| 1. |
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| 2. |
- Gjestvang, D., et al.
(författare)
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Examination of how properties of a fissioning system impact isomeric yield ratios of the fragments
- 2023
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Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 108:6
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Tidskriftsartikel (refereegranskat)abstract
- The population of isomeric states in the prompt decay of fission fragments-so-called isomeric yield ratios (IYRs)-is known to be sensitive to the angular momentum J that the fragment emerged with, and may therefore contain valuable information on the mechanism behind the fission process. In this work, we investigate how changes in the fissioning system impact the measured IYRs of fission fragments to learn more about what parameters affect angular momentum generation. To enable this, a new technique for measuring IYRs is first demonstrated. It is based on the time of arrival of discrete gamma rays, and has the advantage that it enables the study of the IYR as a function of properties of the partner nucleus. This technique is used to extract the IYR of 134Te, strongly populated in actinide fission, from the three different fissioning systems: 232Th(n, f), 238U(n, f), at two different neutron energies, as well as 252Cf(sf). The impacts of changing the fissioning system, the compound nuclear excitation energy, the minimum J of the binary partner, and the number of neutrons emitted on the IYR of 134Te are determined. The decay code TALYS is used in combination with the fission simulation code FREYA to calculate the primary fragment angular momentum from the IYR. We find that the IYR of 134Te has a slope of 0.004 +/- 0.002 with increase in compound nucleus (CN) mass. When investigating the impact on the IYR of increased CN excitation energy, we find no change with an energy increase similar to the difference between thermal and fast fission. By varying the mass of the partner fragment emerging with 134Te, it is revealed that the IYR of 134Te is independent of the total amount of prompt neutrons emitted from the fragment pair. This indicates that neutrons carry minimal angular momentum away from the fission fragments. Comparisons with the FREYA+TALYS simulations reveal that the average angular momentum in 134Te following 238U(n, f) is 6.0 h over bar . This is not consistent with the value deduced from recent CGMF calculations. Finally, the IYR sensitivity to the angular momentum of the primary fragment is discussed. These results are not only important to help understanding the underlying mechanism in nuclear fission, but can also be used to constrain and benchmark fission models, and are relevant to the gamma -ray heating problem of reactors.
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| 3. |
- Jurado, B., et al.
(författare)
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Investigation of the surrogate-reaction method via the simultaneous measurement of gamma-emission and fission probabilities
- 2017
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. ; 146
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Konferensbidrag (refereegranskat)abstract
- We present the results of two experiments where we have measured for the first time simultaneously the fission and gamma-decay probabilities induced by different surrogate reactions. In particular, we have investigated the 238 U(d,p), 238 U( 3 He,t) and 238 U( 3 He, 4 He) reactions as surrogates for the neutron-induced n + 238 U, n + 237 Np and n + 236 U reactions, respectively. In the region where gamma emission, neutron emission and fission compete, our results for the fission probabilities agree fairly well with the neutron-induced data, whereas our gamma-decay probabilities are significantly higher than the neutron-induced data. The interpretation of these results is not obvious and is discussed within the framework of the statistical model with preliminary results for calculated spin-parity distributions populated in surrogate reactions. We also present future plans for surrogate-reaction studies in inverse kinematics with radioactive-ion beams at storage rings.
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| 4. |
- Gatera, A., et al.
(författare)
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Prompt-fission γ -ray spectral characteristics from Pu 239 (nth,f)
- 2017
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Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 95:6
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present new results for prompt fission γ-ray spectral characteristics from the thermal neutron induced fission of Pu∗240. The measured spectra were unfolded by using the detectors' response functions, simulated with geant4. We obtained in average per fission a γ-ray multiplicity Mγ=(7.35±0.12), a mean photon energy ϵγ=(0.85±0.02) MeV, and an average total energy released in fission Ēγ,tot=(6.27±0.11) MeV. Our results are in good agreement with historical data measured in the 1970s by Verbinski et al. and results from recent calculations in the framework of Monte Carlo Hauser-Feshbach models. Our measured average total energy is slightly smaller than the one deduced previously and present in evaluated data. From this we conclude that the Pu239(nth,f) reaction may be ruled out as possible source of γ heating underestimation, when compared with benchmark calculations based on existing nuclear data.
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| 5. |
- Oberstedt, S., et al.
(författare)
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Prompt fission gamma-ray spectra characteristics - a first summary
- 2015
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Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3884 .- 1875-3892. ; 64, s. 83-90
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Konferensbidrag (refereegranskat)abstract
- In this work we give an overview of our investigations of prompt gamma-ray emission in nuclear fission. This work was conducted during the last five years in response to a high priority nuclear data request formulated by the OECD/NEA. The aim was to reveal data deficiencies responsible for a severe under-prediction of the prompt gamma heating in nuclear reactor cores. We obtained new prompt fission gamma-ray spectral (PFGS) data for Cf-252(SF) as well as for thermal-neutron induced fission on U-235(nth,f) and Pu-241(nth,f). In addition, first PFGS measurements with a fast-neutron beam were accomplished, too. The impact of the new data and future data needs are discussed.
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| 6. |
- Au, A. E., et al.
(författare)
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Altered B-lymphopoiesis in mice with deregulated thrombopoietin signaling
- 2017
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- Thrombopoietin (TPO) is the master cytokine regulator of megakaryopoiesis. In addition to regulation of megakaryocyte and platelet number, TPO is important for maintaining proper hematopoietic stem cell (HSC) function. It was previously shown that a number of lymphoid genes were upregulated in HSCs from Tpo(-/-)mice. We investigated if absent or enhanced TPO signaling would influence normal B-lymphopoiesis. Absent TPO signaling in Mpl(-/-)mice led to enrichment of a common lymphoid progenitor (CLP) signature in multipotential lineage-negative Sca-1(+)c-Kit(+) (LSK) cells and an increase in CLP formation. Moreover, Mpl(-/-)mice exhibited increased numbers of PreB2 and immature B-cells in bone marrow and spleen, with an increased proportion of B-lymphoid cells in the G1 phase of the cell cycle. Conversely, elevated TPO signaling in Tpo(Tg) mice was associated with reduced B-lymphopoiesis. Although at steady state, peripheral blood lymphocyte counts were normal in both models, Mpl(-/-)E mu-myc mice showed an enhanced preneoplastic phase with increased numbers of splenic PreB2 and immature B-cells, a reduced quiescent fraction, and augmented blood lymphocyte counts. Thus, although Mpl is not expressed on lymphoid cells, TPO signaling may indirectly influence B-lymphopoiesis and the preneoplastic state in Myc-driven B-cell lymphomagenesis by lineage priming in multipotential progenitor cells.
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| 7. |
- Au, A. E., et al.
(författare)
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Proinflammatory microenvironment promotes lymphoma progression in mice with high megakaryocyte and TPO levels
- 2023
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Ingår i: Blood Advances. - : American Society of Hematology. - 2473-9529 .- 2473-9537. ; 7:8, s. 1560-1571
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Tidskriftsartikel (refereegranskat)abstract
- Platelets have been shown to enhance the survival of lymphoma cell lines, but it is unclear if they play a role in lymphoma. Here we investigate a potential role for platelets and/or megakaryocytes in Eµ-myc lymphoma progression. Eµ-myc tumour cells were transplanted into recipient wild-type control mice, Mpl-/-, or TpoTg mice, which exhibit normal, low and high platelet and megakaryocyte counts, respectively. Transplanted TpoTg mice exhibited enhanced lymphoma progression with increased WBC counts, spleen and lymph node weights and enhanced liver infiltration when compared to wild-type. Conversely, tumour bearing Mpl-/- mice presented with reduced WBC counts, lymph node weights and less liver infiltration when compared to wild-type. Utilizing a Mpl-deficient thrombocytopenic immunocompromised mouse model, our results were confirmed with the human NHL GRANTA cell line. While we found that platelets and platelet released molecules supported Eµ-myc tumour cell survival in vitro, pharmacological inhibition of platelet function or anticoagulation in Eµ-myc transplanted wild-type mice did not improve disease outcome. Furthermore, transient platelet depletion or sustained Bcl-xL dependent thrombocytopenia did not alter lymphoma progression. Cytokine analysis of the bone marrow fluid microenvironment revealed increased levels of the proinflammatory molecule interleukin (IL)-1 in TpoTg mice, whereas levels were lowered in Mpl-/- mice. Moreover, RNA sequencing of blood-resident Eµ-myclymphoma cells from TpoTgand wild-type mice after tumour transplant revealed upregulation of hallmark gene sets associated with inflammatory response in TpoTg mice. We propose that a pro-inflammatory microenvironment in TpoTgmice promoted lymphoma progression.
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| 8. |
- Lebois, M., et al.
(författare)
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Studies for γ-ray emission in the fission process with LICORNE
- 2016
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. ; 122:01010
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Konferensbidrag (refereegranskat)abstract
- The LICORNE neutron source is a new device at the ALTO facility. Its use of inverse kinematics makes the production of naturally focused neutron beams possible with an energy range of 0.5 to 4 MeV. This is perfect for any studies concerning fast neutron induced reaction based on detection setup that require to be placed in a compact geometry - such as Ge based ? detection setup. In this paper, neutron production with LICORNE is described. The development of a gascell target and the extension of the energy range up to 7 MeV with the p(11B,n)11C are presented. An overview of the major research fields studied with LICORNE is given and two types of experiment are presented. The first one dedicated to prompt fission ?-ray emission in fission, as a function of incident neutron energy, is described. Some preliminary results are shown. The second, in the context of the MINORCA campaign, is detailed. The most recent outcomes in the data analysis process are also presented.
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| 9. |
- Oberstedt, Andreas, 1961, et al.
(författare)
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Prompt fission gamma-ray spectra characteristics - systematics and predictions
- 2015
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Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3884 .- 1875-3892. ; 64, s. 91-100
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Konferensbidrag (refereegranskat)abstract
- Revised systematics for prompt fission gamma-ray spectra (PFGS) characteristics as function of both atomic and mass number of the compound system, derived from recent experiments on thermal-neutron induced and spontaneous fission, is presented and applied to fission induced by fast neutrons. Results from these calculations for U-238(n, f) and U-235(n, f) for incident neutron energies from 0 to 20 MeV are compared to new experimental results, exhibiting nice agreement. Very recent PFGS measurements for Pu-240(sf) and Pu-242(sf) have been evaluated and the determined PFGS characteristics are shown to also fit well with the systematics. From this we conclude that the obtained systematics, although purely empirical, is indeed a useful tool for the prediction of average total gamma-ray energy released in prompt fission, mean energy per photon as well as average photon multiplicity for fissioning systems, which are difficult or even impossible to study experimentally. (C) 2015 The Authors. Published by Elsevier B.V.
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| 10. |
- Oberstedt, S., et al.
(författare)
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Future research program on prompt gamma-ray emission in nuclear fission
- 2015
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Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-601X .- 1434-6001. ; 51:12, s. 1-9
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Forskningsöversikt (refereegranskat)abstract
- In recent years the measurement of prompt fission gamma-ray spectra (PFGS) has gained renewed interest, after about forty years since the first comprehensive studies of the reactions U-235(n(th), f), Pu-239(n(th), f) and Cf-252(sf). The renaissance was initiated by requests for new values especially for.-ray multiplicity and average total energy release per fission in neutron-induced fission of U-235 and Pu-239. Both isotopes are considered the most important ones with respect to the modeling of innovative cores required for the Generation-IV reactors, the majority working with fast neutrons. During the last 5 years we have conducted a systematic study of spectral data for thermal-neutron-induced fission on U-235 and Pu-241 as well as for the spontaneous fission of Cf-252 with unprecedented accuracy. From the new data we conclude that those reactions do not considerably contribute to the observed heat excess and suspect other reactions playing a significant role. Possible contributions may originate from fast-neutron-induced reactions on U-238, which is largely present in the fuel, or from gamma-induced fission from neutron capture in the construction material. A first experiment campaign on prompt gamma-ray emission from fast-neutron-induced fission on U-235,U-238 was successfully performed in order to test our assumptions. In the following we attempt to summarize, what has been done in the field to date, and to motivate future measurement campaigns exploiting dedicated neutron and photon beams as well as upcoming highly efficient detector assemblies.
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