Abstract
The fission cross section of ^{232}Th has been measured at fast neutron energies, using a setup based on Micromegas detectors. The experiment was performed at the 5.5 MV Van de Graaff Tandem accelerator in the neutron beam facility of the National Centre for Scientific Research “Demokritos”. The quasi-monoenergetic neutron beams were produced via the ^{3}H(p,n), ^{2}H(d,n) and ^{3}H(d,n) reactions, while the ^{238}U(n,f) and ^{235}U(n,f) reactions were used as references, in order to acquire cross-section data points in the energy range 2–18 MeV. The characterization of the actinide samples was performed via alpha -spectroscopy with a Silicon Surface Barrier (SSB) detector, while Monte Carlo simulations with the FLUKA code were used to achieve the deconvolution of the ^{232}Th alpha peak from the alpha background of its daughter nuclei present in the spectrum. Special attention was given to the study of the parasitic neutrons present in the experimental area, produced via charged particle reactions induced by the particle beam and from neutron scattering. Details on the data analysis and results are presented.
Highlights
Accurate cross-section data of neutron-induced reactions on actinides are of considerable importance for the design of advanced nuclear systems, such as Generation IV reactors and Accelerator-Driven Systems (ADS)
The fission cross-section results for 232Th, obtained by the analysis presented in Sect. 3 are presented in Table 4 along with their statistical uncertainties
0.117 ± 0.005 0.112 ± 0.003 0.135 ± 0.004 0.137 ± 0.004 0.142 ± 0.004 0.137 ± 0.004 0.147 ± 0.004 0.135 ± 0.004 0.304 ± 0.005 0.383 ± 0.023 0.456 ± 0.018 0.50 ± 0.04 used as reference for the cross section calculation at all neutron energies, while the 235U(n,f) was used in addition for the 2.0 and 2.5 MeV irradiations
Summary
Accurate cross-section data of neutron-induced reactions on actinides are of considerable importance for the design of advanced nuclear systems, such as Generation IV reactors and Accelerator-Driven Systems (ADS). The main disadvantage of the thorium cycle is the production of 232U, with a half-live of 73.6 years, accompanied by its daughters which include strong γ -ray emitters with very short halflives. This results in a buildup of the radiation dose, which becomes a problem when storing the spent fuel. The experimental setup, analysis procedure and Monte Carlo simulations are presented in this work, leading to the determination of the cross section for the 232Th(n,f) reaction
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