| 1. |
- Al-Adili, Ali, et al.
(författare)
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Neutron-multiplicity experiments for enhanced fission modelling
- 2017
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 9782759890200
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Konferensbidrag (refereegranskat)abstract
- The nuclear de-excitation process of fission fragments (FF) provides fundamental information for the understanding of nuclear fission and nuclear structure in neutron-rich isotopes. The variation of the prompt-neutron multiplicity, ν(A), as a function of the incident neutron energy (En) is one of many open questions. It leads to significantly different treatments in various fission models and implies that experimental data are analyzed based on contradicting assumptions. One critical question is whether the additional excitation energy (Eexc) is manifested through an increase of ν(A) for all fragments or for the heavy ones only. A systematic investigation of ν(A) as a function of En has been initiated. Correlations between prompt-fission neutrons and fission fragments are obtained by using liquid scintillators in conjunction with a Frisch-grid ionization chamber. The proof-of-principle has been achieved on the reaction 235U(nth,f) at the Van De Graff (VdG) accelerator of the JRC-Geel using a fully digital data acquisition system. Neutrons from 252Cf(sf) were measured separately to quantify the neutron-scattering component due to surrounding shielding material and to determine the intrinsic detector efficiency. Prelimenary results on ν(A) and spectrum in correlation with FF properties are presented.
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| 2. |
- Al-Adili, Ali, et al.
(författare)
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Prompt fission neutron yields in thermal fission of U-235 and spontaneous fission of Cf-252
- 2020
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Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 102:6
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Tidskriftsartikel (refereegranskat)abstract
- Background: The sharing of excitation energy between the fission fragments is one of the key issues in studying nuclear fission. One way to address this is by studying prompt-fission neutron multiplicities as a function of other fission observables such as the mass, (nu) over bar (A). These are vital benchmark data for both fission and nuclear deexcitation models, putting constrains on the fragment excitation energy and hence on the competing prompt neutron/gamma-ray emission. Despite numerous detailed studies, recent measurements done at JRC-Geel with the SCINTIA array in the epithermal region show surprisingly strong discrepancies to earlier thermal fission data and the Wahl systematics. Purpose: The purpose was to perform measurements of the prompt-fission neutron multiplicity, as a function of fragment mass and total kinetic energy (TKE), in U-235(n(th), f) and Cf-252(sf), to verify and extend the SCINTIA results. Another goal was to validate the analysis methods, and prepare for planned investigations at excitation energies up to 5.5 MeV. Methods: The experiments were conducted at the former 7 MV Van de Graaff facility in JRC-Geel, using a Twin Frisch-Grid Ionization Chamber and two liquid scintillation detectors. A neutron beam with an average energy of 0.5 MeV was produced via the Li-7(p,n) reaction. The neutrons were thermalized by a 12 cm thick block of paraffin. Digital data acquisition systems were utilized. Comprehensive simulations were performed to verify the methodology and to investigate the role of the mass and energy resolution on measured (nu) over bar (A) and (nu) over bar (TKE) values. The simulation results also revealed that the partial derivative(nu) over bar/partial derivative A and partial derivative(TKE) over bar/partial derivative(nu) over bar are affected by the mass and energy resolution. However, the effect is small for the estimated resolutions of this work. Detailed Fluka simulations were performed to calculate the fraction of thermal neutron-induced fission, which was estimated to be about 98%. Results: The experimental results on (nu) over bar (A) are in good agreement with earlier data for Cf-252(sf). For U-235(n(th), f), the (nu) over bar (A) data is very similar to the data obtained with SCINTIA, and therefore we verify these disclosed discrepancies to earlier thermal data and to the Wahl evaluation. The experimental results on (nu) over bar (TKE) are also in agreement with the data at epithermal energies. For Cf-252(sf) a slope value of partial derivative(TKE) over bar/partial derivative(nu) over bar = (-12.9 f 0.2) MeV/n was obtained. For U-235(n(th), f) the value is (-12.0 +/- 0.1) MeV/n. Finally, the neutron spectrum in the center-of-mass system was derived and plotted as a function of fragment mass. Conclusions: This work clearly proves the lack of accurate correlation between fission fragment and neutron data even in the best-studied reactions. The new results highlight the need of a new evaluation of the prompt-fission multiplicity for U-225(n(th), f).
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| 3. |
- Andersson, Peter, 1981-, et al.
(författare)
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Coincidence spectroscopy for increased sensitivity in radionuclide monitoring
- 2022
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The majority of the energy in a nuclear explosion is released in the immediate blast and the initial radiation accounts. The remaining fraction is released through radioactive decay of the explosion's fission products and neutron activation products over a longer time span. This allows for the detection of a nuclear explosion by detecting the presence of residual decay. Radionuclide monitoring stations for detection of radioactive emissions to the atmosphere is thereby an important tool in the verification of compliance with nuclear disarmament treaties. In particular, the globally spanning radionuclide station network of the International Monitoring System (IMS) has been implemented for verification of the Comprehensive Nuclear-Test-Ban Treaty.High Purity Germanium (HPGe) detectors are workhorses in radionuclide monitoring. The detection of characteristic gamma rays can be used to disclose the presence of signature nuclides produced innuclear weapon tests. A particular development that has potential to improve the sensitivity of radionuclide monitoring is the coincidence technique where decaying nuclides that emit several coincident gamma rays can be detected at much smaller activity concentrations than with conventional gamma spectroscopy.In this project, dedicated gamma-gamma coincidence detectors are being developed, utilizing electronically segmented HPGe detectors. These detectors are expected to be highly sensitive to low-activity samples of nuclides that present coincident emissions of gamma rays. In this paper we present the concept, define performance parameters, and explore the performance of such detectors to a subset of radionuclides of particular CTBT relevance. In addition, we discuss the path forward in developing a next generation gamma-gamma coincidence spectroscopy system of segmented HPGe.
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| 4. |
- Cannarozzo, Simone, et al.
(författare)
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Global comparison between experimentally measured isomeric yield ratios and nuclear model calculations
- 2023
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Ingår i: European Physical Journal A. - : Springer. - 1434-6001 .- 1434-601X. ; 59:12
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Tidskriftsartikel (refereegranskat)abstract
- The level density steers transition probabilities between different states in the decay and de-excitation of excited nuclei. Reliable level density modelling is, therefore, key in describing, e.g., de-excitation of fission fragments, with implications on neutron and gamma-rays multiplicities, and also manifested in the population of isomeric states. We test six currently used level density models and the spin distribution in the level density by comparing calculations with measured isomeric yield ratios. The model calculations are performed with the TALYS code and experimental data for nuclear reactions populating spin isomers are retrieved from the EXFOR database. On average, calculations are in agreement with measured data. However, we find that the population of the high-spin state in an isomeric pair is clearly favoured in all of the six studied level density models. Further studies are then performed on the three used phenomenological level density models, to investigate the significance of their effect. We find that a significant reduction of the spin width distribution improves the agreement between calculated and experimentally observed isomeric yield ratios. This result is independent of the incident particle in the nuclear reaction. The needed reduction of the spin width distribution to comply with empirical data has, e.g., implications for studies in angular momentum generation in fission using isomeric yield rations, calculations of anti-neutrino spectra from nuclear reactors, as well as neutron and gamma-ray multiplicities in nuclear reactor calculations.
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| 5. |
- Gomez L, Ana Maria, 1993-, et al.
(författare)
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Determination of the Plasma Delay Time in PIPS detectors for fission fragments at the LOHENGRIN spectrometer
- 2023
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Ingår i: 15<sup>th</sup> International Conference on Nuclear Data for Science and Technology (ND2022). - : EDP Sciences.
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Konferensbidrag (refereegranskat)abstract
- The VElocity foR Direct particle Identification spectrometer (VERDI) is a 2E-2v fission spectrometer that allows the measurement of the total mass distribution of secondary fission fragments with a resolving power of 1-2 u. It consists of two time-of-flight (ToF) arms, with one Micro Channel Plate (MCP) detector and up to 32 Silicon PIPS (Passive Implanted Planar Silicon) detectors per arm. The MCPs provide the start timing signals and the PIPS detectors provide both the energy and the stopping ToF signals. In real conditions, the PIPS signals are affected by the formation of plasma from the interaction between the heavy ions and the detector material. The plasma contributes to a reduction in signal amplitude, resulting in a Pulse Height Defect (PHD), and introduces a signal delay, known as Plasma Delay Time (PDT). An experiment to characterize the PDT and PHD was performed at the LOHENGRIN recoil separator of the Institut Laue Langevin (ILL). Characteristic fission fragments from the 239Pu(n,f) reaction were separated based on their A/Q and E/Q ratios, allowing the measurement of a wide range of energies from 21 to 110 MeV and masses between 80 and 149 u. Six PIPS detectors were characterized to study their individual responses to the PDT and PHD effects. The signals were recorded in a digital acquisition system to completely exploit the offline analysis capabilities. Achieved combined timing and energy resolutions for fission fragments varied between 72(2) ps and 100(4) ps and 1.4% - 2% (FWHM), respectively. Preliminary PHD and PDT data are presented from the masses A=85, 95, 130 and 143. The PHD trends are strongly correlated with both the ion energy and mass. The PDT, on the other hand, shows a strong variation as a function of the ion kinetic energy but a smaller dependence on the ion mass.
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| 6. |
- Grape, Sophie, 1982-, et al.
(författare)
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State-of-the-Art Report : Prepared by Working Group 4: Technical nuclear non-proliferation and safeguards under the Alva Myrdal Centre for nuclear disarmament
- 2022
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The Alva Myrdal Centre for nuclear disarmament (AMC) was established in 2021. AMC consists of six working Groups, and one of them - Working Group 4 - is called Technical nuclear non-proliferation and safeguards. This is the State-of-the-Art Report of that working group. The objective with the report is to provide an overview of the technical fields relevant to the working group and to highlight where research and activities within the working group may contribute to global nuclear disarmament. The report gives a brief explanation of actors in the field, introduces nuclear materials and assay techniques, and then continues to elaborate on challenges and needs associated with nuclear measurements and assessments in the fields of non-proliferation, nuclear safeguards and nuclear disarmament. A section is also devoted to the management of nuclear weapons materials after disarmament. Lastly, the report contains a section on interdisciplinary research and development in nuclear disarmament, and information about technical education and training in the non-proliferation and disarmament field.
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| 7. |
- Göök, Alf, et al.
(författare)
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A position-sensitive twin ionization chamber for fission fragment and prompt neutron correlation experiments
- 2016
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier B.V.. - 0168-9002 .- 1872-9576. ; 830, s. 366-374
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Tidskriftsartikel (refereegranskat)abstract
- A twin position-sensitive Frisch grid ionization chamber, intended as a fission fragment detector in experiments to study prompt fission neutron correlations with fission fragment properties, is presented. Fission fragment mass and energies are determined by means of the double kinetic energy technique, based on conservation of mass and linear momentum. The position sensitivity is achieved by replacing each anode plate in the standard twin ionization chamber by a wire plane and a strip anode, both readout by means of resistive charge division. This provides information about the fission axis orientation, which is necessary to reconstruct the neutron emission process in the fully accelerated fragment rest-frame. The energy resolution compared to the standard twin ionization chamber is found not to be affected by the modification. The angular resolution of the detector relative to an arbitrarily oriented axis is better than 7° FWHM. Results on prompt fission neutron angular distributions in 235U(n,f) obtained with the detector in combination with an array of neutron scintillation detectors is presented as a proof of principle.
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| 8. |
- Göök, Alf, et al.
(författare)
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Neutron Multiplicity Correlations with Fission Fragment Mass and Energy from Pu-239(n,f)
- 2020
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Ingår i: ND 2019. - : EDP Sciences.
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Konferensbidrag (refereegranskat)abstract
- There exists experimental evidence for strong fluctuations of the average neutron multiplicity from resonance to resonance in Pu-239(n,f). These fluctuations have been shown to impact nuclear reactor benchmarks by reducing the criticality. The fluctuating neutron multiplicity can be explained as a consequence of the competition between direct fission and the (n,gamma f) process. However, there is also evidence for fluctuations of the fission fragment mass yields from resonance to resonance. The mass yield fluctuations may also contribute to fluctuations of the neutron multiplicity averaged over all fission fragment masses. In order to model the contribution to the neutron multiplicity fluctuations by the fission fragment mass yield fluctuations new data on the correlations between fission fragment properties and neutron multiplicities are in need. We present experiments carried out to determine prompt neutron multiplicity correlations with fission fragment masses and total kinetic energies in the reaction Pu-239(n,f). The experiment has been performed at the GELINA facility at JRC-Geel. A twin position-sensitive Frisch-grid ionization chamber is used for fission fragment identification via the double kinetic energy technique. An array of scintillation detectors is employed for neutron counting. Correlations between average neutron multiplicities and fission fragment properties have been measured with improved resolution in both mass and TKE, compared to data from the literature.
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| 9. |
- Hambsch, Franz-Josef, et al.
(författare)
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Prompt fission neutron emission from 235U(n,f): thermal and resonance region
- 2015
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Ingår i: Conference: 14th International Conference on Nuclear Reaction Mechanisms - CERN-Proceedings-2015-001, At Villa Monastero, Varenna, Italy. - 9789290834182
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Konferensbidrag (refereegranskat)abstract
- For nuclear modelling and improved evaluation of nuclear data, knowledge of fluctuations of the prompt neutron multiplicity as a function of incident neutron energy is requested for the major actinides 235U and 239Pu. Experimental investigations of the prompt fission neutron emission in resonance-neutron induced fission on 235U are taking place at the GELINA facility of the IRMM. The experiment employs an array of scintillation detectors (SCINTIA) in conjunction with a newly designed 3D position-sensitive twin Frisch-grid ionization chamber. In addition, the mass-dependent prompt neutron multiplicity, (A), has attracted particular attention. Recent, sophisticated nuclear fission models predict that the additional excitation energy, brought into the fission system at higher incident neutron energies, leads to an increased neutron multiplicity only for heavy fragments, as observed in the 237Np(n,f) reaction. A first feasibility study has been performed at the JRC-IRMM VdG accelerator to measure nu(A) for 235U(n,f).
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| 10. |
- Jansson, Kaj, 1987-, et al.
(författare)
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The new double energy-velocity spectrometer VERDI
- 2017
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Ingår i: ND 2016: INTERNATIONAL CONFERENCE ON NUCLEAR DATA FOR SCIENCE AND TECHNOLOGY. - Les Ulis : EDP Sciences. - 9782759890200
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Konferensbidrag (refereegranskat)abstract
- VERDI (VElocity foR Direct particle Identification) is a fission-fragment spectrometer recently put into operation at JRC-Geel. It allows measuring the kinetic energy and velocity of both fission fragments simultaneously. The velocity provides information about the pre-neutron mass of each fission fragment when isotropic prompt-neutron emission from the fragments is assumed. The kinetic energy, in combination with the velocity, provides the post-neutron mass. From the difference between pre- and post-neutron masses, the number of neutrons emitted by each fragment can be determined. Multiplicity as a function of fragment mass and total kinetic energy is one important ingredient, essential for understanding the sharing of excitation energy between fission fragments at scission, and may be used to benchmark nuclear de-excitation models. The VERDI spectrometer design is a compromise between geometrical efficiency and mass resolution. The spectrometer consists of an electron detector located close to the target and two arrays of silicon detectors, each located 50 cm away from the target. In the present configuration pre-neutron and post-neutron mass distributions are in good agreement with reference data were obtained. Our latest measurements performed with spontaneously fissioning 252Cf is presented along with the developed calibration procedure to obtain pulse height defect and plasma delay time corrections.
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| 11. |
- Litaize, Olivier, et al.
(författare)
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New results in the modeling of fission and radiative neutron capture with FIFRELIN
- 2023
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Ingår i: 15TH INTERNATIONAL CONFERENCE ON NUCLEAR DATA FOR SCIENCE AND TECHNOLOGY, ND2022. - : EDP Sciences.
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Konferensbidrag (refereegranskat)abstract
- The FIFRELIN Monte Carlo code has been upgraded recently by adding new capabilities, additional models and updated databases. Several examples are presented in this work as well as three different applications related to the prompt component in fission, gamma cascades from thermal neutron capture and the delayed component in fission associated to the time evolution of decay heat.
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| 12. |
- Oberstedt, A., et al.
(författare)
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Time response and its impact on prompt fission gamma-ray spectra characteristics
- 2020
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Ingår i: European Physical Journal A. - : Springer Nature. - 1434-6001 .- 1434-601X. ; 56:7
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Tidskriftsartikel (refereegranskat)abstract
- The time dependence of prompt gamma-ray spectral characteristics, in particular themultiplicity, was studied during the first 10 ns after the spontaneous fission of Cf-252. The impact of prompt window and experimental time resolution on the determination of prompt multiplicities is assessed and described mathematically. As a consequence we are able to offer corrections that allow a reliable comparison of results from different measurements. An apparent discrepancy between a theoretical and an experimentally found time dependence is explained by the influence of a finite experimental timing resolution as well as the choice of the prompt timing window.
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| 13. |
- Oberstedt, S., et al.
(författare)
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Prompt fission γ -ray spectrum characteristics from Pu 240 (sf) and Pu 242 (sf)
- 2016
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Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 93:5
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present first results for prompt fission γ-ray spectra (PFGS) characteristics from the spontaneous fission (sf) of Pu240 and Pu242. For Pu242(sf) we obtained, after proper unfolding of the detector response, an average energy per photon ϵγ=(0.843±0.012) MeV, an average multiplicity Mγ=(6.72±0.07), and an average total γ-ray energy release per fission Ēγ,tot = (5.66 ± 0.06) MeV. The Pu240(sf) emission spectrum was obtained by applying a so-called detector-response transformation function determined from the Pu242 spectrum measured in exactly the same geometry. The results are an average energy per photon ϵγ=(0.80±0.07) MeV, the average multiplicity Mγ = (8.2 ± 0.4), and an average total γ-ray energy release per fission Ēγ,tot = (6.6 ± 0.5) MeV. The PFGS characteristics for Pu242(sf) are in very good agreement with those from thermal-neutron-induced fission on Pu241 and scales well with the corresponding prompt neutron multiplicity. Our results in the case of Pu240(sf), although drawn from a limited number of events, show a significantly enhanced average multiplicity and average total energy, but may be understood from a different fragment yield distribution in Pu240(sf) compared to that of Pu242(sf).
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| 14. |
- Peck, M., et al.
(författare)
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Pulse-height defect of Ar+CF4 mixtures as a counting gas for fission-fragment detectors
- 2019
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier B.V.. - 0168-9002 .- 1872-9576. ; 919, s. 105-112
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Tidskriftsartikel (refereegranskat)abstract
- For the detection of energetic charged particles, gaseous ionization detectors use a variety of counting gases. We studied the properties of non-flammable, high stopping-power Ar+CF4 as counting gas. We assess the usability of different mixtures for compact, high-luminosity fast ionization chambers for future applications in nuclear photonics. The pulse-height defect (PHD) of Ar+CF4 mixtures at different pressures has been extracted in comparison to P-10 gas (90%Ar+10%CH4) for fragments from 252Cf spontaneous fission in a twin Frisch-grid ionization chamber. For the different mixtures of Ar+CF4 (P-10), a PHD of 4.5–11MeV (4MeV) and 6–12MeV (5.5MeV) for light and heavy fragments, respectively, have been measured. Based on these findings, reconstructed 252Cf mass and total kinetic energy distributions are consistent with literature, which demonstrates success in the PHD correction procedure.
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| 15. |
- Petrovic, Jana, et al.
(författare)
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Rapid imaging of special nuclear materials for nuclear nonproliferation and terrorism prevention
- 2021
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 7:21
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Tidskriftsartikel (refereegranskat)abstract
- We introduce a neutron-gamma emission tomography (NGET) technique for rapid detection, three-dimensional imaging, and characterization of special nuclear materials like weapons-grade plutonium and uranium. The technique is adapted from fundamental nuclear physics research and represents a previously unexplored approach to the detection and imaging of small quantities of these materials. The method is demonstrated on a radiation portal monitor prototype system based on fast organic scintillators, measuring the characteristic fast time and energy correlations between particles emitted in nuclear fission processes. The use of these correlations in real time in conjunction with modern machine learning techniques provides unprecedented imaging efficiency and high spatial resolution. This imaging modality addresses global security threats from terrorism and the proliferation of nuclear weapons. It also provides enhanced capabilities for addressing different nuclear accident scenarios and for environmental radiological surveying.
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| 16. |
- Piau, V., et al.
(författare)
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Neutron and gamma multiplicities calculated in the consistent framework of the Hauser-Feshbach Monte Carlo code FIFRELIN
- 2023
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Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 837
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Tidskriftsartikel (refereegranskat)abstract
- Monte-Carlo simulations to calculate the number of prompt particles emitted during fission were performed using the FIFRELIN code and compared to recent experimental data. We show that we are able to reproduce both the neutron and gamma-ray multiplicity distributions as a function of the pre-neutron mass of the fission fragments using a single consistent set of parameters. This result was made possible by using an energy-dependent spin cut-off model, driving the initial total angular momentum of the fission fragments, together with microscopic level densities from the HFB plus combinatorial method. We also discuss, how the initial excitation-energy sharing shapes the TKE-dependent gamma-ray multiplicity.(c) 2022 French Alternative Energies and Atomic Energy Commission (CEA). Published by Elsevier B.V.This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3.
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| 17. |
- Qi, L., et al.
(författare)
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Potential of prompt γ -ray emission studies in fast-neutron induced fission : a first step
- 2020
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Ingår i: European Physical Journal A. - : Springer Nature. - 1434-6001 .- 1434-601X. ; 56:3
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Tidskriftsartikel (refereegranskat)abstract
- Prompt γ-ray spectra emitted in fast-neutron induced fission of 239Pu have been recently measured by using the LICORNE directional neutron source at En = 1.8 MeV. The results are used in parallel with the measurements of fast-neutron induced fission of 238U and spontaneous fission of 252Cf to assess the potential of such reactions and observables, in contributing to the understanding of fission. The γ-ray spectra were measured and analyzed under similar conditions, allowing a consistent and robust comparison between the three systems. They are further compared to Monte–Carlo simulations based on two widely-used semi-empirical codes, FREYA and GEF. Differences in the low and high energy portions of the spectrum are interpreted based on simple arguments involving nuclear structure and evaporation effects. The significance and potential of experimental campaigns of this kind, as well as current limitations, are highlighted, together with straightforward but mandatory extensions.
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| 18. |
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| 19. |
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| 20. |
- Robertson, Gustav, Ph.D. student, 1986-, et al.
(författare)
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Model inadequacy in fuel performance code calibration : Derivative-based parameter uncertainty inflation
- 2024
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Ingår i: Annals of Nuclear Energy. - : Elsevier. - 0306-4549 .- 1873-2100. ; 208
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Tidskriftsartikel (refereegranskat)abstract
- Fuel performance codes are used to forecast fuel behavior and ensure safe operation. These analyses must typically include prediction uncertainties, and fuel performance models need calibration. Consequently, code calibration must derive the best estimates and corresponding uncertainties of model parameters for subsequent propagation.Bayesian calibration is popular for generating the probability distribution of model parameters. However, model inadequacy disrupts these techniques, typically resulting in underestimated uncertainties. Earlier research showcased the incorporation of model inadequacy by model parameter inflation. The method demands cheap code predictions and derivatives, which required further research to develop differentiated Gaussian process surrogates.This work combines those techniques into a complete methodology. We demonstrate it by calibrating Transuranus against fission gas release and cladding oxidation data. The result is model parameter uncertainties that primarily explain the discrepancies between the predictions and corresponding measurements, except when the output behaves highly non-linearly.
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| 21. |
- Salvador-Castiñeira, P., et al.
(författare)
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Neutron-induced fission cross section of Pu 240 from 0.5 MeV to 3 MeV
- 2015
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Ingår i: Physical Review C. Nuclear Physics. - : American Physical Society (APS). - 0556-2813 .- 1089-490X. ; 92:1
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Tidskriftsartikel (refereegranskat)abstract
- Pu240 has recently been pointed out by a sensitivity study of the Organization for Economic Cooperation and Development (OECD) Nuclear Energy Agency (NEA) to be one of the isotopes whose fission cross section lacks accuracy to meet the upcoming needs for the future generation of nuclear power plants (GEN-IV). In the High Priority Request List (HPRL) of the OECD, it is suggested that the knowledge of the Pu240(n,f) cross section should be improved to an accuracy within 1-3 %, compared to the present 5%. A measurement of the Pu240 cross section has been performed at the Van de Graaff accelerator of the Joint Research Center (JRC) Institute for Reference Materials and Measurements (IRMM) using quasi-monoenergetic neutrons in the energy range from 0.5 MeV to 3 MeV. A twin Frisch-grid ionization chamber (TFGIC) has been used in a back-to-back configuration as fission fragment detector. The Pu240(n,f) cross section has been normalized to three different isotopes: Np237(n,f), 235U(n,f), and 238U(n,f). Additionally, the secondary standard reactions were benchmarked through measurements against the primary standard reaction 235U(n,f) in the same geometry. A comprehensive study of the corrections applied to the data and the associated uncertainties is given. The results obtained are in agreement with previous experimental data at the threshold region. For neutron energies higher than 1 MeV, the results of this experiment are slightly lower than the ENDF/B-VII.1 evaluation, but in agreement with the experiments of Laptev et al. (2004) as well as Staples and Morley (1998).
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| 22. |
- Salvador-Castiñeira, P., et al.
(författare)
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Neutron-induced fission cross sections of Pu 242 from 0.3 MeV to 3 MeV
- 2015
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Ingår i: Physical Review C. Nuclear Physics. - : American Physical Society. - 0556-2813 .- 1089-490X. ; 92:4
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Tidskriftsartikel (refereegranskat)abstract
- The majority of the next generation of nuclear power plants (GEN-IV) will work in the fast-neutron-energy region, as opposed to present day thermal reactors. This leads to new and more accurate nuclear-data needs for some minor actinides and structural materials. Following those upcoming demands, the Organisation for Economic Cooperation and Development Nuclear Energy Agency performed a sensitivity study. Based on the latter, an improvement in accuracy from the present 20% to 5% is required for the Pu242(n,f) cross section. Within the same project both the Pu240(n,f) cross section and the Pu242(n,f) cross section were measured at the Van de Graaff accelerator of the Joint Research Centre at the Institute for Reference Materials and Measurements, where quasimonoenergetic neutrons were produced in an energy range from 0.3 MeV up to 3 MeV. A twin Frisch-grid ionization chamber has been used in a back-to-back configuration as fission-fragment detector. The Pu242(n,f) cross section has been normalized to three different isotopes: Np237(n,f), U235(n,f), and U238(n,f). A comprehensive study of the corrections applied to the data and the uncertainties associated is given. The results obtained are in agreement with previous experimental data at the threshold region up to 0.8 MeV. The resonance-like structure at 0.8 to 1.1 MeV, visible in the evaluations and in most previous experimental values, was not reproduced with the same intensity in this experiment. For neutron energies higher than 1.1 MeV, the results of this experiment are slightly lower than the Evaluated Nuclear Data File/B-VII.1 evaluation but in agreement with the experiment of Tovesson et al. (2009) as well as Staples and Morley (1998). Finally, for energies above 1.5 MeV, the results show consistency with the present evaluations.
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| 23. |
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| 24. |
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| 25. |
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| 26. |
- Travar, M., et al.
(författare)
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Experimental information on mass- and TKE-dependence of the prompt fission gamma-ray multiplicity
- 2021
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 817, s. 136293-
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Tidskriftsartikel (refereegranskat)abstract
- Prompt gamma rays from the spontaneous fission of Cf-252 were measured with cerium-doped LaBr3 detectors. The average prompt fission gamma-ray multiplicity, M-gamma, was determined as a function of fragment mass number (A) and total kinetic energy (TKE). High-statistics data, obtained from three detectors of different size at different angles relative to the fission chamber, confirms unequivocally a saw-tooth like shape of the gamma multiplicity as a function of fragment mass, in contrast to previously published data. In addition, the TKE-dependence of M-gamma was determined experimentally and compared with recent data.
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| 27. |
- Trombetta, Débora M., et al.
(författare)
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On the use of ?/n correlations in multiplicity counting in small samples
- 2022
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 1040
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Tidskriftsartikel (refereegranskat)abstract
- The use of liquid scintillation detectors provides the possibility to acquire information about both gamma-rays and neutrons. The capability of plutonium detection via gamma/n coincidences in liquid scintillation detectors is well demonstrated in the literature, and it is also acknowledged that correlated gamma/n detection can offer better sensitivity and signal to noise ratio compared to neutron-neutron for some applications. In this paper we perform an assessment of the use of gamma/n coincidence counting in small samples, what may have use in the context of nuclear safeguards. We formulate the expected number of gamma/n coincidences and calculate the average and covariance of gamma-ray and neutron multiplicities for Pu-238, Pu-240, Pu-242 and Cf-252. The multiplicative coefficients for the Pu-240 effective mass equation was then calculated using gamma/n coincidences, and Monte Carlo simulations performed in order to model the detection of neutrons and gamma-rays inside liquid scintillation detectors. We conclude that gamma/n coincidence counting still has potential capabilities when the objective is the detection of plutonium, but its use for plutonium effective mass quantification is limited compared to n/n coincidence counting. Nevertheless, the method could still be applicable for the purpose of plutonium mass quantification by using a calibration curve that is specific to a sample's mass and size.
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