Seminarium Fizyki Jądra Atomowego

Multi-humped fission barriers, as they occur in the actinide region, give rise to fission isomerism. Such barrier shapes can be described within various theoretical models. Experimentally measured observables of nuclear fission isomers—such as the half-life, excitation energy of the fission isomer, kinetic energy of the fission fragments, and the isomer-to-ground-state population ratio—allow for testing theoretical predictions and verifying the role of shell effects in nuclear structure.
Studies of the fission isomer properties of 240,242Am were performed at the IGISOL facility at the JYFL Accelerator Laboratory, University of Jyväskylä, Finland. Fission isomeric states were populated via deuteron-induced fusion–evaporation reactions on a 242Pu target. The decays of the fission isomers were detected using silicon detectors calibrated with a 252Cf fission source.
The measurements provided detailed information on kinetic energy spectra, total kinetic energies, and mass distributions for 240,242Am. A new method was proposed to derive post-neutron-emission mass distributions, as well as proton- and neutron-number multiplicity distributions of the fission fragments, from their kinetic energy distributions. In addition, the emission probabilities of prompt neutrons in the fission process were extracted. Using data for the 252Cf fission isomer as a reference, the validity of the method was verified.
The obtained results for 240,242Am and 252Cf are consistent with GEF model predictions and previous measurements. These findings contribute to a better understanding of shell effects and fission barrier structures in the actinide region.