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  • 1.
    Birgersson, Evert
    et al.
    Örebro University, School of Science and Technology.
    Oberstedt, Andreas
    Örebro University, School of Science and Technology.
    Oberstedt, Stephan
    Hambsch, Franz-Josef
    Properties of the reaction 238U(n, f) at the vibrational resonances2009In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 817, no 1-4, p. 1-34Article in journal (Refereed)
    Abstract [en]

    Recent fission cross-section calculations for the reaction 238U(n, f ), based on an extended statistical model, predict a significant change of fission fragment properties, such as the mean mass by A = 1.5 and a notable increase in total kinetic energy in the region of the vibrational resonance at an incident neutron energy En = 0.9 MeV. This model includes individual fission cross-sections by the asymmetric standard 1 (S1) and standard 2 (S2) as well as the symmetric super-long (SL) mode. In order to verify the model predictions, a dedicated experiment on 238U has been carried out to measure fission-fragment mass yield distributions for incident neutron energies from En = 2.0 MeV down to 0.9 MeV, where the fission characteristics at the vibrational resonance at En = 0.9 MeV were investigated for the first time. The previously reported distinct structure in the angular anisotropy around En = 1.2 and 1.6 MeV wasobserved at En = 0.9 MeV as well. The predicted large changes in fission fragment mass yield and total kinetic energy could not be confirmed. In the resonance the mean total kinetic energy is only about 0.5 MeV higher than at En = 1.8 MeV. At the same time, a slight decrease of the mean heavy fragment mass was observed, probably indicating a slightly increased contribution of the S1 fission mode.

  • 2.
    Birgersson, Evert
    et al.
    Örebro University, Department of Natural Sciences.
    Oberstedt, Stephan
    Oberstedt, Andreas
    Örebro University, Department of Natural Sciences.
    Hambsch, Franz-Josef
    Rochman, Dimitri
    Tsekhanovich, Igor
    Raman, Subramanian
    Light fission-fragment mass distribution from the reaction 251Cf(nth, f)2007In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 791, no 1-2, p. 1-23Article in journal (Refereed)
    Abstract [en]

    For mass numbers A = 80 to 124 the recoil mass spectrometer LOHENGRIN of the Institute Laue-Langevin in Grenoble was used to measure with high resolution the light fission-fragment mass yields and kinetic energy distributions from thermal-neutron induced fission of 252Cf* for the first time, using 251Cf as target material. The obtained mean light fragment mass AL = (107 ± 2) and the corresponding mean kinetic energy Ek,L = (103±2) MeV are within the expected trend. Emission yields around A = 115 are enhanced and the corresponding mean kinetic energy is higher compared to spontaneous fission of 252Cf. This could be explained by the existence of an additional super-deformed fission mode.

  • 3.
    Göök, A.
    et al.
    Örebro University, School of Science and Technology.
    Chernykh, M.
    Eckardt, C.
    Enders, J.
    von Neumann-Cosel, P.
    Oberstedt, Andreas
    Örebro University, School of Science and Technology.
    Oberstedt, S.
    Richter, A.
    Fragment characteristics from fission of (238)U and (234)U induced by 6.5-9.0 MeV bremsstrahlung2011In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 851, no 1, p. 1-16Article in journal (Refereed)
    Abstract [en]

    Fission of (238)U and (234)U induced by bremsstrahlung of 6.5-9.0 MeV endpoint energy has been investigated at the superconducting Darmstadt electron linear accelerator S-DALINAC. Using a twin Frisch grid ionization chamber, fission-fragment energy and mass distributions have been determined by means of the double kinetic-energy technique. Results on the fission-fragment characteristics from (238)U(gamma, f) are in agreement with results from the literature. In addition fission-fragment mass and energy distributions from (234)U(gamma, f) are presented for the first time in this energy region. An analysis of fission modes within the Brosa model has been performed. The relative yield of the S 1 mode was found to be (13 +/- 3)% in (234)U and (35 +/- 2)% in (238)U. (C) 2010 Elsevier B.V. All rights reserved.

  • 4. Oberstedt, Stephan
    et al.
    Oberstedt, Andreas
    Örebro University, Department of Natural Sciences.
    Rochman, Dimitri
    Gönnenwein, Friedrich
    Tsekhanovich, Igor
    Becker, Julia
    Örebro University, Department of Natural Sciences.
    Sartz, Annika
    Örebro University, Department of Natural Sciences.
    Bax, Hugo
    Hambsch, Franz-Josef
    Raman, Subramanian
    Light charged particle emission in the reaction 251Cf(nth, f)2005In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 761, no 3-4, p. 173-189Article in journal (Refereed)
    Abstract [en]

    High resolution measurements of light charged particles (LCP) emitted in thermal neutron-induced fission of 252Cf ∗ (E=6.2 MeV) have been performed with the recoil mass-separator LOHENGRIN. For this compound nuclear system emission yields of LCPs, their mean kinetic energies and widths have been obtained for 8 isotopes with nuclear charges Z⩾2. For 13 further isotopes the emission yields were estimated on the basis of systematics on their kinetic energy distributions. 34Al and 36Si emission has been observed for the first time in thermal neutron-induced fission.

  • 5.
    Tovesson, Fredrik
    et al.
    Örebro University, Department of Natural Sciences.
    Birgersson, E.
    Örebro University, Department of Natural Sciences.
    Flenéus, M.
    Örebro University, Department of Natural Sciences.
    Fogelberg, B.
    Fritsch, V.
    Gustafsson, C.
    Örebro University, Department of Natural Sciences.
    Hambsch, F.-J.
    Oberstedt, Andreas
    Örebro University, Department of Natural Sciences.
    Oberstedt, Stephan
    Ramström, E.
    Tudora, A.
    Vladuca, G.
    233Pa(n, f) cross section up to En=8.5 MeV2004In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 733, no 1-2, p. 3-19Article in journal (Refereed)
    Abstract [en]

    The energy dependence of the neutron-induced fission cross section of 233Pa has been measured directly for the first time from the fission threshold up to En=8.5 MeV. This reaction plays an important role in the thorium-uranium fuel cycle, and is thus of interest for the design and modeling of advanced reactor and transmutation facilities. The existing information in the ENDF/B-VI and JENDL-3.3 evaluated nuclear data files differ by a factor of two for the 233Pa(n, f) cross section values and show different fission threshold energies. Our new experimental data give lower cross section values than both evaluations and resolves the question about the threshold energy. In addition to the experimental investigation, also a new theoretical calculation of the reaction cross section has been performed with the statistical model code STATIS, showing a good agreement with the experimental data.

  • 6. Vladuca, G.
    et al.
    Hambsch, F.-J.
    Tudora, A.
    Oberstedt, S.
    Oberstedt, Andreas
    Örebro University, Department of Natural Sciences.
    Tovesson, F.
    Örebro University, Department of Natural Sciences.
    Filipescu, D.
    Calculation of the neutron-induced fission cross section of 233Pa up to 20 MeV2004In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 740, no 1-2, p. 3-19Article in journal (Refereed)
    Abstract [en]

    Since very recently, direct measurements of the 233Pa(n,f) cross-section are available in the energy range from 1.0 to 8.5 MeV. This has stimulated a new, self-consistent, neutroncross-section evaluation for the n+233Pa system, in the incident neutron energy range 0.01–20MeV. Since higher fission chances are involved also the lighter Pa-isotopes had to be re-evaluated in a consistent manner. The results are quite different compared to earlier evaluation attempts. Since 233Pa is a key isotope in the thorium based fuel cycle the quality of its reaction cross-sections is important for the modeling of future advanced fuel and reactor concepts. The present status of the evaluated libraries is that they differ by a factor of two in the absolute fissioncross-section and also in the threshold energy value.

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