The Solubility and Sorption of Lead-210 and Carbon-14 in a Near-Field Environment

1987 ◽  
Vol 112 ◽  
Author(s):  
S. Bayliss ◽  
F. T. Ewart ◽  
R. M. Howse ◽  
J. L. Smith-Briggs ◽  
H. P. Thomason ◽  
...  
Keyword(s):  
Phase Separation ◽  
Near Field ◽  
Experimental Studies ◽  
Solubility Limit ◽  
Maximum Solubility ◽  
Separation Techniques ◽  
Sorption Behaviour ◽  
High Ph ◽  
Carbon 14 ◽  
Lead 210

AbstractThis paper reports the results of some recent experimental studies of the solubility and sorption behaviour of lead-210 and carbon-14 under cementitious near-field conditions.These studies have shown that under these conditions carbon-14 will have a maximum solubility limit of 10−4 M and that the distribution ratio, RD, will increase with increasing carbon-14 concentrations from 10−9 to 10−7 M. Not all of the carbon in the cement is available for exchange with carbon in the pore water. Differences in values of RD are observed between the two cement grout types studied, SRPC and OPC/BFS. Lead has been shown to have a maximum solubility limit of about 10−3 M at high pH. Good agreement is obtained between these measurements and thermodynamic modelling using the PHREEQE code. No differences were observed between lead solubilities under reducing or oxidising conditions at high pH values using the same phase separation techniques. Lead is particularly sensitive to the phase separation techniques employed. A factor of up to 250 difference is observed between 25000 and 30000 molecular weight cut-off filters. The values of RD for lead increase with decreasing lead concentrations and the values of RD for 10−3 M solutions are observed to be 500 mlg−1 for SRPC and 1300 mlg−1 for OPC/BFS.

Study of the Consequences of Secondary Water Radiolysis within and Surrounding a Defective Canister

2000 ◽  
Vol 663 ◽  
Author(s):  
Jinsong Liu ◽  
Bo Strömberg ◽  
Ivars Neretnieks
Keyword(s):  
Near Field ◽  
Experimental Studies ◽  
Solubility Limit ◽  
Balance Model ◽  
Water Radiolysis ◽  
Spent Fuel ◽  
Secondary Minerals ◽  
First Case ◽  
Bentonite Buffer

ABSTRACTA model has been developed to study the effects of secondary water radiolysis caused by dispersed radionuclides in a bentonite buffer surrounding a copper canister. The secondary radiolysis is the radiolysis caused by radionuclides that have been released from the spent fuel and are present either as solutes in the pore-water, as sorbed species on the surface of other minerals, or as secondary minerals. The canister is assumed to be initially defective with a hole of a few millimeters on its wall. The small hole will considerably restrict the transport of oxidants through the canister wall and the release of radionuclides to the outside of the canister. The dissolution of the spent fuel is assumed to be controlled by chemical kinetics at rates extrapolated from experimental studies. Two cases have been considered with the purpose to illustrate the behaviors of both conservative and non-conservative nuclides. The nuclides that are most relevant are those expected to be the dominant α-emitters in the long-term (e.g. 239Pu, 240Pu, 241Am). In the first case it is assumed that there is no precipitation of secondary minerals of the relevant radionuclides inside the canister. In the second case it is assumed that the radionuclide concentration within the canister is controlled by its respective solubility limit. The radionuclide released to the surrounding buffer is then predicted using a mass balance model. The modelling results show that in both cases, the spent fuel will not be oxidized at a rate significantly faster compared to the case where secondary radiolysis is completely neglected. In the first case, however, a large domain of the near-field can be oxidized due to a much faster depletion of reducing minerals in the buffer, compared to the case where secondary radiolysis is neglected. In the second case, the effects of the secondary water radiolysis will be quite limited.

scholarly journals Optical Sensitivity of Waveguides Inscribed in Nanoporous Silicate Framework

Nanomaterials ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 123
Author(s):  
Zhong Lijing ◽  
Roman A. Zakoldaev ◽  
Maksim M. Sergeev ◽  
Andrey B. Petrov ◽  
Vadim P. Veiko ◽  
...  
Keyword(s):  
Refractive Index ◽  
Near Field ◽  
Experimental Studies ◽  
Laser Pulses ◽  
Femtosecond Laser Pulses ◽  
Direct Writing ◽  
Sensor Applications ◽  
Refractive Index Contrast ◽  
Optical Sensitivity ◽  
Index Contrast

Laser direct writing technique in glass is a powerful tool for various waveguides’ fabrication that highly develop the element base for designing photonic devices. We apply this technique to fabricate waveguides in porous glass (PG). Nanoporous optical materials for the inscription can elevate the sensing ability of such waveguides to higher standards. The waveguides were fabricated by a single-scan approach with femtosecond laser pulses in the densification mode, which resulted in the formation of a core and cladding. Experimental studies revealed three types of waveguides and quantified the refractive index contrast (up to Δn = 1.2·10−2) accompanied with ~1.2 dB/cm insertion losses. The waveguides demonstrated the sensitivity to small objects captured by the nanoporous framework. We noticed that the deposited ethanol molecules (3 µL) on the PG surface influence the waveguide optical properties indicating the penetration of the molecule to its cladding. Continuous monitoring of the output near field intensity distribution allowed us to determine the response time (6 s) of the waveguide buried at 400 µm below the glass surface. We found that the minimum distinguishable change of the refractive index contrast is 2 × 10−4. The results obtained pave the way to consider the waveguides inscribed into PG as primary transducers for sensor applications.

Phase Separation of β-SN in Strained, Compositionally Metastable Ge1-xSnx Alloys

1995 ◽  
Vol 398 ◽  
Author(s):  
Joshua W. Kriesel ◽  
Susanne M. Lee
Keyword(s):  
Phase Separation ◽  
Electron Microprobe ◽  
Rf Sputtering ◽  
Melting Behavior ◽  
Solubility Limit ◽  
X Ray Diffraction ◽  
Solid Solubility Limit ◽  
Transformation Mechanisms ◽  
Subsequent Phase ◽  
Kinetics Of

ABSTRACTUsing rf sputtering and post-deposition annealing in a differential scanning calorimeter (DSC), we manufactured bulk (4000 nm) films of crystalline Ge0.83Sn0.17. This Sn concentration is much greater than the solid solubility limit of Sn in Ge (x ≤ 0.01). Continued annealing thermally induces Sn phase separation from the alloy, limiting the ultimate attainable grain size in the metastable crystals. We examine, here, the mechanisms and kinetics of the processes limiting the size of the Ge0.83Sn0.17 polycrystals. From a combination of DSC, electron microprobe, and x-ray diffraction (XRD) measurements, we propose phase transformation mechanisms corresponding to crystallization of amorphous Ge0.83Sn0.17, crystallization of an as-yet unidentified phase of Sn, and phase separation of Sn from the Ge1-xSnx crystals. We were unable to observe the unidentified phase of Sn in XRD, but the phase must be present in the material to account for the quantitative discrepancies (as much as 8 at.%) in Sn percentages determined from each of the DSC, XRD, and electron microprobe measurements. Our models for the various transformation kinetics were corroborated by the subsequent phase-separated Sn melting behavior observed in the DSC: two Sn melting endotherms, one of which was 20–100°C lower than the bulk melting temperature of Sn. This depressed temperature endotherm we speculate represents liquefaction of nanometer-sized (β–Sn clusters.

Inverse Ostwald Ripening and Self-Organization of Nanoclusters due to Ion Irradiation

2000 ◽  
Vol 647 ◽  
Author(s):  
K.-H. Heinig ◽  
B. Schmidt ◽  
M. Strobel ◽  
H. Bernas
Keyword(s):  
Phase Separation ◽  
Ion Implantation ◽  
Ostwald Ripening ◽  
Ion Irradiation ◽  
Experimental Studies ◽  
Self Organization ◽  
Mathematical Treatment ◽  
Thermodynamical Equilibrium ◽  
Unusual Behavior ◽  
Thermally Activated

AbstractUnder ion irradiation collisional mixing competes with phase separation if the irradiated solid consists of immiscible components. If a component is a chemical compound, there is another competition between the collisional forced chemical dissociation of the compound and its thermally activated re-formation. Especially at interfaces between immiscible components, irradiation processes far from thermodynamical equilibrium may lead to new phenomena. If the formation of nanoclusters (NCs) occurs during ion implantation, the phase separation caused by ion implantation induced supersaturation can be superimposed by phenomena caused by collisional mixing. In this contribution it will be studied how collisional mixing during high-fluence ion implantation affects NC synthesis and how ion irradiation through a layer of NCs modifies their size and size distribution. Inverse Ostwald ripening of NCs will be predicted theoretically and by kinetic lattice Monte-Carlo simulations. The mathematical treatment of the competition between irradiation-induced detachment of atoms from clusters and their thermally activated diffusion leads to a Gibbs-Thomson relation with modified parameters. The predictions have been confirmed by experimental studies of the evolution of Au NCs in SiO2 irradiated by MeV ions. The unusual behavior results from an effective negative capillary length, which will be shown to be the reason for inverse Ostwald ripening. Another new phenomenon to be addressed is self-organization of NCs in a d-layer parallel to the Si/SiO2 interface. Such d-layers were found when the damage level at the interface was of the order of 1-3 dpa. It will be discussed that the origin of the d-layer of NCs can be assigned to two different mechanisms: (i) The negative interface energy due to collisional mixing gives rise to the formation of tiny clusters of substrate material in front of the interface, which promotes heteronucleation of the implanted impurities. (ii) Collisional mixing in the SiO2produces diffusing oxygen, which may be consumed by the Si/SiO2 interface. A thin layer parallel to the interface becomes denuded of diffusing oxygen, which results in a strong pile up of Si excess. This Si excess promotes heteronucleation too. Independent of the dominating mechanism of self-organization of a d-layer of NCs, its location in SiO2 close to the SiO2/Si interface makes it interesting for non-volatile memory application.

Modelling and Experimental Studies of Sorption in the Near Field of a Cementitious Repository

1989 ◽  
Vol 176 ◽  
Author(s):  
P.L. Brown ◽  
A. Haworth ◽  
R. McCrohon ◽  
S.M. Sharland ◽  
C.J. Tweed
Keyword(s):  
Near Field ◽  
Experimental Studies ◽  
Mass Action ◽  
Chemical Equilibria ◽  
Transport Code ◽  
Mass Action Model ◽  
Action Model ◽  
Modelling Studies ◽  
Simple Mass

ABSTRACTA joint experimental and modelling programme is reported, which aims to improve our understanding of sorption processes of radionuclides onto repository materials. Diffusion/sorption experiments of sorption onto cement are described, although results are limited at this stage. The modelling studies use the coupled chemical equilibria and transport code CHEQMATE to simulate some of these experiments. The chemical part of the model is based on a simple mass-action model of sorption. More detailed comparisons will continue when the experiments are terminated, and the samples are sectioned.

Sorption of radionuclides to a cementitious backfill material under near-field conditions

2012 ◽  
Vol 76 (8) ◽  
pp. 3401-3410 ◽  
Author(s):  
M. Felipe-Sotelo ◽  
J. Hinchliff ◽  
N. Evans ◽  
P. Warwick ◽  
D. Read
Keyword(s):  
Organic Compounds ◽  
Degradation Products ◽  
Cellulose Degradation ◽  
Near Field ◽  
Organic Ligand ◽  
Sorption Isotherms ◽  
Field Conditions ◽  
Sorption Behaviour ◽  
Backfill Material ◽  
Order Of Magnitude

AbstractThe sorption behaviour of I−, Cs+, Ni2+, Eu3+, Th4+ and UO2+2on NRVB (Nirex reference vault backfill) a possible vault backfill, at pH 12.8 was studied. Sorption isotherms generated were compared to results obtained in the presence of cellulose degradation products (CDP). Whereas Cs was not affected by the presence of the organic compounds, a notable reduction in the sorption of Th and Eu to cement was observed. The results also indicated limited removal of Ni from solution (with or without an organic ligand) by sorption, the concentration in solution seemingly being determined solely by solubility processes. In the case of uranium, the presence of CDP increased the sorption to cement by almost one order of magnitude. Further studies into the uptake of CDP by cement are being undertaken to identify the mechanism(s) responsible.

scholarly journals Dynamic near-field microwave diagnostics of lungs.

2021 ◽  
Vol 2021 (8) ◽  
Author(s):  
L.A. Bokeria ◽  
◽  
T.T. Kakuchaya ◽  
A.M. Kuular ◽  
Ye.S. Maksimovitch ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Inverse Problems ◽  
Integral Equations ◽  
Near Field ◽  
Experimental Studies ◽  
Heart Activity ◽  
Blood Content ◽  
Air Content ◽  
Microwave Diagnostics ◽  
Biomedical Diagnostics

Results of theoretical and experimental studies of the method of the near-field microwave tomography of the thorax are presented. Integral equations of inverse tomography problem of 3D blood- and air content inhomogeneities by data of multisensory measurements are obtained. Methods of air and blood content profiling in processes of breathing and heart activity by data of bistatic measurements of the scattered signal are proposed and solving algorithms of inverse problems are studied in the numerical simulation. Multifrequency and pulse measurements of scattered signals are carried out in processes of cardiorespiratory activity. By data of bistatic measurements of scattered signals parameters from the thorax, profiling relative air- and blood content profiles has been realized. Application possibilities of the method in the biomedical diagnostics are considered.

scholarly journals 14C release from irradiated stainless steel

Radiocarbon ◽  
2018 ◽  
Vol 60 (6) ◽  
pp. 1671-1681 ◽  
Author(s):  
Eva de Visser-Týnová ◽  
Stephen W Swanton ◽  
Stephen J Williams ◽  
Marcel P Stijkel ◽  
Alison J Walker ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Radioactive Waste ◽  
Gas Phase ◽  
Near Field ◽  
Considerable Uncertainty ◽  
Dissolved Carbon ◽  
Carbon 14 ◽  
Fast Release ◽  
Potential Issue ◽  
Made In

ABSTRACTRadiocarbon (14C or carbon-14, half-life 5730 yr) is a key radionuclide in the assessment of the safety of a geological disposal facility (GDF) for radioactive waste. In particular, the radiological impact of gaseous carbon-14 bearing species has been recognized as a potential issue. Irradiated steels are one of the main sources of carbon-14 in the United Kingdom’s radioactive waste inventory. However, there is considerable uncertainty about the chemical form(s) in which the carbon-14 will be released. The objective of the work was to measure the rate and speciation of carbon-14 release from irradiated 316L(N) stainless steel on leaching under high-pH anoxic conditions, representative of a cement-based near field for low-heat generating wastes. Periodic measurements of carbon-14 releases to both the gas phase and to solution were made in duplicate experiments over a period of up to 417 days. An initial fast release of carbon-14 from the surface of the steel is observed during the first week of leaching, followed by a drop in the rate of release at longer times. Carbon-14 is released primarily to the solution phase with differing fractions released to the gas phase in the two experiments: about 1% of the total release in one and 6% in the other. The predominant dissolved carbon-14 releases are in inorganic form (as 14C-carbonate) but also include organic species. The predominant gas-phase species are hydrocarbons with a smaller fraction of 14CO (which may include some volatile oxygen-containing carbon-species). The experiments are continuing, with final sampling and termination planned after leaching for a total of two years.

scholarly journals PhaSePro: the database of proteins driving liquid–liquid phase separation

2019 ◽  
Author(s):  
Bálint Mészáros ◽  
Gábor Erdős ◽  
Beáta Szabó ◽  
Éva Schád ◽  
Ágnes Tantos ◽  
...  
Keyword(s):  
Phase Separation ◽  
Liquid Phase ◽  
Ribosome Biogenesis ◽  
Weak Interactions ◽  
Experimental Studies ◽  
Rna Degradation ◽  
Liquid Phase Separation ◽  
General Mechanism ◽  
Open Questions ◽  
Liquid Liquid Phase Separation

Abstract Membraneless organelles (MOs) are dynamic liquid condensates that host a variety of specific cellular processes, such as ribosome biogenesis or RNA degradation. MOs form through liquid–liquid phase separation (LLPS), a process that relies on multivalent weak interactions of the constituent proteins and other macromolecules. Since the first discoveries of certain proteins being able to drive LLPS, it emerged as a general mechanism for the effective organization of cellular space that is exploited in all kingdoms of life. While numerous experimental studies report novel cases, the computational identification of LLPS drivers is lagging behind, and many open questions remain about the sequence determinants, composition, regulation and biological relevance of the resulting condensates. Our limited ability to overcome these issues is largely due to the lack of a dedicated LLPS database. Therefore, here we introduce PhaSePro (https://phasepro.elte.hu), an openly accessible, comprehensive, manually curated database of experimentally validated LLPS driver proteins/protein regions. It not only provides a wealth of information on such systems, but improves the standardization of data by introducing novel LLPS-specific controlled vocabularies. PhaSePro can be accessed through an appealing, user-friendly interface and thus has definite potential to become the central resource in this dynamically developing field.

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