Photofission Fragment Characteristics of 234,238U and 232Th in the Barrier Region

Tests of ionization chambers for future photofission experiments

“…The missing corrections influence in particular the heavy fission fragment, which loses more energy, resulting in a slightly broadened peak. We estimate the mass resolution after corrections to be comparable to the established single twin-Frisch-grid ion chambers, where the corrections depend on the target thickness [5].…”

“…Hence, besides using intense bremsstrahlung at the Superconducting-DArmstadt LINear ACcelerator (S-DALINAC) [2] or monochromatic γ-ray beams at the future ELI-NP facility [3], significant amounts of target material need to be placed in the beam to reach sufficient luminosity. Target thickness, however, influences the extracted experimental results and limits the resolution of the fission-fragment properties [4,5]. To avoid this negative effect and yet gain a better experimental luminosity, multiple fission targets may be installed in a multi-cathode chamber inside the beam.…”

“…Another benefit of studying several targets simultaneously is to measure the properties of the fission fragments detected in each detector segment parallel, thereby, e.g., allowing to calibrate relative energies between the chamber parts. Photofission experiments on 234,238 U and 232 Th in the excitation energy region close to the fission barrier have been carried out using bremsstrahlung at the injector of the S-DALINAC [6], and the fission fragment properties have been studied with a twin Frisch-grid ionization chamber using a thin target on a backing transparent for both fission fragments located at the common cathode [7]. The determination of fission fragment masses was based on the well established double-kinetic-energy (2E) technique, and the fragment polar emission angle was extracted from the drift time of the ionization electrons [8].…”