Speaker
Description
Despite the notorious advances in different theoretical models [1] and the development of new experimental setups that increase the access to the fission observables [2], there are still several phenomena in the fission process that are not reproduced with enough accuracy and whose origin is unclear. One of these occurrences is the so-called "Thorium Anomaly", which refers to the observed fission probabilities [3] and fission yields [4] around Thorium, that deviate from the behaviour of heavier actinides [5]. The scarce dataset and limited number of observables prevent so far to fully comprehend this sudden variation. The correlation between several parameters would allow to shed light on the current understanding.
Following the advantages of inverse-kinematics, a new experiment was conducted with the newly accelerated 232Th beam at Coulomb energies. Fusion, inelastic scattering and transfer reactions produced with a 12C target permitted to populate fissioning systems such as 232Th, 233Pa or 234U. The utilized experimental setup consisted on the VAMOS++ spectrometer [6], which was in charge of obtaining the isotopic identification of complete fission fragment distributions and their velocity vector. Moreover, the magnetic spectrometer was combined with a highly stripped silicon detector (PISTA), that allows the event-by-event identification of the fissioning system and the reconstruction of its excitation energy with high resolution [7] by measuring the target-like partner. The combination of both devices permits to systematically study the correlation between the fission observables for several nuclei, within the same configuration.
In this work, the elemental and isotopic fission fragment yields of 232Th will be presented. Having a simultaneous measurement of these yields with the excitation energy of the corresponding fissioning system, the evolution of these observables can also be investigated. The comparison between Thorium yields and heavier actinides gives more experimental insight into the understanding of the "Thorium anomaly".
References
[1] Schunck, N and Robledo, LM , Reports on Progress in Physics 79 (2016) 116301.
[2] Schmidt, K. H., Benlliure, J., & Junghans, A. R. (2001). Fission of nuclei far from stability. Nuclear Physics A, 693(1-2), 169-189.
[3] Back, B. B., Britt, H. C., Garrett, J. D., & Hansen, O. (1972). Subbarrier fission resonances in Th isotopes. Physical Review Letters, 28(26), 1707
[4] Berriman, A. C., Hinde, D. J., Jeung, D. Y., Dasgupta, M., Haba, H., Tanaka, T., ... & Williams, E. (2022). Energy dependence of p+ Th 232 fission mass distributions: Mass-asymmetric standard I and standard II modes, and multichance fission. Physical Review C, 105(6), 064614
[5] Schmidt, K. H., et al. (2024). Identifying and overcoming deficiencies of nuclear data on the fission of light actinides by use of the GEF code. Annals of Nuclear Energy, 208, 110784.
[6] M.Rejmund et al., Nuclear Instruments and Methods in Physics Research A 646 (2011) 184-191.
[7] Bégué - Guillou, L., Lemasson, A., Morfouace, P., Ramos, D., Taieb, J., Frankland, J. D., ... & Tonchev, A. P. (2026). Performance of the Particle-Identification Silicon-Telescope Array coupled with the VAMOS++ magnetic spectrometer. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1090, 171671.