| 1. |
- Alcayne, V., et al.
(författare)
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A Segmented Total Energy Detector (sTED) optimized for (n,ϒ) cross-section measurements at n_TOF EAR2
- 2024
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Ingår i: Radiation Physics and Chemistry. - : Elsevier. - 0969-806X .- 1879-0895. ; 217
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Tidskriftsartikel (refereegranskat)abstract
- The neutron time-of-flight facility n_TOF at CERN is a spallation source dedicated to measurements of neutroninduced reaction cross-sections of interest in nuclear technologies, astrophysics, and other applications. Since 2014, Experimental ARea 2 (EAR2) is operational and delivers a neutron fluence of similar to 4 center dot 10(7) neutrons per nominal proton pulse, which is similar to 50 times higher than the one of Experimental ARea 1 (EAR1) of similar to 8 center dot 10(5) neutrons per pulse. The high neutron flux at EAR2 results in high counting rates in the detectors that challenged the previously existing capture detection systems. For this reason, a Segmented Total Energy Detector (sTED) has been developed to overcome the limitations in the detector's response, by reducing the active volume per module and by using a photo-multiplier (PMT) optimized for high counting rates. This paper presents the main characteristics of the sTED, including energy and time resolution, response to gamma-rays, and provides as well details of the use of the Pulse Height Weighting Technique (PHWT) with this detector. The sTED has been validated to perform neutron-capture cross-section measurements in EAR2 in the neutron energy range from thermal up to at least 400 keV. The detector has already been successfully used in several measurements at n_TOF EAR2.
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| 2. |
- Andersson, Martin, et al.
(författare)
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IDACstar2.0: A MCNP application to perform realistic dose estimations from internal or external contamination with radiopharmaceuticals
- 2022
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X. ; 193
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Tidskriftsartikel (refereegranskat)abstract
- The IDACstar (Internal Dose Assessment by Computer) software is a Monte Carlo based standalone MCNP input generator software developed to perform complex radiation dose calculations using both the paediatric and adult ICRP reference phantoms. An extension of the IDACstar software was applied to two different exposure scenarios. One of the scenarios was a hypothetical case of a contaminated diaper from urine of a 1-year old patient undergoing a diagnostic kidney examination with 99mTc-labelled mercaptoacetyl triglycerine (MAG3), which resulted in an effective dose estimate of 0.088 mSv to the child. The second case was a clinical case of 18F-FDG extravasation in an adult patient and applied to all 10 age-specific phantoms with weight-modified administrations of the radiopharmaceutical. The effective dose was estimated for the 15-, 10-, 5- and 1- year old as 5.1 mSv, 4.9 mSv, 4.7 mSv, and 4.7 mSv, respectively. The updated version of the IDACstar software provides the possibility of performing realistic dose estimations to paediatric patients from internal or external contamination with radiopharmaceuticals. © 2021
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| 3. |
- Arectout, A., et al.
(författare)
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Optimization of the n-type HPGe detector parameters using the "design of experiments" technique
- 2021
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X. ; 189
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a new procedure to optimize the geometric parameters of a n-type coaxial HPGe detector. It is based on a statistical technique called "Design of Experiments" (DoE). This technique aims to identify the most influential parameters and to determine the optimal configuration. In this work, The effects of each parameter on the detector responses have been investigated by a fractional factorial design. Only the most influential factors contributing to the detector response have been selected. Precise modeling of these factors was then performed using a full factorial design. Based on the results obtained from this design, the full energy peak efficiencies according to the geometric parameters were modeled by a multiple-linear regression. These models have been statistically validated by analysis of variance (ANOVA). The optimal combination of the geometric parameters has been identified using the desirability function approach, which is a useful tool to optimize multi-response problems. A verification test was performed to validate the results obtained. It was observed that the relative deviation found between experimental and simulated values was less than 5%.
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| 4. |
- Dispenza, C., et al.
(författare)
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On the nature of macroradicals formed upon radiolysis of aqueous poly(N-vinylpyrrolidone) solutions
- 2020
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Ingår i: Radiation Physics and Chemistry. - : Elsevier. - 0969-806X .- 1879-0895. ; 174
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Tidskriftsartikel (refereegranskat)abstract
- In this work we have explored the nature of macroradicals formed upon radiolysis of aqueous poly(N-vinylpyrrolidone) (PVP) solutions using pulse radiolysis, density functional theory (DFT) and literature data. On the basis of literature data on site-specific kinetics of hydrogen abstraction from simple amides and spectra corresponding to specific radical sites on the same amides we have assessed the distribution of H-atom abstraction by •OH radicals from different positions on the pyrrolidone ring and the polymer backbone. Pulse radiolysis experiments performed at different doses per pulse and different PVP concentrations demonstrate that the H-abstracting radiolysis products are not quantitatively scavenged by the polymer when the dose per pulse exceeds ≈40 Gy. The implications of this are discussed in the context of radical-initiated crosslinking reactions. At a mass fraction of 0.1% PVP and doses per pulse ranging from 7 Gy to 117 Gy, the overall radical decay observed at 390 nm follows second order kinetics with rate constants on the order of 109 dm3 mol-1 s-1.
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| 5. |
- Eliasson, Linda, et al.
(författare)
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Low-pressure measurements of energy depositions in nanometre objects with a single ionisation chamber in a 60 Co beam using the variance-covariance method
- 2024
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X .- 1879-0895. ; 221
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Tidskriftsartikel (refereegranskat)abstract
- Dose -mean lineal energies were measured using the variance-covariance method and commercial ionisation chambers in a therapy level 60 Co field at several different air pressures. The results confirmed the trend from previous studies and the experimental data was extended down to a simulated object diameter of 4.2 nm using a low -noise electrometer. The variance-covariance method was adapted to consecutive charge integrations from a single ionisation chamber and used to correct for signal variations due to pressure drifts in the ion chamber. Monte Carlo simulations using MCNP 6.2 were performed, and the results follow the trend of the experimental values in the nanometric region.
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| 6. |
- Filipponi, A., et al.
(författare)
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Local lattice relaxation around Tl substitutional impurities in a NaI(Tl) scintillator crystal
- 2020
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 1879-0895 .- 0969-806X. ; 177
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Tidskriftsartikel (refereegranskat)abstract
- A Thallium (Tl) L3-edge x-ray absorption experiment was performed on a NaI(Tl) scintillation crystal at room temperature using fluorescence detection. The data analysis provides clear evidence for a ≃5 % average bond length expansion of the first shell I atoms surrounding the Tl impurities with respect to the Na-I crystallographic bond-length. Possible evidence for a slight expansion of the second and third shells is obtained. The data are compatible with a previous experiment performed at liquid nitrogen temperature considering thermal expansion. A critical review of existing theoretical predictions and density functional theory supercell calculations support present findings and suggest the opportunity to perform a high quality temperature dependent experiment.
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| 7. |
- Hansson, Niklas, 1992, et al.
(författare)
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Exploring H2-effects on radiation-induced oxidative dissolution of UO2-based spent nuclear fuel using numerical simulations
- 2023
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X .- 1879-0895. ; 210, s. 111055-
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Tidskriftsartikel (refereegranskat)abstract
- Using a recently developed approach for numerical simulation of radiation-induced oxidative dissolution of spent nuclear fuel, we have explored the impact of three possible contributions to the inhibiting effect of molecular hydrogen. The three contributions are (1) effect on oxidant production in irradiated water, (2) reduction of oxidized uranium catalyzed by noble metal inclusions (fission products) and (3) reaction with surface-bound hydroxyl radicals preventing the oxidation of uranium. The simulations show that the first contribution is of fairly small importance while the second contribution can result in complete inhibition of the oxidative dissolution. This is well in line with previous work. Interestingly, the simulations imply that the third contribution, the reaction between H2 and the surface-bound hydroxyl radical formed upon reaction between the radiolysis product H2O2 and UO2, can account for the inhibition observed in systems where noble metal inclusions are not present. This is discussed in view of previously published experimental data.
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| 8. |
- Hansson, Niklas, 1992, et al.
(författare)
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Geometrical aspects of alpha dose rates from UO2 based fuels
- 2022
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X .- 1879-0895. ; 199, s. 110336-
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Tidskriftsartikel (refereegranskat)abstract
- Models for calculating dose rates of spherical particles as well as in fuel cracks are important for radionuclide source term estimations. Dose rates from UO2 based fuels were calculated for planar, spherical, and crack geometries. The escape probability for a-particles in spherical UO2 particles was derived as a continuous equation. The dose rate increased with increasing spherical radius due to the decreasing relative volume of the surrounding water layer. The model produced escape probabilities that were closely predicted by the theoretical derivation. It was shown that the dose rate in water filled fuel cracks with width smaller than the range of an alpha-particle led to dissolution rates that were lower per unit surface area.
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| 9. |
- Horne, Gregory P., et al.
(författare)
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DEHBA (di-2-ethylhexylbutyramide) gamma radiolysis under spent nuclear fuel solvent extraction process conditions
- 2020
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Ingår i: Radiation Physics and Chemistry. - : Elsevier. - 0969-806X .- 1879-0895. ; 170
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Tidskriftsartikel (refereegranskat)abstract
- Di-2-ethylhexylbutyramide (DEHBA) has been proposed as part of a hydro-reprocessing solvent extraction system for the co-extraction of uranium and plutonium from spent nuclear fuel. However, there remains a lack of quantitative understanding of the impact of chemical environment on the radiation chemistry of DEHBA, especially under conditions expected in real-world solvent extraction processes. Therefore, we have undertaken a systematic investigation into the radiolytic degradation of DEHBA in n-dodecane under fully aerated and biphasic conditions. DEHBA integrity and degradation product formation were measured for both extraction (in contact with 4.0 M HNO3(aq)) and stripping (in contact with 0.1 M HNO3(aq)) formulations. At the lower acidity the rate of DEHBA/n-dodecane degradation was slow (G = -0.26 +/- 0.02 mu M J(-1)) whereas at the higher acidity this degradation was about 35% faster (G= -0.35 +/- 0.02 mu M J(-1)). Both values were much less than analogous measurements under deaerated conditions. Under continuously aerated conditions, FTIR and ESI-MS measurements identified the two major degradation products, bis-2-ethylhexylamine (b2EHA) and N-(2-ethylhexyl)butyramide (MEHBA), as well as the presence of additional oxidized product species. Solvent system performance was also investigated using uranium extraction and strip distribution ratio measurements. These studies showed that there was only minimal change in uranium extraction and stripping performance with absorbed gamma dose.
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| 10. |
- Jazrawi, S., et al.
(författare)
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Commissioning the FAst TIMing array (FATIMA) at FAIR Phase-0 : Half-lives of excited states in the N=50 isotones 96Pd and 94Ru
- 2022
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X .- 1879-0895. ; 200
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports results of the first experiment of the DESPEC Phase-0 campaign at GSI, which focused on the study of neutron-deficient nuclei approaching 100Sn. These data provide the first extended commissioning experiment for the DESPEC collaboration within NuSTAR. We present results on electromagnetic transition rates associated with the decays from excited states populated following the formation of I pi = 8+ proton 'seniority -isomer' states in the N = 50 isotones 94Ru and 96Pd. Direct half-life measurements via gamma-gamma coincidences using the FATIMA detector array consisting of 36 LaBr3(Ce) scintillators have determined the reduced matrix elements associated with decays between low-lying states in these semi-magic nuclei. The extracted half-lives for yrast I pi = 6+ and 4+ states in 96Pd and the 6+ state in 94Ru are consistent with the published, highest-precision values for these nuclei.
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| 11. |
- Jonsson, Mats, 1967-
(författare)
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Exploring the impact of groundwater constituents and irradiation conditions on radiation-induced corrosion of copper
- 2023
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X .- 1879-0895. ; 211
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the impact of groundwater constituents and irradiation conditions on radiation induced corrosion of copper have been studied using numerical simulations based on the recently published mechanism. The simulations show that the amount of corrosion at a given total absorbed radiation dose will increase with decreasing dose rate. Furthermore, hydroxyl radical scavengers in general have a very marginal effect on the rate of corrosion while scavengers of the hydrated electron almost double the rate of corrosion. Sulfide present under relevant conditions has a significant effect on the corrosion rate and reduces the rate by 80% already at the lowest expected concentration and flux. Fe2+ present under relevant conditions does not influence the rate of corrosion significantly. Also initially dissolved oxygen has a very marginal effect on the process. Dissolved organic material scavenge hydroxyl radicals upon formation of C-centered radicals which in turn react with molecular oxygen. In systems where peroxyl radical recombination is not dominating, i.e., where there are solutes reactive towards peroxyl radicals, the presence of dissolved organic material can reduce the rate of corrosion by almost 99%. The pH and the presence of Cl-, HCO3- and SO42-have relatively small effects. In general, radiation induced corrosion is 20-40% slower at pH = 9 as compared to pH = 7.4 and the presence of HCO3- increases the rate of corrosion somewhat at pH = 9 as compared to pure water at the same pH.
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| 12. |
- Li, Zhuofeng, et al.
(författare)
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Inorganic/organic hybrid nanoparticles synthesized in a two-step radiation-driven process
- 2022
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X .- 1879-0895. ; 197, s. 110166-
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we have synthesized inorganic-organic hybrid nanoparticles via radiation synthesis of inorganic nanoparticles (Ag and CeO2) in aqueous dispersions containing radiation-synthesized poly(N-vinyl pyrrolidone) (PVP) nanogels (NG). The experiments show that there are strong interactions between the inorganic precursors (Ag+ and Ce3+) and the nanogel prior to irradiation. The two hybrid systems (Ag/NG and CeO2/NG) were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD confirms the formation of crystalline Ag and CeO2. TEM reveals that the inorganic nanoparticles are evenly distributed in/on the nanogel. Both XRD and TEM show that size of the inorganic particles is controlled by the nanogel.
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| 13. |
- Ntemou, Eleni, et al.
(författare)
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Energy deposition by H and He ions at keV energies in self-supporting, single crystalline SiC foils
- 2022
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Ingår i: Radiation Physics and Chemistry. - : Elsevier. - 0969-806X .- 1879-0895. ; 194
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Tidskriftsartikel (refereegranskat)abstract
- The specific energy deposition of H and He ions in SiC has been studied for both random and channeling orientations. The experiments were carried out in transmission geometry using the Time-of-Flight Medium Energy Ion Scattering System at the 350 keV Danfysik Implanter at Uppsala University. The target was a self-supporting, single crystalline cubic 3C-SiC (100) foil with nominal thickness of 200 nm. The measured stopping cross sections are compared with data available from the literature and theoretical predictions. The results for random geometries reveal slightly lower values than predicted by SRIM for H projectiles whereas for He projectiles good agreement was observed over the whole energy range studied. Higher specific energy loss is observed along random trajectories in comparison to channeling geometry, for all measured energies and for both H and He ions. For H ions, however, differences are minor, whereas for He ions, they are found generally more pronounced.
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| 14. |
- Pasi, Anna-Elina, 1993, et al.
(författare)
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Radiolytic degradation of dimethyl telluride in aqueous solutions
- 2023
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 1879-0895 .- 0969-806X. ; 207
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Tidskriftsartikel (refereegranskat)abstract
- The formation of volatile radioactive species is a major concern in severe nuclear reactor accident scenarios. Release of radioactive material to the environment is highly governed by the volatility of the species and therefore it its crucial to understand the behavior of any such species during the accident and the days and weeks following. One of the volatile, yet highly understudied fission products is tellurium. Although tellurium has been released in significant amounts during the major nuclear accidents that have occurred, the knowledge of the behavior is still lacking. Here we present results on the radiolysis of dimethyl telluride, a highly volatile species shown to form in accident conditions. The behavior of dimethyl telluride was investigated under gamma irradiation in various aqueous solutions and conditions representative to severe nuclear reactor accident conditions. The results suggest that dimethyl telluride is relatively stable towards gamma irradiation and its degradation is highly affected by the amount of dissolved oxygen and competing species. It was found that dimethyl telluride degrades via oxidative processes by reacting with oxidizing radiolysis products e.g. •OH, O.-. In the absence of oxygen, several volatile telluride dimers were observed. The results presented here increase the interest in organic tellurides in severe accident conditions and highlight the need for further investigation of the re-volatilization and mitigation of volatile tellurium species.
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| 15. |
- Sagstuen, Einar, et al.
(författare)
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Radicals in ammonium tartrate at 295 K by X-radiation : Revised radical structures by EMR and DFT analyses
- 2022
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Ingår i: Radiation Physics and Chemistry. - : Pergamon-Elsevier Science Ltd. - 0969-806X .- 1879-0895. ; 196
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Tidskriftsartikel (refereegranskat)abstract
- The simple amino acid l-alpha-alanine (ala) in polycrystalline form was among the first substances to be proposed and subsequently developed for Electron Paramagnetic Resonance (EPR)-based solid state radiation dosimetry. One disadvantage with ala is a relatively low sensitivity for doses below a few gray (Gy) which is a dose range of particular interest in medical, accident and environmental applications. A number of other compounds have been screened and some of these have shown a better sensitivity to radiation exposure than ala, in some cases up to a factor of 7-8. In particular ammonium tartrate (AT) and lithium formate (LiFo) have been taken into practical use. The present work was initially aimed to investigate the low-temperature radical products in AT, and the reactions leading to the product of dosimetric interest at room temperature. As a part of these studies, the previously characterized major room temperature radical product was re-investigated using single crystal electron magnetic resonance (EMR) techniques combined with periodic density functional theory (DFT) -type quantum chemical calculations. Surprisingly, this study showed that the molecular structure of the dominant radical at room temperature is somewhat different from that previously proposed. Furthermore, a second room temperature radical, previously not well characterized, was carefully investigated and three hyperfine coupling tensors were determined. These three tensors were sufficient to simulate all experimental observations for the second radical but not alone sufficient to permit an unambiguous molecular structure of the defect to be determined. It appears that the EPR resonance from this radical does not influence the dosimetric potential of AT.
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| 16. |
- Schmidt, H., et al.
(författare)
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Gamma and pulsed electron radiolysis studies of CyMe 4 BTBP and CyMe 4 BTPhen: Identification of radiolysis products and effects on the hydrometallurgical separation of trivalent actinides and lanthanides
- 2021
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 1879-0895 .- 0969-806X. ; 189
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Tidskriftsartikel (refereegranskat)abstract
- The radiolytic stability of the highly selective ligands CyMe4BTBP and CyMe4BTPhen against ionizing gamma radiation was studied in 1-octanol solution. CyMe4BTBP and CyMe4BTPhen are important extractants for a potential treatment of used nuclear fuel. They were studied under identical experimental conditions to directly compare the effects of gamma and pulsed electron radiolysis on the ligands and systematically study the influence of structural changes in the ligand backbone. Distribution ratios of Am3+, Cm3+ and Eu3+, the residual concentration of CyMe4BTBP and CyMe4BTPhen in solution, and the formation of radiolysis products were studied as a function of absorbed gamma dose and presence of an acidic aqueous phase during irradiation. Quantitative and semi-quantitative analyses were used to elucidate the radiolysis mechanism for both ligands. Addition products of alpha-hydroxyoctyl radicals formed through radiolysis of the 1-octanol diluent to the ligand molecules were identified as the predominant radiolysis products. These addition products also extract trivalent metal ions, as distribution ratios remained high although the parent molecule concentrations decreased. Therefore, the utilization time of a solvent using these extractants under the harsh conditions of used nuclear fuel treatment could be considerably longer than expected. Understanding the radiolysis mechanism is crucial for designing more radiation resistant extractants.
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| 17. |
- Soroka, Inna, et al.
(författare)
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Particle size effect of Ag-nanocatalysts deposited on carbon as prepared by γ-radiation induced synthesis
- 2020
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Ingår i: Radiation Physics and Chemistry. - : Elsevier. - 0969-806X .- 1879-0895. ; 169
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Tidskriftsartikel (refereegranskat)abstract
- The effect of silver particle sizes on the catalytic performance of Ag/C electrodes for oxygen reduction reaction (ORR) was studied. The Ag particles were precipitated from AgNO3 solutions on Vulcan XC-72 carbon as support by γ-radiation induced synthesis method. The structural and morphological characterizations of the electrode materials were done by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that particles with smaller diameters, 11 ± 6 nm, possess higher catalytic activity for ORR (50 mA/cm2 at 0.3 V) as compared to those with larger diameters, 41 ± 5 nm, ORR activity is 25 mA/cm2 at 0.3 V. The observed effect may be explained by an increased amount of low coordinated atoms in smaller particles as compared to the larger ones.
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