| 1. |
- Acharya, Govatsa, et al.
(författare)
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Investigation of a self-actuated, gravity-driven shutdown system in a small lead-cooled reactor
- 2020
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Ingår i: International Conference on Physics of Reactors. - : EDP Sciences. ; , s. 1456-1463
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Konferensbidrag (refereegranskat)abstract
- Passive safety systems in a nuclear reactor allow to simplify the overall plant design, beside improving economics and reliability, which are considered to be among the salient goals of advanced Generation IV reactors. This work focuses on investigating the application of a self-actuated, gravity-driven shutdown system in a small lead-cooled fast reactor and its dynamic response to an initiating event. The reactor thermal-hydraulics and neutronics assessment were performed in advance. According to a first-order approximation approach, the passive insertion of shutdown assembly was assumed to be influenced primarily by three forces: gravitational, buoyancy and fluid drag. A system of kinematic equations were formulated a priori and a MATLAB program was developed to determine the dynamics of the assembly. Identifying the delicate nature of the balance of forces, sensitivity analysis for coolant channel velocities and assembly foot densities yielded an optimal system model that resulted in successful passive shutdown. Transient safety studies, using the multi-point dynamics code BELLA, showed that the gravity-driven system acts remarkably well, even when accounting for a brief delay in self-actuation. Ultimately the reactor is brought to a sub-critical state while respecting technological constraints.
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| 2. |
- Al-Adili, Ali, et al.
(författare)
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Isomer yields in nuclear fission
- 2021
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 256
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Tidskriftsartikel (refereegranskat)abstract
- The generation of angular momentum in the fission process is still an open question. To shed light on this topic, we started a series of measurements at the IGISOL-JYFLTRAP facility in Finland. Highprecision measurements of isomeric yield ratios (IYR) are performed with a Penning trap, partly with the aim to extract average root-mean-square (rms) quantities of fragment spin distributions. The newly installed Phase-Imaging Ion-Cyclotron Resonance (PI-ICR) technique allows the separation of masses down to tens of keV, which is suffcient to disentangle many isomers. In this paper, we first summarize the previous measurements on the neutron and proton-induced fission of uranium and thorium, e.g. the odd cadmium and indium isotopes (119 ≤ A ≤ 127). The measurements revealed systematic trends as function of mass number, which stimulated further exploration. A recent measurement was performed at IGISIOL and several new IYR data will soon be published, for the first time. Secondly, we employ the TALYS nuclear-reaction code to model one of the newly measured isomer yields. Detailed GEF and TALYS calculations are discussed for the fragment angular momentum distribution in 134I.
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| 3. |
- Alberdi, Antxon, et al.
(författare)
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The jet of the Low Luminosity AGN of M81. Evidence of Precession
- 2013
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. ; 61
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Konferensbidrag (refereegranskat)abstract
- In this contribution, we summarize our main results of a big campaign of global VLBI observations of the AGN in M81 (M81*) phase-referenced to the radio supernova SN 1993J. Thanks to the precise multi-epoch and multi-frequency astrometry, we have determined the normalized core-shift of the relativistic jet of M81* and estimated both the magnetic field and the particle density at the jet base. We have also found evidence of jet precession in M81* coming from the systematic time evolution of the jet orientation correlated with changes in the overall flux density.
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| 4. |
- Atomassa, Ermias, et al.
(författare)
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Feasibility studies for nucleon structure measurements with PANDA
- 2014
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 81
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Tidskriftsartikel (refereegranskat)abstract
- The study of nucleon structure is one of the main physics goals of PANDA to be built at the FAIR accelerator complex. The excellent particle identification performance of the PANDA detector will enable measurements of exclusive channels p̄ p -> e^+e^- and p̄ p -> pi^0 J/psi -> pi^0e^+e^- to extract the electromagnetic form factors of protons and pi-nucleon Transition Distribution Amplitudes (pi-N TDAs). After a brief description of the PANDA apparatus and a method to handle momentum resolution degradation due to Bremsstrahlung, the physics of pi-N TDAs is discussed. An estimate for the expected signal to background ratio for p̄ p -> pi^0 J/psi -> pi^0e^+e^- that takes into account the main background source is given.
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| 5. |
- Audouin, L., et al.
(författare)
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High-precision measurement of isotopic fission yields of 236 U
- 2018
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. ; 193
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Konferensbidrag (refereegranskat)abstract
- We report on the second SOFIA experiment, dedicated to the fission yields of 236U∗, analog to 235U(n,f). The measurement is based on the inverse kinematics method, using a relativistic, secondary beam of 236U. Both fission fragments are identified in mass and charge in the SOFIA recoil spectrometer. The obtained isotopic yields are compared with existing spectroscopy measurements and the elemental yields are used to discuss the treatment of the even-odd effect with energy in nuclear data libraries.
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| 6. |
- Babaahmadi, Arezou, 1985, et al.
(författare)
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Electrochemical migration technique to accelerate ageing of cementitious materials
- 2013
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. - 9782759810468 ; 56
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Konferensbidrag (refereegranskat)abstract
- Durability assessment of concrete structures for constructions in nuclear waste repositories requires long term service life predictions. As deposition of low and intermediate level radioactive waste (LILW) takes up to 100 000 years, it is necessary to analyze the service life of cementitious materials in this time perspective. Using acceleration methods producing aged specimens would decrease the need of extrapolating short term data sets. Laboratory methods are therefore, needed for accelerating the ageing process without making any influencing distortion in the properties of the materials. This paper presents an electro-chemical migration method to increase the rate of calcium leaching from cementitious specimens. This method is developed based on the fact that major long term deterioration process of hardened cement paste in concrete structures for deposition of LILW is due to slow diffusion of calcium ions. In this method the cementitious specimen is placed in an electrochemical cell as a porous path way through which ions can migrate at a rate far higher than diffusion process. The electrical field is applied to the cell in a way to accelerate the ion migration without making destructions in the specimen's micro and macroscopic properties. The anolyte and catholyte solutions are designed favoring dissolution of calcium hydroxide and compensating for the leached calcium ions with another ion like lithium.
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| 7. |
- Backs, Alex, et al.
(författare)
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Development and first results of a magnetic sample environment for polarized neutron imaging of thin metal sheets
- 2023
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Ingår i: EPJ Web of Conferences. - 2100-014X. ; 286
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Tidskriftsartikel (refereegranskat)abstract
- Polarized neutron imaging brings the great advantage of analyzing bulk magnetic properties with good spatial resolution. The technique is based on the interaction of the neutron spin with magnetic samples or free magnetic fields and observing the changes to a spin-polarized neutron beam. The high sensitivity to even small magnetic fields is a benefit in obtaining magnetization information but simultaneously a challenge in instrumentation, since magnetic environments for the polarized neutron beam and for the sample, as well as the fringe field from the magnetic sample itself all affect the measurement and can give rise to unwanted effects. We have used finite element simulations and ray tracing simulations, to design and analyze a magnetic sample environment devised for the measurement of ferromagnetic metal sheets. Here we show an analysis of performance of the experimental setup based on the simulation results and compare them to first experimental results on a grain oriented silicon steel sample.
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| 8. |
- Balibrea-Correa, J., et al.
(författare)
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First measurement of the 94Nb(n,γ) cross section at the CERN n_TOF facility
- 2023
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 279
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Tidskriftsartikel (refereegranskat)abstract
- One of the crucial ingredients for the improvement of stellar models is the accurate knowledge of neutron capture cross-sections for the different isotopes involved in the s-,r- and i- processes. These measurements can shed light on existing discrepancies between observed and predicted isotopic abundances and help to constrain the physical conditions where these reactions take place along different stages of stellar evolution.In the particular case of the radioactive 94Nb, the 94Nb(n,γ) cross-section could play a role in the determination of the s-process production of 94Mo in AGB stars, which presently cannot be reproduced by state-of-the-art stellar models. There are no previous 94Nb(n,γ) experimental data for the resolved and unresolved resonance regions mainly due to the difficulties in producing highquality samples and also due to limitations in conventional detection systems commonly used in time-of-flight experiments.Motivated by this situation, a first measurement of the 94Nb(n,γ) reaction was carried out at CERN n_TOF, thereby exploiting the high luminosity of the EAR2 area in combination with a new detection system of small-volume C6D6-detectors and a high quality 94Nb-sample. The latter was based on hyper-pure 93Nb material activated at the high-flux reactor of ILL-Grenoble. An innovative ring-configuration detection system in close geometry around the capture sample allowed us to significantly enhance the signal-to-background ratio. This set-up was supplemented with two conventional C6D6-detectors and a highresolution LaCl3(Ce)-detector, which will be employed for addressing reliably systematic effects and uncertainties.At the current status of the data analysis, 18 resonance in 94Nb+n have been observed for the first time in the neutron energy range from thermal up to 10 keV.
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| 9. |
- Beck, Christian, et al.
(författare)
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Notes on Fitting and Analysis Frameworks for QENS Spectra of (Soft) Colloid Suspensions
- 2022
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 272, s. 01004-01004
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Tidskriftsartikel (refereegranskat)abstract
- With continuously improving signal-to-noise ratios, a statistically sound analysis of quasi-elasticneutron scattering (QENS) spectra requires to fit increasingly complex models which poses several challenges.Simultaneous fits of the spectra for all recorded values of the momentum transfer become a standard approach.Spectrometers at spallation sources can have a complicated non-Gaussian resolution function which has to bedescribed most accurately. At the same time, to speed up the fitting, an analytical convolution with this resolutionfunction is of interest. Here, we discuss basic concepts to efficient approaches for fits of QENS spectra basedon standard MATLAB and Python fit algorithms. We illustrate the fits with example data from IN16B, BASIS,and BATS.
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| 10. |
- Bensby, Thomas, et al.
(författare)
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Chemical constraints on the formation of the Galactic thick disk
- 2012
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Ingår i: Assembling the Puzzle of the Milky Way. - : EDP Sciences. - 2101-6275 .- 2100-014X. ; 19
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Konferensbidrag (refereegranskat)abstract
- We highlight some results from our detailed abundance analysis study of 703 kinematically selected F and G dwarf stars in the solar neighbourhood. The analysis is based on spectra of high-resolution (R = 45 000 to 110 000) and high signal-to-noise (S/N approximate to 150 to 300). The main findings include: (1) at a given metallicity, the thick disk abundance trends are more alpha-enhanced than those of the thin disk; (2) the metal-rich limit of the thick disk reaches at least solar metallicities; (3) the metal-poor limit of the thin disk is around [Fe/H] approximate to -0.8; (4) the thick disk shows an age-metallicity gradient; (5) the thin disk does not show an age-metallicity gradient; (6) the most metal-rich thick disk stars at [Fe/H] approximate to 0 are significantly older than the most metal-poor thin disk stars at [Fe/H] approximate to -0.7; (7) based on our elemental abundances we find that kinematical criteria produce thin and thick disk stellar samples that are biased in the sense that stars from the low-velocity tail of the thick disk are classified as thin disk stars, and stars from the high-velocity tail of the thin disk are classified as thick disk stars; (8) age criteria appears to produce thin and thick disk stellar samples with less contamination.
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