Production and use of 13N labeled N2O5 to determine gas-aerosol interaction kinetics

Dinitrogen pentoxide has aroused significant interest in atmospheric chemistry because of its importance in the night time chemistry of nitrogen oxides to influence the tropospheric oxidation capacity. We have used an established method of 13N production to synthesize 13N labeled N2O5 for the first time in order to study N2O5 uptake kinetics on aerosol particles. 13N is produced via the 16O(p, α)13N reaction in a gas target attached to the IP2 endstation of the Injector 2 cyclotron at PSI. The 13NO produced in the gas target is transported to a laboratory where it is mixed, under dry conditions, with non-labeled NO and O3 in a gas reactor, giving 13NNO5. The N2O5 thus produced is fed into an aerosol flow tube together with a humidified aerosol gas flow. The gaseous species present in the resulting gas flow are selectively separated via a narrow parallel plate diffusion denuder system, while aerosol particles can be trapped on a particle filter placed at the end of the denuder system. The activity of the 13N labeled species trapped on the denuder plates and in the particle filter can be monitored via scintillation counters. A system for the routine online production of 13N labeled N2O5 has been assembled and used to assess the conformity of the results by kinetic modeling of gas phase N2O5 chemistry, showing good agreement. A few exemplary experiments of uptake of labelled N2O5 to ammonium sulfate and citric acid particles are presented that are in good agreement with results obtained with other methods reported in the literatur

Sorption Profile of Low Specific Activity 99Mo on Nanoceria-Based Sorbents for the Development of 99mTc Generators: Kinetics, Equilibrium, and Thermodynamic Studies.

99Mo/99mTc generators play a significant role in supplying 99mTc for diagnostic interventions in nuclear medicine. However, the applicability of using low specific activity (LSA) 99Mo asks for sorbents with high sorption capacity. Herein, this study aims to evaluate the sorption behavior of LSA 99Mo towards several CeO2 nano-sorbents developed in our laboratory. These nanomaterials were prepared by wet chemical precipitation (CP) and hydrothermal (HT) approaches. Then, they were characterized using XRD, BET, FE-SEM, and zeta potential measurements. Additionally, we evaluated the sorption profile of carrier-added (CA) 99Mo onto each material under different experimental parameters. These parameters include pH, initial concentration of molybdate solution, contact time, and temperature. Furthermore, the maximum sorption capacities were evaluated. The results reveal that out of the synthesized CeO2 nanoparticles (NPs) materials, the sorption capacity of HT-1 and CP-2 reach 192 ± 10 and 184 ± 12 mg Mo·g-1, respectively. For both materials, the sorption kinetics and isotherm data agree with the Elovich and Freundlich models, respectively. Moreover, the diffusion study demonstrates that the sorption processes can be described by pore diffusion (for HT-synthesis route 1) and film diffusion (for CP-synthesis route 2). Furthermore, the thermodynamic parameters indicate that the Mo sorption onto both materials is a spontaneous and endothermic process. Consequently, it appears that HT-1 and CP-2 have favorable sorption profiles and high sorption capacities for CA-99Mo. Therefore, they are potential candidates for producing a 99Mo/99mTc radionuclide generator by using LSA 99Mo

Decomposition studies of group 6 hexacarbonyl complexes. Part 2: Modelling of the decomposition process

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

Developing a Chromatographic 99mTc Generator Based on Mesoporous Alumina for Industrial Radiotracer Applications: A Potential New Generation Sorbent for Using Low-Specific-Activity 99Mo.

The commercial low-pressure column chromatographic 99Mo/99mTc generator represents a reliable source of onsite, ready-to-use 99mTc for industrial applications. These generators use fission-produced 99Mo of high specific activity, posing serious production challenges and raising proliferation concerns. Therefore, many concepts are aimed at using low-specific-activity (LSA) 99Mo. Nonetheless, the main roadblock is the low sorption capacity of the used alumina (Al2O3). This study investigates the feasibility of using commercial alumina incorporated with LSA 99Mo to develop a useful 99Mo/99mTc generator for industrial radiotracer applications. First, the adsorption profiles of some commercial alumina sorbents for LSA 99Mo were tested under different experimental conditions. Then, the potential materials to develop a 99Mo/99mTc generator were selected and evaluated regarding elution yield of 99mTc and purity. Among the sorbents investigated in this study, mesoporous alumina (SA-517747) presented a unique sorption-elution profile. It demonstrated a high equilibrium and dynamic sorption capacity of 148 ± 8 and 108 ± 6 mg Mo/g. Furthermore, 99mTc was eluted with high yield and adequate chemical, radiochemical, and radionuclidic purity. Therefore, this approach provides an efficient and cost-effective way to supply onsite 99mTc for radiotracer applications independent of fission-produced 99Mo technology

Prediction of the thermal release of transactinide elements (112 ≤ Z ≤ 116) from metals

Metallic catcher foils have been investigated on their thermal release capabilities for future superheavy element studies. These catcher materials shall serve as connection between production and chemical investigation of superheavy elements (SHE) at vacuum conditions. The diffusion constants and activation energies of diffusion have been extrapolated for various catcher materials using an atomic volume based model. Release rates can now be estimated for predefined experimental conditions using the determined diffusion values. The potential release behavior of the volatile SHE Cn (E112), E113, Fl (E114), E115, and Lv (E116) from polycrystalline, metallic foils of Ni, Y, Zr, Nb, Mo, Hf, Ta, and W is predicted. Example calculations showed that Zr is the best suited material in terms of on-line release efficiency and long-term operation stability. If higher temperatures up to 2773K are applicable, tungsten is suggested to be the material of choice for such experiment

Decomposition studies of group 6 hexacarbonyl complexes. Part 2: Modelling of the decomposition process

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

Adsorption interaction of carrier-free thallium species with gold and quartz surfaces

The adsorption interactions of thallium and its compounds with gold and quartz surfaces were investigated. Carrier-free amounts of thallium were produced in nuclear fusion reactions of alpha particles with thick gold targets. The method chosen for the studies was gas thermochromatography and varying the redox potential of the carrier gases. It was observed that thallium is extremely sensitive to trace amounts of oxygen and water, and can even be oxidized by the hydroxyl groups located on the quartz surface. The experiments on aquartz surface with O2, He, H2 gas in addition with water revealed the formation and deposition of only one thallium species - TlOH. The adsorption enthalpy was determined to be Δ HSiO2ads(TlOH) = −134±5kJ mol−1. Aseries of experiments using gold as stationary surface and different carrier gases resulted in the detection of two thallium species - metallic Tl (H2 as carrier gas) and TlOH (O2, O2+H2O and H2+H2O as pure carrier gas or carrier gas mixture) with Δ HAuads(Tl) = −270±10kJ mol− and Δ HAuads(TlOH) = −146±3kJ mol−1. These data demonstrate a weak interaction of TlOH with both quartz and gold surfaces. The data represent important information for the design of future experiments with the heavier homologue of Tl in group 13 of the periodic table - element 113 (E113