Study of the fission cross-section of 230Th at the CERN n_TOF facility

Accurate data on neutron induced reactions on actinides is of considerable importance for the design of advanced nuclear systems and alternative fuel cycles. Specifically, 230Th is present in the thorium cycle produced from the decay of 234U. Thus, knowledge of the 230Th(n,f) reaction cross-section is strongly required. However, few experimental datasets exist in literature with large deviations among them, covering the energy range between 0.2 to 25 MeV. In addition, the study of fission cross-sections is of great interest in the research of the fission process related to the structure of the fission barriers. In the case of the thorium isotopes, narrow resonances and fine structures appear in the threshold region of the fission cross-section, known as the thorium anomaly. Specifically, previous measurements on the fission cross-section of 230Th revealed a main resonance at En =715 keV and additional fine structures, but with high discrepancies among the measured cross-section values. The scope of this work is to provide cross-section data for the 230Th(n,f) reaction, covering a wide energy range from the fission threshold up to 400 MeV. For this reason the experiment was performed in both experimental areas EAR-1 and EAR-2 of the CERN n_TOF facility. Seven high purity targets of the natural, unstable but very rare isotope 230Th, were produced at JRC-Geel in Belgium. The experimental setup was based on Micromegas detectors, while the 235U(n,f) cross-section was used as reference. A detailed description of the experimental setup, the analysis procedure, starting from the raw data to the final cross-section results, including the Monte-Carlo simulations performed and the theoretical study of the 230Th(n,f) reaction with the EMPIRE code are presented.