Fission dynamics from saddle-to-scission, and even beyond, is a non-equilibrium quantum process and its description within a fully quantum many-body framework has been a formidable problem to find its solution in theoretical physics for more than 8 decades now. Within the Time-Dependent Density Functional Theory (TDDFT) extended to superfluid fermion systems, which is a mathematically...
Recent experiments have provided strong evidence that the angular momentum of fission fragments follows a sawtooth pattern as a function of their mass. Reproducing this behavior without fitting it explicitly requires microscopic models capable of describing the physics of scission without adjustable parameters. Using the Hartree-Fock-Bogoliubov theory and symmetry restoration techniques, we...
The understanding of angular momentum generation in the fission process is important not only for a complete description of nuclear fission but also determines the neutron/gamma competition and total number of gamma rays emitted in fission fragment decay. This knowledge impacts the gamma-heating problem in nuclear energy applications and also for understanding the accessibility of excited...
Prompt fission gamma-ray observables depend on the angular momenta of fission fragments (FFs). However, as neutron emission is much faster than gamma emission, extraction of FF spin properties can be subject to uncertainties due to the corrections for neutron emission. For example, in FREYA and CGMF, two simulation codes modeling the prompt neutron and gamma emissions from FFs, the neutron...
Authors:
Olivier Litaize, Achment Chalil, Abdelaziz Chebboubi, Valentin Piau, Mathias Sabathé, Olivier Serot, Pierre Tamagno
Angular momenta in fission can be discussed at different time steps of the process for different systems: incoming particle, target nucleus, compound nucleus at saddle, at scission for both nascent fission fragments, fission fragments before neutron emission, after...
R. Vogt1,2
1 Nuclear and Chemical Sciences Division, Lawrence Livermore National Laboratory, Livermore, CA 94551, USA
2 Physics and Astronomy Department, University of California at Davis, Davis, CA 95616, USA
The fission simulation model FREYA is well suited for studying the role of angular momentum in fission because it obeys all conservation laws, including linear and angular...
Prompt γ-rays from fission fragments have information on the mechanism of the spins of a fragment, and is important to investigate the mechanism of spin population in fission. We have measured the γ-ray spectrum in 235U(nth,f) using thermal neutron beam supplied from the High-Flux Reactor of ILL, Grenoble, France. By significantly improving the detection efficiency and gaining accumulated...
Jingde Chen, Chikako Ishizuka, Satoshi Chiba
Angular momentum of fission fragments (FFs) is an important physics quantity which governs the statistical decay of excited FFs through conservation law formulated as the Hauser-Feshbach theory, which leads to the independent fission products. Indeed, spins of the fission fragments are “measured” by applying the Hauser-Feshbach theory to interpret...
B.G. Carlsson, T. Døssing, J. Randrup, S. Åberg
T. Døssing1, B.G. Carlsson2, J. Randrup3, and S. Åberg2
1Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen Ø, Denmark,
2Mathematical Physics, Lund University, 221 00 Lund, Sweden,
3Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
The angular momentum of fission fragments is calculated...
We present recent experimental results that indicate the existence of significant correlations between the fragments’ angular momenta and excitation energies. Both the experiment we present are based on the Chi-Nu array at the Los Alamos Neutron Science Center but are independent observations of the spin-energy correlations in fission. We find evidence of event-by-event neutron-gamma...
Alf Göök, Andreas Oberstedt, Stephan Oberstedt, Olivier Litaize, Abdelaziz Chebboubi
The nuclei generated at scission are left in highly excited states, and will dissipate their excitation energy and angular momentum through the emission of neutrons, photons and conversion electrons. In this context, the study of prompt γ-ray emission is an interesting tool to assess the angular momenta of...
Isomeric yield ratios are among the observables to study angular momenta of fission fragments. The most common way to obtain such ratios relies on gamma spectroscopy. Recently, direct mass measurement methods have achieved mass resolving power that makes them relevant for isomeric yield ratio studies. This talk will give an overview of the used experimental techniques, and summarize the status...
Usually, fission product angular momentum is studied through prompt γ emission. A complementary technique is to use the isomeric ratio. This observable is of interest because it preserves the initial angular momentum information resulting from the fission process just after the prompt particle emission.
The coupling of the LOHENGRIN recoil spectrometer (located at the Institut Laue- Langevin,...
An observable that is strongly coupled to a fission fragment's angular momentum is its isomeric yield ratio (IYR), defined by the amount of fragment decays that passes though a metastable state. Though this observable is limited to fragments with such isomeric states, the IYR is known to be sensitive to small changes in the fragment's angular momentum distribution. Isomeric yield ratios have...
