Measurement of the $^{244}$Cm, $^{246}$Cm and $^{248}$Cm neutron-induced capture cross sections at the CERN n_TOF facility

Abstract

Accurate neutron capture cross section data for minor actinides (MAs) are required to estimate the production and transmutation rates of MAs in light water reactors, critical fast reactors like Gen-IV systems, and other innovative reactor systems such as accelerator driven systems (ADS). In particular, $^{244}$Cm, $^{246}$Cm and $^{248}$Cm ($^{244,246,248}$Cm) play an important role in the transport, storage and transmutation of the nuclear waste of the actual nuclear reactors, due to the contribution of these isotopes to the radiotoxicity, neutron emission, and decay heat in the spent nuclear fuel. Also, capture reactions in these Cm isotopes open the path for the formation of heavier elements such as Bk and Cf. Recent sensitivity studies have shown that the uncertainties in the evaluations of $^{244,246,248}$Cm in the resonance region are too big to obtain the desired uncertainties in the characterisation of the spent fuel of conventional nuclear reactors.\\ In order to reduce the uncertainties, new measurements of the $^{244,246,248}$Cm capture cross sections have been performed at n\_TOF. There are only two previous capture measurements of the cross sections of these isotopes. The first measurement was carried out in 1969 by Moore \textit{et al.} using an underground nuclear explosion, and the cross sections were measured between 20 eV and 1 keV. The second measurement was performed in J-PARC by Kimura \textit{et al.} in 2010 with germanium detectors, and the cross sections were measured between 4 and 30 eV.\\ The measurements at the n\_TOF facility have been performed with two different samples, one prepared to measure the cross section of $^{244}$Cm and the other to measure the cross sections of $^{246,248}$Cm. The two samples were the same as the ones used in the previous Cm capture measurement at J-PARC. The cross section of $^{244}$Cm has been measured in the first experimental area of n\_TOF (\gls{EAR1}) located at 185 meters with the Total Absorption Calorimeter (TAC) in the energy range between 7 and 100 eV, and in the second experimental area (\gls{EAR2}) located at 19 meters with C$_6$D$_6$ detectors in the energy range between 7 and 300 eV. The results obtained for the two areas are compatible. In \gls{EAR2} the cross sections of $^{246}$Cm and $^{248}$Cm have also been measured, in the energy range between 4 and 400 eV and between 7 and 100 eV, respectively. In addition, the resonances of $^{240}$Pu, present in the samples due to the decay of $^{244}$Cm, have been analysed between 20 and 190 eV. The $^{244,246,248}$Cm and $^{240}$Pu cross sections have been normalised to the first resonance of $^{240}$Pu. \\ In total, 36 resonances of Cm have been fitted, implementing the SAMMY code, and the uncertainties in the resonance parameters are smaller than the uncertainties in the two previous measurements for most of the resonances, improving the status of the nuclear data for these isotopes