Speaker
Description
Despite the numerous theoretical [1] and experimental [2] works published very recently, the way in which fission fragments acquire their angular momentum is still an open question. This angular momentum generation mechanism is important not only for improving our understanding of the fission process, but also for nuclear energy applications, since fission fragments angular momentum strongly impact the prompt gamma spectra and consequently decay heat in a reactor.
In this context, within the framework of a collaboration between the ‘Laboratoire de Physique Subatomique et Corpusculaire’ (LPSC, France), the ‘Institut Laue Langevin’ (ILL, France) and the CEA-Cadarache (France), an experimental program was developed on the LOHENGRIN mass-spectrometer with the aim of measuring isomeric ratio of some fission products for different thermal neutron induced fission reactions. This presentation will be focused on results obtained for the spherical nucleus 132-Sn following thermal neutron induced fission of both 235-U and 241-Pu targets. To further constrain the angular momentum generation models, 132-Sn isomeric ratio (IR) is measured as a function of its kinetic energy (Ek). The angular momentum is determined by combining our experimental data with calculations performed with the FIFRELIN Monte-Carlo code [3]. A clear angular momentum decrease with Ek is observed for both reactions. A comparison of the present work with the predictions of the Madland-England model [4], the GEF [5] code and the FIFRELIN code will be also discussed.
Lastly, we investigate the dependence of the 132-Sn angular momentum with the incident neutron energy, from thermal region up to the first chance fission. For that, the four free available parameters in FIFRELIN are selected in order to reproduce the average prompt neutron multiplicity. In this way, the angular momentum is deduced for each neutron energy. These results are discussed in terms of the impact of the fission fragment deformation at scission on the spin assignment.
References
[1] J. Randrup and R. Vogt, Phys. Rev. Lett. 127, 062502 (2021), and references therein
[2] C.J. Sears et al., Nuclear Data Sheets 173 (2021) 118–143, and references therein
[3] O. Litaize, O. Serot, and L. Berge, Eur. Phys. J. A 51, 177 (2015)
[4] D. G. Madland and T. R. England, Nucl. Sci. Eng. 64, 859 (1977)
[5] K. H. Schmidt et al., Nucl. Data Sheets 131, 107 (2016)