Abstract
This paper presents recent experimental results on the yield of prompt fission γ rays from the spontaneous fission of Cf252. We use an ionization chamber to tag fission events and measure the masses and kinetic energies of the fission fragments and trans-stilbene organic scintillators to measure the neutrons and γ rays emitted by the fission fragments. The combination of the ionization chamber and trans-stilbene scintillators allows us to determine the properties of neutrons and γ rays in coincidence with the fragments. The yield of γ rays is known to be influenced by the angular momenta (AM) of the fission fragments. We present experimental evidence indicating that the total γ-ray multiplicity, i.e., the sum of both fragments' emission, saturates at sufficiently high internal fragment excitation energies. We also observe distinct behaviors for the yield of γ rays from the light and heavy fragments, which for certain mass and total kinetic energy (TKE) regions are weakly or anticorrelated, indicating the presence of complex AM generation modes. We also observed a mass- and TKE-dependent anisotropy of the γ rays, which challenges and expands on the conventional notion that the fragments' AM are always aligned perpendicularly to the fission axis. Moreover, the dependence of the anisotropy on mass and TKE indicates a dependence of these properties on the specific fission channels, thus providing an insight into the deformations and dynamics in fission and their connection with experimentally observable quantities.
| Original language | English |
|---|---|
| Article number | 054617 |
| Journal | Physical Review C |
| Volume | 109 |
| Issue number | 5 |
| DOIs | |
| State | Published - May 2024 |
Funding
The authors would like to thank O. Litaize and the developers of the fifrelin code for providing the analyzed events as well as useful discussion. This work was in part supported by the Office of Defense Nuclear Nonproliferation Research and Development (DNN R & D), National Nuclear Security Administration, U.S. Department of Energy. This work was funded in-part by the Consortium for Monitoring, Technology, and Verification under Department of Energy National Nuclear Security Administration Award No. DE-NA0003920. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357. This research used resources of Argonne National Laboratory's ATLAS facility, which is a DOE Office of Science User Facility. Authors also gratefully acknowledge the use of the Bebop cluster in the Laboratory Computing Resource Center (LCRC) at Argonne National Laboratory. The work of V.A.P. was performed under the auspices of UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. S.M. is grateful to Prof. Kiedrowski at the University of Michigan for helpful discussion regarding Legendre polynomial extraction. Authors would like to acknowledge the efforts in the design and support during operation provided by the LETS group at the Physics Division of ANL, especially M. Oberling and R. Knaack.