| 1. |
- Muscas, Giuseppe, et al.
(författare)
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Evolution of the magnetic structure with chemical composition in spinel iron oxide nanoparticles
- 2015
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Ingår i: Nanoscale. - : The Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 7:32, s. 13576-13585
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic properties of iron oxide nanoparticles with spinel structure are strictly related to a complex interplay between cationic distribution and the presence of a non-collinear spin structure (spin canting). With the aim to gain better insight into the effect of the magnetic structure on magnetic properties, in this paper we investigated a family of small crystalline ferrite nanoparticles of the formula CoxNi1-xFe2O4 (0 [less-than-or-equal] x [less-than-or-equal] 1) having equal size ([approximate]4.5 nm) and spherical-like shape. The field dependence of magnetization at low temperatures indicated a clear increase of magnetocrystalline anisotropy and saturation magnetization (higher than the bulk value for CoFe2O4: [similar]130 A m2 kg-1) with the increase of cobalt content. The magnetic structure of nanoparticles has been investigated by Mossbauer spectroscopy under an intense magnetic field (8 T) at a low temperature (10 K). The magnetic properties have been explained in terms of an evolution of the magnetic structure with the increase of cobalt content. In addition a direct correlation between cationic distribution and spin canting has been proposed, explaining the presence of a noncollinear spin structure in terms of superexchange interaction energy produced by the average cationic distribution and vacancies in the spinel structure.
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| 2. |
- Sayed, F., et al.
(författare)
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Surface Effects in Ultrathin Iron Oxide Hollow Nanoparticles : Exploring Magnetic Disorder at the Nanoscale
- 2018
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 122:13, s. 7516-7524
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Tidskriftsartikel (refereegranskat)abstract
- A detailed study of the structural and magnetic properties of polycrystalline hollow gamma-Fe2O3 nanoparticles of similar to 9.4 nm size was performed. High-resolution transmission electron microscopy images confirmed the crystalline structure and the presence of a ultrathin shell thickness of similar to 1.4 nm, implying a very high surface/volume ratio. These hollow nanoparticles were investigated using zero-field and in-field Fe-57 Mossbauer spectrometry. The zero-field hyperfine structure suggests some topological disorder, whereas the infield one shows the presence of a comp magnetic structure that can be fairly described as two opposite pseudosperomagnetic sublattices attributed to octahedral and tetrahedral iron sites. Such an unusual feature is consistent with the presence of noncollinear spin structure originated from the increased surface due to the hollow morphology. Such a complex local spin structure evidenced from Mossbauer experiments was correlated with exchange bias coupling showing at low temperature by magnetization measurements. Monte Carlo simulations on a ferrimagnetic hollow nanoparticle unambiguously corroborate the critical role of the surface anisotropy on the noncollinearity of spin structure in our samples.
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| 3. |
- Von Lensa, W., et al.
(författare)
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Red-impact : A European research programme to assess the impact of partitioning and transmutation on final nuclear waste disposal
- 2008
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Ingår i: Int. Congr. Adv. Nucl. Power Plants - ICAPP, "Nucl. Renaiss. Work". - 9781604238716 ; , s. 2564-2573
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Konferensbidrag (refereegranskat)abstract
- It is the objective of the EU-funded 'Red-Impact' project to analyse the impact of partitioning, transmutation and waste reduction technologies on the final nuclear waste disposal. The partnership of 25 organisations is originating from European nuclear industry, waste agencies, research centres and universities. The system studies focus on a realistic evolution of P&T technologies and advanced fuel cycles which can be deployed incrementally on an industrial scale as well as on future developments such as reactors of the third and fourth generation (Gen III & Gen IV) and Accelerator Driven Systems (ADS). A comprehensive inventory of all existing and foreseen nuclear fuel cycle facilities in Europe has been performed including a review on worldwide ongoing R&D programs on P&T. Thus, it was possible to select a set of three so-called "industrial scenarios", taking into account industrial feasibility of alternate strategies leading to increased actiniae burning and reduced actinide generation based on direct disposal (reference case) or MOXfuel for LWR and plutonium recycle in Sodium Fast Reactors (SFR). R&D needs for the development of processes and technologies have also been addressed. In addition, three 'innovative scenarios ' have been identified allowing multi-recycling of plutonium and minor actinides in SFR and Accelerator-Driven Systems (ADS) as well as GANEX or COEXprocess and PYRO reprocessing technologies. Waste streams have been calculated for all of these scenarios including the transition from the present situation towards new fuel cycle options. These data provide the input to specific analyses on the impact on geological disposal in different host formations such as granite, clay and salt. The results show that advanced fuel cycles influence the required size of the geological repository in case of disposal in clay, salt or hard rock formations. Recycling of all the actinides results in a reduction of the necessary gallery length (depending on geology and design) at least by a factor 3. If additionally cesium and strontium are extracted from the high-level waste for separate decay, the reduction factor will become 10 or more. In the frame of the project, the feasibility and the impact of the Cs or Sr separated management were not assessed or evaluated. Transmutation of the actinides fast neutron spectrum reactors (FR or ADS) results in a limited reduction of the maximum dose because the dose is essentially due to long-lived fission and activation products. On the other hand, reprocessing the spent fuel decreases the maximum dose at the storage with a factor 5 because a considerable fraction of the iodine is separated from the high level waste during reprocessing. The radiotoxicity in the high level waste or spent fuel as well as human intrusion doses after 500 years are drastically reduced by the transmutation of the actinides. Evaluating actinide minimization systems and industrialised P&T in general requires an assessment of relevant nuclear fuel cycles especially with regard to the economic, environmental and societal advantages/disadvantages (i.e. the sustainability of the fuel cycles). Thus, a set of indicators has been derived for each of these areas. The results are analysed using the multi-criterion analysis approach which allows the importance of each of the indicators to be specified.
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| 4. |
- Westlén, Daniel, et al.
(författare)
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Impact of P&T on geological repositories an overview of the euratom red impact project
- 2007
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Ingår i: GLOBAL 2007. - 0894480553 - 9780894480553 ; , s. 772-781
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Konferensbidrag (refereegranskat)abstract
- The European Commission project Red Impact is in a state of conclusion after three years. Within the project, the consequences of P&T on, mainly, geological disposal have been investigated. Six scenarios have been developed, including three considered to be deployable today, and three more advanced scenarios including P&T in different ways. The scenarios all have different strengths and weaknesses, which are discussed in the present paper.
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