krypton. The distribution coefficients of cesiumwere largest on biotite (0.304±0.005 m 3 /kg in 10 -8 M). Furthermore, the sorption of cesiumon quartzwas found to be negligibly small in all investigated concentrations and the sorption of cesium on potassium feldspar and plagioclase showed similar behavior against a concentration isotherm with distribution coefficients of 0.0368±0.0004 m 3 /kg and 0.18±0.04 m 3 /kg in 10 -8 M. Finally, cesium sorption behavior on crushed granodiorite followed the trend of one of its most abundant mineral, plagioclase with distribution coefficient values of 0.107±0.003 m 3 /kg in 10 -8 M. At low concentrations (<1.0·10 -6 M) cesiumwas sorbed on the frayed edge sites of biotite and once these sites are fully occupied cesium sorbs additionally to the Type II and Planar sites. As a consequence, the sorption of cesium on biotite is decreased at concentrations >1.0·10 -6 M. Secondly cesium sorption on potassium feldspar and plagioclase showed similar non-linear behavior with varying concentration. The results were used to assist the interpretation of cesium diffusion process in the 2.5 year in-situ experiment carried out in the underground laboratory at Grimsel test site in Switzerland (2007–2009).

Solubility studies were conducted with HfO 2 (cr) solid as a function HCl and ionic strength ranging from 2.0 to 0.004 mol kg −1 . These studies involved 1) using two different amounts of the solid phase, 2) acid washing the bulk solid phase, 3) preheating the solid phase to 1400 °C, and 4) heating amorphous HfO 2 (am) suspensions to 90 °C to ascertain whether the HfO 2 (am) converts to HfO 2 (cr) and to determine the solubility from the oversaturation direction. Based on the results of these treatments it is concluded that the HfO 2 (cr) contains a small fraction of less crystalline, but not amorphous, material [HfO 2 (lcr)] and this, rather than the HfO 2 (cr), is the solubility-controlling phase in the range of experimental variables investigated in this study. The solubility data are interpreted using both the Pitzer and SIT models and they provide log 10 K 0 values of −(59.75±0.35)and −(59.48±0.41), respectively, for the solubility product of HfO 2 (lcr)[HfO 2 (lcr) + 2H 2 O ⇌ Hf 4+ + 4OH − ]. The log 10 of the solubility product of HfO 2 (cr)is estimated to be < −63. The observation of a small fraction of less crystalline higher solubility material is consistent with the general picture that mineral surfaces are often structurally and/or compositionally imperfect leading to a higher solubility than the bulk crystalline solid. This study stresses the urgent need, during interpretation of solubility data, of taking precautions to make certain that the observed solubility behavior for sparingly-soluble solids is assigned to the proper solid phase.

Carbon-based nanomaterials have piqued the interest of several researchers. At the same time, radioactive labeling is a powerful tool for studying processes in different systems, including biological and organic; however, the introduction of radioactive isotopes into carbon-based nanomaterial remains a great challenge. We have used the Langmuir hydrogen dissociation method to introduce tritium in single-walled carbon nanotubes and graphene oxide. The technique allows us to achieve a specific radioactivity of 107 and 27 Ci/g for single-layer graphene oxide and single-walled carbon nanotubes, respectively. Based on the analysis of characteristic Raman modes at 1350 and 1580 cm −1 , a minimal amount of structural changes to the nanomaterials due to radiolabeling was observed. The availability of a simple, nondestructive, and economic technique for the introduction of radiolabels to single-walled carbon nanotubes and graphene oxide will ultimately expand the applicability of these materials.