| 1. |
- Björkbacka, Åsa, et al.
(författare)
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Radiation induced corrosion of copper for spent nuclear fuel storage
- 2013
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X .- 1879-0895. ; 92, s. 80-86
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Tidskriftsartikel (refereegranskat)abstract
- The long term safety of repositories for radioactive waste is one of the main concerns for countries utilizing nuclear power. The integrity of engineered and natural barriers in such repositories must be carefully evaluated in order to minimize the release of radionuclides to the biosphere. One of the most developed concepts of long term storage of spent nuclear fuel is the Swedish KBS-3 method. According to this method, the spent fuel will be sealed inside copper canisters surrounded by bentonite clay and placed 500 m down in stable bedrock. Despite the importance of the process of radiation induced corrosion of copper, relatively few studies have been reported. In this work the effect of the total gamma dose on radiation induced corrosion of copper in anoxic pure water has been studied experimentally. Copper samples submerged in water were exposed to a series of total doses using three different dose rates. Unirradiated samples were used as reference samples throughout. The copper surfaces were examined qualitatively using IRAS and XPS and quantitatively using cathodic reduction. The concentration of copper in solution after irradiation was measured using ICP-AES. The influence of aqueous radiation chemistry on the corrosion process was evaluated based on numerical simulations. The experiments show that the dissolution as well as the oxide layer thickness increase upon radiation. Interestingly, the evaluation using numerical simulations indicates that aqueous radiation chemistry is not the only process driving the corrosion of copper in these systems.
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| 2. |
- Dynowska, E., et al.
(författare)
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Structural and magnetic properties of GaSb:MnSb granular layers
- 2011
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X. ; 80:10, s. 1051-1057
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Konferensbidrag (refereegranskat)abstract
- The results of structural and magnetic characterization of GaMnSb layers grown on GaSb(0 0 1) and GaAs(1 1 1) substrates are presented. The presence of hexagonal, highly oriented MnSb inclusions embedded in GaSb matrix has been demonstrated. The lattice parameters of these inclusions were the same as those for bulk MnSb for the layers grown on GaSb(1 0 0) substrate while for the layers grown on GaAs(1 1 1) the MnSb inclusions were strained. The influence of a presence of MnSb clusters on the lattice parameter of GaSb matrix has been demonstrated. It was confirmed that in all cases the MnSb clusters exhibit a ferromagnetic: behavior at room temperature. (C) 2011 Elsevier Ltd. All rights reserved.
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| 3. |
- Ekberg, Christian, 1967, et al.
(författare)
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Using At-211 as internal alpha radiolysis source allowing for simple detection of radiolysis products
- 2010
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 1879-0895 .- 0969-806X. ; 79:4, s. 454-456
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Tidskriftsartikel (refereegranskat)abstract
- The determination of radiolysis products is an important field both for the basic understanding of the radiolysis process and for process development. The latter case mainly dealing with processes for handling radioactive wastes. There are several kinds of radiolysis processes that originate from the different kinds of radiation. Gamma rays and high-energy beta has a high ability to penetrate barriers while alpha irradiation in principle has to be performed with the radiation emitting nuclide inside the actual sample. This can be a problem since most laboratories able to identify radiolysis products cannot handle alpha contaminated samples. In this paper we suggest the use of At-211 as internal alpha emitting radionuclide. Due to its short half-life and decay to more or less stable daughters the radiolysis products may be examined using normal equipment without causing contamination.
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| 4. |
- Guziewicz, E., et al.
(författare)
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Synchrotron photoemission study of (Zn,Co)O films with uniform Co distribution
- 2011
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X. ; 80:10, s. 1046-1050
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Konferensbidrag (refereegranskat)abstract
- We present results of a resonant photoemission study of (Zn,Co)O films with Co content between 2% and 7%. The films were grown by Atomic Layer Deposition (ALD) at low temperature of 160 degrees C and show fully paramagnetic behavior. The Co ions are uniformly distributed in the ZnO matrix and are free of foreign phases and metal accumulations as indicated by TEM data. The electronic structure of (Zn,Co)O films was studied by Resonant Photoemission Spectroscopy across the Co3p-Co3d photoionization threshold. We have observed that the resonant enhancement of the photoemission intensity from the Co3d shell is not the same for samples with different cobalt content. We suggest that the Co3d contribution to the valence band depends on both Co and H content. (C) 2011 Elsevier Ltd. All rights reserved.
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| 5. |
- Holmboe, Michael, 1978-, et al.
(författare)
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Effect of γ-radiation on Radionuclide Retention in Compacted Bentonite
- 2011
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X .- 1879-0895. ; 80:12, s. 1371-1377
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Tidskriftsartikel (refereegranskat)abstract
- Compacted bentonite is proposed as an engineered barrier in many concepts for disposal of high level nuclear waste. After the initial deposition however, the bentonite barrier will inevitably be exposed to ionizing radiation (mainly gamma) under anoxic conditions. Because of this, the effects of gamma-radiation on the apparent diffusivity values and sorption coefficients in bentonite for Cs(+) and Co(2+) were tested under different experimental conditions. Radiation induced effects on sorption were in general more noticeable for Co(2+) than for Cs(+), which generally showed no significant differences between irradiated and unirradiated clay samples. For Co(2+) however, the sorption to irradiated MX80 was significantly lower than to the unirradiated clay samples regardless of the experimental conditions. This implies that gamma-radiation may alter the surface characteristics contributing to surface complexation of Co(2+). With the experimental conditions used, however, the effect of decreasing sorption was not large enough to be reflected on the obtained D. values.
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| 6. |
- Holmboe, Michael, 1978-, et al.
(författare)
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Influence of γ-radiation on the reactivity of Montmorillonite towards H2O2
- 2012
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X .- 1879-0895. ; 81:2, s. 190-194, s. 1001-1013
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Tidskriftsartikel (refereegranskat)abstract
- Compacted and water saturated bentonite will be used as an engineered barrier in deep geological repositories for radioactive waste in many countries. Due to the high dose rate of ionizing radiation outside the canisters holding the nuclear waste, radiolysis of the interlayer and pore water in the compacted bentonite is unavoidable. Upon reaction with the oxidizing and reducing species formed by water radiolysis (OH•, e-(aq), H•, H202, H2, H02•, H30+), the overall redox properties in the bentonite barrier may change. In this study the influence of γ-radiation on the structural Fe(II)/Fe(III) content in montmorillonite and its reactivity towards hydrogen peroxide (H2O2) was investigated in parallel experiments. The results show that under anoxic conditions the structural Fe(II)/FeTot ratio of dispersed montmorillonite are increased from ≤ 3 to 25-30% after γ-doses comparable to repository conditions. Furthermore, a strong correlation between the structural Fe(II)/FeTot ratio and the H2O2 decomposition rate in montmorillonite dispersions was found. This correlation was further verified in experiments with consecutive H2O2 additions, since the structural Fe(II)/FeTot ratio was seen to decrease concordantly. This work shows that the structural iron in montmorillonite could be a sink for one of the major oxidants formed upon water radiolysis in the bentonite barrier, H2O2.
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| 7. |
- Liljequist, David, 1946-
(författare)
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Discussion of coherent and incoherent contributions to the spatial distribution of very low energy electrons elastically scattered in liquid water
- 2011
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X .- 1879-0895. ; 80:3, s. 291-303
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Tidskriftsartikel (refereegranskat)abstract
- The occurrence of diffraction effects versus the validity of trajectory simulation of the elastic scattering of very low energy electrons in liquid water is discussed. A simple model is used where the water molecules are represented by point scatterers, distributed randomly with or without short-range order. It is shown that the average spatial distribution of elastically scattered electrons within such a medium may be unambiguously divided into a coherent and an incoherent part. The calculation is based on the method of self-consistent quantum multiple scattering, and is performed for one wavelength where trajectory simulation is a valid approximation and one wavelength where it is not. The relation of the point scatterer model to advanced methods used for calculating quantum multiple scattering of electrons within clusters of atoms is briefly discussed. The point-scatterer quantum calculations are compared to corresponding trajectory simulations and to solutions of the Helmholtz–Foldy equation. Results indicate that 1) the coherence length for electrons scattered in a medium with random-like variations in scatterer positions is limited by elastic as well as inelastic scattering, and may taken to be equal to the total mean free path; 2) diffraction effects may occur due to short-range order in the medium, or by means of coherent scattering from spatially fixed structures (e.g., boundaries or interfaces) provided that the distance between such objects does not greatly exceed the coherence length; 3) trajectory simulation of the elastic scattering process gives a good approximation of the average quantum scattering in the medium, provided that the wavelength is not larger than the average distance between the scatterers; the effect of coherent scattering on the electron spatial distribution within the medium is then small or absent. The results further show that the Helmholtz–Foldy equation, which otherwise may be used to calculate the coherent part, is not generally a good approximation at long wavelengths in the presence of short-range order.
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| 8. |
- Liljequist, David
(författare)
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On the sampling of step length in Monte Carlo simulation of trajectories with very small mean free path
- 2012
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X .- 1879-0895. ; 81:11, s. 1703-1709
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Tidskriftsartikel (refereegranskat)abstract
- In an event-by-event simulation of the trajectory of a particle moving in matter it is usually assumed that the probability for the particle to travel a distance s without interaction is exp(-s/lambda), where lambda = (n . sigma)(-1) is the total mean free path, n the number of scatterers per unit volume and sigma the total cross section per scatterer. The step length s between scattering events is then generated by means of a sampling formula s = -lambda ln(1-R), where R a random number in the interval 0 < R < 1. It is here argued that this conventional sampling method, which basically assumes that the scattering medium may be regarded as a homogeneous continuum, may be erroneous unless lambda is much larger than the average distance d(nn) between nearest neighbour scatterers, estimated by d(nn) = n(-1/3). An alternative sampling method (M sampling) is proposed with a fixed step length D = d(nn) and a finite probability I = 1-exp(-D/lambda) of a single elastic or inelastic scattering event at the end of each step. According to this method, conventional sampling may exaggerate the number of events per unit path length; the corrected mean free path between events is found to be lambda(c) = D/(1-exp(-D/lambda)). The correction is substantial when lambda is comparable to or smaller than D, in practice for very low energy particles in liquids and solids. Consequently, quantities like stopping power may then be overestimated, while transport mean free path may be underestimated. In the opposite limit lambda >> D, conventional and M sampling produce the same result. Present results further indicate that conventional sampling using the corrected total mean free path lambda(c) is a good approximation to M sampling.
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| 9. |
- Liljequist, David, et al.
(författare)
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On the validity of trajectory methods for calculating the transport of very low energy ( < 1 keV) electrons in liquids and amorphous media
- 2014
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X .- 1879-0895. ; 99, s. 45-52
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Tidskriftsartikel (refereegranskat)abstract
- It is easily demonstrated that a trajectory picture of low energy electron transport in condensed matter is not compatible with the Heisenberg uncertainty principle. The uncertainty in the position of a low energy electron is large and may in fact be larger than an entire simulated trajectory. This might be interpreted to mean that trajectory methods are not applicable. However, this conclusion is not correct. In the present paper, the evidence for the validity of low energy electron trajectory simulation is discussed, as well as the wave aspects and quantum nature of low energy electron transport in liquids and amorphous solids. It is pointed out that the validity of a trajectory approach to low energy electron transport in a liquid or amorphous solid partly is due to its ability to reproduce the average results of coherent elastic multiple wave scattering in a randomlike medium, and moreover that this ability may be further enhanced by the presence of inelastic scattering. The resulting validity of the trajectory method may be referred to as circumstancial validity, which is of a nature different from the explicit validity of trajectory methods which are compatible with the uncertainty principle. A previous systematic analysis of the limits of circumstancial validity is revisited and discussed for the basic case of multiple elastic scattering of a particle in a random medium of point scatterers. The detailed limits of circumstancial validity are graphically demonstrated in terms of particle wavelength, average distance between scatterers and elastic mean free path. Their immediate applicability to neutron transport is noted. The approximate nature of the point scatterer model as regards electron transport is adressed. In order to obtain an extrapolation of the result of the point scatterer model, it is observed that an increasing error of the trajectory method appears together with an increased amplitude of the multiple wave scattering taking place within the medium. On the basis of this observation, an extrapolation is proposed which provides a rough estimate of the relative error of the trajectory method when applied to multiple elastic scattering of low energy electrons in real liquids or amorphous solids.
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| 10. |
- Maeyama, T., et al.
(författare)
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Production of a fluorescence probe in ion-beam radiolysis of aqueous coumarin-3-carboxylic acid solution-2: Effects of nuclear fragmentation and its simulation with PHITS
- 2011
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 1879-0895 .- 0969-806X. ; 80:12, s. 1352-1357
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Tidskriftsartikel (refereegranskat)abstract
- The G(OH) values in aqueous coumarin-3-carboxylic-acid (3-CCA) solutions irradiated with (12)C(6+) beams having the energies of 135, 290 and 400 MeV/u were measured by a fluorescent method around the Bragg peak, with 0.6 mm intervals, and quartz cells of 1 cm optical lengths, at the Heavy Ion Medical Accelerator in Chiba, National Institute of Radiological Sciences (NIRS). For each ion, the G(OH) has been calculated as a function of dose average LET and position. The calculated results have been compared to measurements, and the results, reproducibility and reliability of the calculations are discussed in the paper.
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| 11. |
- Sagstuen, Einar, et al.
(författare)
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Free radical products in X-irradiated Rochelle salt: low temperature ENDOR and DFT studies
- 2012
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Ingår i: Radiation Physics and Chemistry. - : Elsevier. - 0969-806X .- 1879-0895. ; 81:2, s. 168-179
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Tidskriftsartikel (refereegranskat)abstract
- Single crystals of Rochelle salt, [(-)OOC-CHOH-CHOH-COO(-), Na(+) K(+)]center dot 4H(2)O, X-irradiated at 10 K, have been examined using EPR, ENDOR and EIE spectroscopic techniques to characterize the radiation induced radicals stable at that temperature and their reactions upon warming. The one-electron gain product was observed and from the hyperfine interaction with a beta-proton it was unambiguously centered at the C(4) position of the tartrate moiety. An additional nearly isotropic hyperfine structure of about 21 MHz was tentatively assigned to interaction with a sodium ion exhibiting a close contact to O(3) in the crystal. Evidence was obtained that the one-electron reduced radical had become protonated at one of the C(4) bonded carboxyl oxygens, most probably O(4). No evidence for the corresponding C(1)-centered reduction product was found. Two resonance lines (R2, A1) were shown by EIE to belong to a species formed by decarboxylation at C(3), a secondary oxidation product. Two other resonance lines (K1, K2) were assigned to two varieties of another decarboxylation radical, centered at C(2), distinguished by differences in the potassium ion coordination. Furthermore, one other resonance line (A2) was tentatively ascribed to a third decarboxylation radical, centered at the opposite end of the tartrate moiety. The precursor of these products, that is, the one-electron loss product, was not observed after X-irradiation at 10 K. Thermally induced free radical reactions followed by EPR in the temperature range of 12-119K indicate that a water molecule or a hydroxyl ion is eliminated from the one-electron reduction product radical and that a C(3)-centered radical is formed. The reduction and oxidation reaction pathways of hydroxy acid derivatives are discussed.
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| 12. |
- Wolska, A., et al.
(författare)
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MnSb inclusions in the GaSb matrix studied by X-ray absorption spectroscopy
- 2011
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X. ; 80:10, s. 1026-1030
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Konferensbidrag (refereegranskat)abstract
- The MBE processes were performed in order to form the MnSb inclusions. Two kinds of substrates (GaSb and GaAs) as well as growth temperatures (450 and 520 degrees C) were examined. SEM imaging was performed to determine the shape and size of formed inclusions. In all the samples the inclusions of few hundred nm were formed. Their shapes depended strongly on the type of substrate while the size slightly increases with the growth temperature. The X-ray absorption techniques were used to monitor the local structure around Mn atoms and confirmed that the neighborhood of Mn atoms in the layers was close to that of the MnSb reference powder. We succeed in the formation of the GaSb layers with Mn assembled only into MnSb inclusions on both types of substrates: GaAs(1 1 1)A and GaSb(1 00). However, in case of the GaAs(1 1 1)A substrates, the atomic order around Mn atoms in MnSb inclusions is less perfect than in case of the GaSb(1 0 0) substrates. (C) 2011 Elsevier Ltd. All rights reserved.
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| 13. |
- Wolska, A., et al.
(författare)
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Structural and magnetic properties of Mn(+) implanted silicon crystals studied using X-ray absorption spectroscopy techniques
- 2011
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X .- 1879-0895. ; 80:10, s. 1119-1124
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Tidskriftsartikel (refereegranskat)abstract
- The implantation of Mn ions into two Si substrates with different doping (P or B), resistivity and oxygen content was performed at low and high substrate temperatures. Different post-implantation processing was carried out to study its influence on the structural and magnetic properties of these samples. The local order around the Mn atoms was characterized by X-ray absorption fine structure techniques and the magnetic properties of the Mn ionic cores were determined by means of X-ray magnetic circular dichroism measurements. The results are discussed in relation to the structural and macroscopic magnetic properties. It is shown that the amorphous matrix speeds up the formation of MnSi(x) inclusions. However, the existence of inclusions or the type of electrically active dopants is not directly related to the magnetic properties. Therefore, in the performed studies, the importance of structural defects on the magnetic properties was confirmed. A localized magnetic moment carried by the Mn ionic cores could not be detected by means of dichroic measurements.
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