Detector for fission fragments from electrofission reactions at the S-DALINAC

• Subject Area: Particles, Nuclei and Fields
• Term: Funded in 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 541476531

One of the big questions in fundamental science is the origin of heavy chemical elements in the Universe. The gravitational-wave signal GW170817 and its associated kilonova transient in the electromagnetic spectrum provided direct evidence for the synthesis of rare-earth metals in binary neutron-star merger events that offer conditions for the rapid neutron capture process (r-process) for fast synthesis of heavy elements. Mass accumulation due to capture of free neutrons and associated fast beta-decays terminates in the actinide region when fission reactions start to compete. Fission fragments form then new seed nuclei for the r-process. Detailed modelling of the r-process requires reliable fission models for experimentally inaccessibly neutron-rich actinides and refined data on actinides closer to stability for testing those. For better data on nuclear fission reactions, it is proposed to establish a detector for electron-induced fission processes of actinides at the Institute for Nuclear Physics of the Technische Universität Darmstadt. The electron beam provided by the S-DALINAC electron accelerator will be used to induce fission reactions of actinide targets. Scattered electrons will be detected with the QCLAM magnetic spectrometer and, for the first time in electrofission reactions, both fission products will be detected by the proposed experimental setup with mass resolution down to 1 u in coincidence with the scattered electron. To this end, the DEFERA detector will consist of a Start detector which provides the timing information of the scattered electron, and a set of Fission Fragment Detector Modules (FFDMs) placed around the target. Each one of these modules consists of a cooled Double-Sided Silicon-Strip Detector (DSSSD). Hence, the FFDMs serve as Stop detectors with sufficient time-resolution and as a calorimeter providing the timing information and the kinetic energy of the fragment, simultaneously. By measuring the velocity, obtained from the time-of-flight and the flight distance from the target to the FFDMs, and the kinetic energy of both fission fragments in coincidence with the scattered electron, it is possible to determine the fission mass yield for every fragment individually. Since the energy loss of the scattered electron is measured, the mass yields can be obtained as a function of nuclear excitation energy with world-wide highest resolution. The overdetermined data (including the known mass of the target nuclei) will allow to study for the first time the fission mass distribution and neutron multiplicity as a function of excitation energy on Thorium, Uranium, Plutonium, and Curium isotopes. They will test contemporary microscopic models for fission processes of heavy nuclei and serve the timely needs for improved fission models. The latter are required for extrapolation to exotic neutron-rich actinides for understanding the termination of the r-process in binary neutron star merger events in the “r-process fission cycle”.

• DFG Programme: Major Research Instrumentation
• Major Instrumentation: Detektor für Spaltfragmente aus Elektrospaltungsreaktionen am S-DALINAC
• Instrumentation Group: 0260 Strahlungsmeßplätze (außer 033, 330-339, 405 und 615-619)
• Applicant Institution: Technische Universität Darmstadt
• Leader: Professor Dr. Norbert Andreas Pietralla