Marius Torsvoll

• Torsvoll, Marius; Wirgenes, Maia Oline Grund; Al-Adili, Ali; Haug, Henrik Sørlie; Heines, Johannes Sørby & Siem, Sunniva [Show all 13 contributors for this article] (2026). Very asymmetric fission yields of 233U(nth, f) at LOHENGRIN. Full text in Research Archive Show summary

  In this work we report on a fission yield experiment done with the LOHENGRIN recoil mass spectrometer. Understanding the dynamics of nuclear fission requires accurate knowledge of the charge and mass distributions of fission fragments, particularly in rare and poorly studied regions. We present a dedicated investigation of the assymetric fission yields in 233U(nth,f), targeting fragment masses below A = 70, a region previously unexplored for this system. A particular focus is on confirming an expected enhancement of the yields of fragments near mass 70, potentially indicative of a super-asymmetric fission mode influenced by nuclear structure effects, such as the Z = 28 major shell closure. The experiment employed the LOHENGRIN recoil mass spectrometer in combination with a ΔE/E Frischgrid ionization chamber. This allows the identification of the mass of light fission fragments. The far asymmetric mass region will serve for benchmarking theoretical models and improving our understanding of shell effects in fission. During the presentation, we discussed the necessary correction steps during the analysis, including digital signal processing, scanning ionic charge and kinetic energy distributions, and target burn-up. Moreover, we discuss a comparison of different foil stacks that can be used as passive attenuators in the next beam-time campaign. Preliminary results from this work suggest a yield enhancement in the studied region, implying that the fissioning system U234* may exhibit a similar effect like the heavier systems. We finish by discussing the outlook and preparations for upcoming beam times at ILL.

• Torsvoll, Marius; Wirgenes, Maia Oline Grund; Al-Adili, Ali; Solders, Andreas; Köster, Ulli & Daugas, Jean-Micheal [Show all 13 contributors for this article] (2026). Very asymmetric fission yields in U(n,f) at LOHENGRIN. Full text in Research Archive Show summary

  The super assymmetric fission mode and yield enhancement around A = 70 has been observed in actinides as light as U. Modern fission codes modeling the fission process do not predict an enhancement like that found in U233 and heavier actinides. The super asymmetric region has not been measured for U233 and our goal is to explore the yields in the mass region from A = 90 to A = 67. In summary our goal is to extract the unmeasured fission yields in the super asymmetric region of U233(nth, f) with a special emphasis on investigating the possibility of a yield enhancement at atomic mass number A = 70

• Torsvoll, Marius; Al-Adili, Ali; Haug, Henrik Sørlie; Heines, Johannes Sørby; Wirgenes, Maia Oline Grund & Siem, Sunniva [Show all 10 contributors for this article] (2025). Very asymmetric fission yields of 233U(nth, f) at LOHENGRIN. Full text in Research Archive Show summary

  Super asymmetric fission represents a rare but informative fission mode, providing sensitive insight into shell effects and scission configurations in the nuclear fission process. In this work, new measurements of neutron induced fission of U233 at thermal neutron energies are presented, with a particular focus on very light fission fragments with mass numbers below A = 80. The experiment was performed at the Institut Laue Langevin using the LOHENGRIN recoil mass spectrometer in combination with a delta E-E Frisch grid ionization chamber. For the first time, fission yields of U233(nth,f)have been measured from A = 90 down to A = 68. The data promise to be important benchmarks for fission model development and are also relevant for applications related to the thorium fuel cycle.

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