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Sökning: L773:2100 014X OR L773:2101 6275 > (2020-2023)

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1.
  • Nagy, Lajos, 1991, et al. (författare)
  • Measurements and simulations to investigate the feasibility of neutron multiplicity counting in the current mode of fission chambers
  • 2020
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. ; 225
  • Konferensbidrag (refereegranskat)abstract
    • In two earlier papers [1], [2] we investigated the possibility of extracting traditional multiplicity count rates from the cumulants of fission chamber signals in current mode. It was shown that if all neutrons emitted from the sample simultaneously are also detected simultaneously, the multiplicity rates can be retrieved from the first three cumulants of the currents of up to three detectors, but the method breaks down if the detections of neutrons of common origin take place with a time delay spread wider than the pulse shape. To remedy these shortcomings, in this work we extended the theory to two- and three-point distributions (correlations). It was found thatthe integrals of suitably chosen two- and three-point moments with respect to the time differences become independent of the probability density of the time delays of detections. With this procedure, the multiplicity rates can be retrieved from the detector currents for arbitrary time delay distributions. To demonstrate the practical applicability of the proposed method, a measurement setup was designed and built. The statistics (shape and amplitude distribution) of the detector pulse were investigated as important parameters of the theoretical model. Simulations were performed to estimate the expected value of the multiplicity rates in the built setup. Measurements were performed and two types of moments (the mean and the covariance function) of the recorded detector signals were calculated. Values of singles rates were successfully recovered.
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2.
  • Acharya, Govatsa, et al. (författare)
  • Investigation of a self-actuated, gravity-driven shutdown system in a small lead-cooled reactor
  • 2020
  • Ingår i: International Conference on Physics of Reactors. - : EDP Sciences. ; , s. 1456-1463
  • 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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3.
  • Al-Adili, Ali, et al. (författare)
  • Isomer yields in nuclear fission
  • 2021
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 256
  • 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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4.
  • Backs, Alex, et al. (författare)
  • Development and first results of a magnetic sample environment for polarized neutron imaging of thin metal sheets
  • 2023
  • Ingår i: EPJ Web of Conferences. - 2100-014X. ; 286
  • 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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5.
  • Balibrea-Correa, J., et al. (författare)
  • First measurement of the 94Nb(n,γ) cross section at the CERN n_TOF facility
  • 2023
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 279
  • 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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6.
  • Beck, Christian, et al. (författare)
  • Notes on Fitting and Analysis Frameworks for QENS Spectra of (Soft) Colloid Suspensions
  • 2022
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 272, s. 01004-01004
  • 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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7.
  • Biscarat, Catherine, et al. (författare)
  • New developments in cost modeling for the LHC computing
  • 2020
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 245, s. 03014-03014
  • Tidskriftsartikel (refereegranskat)abstract
    • The increase in the scale of LHC computing during Run 3 and Run 4 (HL-LHC) will certainly require radical changes to the computing models and the data processing of the LHC experiments. The working group established by WLCG and the HEP Software Foundation to investigate all aspects of the cost of computing and how to optimise them has continued producing results and improving our understanding of this process. In particular, experiments have developed more sophisticated ways to calculate their resource needs, we have a much more detailed process to calculate infrastructure costs. This includes studies on the impact of HPC and GPU based resources on meeting the computing demands. We have also developed and perfected tools to quantitatively study the performance of experiments workloads and we are actively collaborating with other activities related to data access, benchmarking and technology cost evolution. In this contribution we expose our recent developments and results and outline the directions of future work.
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8.
  • Bott, Lukas Thomas, et al. (författare)
  • Coulomb dissociation of O-16 into He-4 and C-12
  • 2023
  • Ingår i: NUCLEAR PHYSICS IN ASTROPHYSICS - X, NPA-X 2022. - : EDP Sciences. - 2100-014X. ; 279
  • Konferensbidrag (refereegranskat)abstract
    • We measured the Coulomb dissociation of O-16 into He-4 and C-12 within the FAIR Phase-0 program at GSI Helmholtzzentrum fur Schwerionenforschung Darmstadt, Germany. From this we will extract the photon dissociation cross section O-16(alpha,gamma)C-12, which is the time reversed reaction to C-12(alpha,gamma)O-16. With this indirect method, we aim to improve on the accuracy of the experimental data at lower energies than measured so far. The expected low cross section for the Coulomb dissociation reaction and close magnetic rigidity of beam and fragments demand a high precision measurement. Hence, new detector systems were built and radical changes to the (RB)-B-3 setup were necessary to cope with the high-intensity O-16 beam. All tracking detectors were designed to let the unreacted O-16 ions pass, while detecting the C-12 and He-4.
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9.
  • Cabelllos, Oscar, et al. (författare)
  • GRE@T-PIONEeR: teaching the nuclear data pipeline using innovative pedagogical methods
  • 2023
  • Ingår i: 15TH INTERNATIONAL CONFERENCE ON NUCLEAR DATA FOR SCIENCE AND TECHNOLOGY, ND2022. - 2100-014X. ; 284
  • Konferensbidrag (refereegranskat)abstract
    • GRE@T-PIONEeR - GRaduate Education Alliance for Teaching the PhysIcs and safety Of NuclEar Reactors - is a project funded by the Euratom – Horizon 2020 Framework Programme which aims at developing and providing specialised and advanced courses in computational and experimental reactor physics at the graduate level (MSc and PhD levels) and post-graduate level, as well as the staff members working in the nuclear industry. One of the work packages of GRE@T-PIONEeR is devoted to developing a specific course on the nuclear data pipeline processes and to present the role of nuclear data to play in calculations of innovative reactor systems. This course covers all steps in the nuclear data life cycle, starting from the measurements to their validation and final use in nuclear reactor calculations. Beyond the technical contents of the courses being developed, the paper describes the use of innovative pedagogical methods and active learning techniques, such as flipped classes, aimed at promoting student learning.
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10.
  • Chatillon, A., et al. (författare)
  • Fission-fragment yields measured in Coulomb-induced fission of U-234,U-235,U-236,U-238 and Np-237,Np-238 with the (RB)-B-3/SOFIA setup
  • 2023
  • Ingår i: 15TH INTERNATIONAL CONFERENCE ON NUCLEAR DATA FOR SCIENCE AND TECHNOLOGY, ND2022. - 2100-014X. ; 284
  • Konferensbidrag (refereegranskat)abstract
    • Low energy fission of (234,235,236,238)u and Np-237,Np-381 radioactive beams, provided by the GSI/FRS facility, has been studied using the (RB)-B-3/SOFIA setup. The latter allows, on an event-by-event basis, to simultaneously identify, in terms of their mass and atomic numbers, the fissioning nucleus in coincidence with both fission fragments after prompt-neutron emission. This presentation reports on new results on elemental, isobaric and isotopic yields.
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11.
  • Dehlin, Fredrik, 1994-, et al. (författare)
  • Implementation of an autonomous reactivity control system in a small lead-cooled fast reactor
  • 2021
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X.
  • Konferensbidrag (refereegranskat)abstract
    • This paper describes the design, implementation and characterisation of an Autonomous Reactivity Control (ARC) system in a small modular lead-cooled fast reactor. The aim of this work was to demonstrate the applicability of the ARC system and to study its dynamic behaviour during an anticipated transient without scram. A simplified one-dimensional model was developed to calculate the heat transfer within the ARC system, and the reactivity worth as a function of the neutron poison’s insertion into the active core was obtained via static neutronic calculations. By coupling the aforementioned models, the ARC’s time-dependent reactivity was derived as a function of the coolant outlet temperature variation. This model was implemented into the BELLA multi-point dynamics code and transient simulations were run. A control rod ejection accident was studied leading to an unprotected transient overpower scenario, in which 350 pcm reactivity was inserted during one second. It was shown that the ARC system provides a forceful negative reactivity feedback and that steady-state temperatures after the transient were reduced by almost 300 K compared to an identical transient without its action. In this scenario, the ARC system managed to stabilise the coolant outlet temperature at a value 100 K above nominal conditions. The implementation of an ARC system provided the reactor with a passively actuated self-regulating reactivity control system able to insert large amounts of negative reactivity in a short amount of time.
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12.
  • Demaziere, Christophe, 1973, et al. (författare)
  • Monte Carlo-based dynamic calculations of stationary perturbations
  • 2020
  • Ingår i: International Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020. - : EDP Sciences. ; 2020-March
  • Konferensbidrag (refereegranskat)abstract
    • Capitalizing on some earlier work, this paper presents a novel Monte Carlo-based approach that allows estimating the neutron noise induced by stationary perturbations of macroscopic cross-sections in the frequency domain. This method relies on the prior computation using Monte Carlo of modified Green’s functions associated to the real part of the dynamic macroscopic cross-sections, mimicking equivalent subcritical problems driven by external neutron sources. Once such modified Green’s functions are estimated, the neutron noise induced by any type of perturbations can be recovered, by solving a linear algebra problem accounting for the interdependence between the real and imaginary parts of the governing balance equations. The newly derived method was demonstrated on a large homogeneous test system and on a small heterogeneous test system to provide results comparable to a diffusion-based solver specifically developed for neutron noise applications. The new method requires the specification by the user of the real part of the Fourier transform of the macroscopic cross-sections. This is accomplished using ACE-formatted cross-section files defined by the user. Beyond this input data preparation, no change to the Monte Carlo source code is necessary. This represents the main advantage of the proposed method as compared to similar efforts requiring extensive modifications to the Monte Carlo source code.
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13.
  • Demaziere, Christophe, 1973, et al. (författare)
  • Neutron noise-based anomaly classification and localization using machine learning
  • 2020
  • Ingår i: International Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020. - : EDP Sciences. ; 2020-March, s. 2913-2921
  • Konferensbidrag (refereegranskat)abstract
    • A methodology is proposed in this paper allowing the classification of anomalies and subsequently their possible localization in nuclear reactor cores during operation. The method relies on the monitoring of the neutron noise recorded by in-core neutron detectors located at very few discrete locations throughout the core. In order to unfold from the detectors readings the necessary information, a 3-dimensional Convolutional Neural Network is used, with the training and validation of the network based on simulated data. In the reported work, the approach was also tested on simulated data. The simulations were carried out in the frequency domain using the CORE SIM+ diffusion-based two-group core simulator. The different scenarios correspond to the following cases: a generic “absorber of variable strength”, axially travelling perturbations at the velocity of the coolant flow (due to e.g. fluctuations of the coolant temperature at the inlet of the core), fuel assembly vibrations, control rod vibrations, and core barrel vibrations. In all those cases, various frequencies were considered and, when relevant, different locations of the perturbations and different vibration modes were taken into account. The machine learning approach was able to correctly identify the different scenarios with a maximum error of 0.11%. Moreover, the error in localizing anomalies had a mean squared error of 0.3072 in mesh size, corresponding to less than 4 cm. The proposed methodology was also demonstrated to be insensitive to parasitic noise and will be tested on actual plant data in the near future.
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14.
  • Demaziere, Christophe, 1973 (författare)
  • Using active learning in hybrid learning environments
  • 2020
  • Ingår i: International Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020. - : EDP Sciences. ; 2020-March, s. 2419-2429
  • Konferensbidrag (refereegranskat)abstract
    • In this paper, an innovative pedagogical approach relying on flipped classroom and offered in a hybrid learning environment combining on-site and off-site attendees is proposed. The set-up is furthermore tested on two short courses offered at Chalmers University of Technology and analyzed using student course evaluation questionnaires. Several elements constitute the backbone of the courses. Such elements are either offered in an asynchronous fashion or in a synchronous fashion. The asynchronous elements are made of textbooks specifically written for the respective courses, pre-recorded short webcasts explaining the key concepts of the textbooks and on-line quizzes giving formative feedback to the students. Such elements should thus be studied by the students before attending the synchronous sessions. Because of the preparatory work made by the students, the synchronous sessions can focus on much more active forms of learning under the teacher’s supervision. The success of the pedagogical approach entirely depends on the contents of the synchronous sessions, which need to be carefully planned and designed so that they promote student learning. Although the hybrid learning environment gives rise to some additional challenges from a teacher’s perspective, it also gives much more flexibility in attracting students from remote locations, without compromising the learning experience.
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15.
  • Dufek, Jan, 1978-, et al. (författare)
  • Optimisation of Monte Carlo burnup simulations
  • 2020
  • Ingår i: International Conference on Physics of Reactors. - : EDP Sciences. ; , s. 804-810
  • Konferensbidrag (refereegranskat)abstract
    • We show here that computing efficiency of Monte Carlo burnup simulations depends on chosen values of certain free parameters, such as the length of the time steps and the number of neutron histories simulated at each Monte Carlo criticality run. The efficiency can thus be improved by optimising these parameters. We have set up a simple numerical model that made it possible for us to test a large number of combinations of the free parameters, and suggest a way to optimise their selection.
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16.
  • Elter, Zsolt, et al. (författare)
  • Development of a modeling approach to estimate radiation from a spent fuel rod quiver
  • 2020
  • Ingår i: PHYSOR 2020. - : EDP Sciences. - 9781527264472
  • Konferensbidrag (refereegranskat)abstract
    • Before encapsulation of spent nuclear fuel in a geological repository, the fuels need to be verified for safeguards purposes. This requirement applies to all spent fuel assemblies, including those with properties or designs that are especially challenging to verify. One such example are quivers, a new type of containers used to hold damaged spent fuel rods. After placing damaged rods inside the quivers, they are sealed with a thick lid and the water is removed. The lid is thick enough to significantly reduce the amount of the gamma radiation penetrating through it, which can make safeguards verification from the top using gamma techniques difficult. Considering that the number of quivers at storage facilities is foreseen to increase in near future, studying the feasibility of verification is timely.In this paper we make a feasibility study related to safeguards verification of quivers, aimed at investigating the gamma and neutron radiation field around a quiver designed by Westinghouse AB and filled with PWR fuel rods irradiated at the Swedish Ringhals site. A simplified geometry of the quiver and the detailed operational history of each rod are provided by Westinghouse and the reactor operator, respectively.The nuclide inventory of the rods placed in the quiver and the emission source terms are calculated with ORIGEN-ARP. The radiation transport is modeled with the Serpent2 Monte Carlo code. The first objective is to assess the capability of the spent fuel attribute tester (SFAT) to verify the content for nuclear safeguards purposes. The results show that the thick quiver lid attenuates the gamma radiation, thereby making gamma radiation based verification from above the quiver difficult.
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17.
  • Fernandez, D., et al. (författare)
  • Experimental study of high-energy fission and quasi-fission dynamics with fusion-induced fission reactions at VAMOS(++)
  • 2023
  • Ingår i: 15TH INTERNATIONAL CONFERENCE ON NUCLEAR DATA FOR SCIENCE AND TECHNOLOGY, ND2022. - 2100-014X. ; 284
  • Konferensbidrag (refereegranskat)abstract
    • During the last decade, the use of inverse kinematics in the experimental study of fission is bringing a wealth of new observables obtained in single measurements, allowing their analysis and their correlations. An ongoing application of this technique is the basis of a series of experiments performed with the variable -mode, large -acceptance VAMOS++ spectrometer at GANIL. A recent experiment has been focused on the survival of the nuclear structure effects at high excitation energy in fission and quasi-fission. The full isotopic identification of fragments, the fission dynamics and the ratio between the production of fragments with even and odd atomic numbers, the so-called proton even -odd effect, are shown. The latter shows a different mechanism for fission and quasi -fission that could be used to separate fission from quasi-fission.
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18.
  • Ferretti, Gabriele, 1963 (författare)
  • Compositeness above the electroweak scale and a proposed test at LHCb
  • 2022
  • Ingår i: EPJ Web Conf.. - : EDP Sciences. - 2100-014X. ; 258
  • Konferensbidrag (refereegranskat)abstract
    • I review attempts to construct models of partial compositeness from strongly coupled gauge theories. A few minimal assumptions allow one to isolate a small number of representative models. After presenting the main idea, I discuss a recent proposal to detect a light pseudo-scalar, predicted in all these models, at the LHCb detector.
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19.
  • Gao, Zhihao, et al. (författare)
  • New design and simulation of the ion guide for neutron-induced fission products at the IGISOL facility
  • 2023
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 284
  • Tidskriftsartikel (refereegranskat)abstract
    • Measurements of independent fission yield distributions in neutron-induced fission at high neutron energies are important for our fundamental understanding of the fission process, and are also relevant for reactor physics applications. So far, measurements of independent fission yields in proton-induced fission have been performed at the IGISOL facility at the University of Jyväskylä, using the Penning trap as a high resolving-power mass-filter. In order to also facilitate measurements of neutron-induced fission, a dedicated ion guide and a proton-to-neutron converter was developed. However, the first measurement indicates that fewer fission products than expected reach the Penning trap. To explore potential reasons and possible improvements, a simulation model was also developed and benchmarked. The benchmark showed that the model is able to reproduce the performance of the ion guide remarkably well and that the main reason for the low yield of fission products is the low collection efficiency of the ion guide.Based on the benchmark, a new ion guide is being designed. In the new design, the positions of the uranium targets and volume of the ion guide have been changed to increase the collection of fission products. This results in a five-fold increase of the yield. However, the collection efficiency of the new ion guide still needs to be improved in order to achieve intensities of the extracted fission products that are large enough to allow for reasonable measurement times.Because the volume of the ion guide is increased significantly, the extraction time of the ions is expected to be longer than that from the previous ion guide. Therefore, an electric field guidance system that consists of a combination of a stationary electric field and an RF-carpet is considered to be deployed. The stationary field, produced from a set of DC-ring electrodes, accelerates the ions towards the RF-carpet at end plate of the ion guide. The RF-carpet consists of a time-dependent field, produced from a radio-frequent structure of concentric rings, with a DC-component that guides the ions towards the exit hole in the center of the end plate. In this paper we present the current status of the simulations and design of the new ion guide.
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20.
  • Gustavsson, Cecilia, Dr, 1973-, et al. (författare)
  • Citizen science in radiation research
  • 2020
  • Ingår i: ND 2019. - : EDP Sciences. - 9782759891061
  • Konferensbidrag (refereegranskat)abstract
    • A growing trend in science is that research institutions reach out to members of the public for participating in research. The reasons for outreach are many, spanning from the desire to collect and/or analyse large sets of data efficiently, to the idea of including the general public on a very fundamental level in science-making and ultimately decision-making. The presented project is curriculum-based and carried out in 240 lower secondary school classes (pupils of age 13-16). The task, as designed by the participating universities, is to collect mushrooms, soil and animal droppings from different parts of Sweden, do preliminary sample preparation and analyses and send the samples to the university institutions for radioactivity measurement. Behind the project is a desire to compare today’s levels of 137Cs with those deposited right after the Chernobyl accident in 1986, but also to study the exchange of caesium between organisms as well as the impacts of biological and geological processes on uptake and retention. The scientific outcome is a geodatabase with the 137Cs activity (Bq/m2) present in the Swedish environment, where radioactivity data can be linked to the species (fungi, competing species, animals foraging), forest type, land type, land use and other environmental factors. The science question is of interest to the general public as foraging for mushrooms, as well as spending recreational time in forests is widely popular in Sweden. In this article, we will discuss the current status of the project and the observations we have made about how well the public can participate in scientific research. Focus will be on organization of the project, such as logistics, preparation of supportive material, feedback and communication between researchers and schools. We will present observations about the impact the project has had on the participants, based on quantitative and qualitative evaluations.
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21.
  • Hursin, Mathieu, et al. (författare)
  • Validation of axial void profile measured by neutron noise techniques in crocus
  • 2020
  • Ingår i: International Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020. - : EDP Sciences. ; 2020-March, s. 1586-1593
  • Konferensbidrag (refereegranskat)abstract
    • Recently a joint project has been carried out between the Paul Scherrer Institut, the Ecole Polytechnique Federale de Lausanne and swissnuclear, an industrial partner, in order to determine the axial void distribution in a channel installed in the reflector of the zero power research reactor CROCUS, using neutron noise techniques. The main objective of the present paper is to report on the validation of the results against an alternative measurement technique using gamma-ray attenuation and simulations with the TRACE code. For the gamma-ray attenuation experiments, the channel used in CROCUS is installed out of the core in a Plexiglass water tank. The source and detector are fixed and the channel is moved axially to keep the geometry of the source/detector arrangement untouched. This is key to measure the void effect by gamma attenuation due to the low contrast of this technique. The paper compares the experimental results obtained with both techniques, with the outcomes of simulations carried out with the TRACE code. Even though the quantitative void fraction estimations are not consistent, the trends obtained with the simulation and experimental techniques are the same. The discrepancies between the various experimental techniques and the simulation outcomes are related to the heterogeneous distribution of the water-air mixture in the radial sections of the channel.
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22.
  • Lantz, Mattias, 1971-, et al. (författare)
  • Gamma spectroscopy methodology for large amounts of environmental samples in Sweden 30 years after the Chernobyl accident
  • 2020
  • Ingår i: ND 2019. - : EDP Sciences. - 9782759891061
  • Konferensbidrag (refereegranskat)abstract
    • In a Swedish citizen science project, more than 200 elementary school classes participated in collecting fungi, soil samples, and droppings from deer and wild boar, from all over Sweden. The samples have been sent to a laboratory at Uppsala University where they are being analyzed through gamma spectroscopy with a shielded HPGe detector. The main objective is to scan the samples for 137Cs from the Chernobyl accident and compare the data with measurements from 1986, but uptake of naturally occuring radionuclides like 40K and radon daughters will also be determined. Together with the soil samples, transfer factors will be derived, and correlations for these factors will be sought for different species of fungi and soil types. The potential for correlating the results with different biological processes will also be investigated, in part through the collected animal droppings. This is a work in progress where the present status of the experimental setup and methodology are presented. Issues with the initial approach for corrections are discussed and preliminary results are presented.
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23.
  • Lee, Wai Tung, et al. (författare)
  • Polarisation Development at the European Spallation Source
  • 2023
  • Ingår i: EPJ Web of Conferences. - 2100-014X. ; 286, s. 03004-03004
  • Tidskriftsartikel (refereegranskat)abstract
    • To meet the ever-increasing user demand, eleven of the fifteen European Spallation Source (ESS) instruments under construction aim to offer polarised neutrons for user experiments. They include an imaging instrument, a SANS instruments, two reflectometers, three diffractometers, and four spectrometers. In conjunction with in-kind contributions and instrumentation grants, the ESS Polarisation Project will support the incorporation of polarisation analysis on eight of the eleven instruments. The project aims to deliver polarised neutrons for first-science experiments as instruments enter operation. Different polariser and polarisation analyser techniques will be available to accommodate the specifics of experiments on a given instrument. Polarised 3He neutron spin filter using either Metastable Optical Pumping (MEOP) or Spin-Exchange Optical Pumping (SEOP) techniques will provide shared-use equipment among many instruments, with SEOP’s main application being in situ beam-polarisation. Several instruments will also use polarising-supermirror devices. To provide wide-bandwidth spin-flipping capability to the time-of-flight instruments, Adiabatic Fast Passage (AFP) neutron spin flippers, also known as gradient-field radiofrequency spin flippers will be the main method of choice. Devices based on the same AFP principle will also be used to flip 3He nuclear spins. We are constructing our first 3He polariser setup, including field coils to produce highly uniform magnetic field. Monte Carlo simulations are being done for the supermirror polarisers. To ensure science-focused development, we are working with university partners in doing scientific experiments with polarised neutrons. These are some of the activities developing polarisation analysis for ESS instruments in our project.
  •  
24.
  • Lerendegui-Marco, J., et al. (författare)
  • New detection systems for an enhanced sensitivity in key stellar (n,γ) measurements
  • 2023
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 279
  • Tidskriftsartikel (refereegranskat)abstract
    • Neutron capture cross-section measurements are fundamental in the study of astrophysical phenomena, such as the slow neutron capture (s-) process of nucleosynthesis operating in red-giant and massive stars. However, neutron capture measurements via the time-of-flight (TOF) technique on key s-process nuclei are often challenging. Difficulties arise from the limited mass (∼mg) available and the high sample-related background in the case of the unstable s-process branching points. Measurements on neutron magic nuclei, that act as s-process bottlenecks, are affected by low (n,γ) cross sections and a dominant neutron scattering background. Overcoming these experimental challenges requires the combination of facilities with high instantaneous flux, such as n_TOFEAR2, with detection systems with an enhanced detection sensitivity and high counting rate capabilities. This contribution reviews some of the latest detector developments in detection systems for (n,γ) measurements at n_TOF, such as i-TED, an innovative detection system which exploits the Compton imaging technique to reduce the dominant neutron scattering background and s-TED, a highly segmented total energy detector intended for high flux facilities. The discussion will be illustrated with results of the first measurement of key the s-process branching-point reaction 79Se(n,γ).
  •  
25.
  • Marcon, Caterina, et al. (författare)
  • Impact of different compilers and build types on Geant4 simulation execution time
  • 2020
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 245, s. 05037-05037
  • Tidskriftsartikel (refereegranskat)abstract
    • Experimental observations and advanced computer simulations in High Energy Physics (HEP) paved the way for the recent discoveries at the Large Hadron Collider (LHC) at CERN. Currently, Monte Carlo simulations account for a very significant amount of computational resources of the Worldwide LHC Computing Grid (WLCG). The current growth in available computing performance will not be enough to fulfill the expected demand for the forthcoming High Luminosity run (HL-LHC). More efficient simulation codes are therefore required.This study focuses on evaluating the impact of different build methods on the simulation execution time. The Geant4 toolkit, the standard simulation code for the LHC experiments, consists of a set of libraries which can be either dynamically or statically linked to the simulation executable. Dynamic libraries are currently the preferred build method.In this work, three versions of the GCC compiler, namely 4.8.5, 6.2.0 and 8.2.0 have been used. In addition, a comparison between four optimization levels (Os, O1, O2 and O3) has also been performed.Static builds for all the GCC versions considered, exhibit a reduction in execution times of about 10%. Switching to newer GCC version results in an average of 30% improvement in the execution time regardless of the build type. In particular, a static build with GCC 8.2.0 leads to an improvement of about 34% with respect to the default configuration (GCC 4.8.5, dynamic, O2). The different GCC optimization flags do not affect the execution times.
  •  
26.
  • Marcon, Caterina, et al. (författare)
  • Studies of GEANT4 performance for different ATLAS detector geometries and code compilation methods
  • 2021
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 251, s. 03005-03005
  • Tidskriftsartikel (refereegranskat)abstract
    • Full detector simulation is known to consume a large proportion of computing resources available to the LHC experiments, and reducing time consumed by simulation will allow for more profound physics studies. There are many avenues to exploit, and in this work we investigate those that do not require changes in the GEANT4 simulation suite. In this study, several factors affecting the full GEANT4 simulation execution time are investigated. A broad range of configurations has been tested to ensure consistency of physical results. The effect of a single dynamic library GEANT4 build type has been investigated and the impact of different primary particles at different energies has been evaluated using GDML and GeoModel geometries. Some configurations have an impact on the physics results and are, therefore, excluded from further analysis. Usage of the single dynamic library is shown to increase execution time and does not represent a viable option for optimization. Lastly, the static build type is confirmed as the most effective method to reduce the simulation execution time.
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27.
  • Massimi, C., et al. (författare)
  • Neutron-induced cross section measurements
  • 2023
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 279
  • Tidskriftsartikel (refereegranskat)abstract
    • Neutron-induced cross sections represent the main nuclear input to models of stellar and Big-Bang nucleosynthesis. While (n,γ) reactions are relevant for the formation of elements heavier than iron, (n,p) and (n,α) reactions can play an important role in specific cases. The time-of-flight method is routinely used at n_TOF to experimentally determine the cross section data. In addition, recent upgrades of the facility will allow the use of activation techniques as well, possibly opening the way to a systematic study of neutron interaction with radioactive isotopes. In the last 20 years n_TOF has provided a large amount of experimental data for Nuclear Astrophysics. Our plan is to carry on challenging measurements and produce nuclear data in the next decades as well.
  •  
28.
  • Mickus, Ignas, et al. (författare)
  • Application of response matrix method to transient simulations of nuclear systems
  • 2020
  • Ingår i: International Conference on Physics of Reactors. - : EDP Sciences. ; , s. 786-793
  • Konferensbidrag (refereegranskat)abstract
    • Until recently, reactor transient problems were exclusively solved by approximate deterministic methods. The increase in available computing power made it feasible to approach the transient analyses with time-dependent Monte Carlo methods. These methods offer the first-principle solution to the space-time evolution of reactor power by explicitly tracking prompt neutrons, precursors of delayed neutrons and delayed neutrons in time and space. Nevertheless, a very significant computing cost is associated with such methods. The general benefits of the Monte Carlo approach may be retained at a reduced computing cost by applying a hybrid stochastic-deterministic computing scheme. Among such schemes are those based on the fission matrix and the response matrix formalisms. These schemes aim at estimating a variant of the Greens function during a Monte Carlo transport calculation, which is later used to formulate a deterministic approach to solving a space-time dependent problem. In this contribution, we provide an overview of the time-dependent response matrix method, which describes a system by a set of response functions. We have recently suggested an approach where the functions are determined during a Monte Carlo criticality calculation and are then used to deterministically solve the space-time behaviour of the system. Here, we compare the time-dependent response matrix solution with the transient fission matrix and the time-dependent Monte Carlo solutions for a control rod movement problem in a mini-core reactor geometry. The response matrix formalism results in a set of loosely connected equations which offers favourable scaling properties compared to the methods based on the fission matrix formalism.
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29.
  • Moldarev, Dmitrii, et al. (författare)
  • Oxygen mobility in yttrium hydride films studied by isotopic labelling
  • 2022
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 261, s. 01001-01001
  • Tidskriftsartikel (refereegranskat)abstract
    • The photochromic properties of oxygen-containing yttrium hydride thin films are directly dependent on the oxygen concentration in the material. We use 16O/18O labelling to study oxidation of YH2 films. Oxygen penetrates the film through grain boundaries and intercolumnar voids oxidising the whole film thickness, without pronounced surface oxidation or self-passivation. Once oxidised, the mobility of oxygen in the films is low and no detectable changes in chemical composition of 18O-labeled YHO films is found under illumination.
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30.
  • Mylonakis, Antonios, 1987, et al. (författare)
  • CORE SIM+ simulations of COLIBRI fuel rods oscillation experiments and comparison with measurements
  • 2020
  • Ingår i: International Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020. - : EDP Sciences. ; 2020-March, s. 2930-2938
  • Konferensbidrag (refereegranskat)abstract
    • At EPFL, the CROCUS reactor has been used to carry out experiments with vibrating fuel rods. The paper presents a first attempt to employ the measured data to validate CORE SIM+, a neutron noise solver developed at Chalmers University of Technology. For this purpose, the original experimental data are processed in order to extract the necessary information. In particular, detector recordings are scrutinized and detrended, and used to estimate CPSDs of detector pairs. These values are then compared with the ones derived from the CORE SIM+ simulations of the experiments. The main trend of the experimental data along with the values for some detectors are successfully reproduced by CORE SIM+. Further work is necessary on both the experimental and computational sides in order to improve the validation process.
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31.
  • Pazsit, Imre, 1948, et al. (författare)
  • Reconstructing the axial void velocity profile in BWRS from measurements of the in-core neutron noise
  • 2020
  • Ingår i: International Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020. - : EDP Sciences. ; 2020-March, s. 211-218
  • Konferensbidrag (refereegranskat)abstract
    • The problem of determining the axial velocity profile from the in-core neutron noise measurements is revisited, with the purpose of developing an objective method for the determination of the void fraction. Until now it was assumed that in order to determine a realistic velocity profile which shows an inflection point and hence has to be at least a third order polynomial, one needs four transit times and hence five in-core detectors at various axial elevations. However, attempts to determine a fourth transit time by adding a TIP detector to the existing four LPRMs and cross-correlate it with any of the LPRMs were unsuccessful so far. In this paper we thus propose another approach, where the TIP detector is only used for the determination of the axial position of the onset of boiling. By this approach it is sufficient to use only three transit times. Moreover, with another parametrisation of the velocity profile, it is possible to reconstruct the velocity profile even without knowing the onset point of boiling, in which case the TIP is not needed. In the paper the principles are explained and the strategy is demonstrated by concrete examples.
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32.
  • Pedersen, Maiken, et al. (författare)
  • Nordugrid ARC Datastaging and Cache Efficiency gains on HPC and cloud resources
  • 2020
  • Ingår i: 24<sup>th</sup> International Conference on Computing in High Energy and Nuclear Physics (CHEP 2019). - : EDP Sciences. ; 245
  • Konferensbidrag (refereegranskat)abstract
    • The Worldwide LHC Computing Grid (WLCG) is today comprised of a range of different types of resources such as cloud centers, large and small HPC centers, volunteer computing as well as the traditional grid resources. The Nordic Tier 1 (NT1) is a WLCG computing infrastructure distributed over the Nordic countries. The NT1 deploys the Nordugrid ARC-CE, which is non-intrusive and lightweight, originally developed to cater for HPC centers where no middleware could be installed on the worker nodes. The NT1 runs ARC in the native Nordugrid mode which contrary to the Pilot mode leaves jobs data transfers up to ARC. ARCs data transfer capabilities together with the ARC Cache are the most important features of ARC. In this article we will describe the datastaging and cache functionality of the ARC-CE set up as an edge service to an HPC or cloud resource, and show the gain in efficiency this model provides compared to a traditional pilot model, especially for sites with remote storage.
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33.
  • Reichert, Manuel, et al. (författare)
  • Gravitational Waves from dark composite dynamics
  • 2022
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X.
  • Konferensbidrag (refereegranskat)abstract
    • We discuss the stochastic gravitational-wave spectrum from dark confinement and chiral phase transitions in the early Universe. Specifically, we look at pure Yang-Mills theory for an arbitrary number of colours as well as SU(3) with quarks in different representations. We utilise thermodynamic Lattice data and map it to effective models, such as the Polyakov-loop and the PNJL model. This allows us to compute gravitational-wave parameters and the corresponding gravitational-wave signal. We compare the signal to future gravitational-wave observatories such as the Big Bang Observer and DECIGO.
  •  
34.
  • Rodriguez-Sancheza, J. L., et al. (författare)
  • Comprehensive investigation of fission yields by using spallation- and (p,2p)induced fission reactions in inverse kinematics
  • 2023
  • Ingår i: 15TH INTERNATIONAL CONFERENCE ON NUCLEAR DATA FOR SCIENCE AND TECHNOLOGY, ND2022. - 2100-014X. ; 284
  • Konferensbidrag (refereegranskat)abstract
    • In the last decades, measurements of spallation, fragmentation and Coulex induced fission reactions in inverse kinematics have provided valuable data to accurately investigate the fission dynamics and nuclear structure at large deformations of a large variety of stable and non -stable heavy nuclei. To go a step further, we propose now to induce fission by the use of quasi -free (p,2p) scattering reactions in inverse kinematics, which allows us to reconstruct the excitation energy of the compound fissioning system by using the four-momenta of the two outgoing protons. Therefore, this new approach might permit to correlate the excitation energy with the charge and mass distributions of the fission fragments and with the fission probabilities, given for the first time direct access to the simultaneous measurement of the fission yield dependence on temperature and fission barrier heights of exotic heavy nuclei, respectively. The first experiment based on this methodology was realized recently at the GM/FAIR facility and a detailed description of the experimental setup is given here.
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35.
  • Sanchez-Espinoza, V. H., et al. (författare)
  • The McSAFE project - High-performance Monte Carlo based methods for safety demonstration : From proof of concept to industry applications
  • 2020
  • Ingår i: International Conference on Physics of Reactors. - : EDP Sciences. ; , s. 943-950
  • Konferensbidrag (refereegranskat)abstract
    • The increasing use of Monte Carlo methods for core analysis is fostered by the huge and cheap computer power available nowadays e.g. in large HPC. Apart from the classical criticality calculations, the application of Monte Carlo methods for depletion analysis and cross section generation for diffusion and transport core simulators is also expanding. In addition, the development of multi-physics codes by coupling Monte Carlo solvers with thermal hydraulic codes (CFD, subchannel and system thermal hydraulics) to perform full core static core analysis at fuel assembly or pin level has progressed in the last decades. Finally, the extensions of the Monte Carlo codes to describe the behavior of prompt and delay neutrons, control rod movements, etc. has been started some years ago. Recent coupling of dynamic versions of Monte Carlo codes with subchannel codes make possible the analysis of transient e.g. rod ejection accidents and it paves the way for the simulation of any kind of design basis accidents as an alternative option to the use of diffusion and transport based deterministic solvers. The H2020 McSAFE Project is focused on the improvement of methods for depletion considering thermal hydraulic feedbacks, extension of the coupled neutronic/thermal hydraulic codes by the incorporation of a fuel performance solver, the development of dynamic Monte Carlo codes and the development of methods to handle large depletion problems and to reduce the statistical uncertainty. The validation of the multi-physics tools developed within McSAFE will be performed using plant data and unique tests e.g. the SPERT III E REA test. This paper will describe the main developments, solution approaches, and selected results.
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36.
  • Schroeder, Frank G., et al. (författare)
  • The Snowmass UHECR White Paper on Ultra-High-Energy Cosmic Rays
  • 2023
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 283
  • Tidskriftsartikel (refereegranskat)abstract
    • This proceeding summarizes the talk given at the opening of the UHECR 2022 conference in L'Aquila on the whitepaper 'Ultra-High-Energy Cosmic Rays: The Intersection of the Cosmic and Energy Frontiers' [Astroparticle Physics 149 (2023) 102819 - arXiv:2205.05845] that has been prepared for the Snow-mass survey in the USA. The whitepaper provides an overview of recent progress and open questions regarding the particle physics and astrophysics related to ultra-high-energy cosmic rays (UHECR) and outlines the connections between the particle and astrophysics aspects of cosmic rays. It also discusses what instrumentation is needed to address the major scientific questions in ultra-high-energy cosmic-ray physics. While the upgraded Pierre Auger Observatory and Telescope Array will remain the workhorses at the highest energies in the current decade, new experiments with significantly higher exposure are needed in the coming decade. Ground arrays featuring simultaneous detection of the position of the shower maximum and the size of the muonic component will enable particle astronomy by measuring the rigidity of individual events. They should be complemented by other detectors maximizing the total exposure. This can be achieved by a few next-generation experiments using the latest developments in detection and analysis techniques: GRAND as a ground-based radio array, and POEMMA as a space-borne stereo fluorescence telescope will feature complementary approaches to provide maximum exposure; IceCube-Gen2 with its surface array, and GCOS aim at increased statistics with high accuracy for particle physics and rigidity-based galactic and extra-galactic astrophysics. While designed to discover the astrophysical cosmic-ray sources at the highest energies, the same experiments also contribute to particle physics, e.g., by studying the muon puzzle in cosmic-ray air showers, and by their discovery potential for exciting new physics, such as certain Dark Matter candidates. With the full whitepaper available as a reference, this proceeding will briefly present the science cases of the experiments, highlighting their individual strengths and outlining how they complement each other.
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37.
  • Sguazzin, M., et al. (författare)
  • Indirect measurements of neutron -induced reaction cross sections at heavy -ion storage rings
  • 2023
  • Ingår i: 15TH INTERNATIONAL CONFERENCE ON NUCLEAR DATA FOR SCIENCE AND TECHNOLOGY, ND2022. - 2100-014X. ; 284
  • Konferensbidrag (refereegranskat)abstract
    • Neutron-induced reaction cross sections of unstable nuclei are essential for understanding the synthesis of heavy elements in stars and for applications in nuclear technology. However, their measurement is very complicated due to the radioactivity of the targets involved. We propose to circumvent this problem by using the surrogate reaction method in inverse kinematics, where the nucleus formed in the neutroninduced reaction of interest is produced by a reaction involving a radioactive heavy -ion beam and a stable, light target nucleus. The probabilities as a function of the compound -nucleus excitation energy for y -ray emission, neutron emission and fission, which can be measured with the surrogate reaction, are particularly useful to constrain model parameters and to obtain more accurate predictions of the neutron-induced reaction cross sections of interest. Yet, the full development of the surrogate method is hampered by numerous longstanding target issues, which can be solved by combining surrogate reactions with the unique and largely unexplored possibilities at heavy -ion storage rings. In this contribution, we describe the developments we are carrying out to measure for the first time simultaneously y-ray emission, neutron emission and fission probabilities at the storage rings of the GSI/FAIR facility. In particular, we will present the first results of the proof of principle experiment, which we performed in June 2022 at the Experimental Storage Ring (ESR)
  •  
38.
  • Sguazzin, M., et al. (författare)
  • Indirect measurements of neutron-induced reaction cross sections at storage rings
  • 2023
  • Ingår i: NUCLEAR PHYSICS IN ASTROPHYSICS - X, NPA-X 2022. - : EDP Sciences. - 2100-014X. ; 279
  • Konferensbidrag (refereegranskat)abstract
    • Neutron-induced reaction cross sections of unstable nuclei are essential for understanding the synthesis of heavy elements in stars. However, their measurement is very difficult due to the radioactivity of the targets involved. We propose to circumvent this problem by using for the first time the surrogate reaction method in inverse kinematics at heavy-ion storage rings. In this contribution, we describe the developments we have done to perform surrogate-reaction studies at the storage rings of GSI/FAIR. In particular, we present the first results of the proof of principle experiment, which we conducted recently at the Experimental Storage Ring (ESR).
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39.
  • Stellhorn, Annika, et al. (författare)
  • Neutron adiabaticity and its impact on data analysis, illustrated for polarized GISANS
  • 2023
  • Ingår i: EPJ Web of Conferences. - 2100-014X. ; 286
  • Tidskriftsartikel (refereegranskat)abstract
    • The significance of neutron spin adiabaticity in the data analysis of polarized Grazing Incidence Small Angle Neutron Scattering (GISANS) is discussed, with the aim of minimizing the number of simulation parameters of complex magnetic models within the neutron scattering cross-section. We illustrate how an estimate of the neutron polarization direction and adiabaticity can be obtained by magnetic field and neutron ray-tracing simulations and compare the results with measurements of the magnetic field map for the beamline used in the GISANS experiment. We show how small deviations from the neutron polarization direction with respect to the magnetic field vector at the sample position significantly affect the data analysis, and how this can be considered within the magnetic model of the scattering cross section using the Distorted Wave Born Approximation.
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40.
  • Sunneborn Gudnadottir, Olga, et al. (författare)
  • Distributed training and scalability for the particle clustering method UCluster
  • 2021
  • Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 251, s. 02054-02054
  • Tidskriftsartikel (refereegranskat)abstract
    • In recent years, machine-learning methods have become increasingly important for the experiments at the Large Hadron Collider (LHC). They are utilised in everything from trigger systems to reconstruction and data analysis. The recent UCluster method is a general model providing unsupervised clustering of particle physics data, that can be easily modified to provide solutions for a variety of different decision problems. In the current paper, we improve on the UCluster method by adding the option of training the model in a scalable and distributed fashion, and thereby extending its utility to learn from arbitrarily large data sets. UCluster combines a graph-based neural network called ABCnet with a clustering step, using a combined loss function in the training phase. The original code is publicly available in TensorFlow v1.14 and has previously been trained on a single GPU. It shows a clustering accuracy of 81% when applied to the problem of multi-class classification of simulated jet events. Our implementation adds the distributed training functionality by utilising the Horovod distributed training framework, which necessitated a migration of the code to TensorFlow v2. Together with using parquet files for splitting data up between different compute nodes, the distributed training makes the model scalable to any amount of input data, something that will be essential for use with real LHC data sets. We find that the model is well suited for distributed training, with the training time decreasing in direct relation to the number of GPU’s used. However, further improvements by a more exhaustive and possibly distributed hyper-parameter search is required in order to achieve the reported accuracy of the original UCluster method.
  •  
41.
  • Vidal-Ferràndiz, Antoni, et al. (författare)
  • A finite element method for neutron noise analysis in hexagonal reactors
  • 2020
  • Ingår i: International Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020. - : EDP Sciences. ; 2020-March, s. 2939-2946
  • Konferensbidrag (refereegranskat)abstract
    • The early detection of anomalies through the analysis of the neutron noise recorded by in-core and ex-core instrumentation gives the possibility to take proper actions before such problems lead to safety concerns or impact plant availability. The study of the neutron fluctuations permits to detect and differentiate anomalies depending on their type and possibly to characterize and localize such anomalies. This method is non-intrusive and does not require any external perturbation of the system. To effectively use the neutron noise for reactor diagnostics it is essential to accurately model the effects of the anomalies on the neutron field. This paper deals with the development and validation of a neutron noise simulator for reactors with different geometries. The neutron noise is obtained by solving the frequency-domain two-group neutron diffusion equation in the first order approximation. In order to solve this partial differential equation a code based on a high order finite element method is developed. The novelty of this simulator resides on the possibility of dealing with rectangular meshes in any kind of geometry, thus allowing for complex domains and any location of the perturbation. The finite element method also permits automatic refinements in the cell size (h-adaptability) and in its polynomial degree (p-adaptability) that lead to a fast convergence. In order to show the possibilities of the neutron noise simulator developed a perturbation in a hexagonal two-dimensional reactor is investigated in this paper.
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42.
  • Yi, Huaiqian, 1993, et al. (författare)
  • Acceleration of a 2-dimensional, 2-energy group neutron noise solver based on a discrete ordinates method in the frequency domain
  • 2020
  • Ingår i: International Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020. - : EDP Sciences. ; 2020-March, s. 2922-2929
  • Konferensbidrag (refereegranskat)abstract
    • The acceleration of the convergence rate is studied for a neutron transport solver to simulate 2-D, 2-energy-group neutron noise problems in the frequency domain. The Coarse Mesh Finite Difference (CMFD) method is compared to the Diffusion Synthetic Acceleration (DSA) method. Numerical tests are performed using heterogeneous system configurations with different boundary conditions. The CMFD scheme leads to a better convergence rate. The results also show that CMFD can accelerate neutron noise problems in a wide range of perturbation frequencies with almost equal efficiency. An unstable convergence behavior is nevertheless observed in problems with purely reflective boundary conditions. Stabilization techniques such as performing multiple transport sweeps, underrelaxing the flux update, and using the lpCMFD method are investigated and improvements can be obtained.
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