Abstract
The measurement of the capture cross-section of fissile elements, of utmost importance for the design of innovative nuclear reactors and the management of nuclear waste, faces particular difficulties related to the $ \gamma$ -ray background generated in the competing fission reactions. At the CERN neutron time-of-flight facility n_TOF we have combined the Total Absorption Calorimeter (TAC) capture detector with a set of three 235U loaded MicroMegas (MGAS) fission detectors for measuring simultaneously two reactions: capture and fission. The results presented here include the determination of the three detection efficiencies involved in the process: $\ensuremath \varepsilon_{TAC}(n,f)$ , $\ensuremath \varepsilon_{TAC}(n,\gamma)$ and $\ensuremath \varepsilon_{MGAS}(n,f)$ . In the test measurement we have succeeded in measuring simultaneously with a high total efficiency the 235U capture and fission cross-sections, disentangling accurately the two types of reactions. The work presented here proves that accurate capture cross-section measurements of fissile isotopes are feasible at n_TOF.
Highlights
The measurement of accurate neutron-induced capture and fission cross-sections is essential for the design of innovative nuclear systems such as ADS and Gen-IV reactors [1,2]
Out of all the neutron-induced cross-sections that play a role in nuclear technology applications, those for which improvement is considered of utmost importance are included in the High Priority Request List [3] of the International Atomic Energy Agency IAEA
Half of the capture cross-section measurements included in this list are of fissile isotopes, and these are very difficult to measure because in such cases the γ-rays generated in fission reactions may constitute a very large background when measuring γ-rays emitted in neutron capture reactions
Summary
The measurement of accurate neutron-induced capture and fission cross-sections is essential for the design of innovative nuclear systems such as ADS and Gen-IV reactors [1,2]. Out of all the neutron-induced cross-sections that play a role in nuclear technology applications, those for which improvement is considered of utmost importance are included in the High Priority Request List [3] of the International Atomic Energy Agency IAEA. Among all those already measured, only 233U is fissile; meaning that below the characteristic fission threshold the fission cross-section is very small and does not compete with the neutron capture or scattering reactions. This new set-up has been used to measure simultaneously the capture and fission cross-sections of 235U using a stack of three thin 235U samples (see [10] for a set-up at LANL tested for a similar purpose)
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