Speaker
Description
Although fission was discovered over 80 years ago and has seen widespread usage, a complete microscopic description of the fission process is yet to be achieved. One important contribution towards that objective is high-precision experimental data. In particular, nuclear fission induced by quasi-monochromatic polarized photons provides unique information due to their selectivity on low-multipolarity excitations, thereby learning about the potential energy landscape around the multi-humped fission barrier as well as determining transition states and channels through which the fission process proceeds.
Measuring mass, total kinetic energy, and polar as well as azimuthal angular distributions of the fission fragments simultaneously in the same detector allows correlations to be examined, e.g. between fragment mass and the identification of transition states. After a brief overview over previous experiments on photofission, this talk will showcase recent ($\gamma$,f) experiments performed at the High-Intensity $\gamma$-ray Source (HI$\gamma$S) at Triangle Universities Nuclear Laboratory (TUNL) using a position-sensitive twin Frisch-grid ionization chamber [1]. We will present results of a pioneering $^{238}$U($\gamma$,f) experiment at an excitation energy of 11.2 MeV [2] as well as early data from a follow-up $^{234}$U($\gamma$,f) experiment investigating multiple excitation energies, including values near the fission barrier.
Supported by HMWK (LOEWE Cluster Nuclear Photonics)
[1] A. Göök et al., “A position-sensitive twin ionization chamber for fission fragment and prompt neutron correlation experiments”, Nucl. Instrum. Methods A, 830, 366 (2016); M. Peck et al., “Performance of a twin position-sensitive Frisch-grid ionization chamber for photofission experiments”, EPJ Web of Conferences, 239, 05011 (2020).
[2] M. Peck, “Correlation experiments in photon-induced nuclear fission”, Dissertation, Technische Universität Darmstadt (2020).
