Neutron-induced fission cross section ofNp237in the keV to MeV range at the CERN n_TOF facility

Abstract

The neutron-induced fission cross section of 237 Np was experimentally determined at the high-resolution and high-intensity facility n TOF, at CERN, in the energy range 100 keV to 9 MeV, using the 235 U(n,f) and 238 U(n,f) cross section standards below and above 2 MeV, respectively. A fast ionization chamber was used in order to detect the fission fragments from the reactions and the targets were characterized as far as their mass and homogeneity are concerned by means of α spectroscopy and Rutherford backscattering spectroscopy respectively. Theoretical calculations within the Hauser-Feshbach formalism have been performed, employing the EMPIRE code, and the model parameters were tuned in order to successfully reproduce the experimental fission cross-sectional data and simultaneously all the competing reaction channels.

Study of the 240Pu(n,f) and 237Np(n,f) reaction cross sections at the new experimental area (EAR2) of the CERN n_TOF facility

“…As shown in fig. 4.68, there is an overall agreement within uncertainties with the latest time-of-flight measurements, performed at the n TOF facility as well, by Diakaki et al [41][42][43] and Paradela et al It is quite remarkable that the three datasets right before the fission plateau, presented a very nice agreement within less than 3% in the region from 800 keV up to 1 MeV. 4.69, were discrepant within up to 7%.…”

“…24a) while smaller but still in need to be resolved 10% discrepancies can be seen in the first chance fission plateau between 1 -6 MeV (fig. 24b) where even the two latest measurements by Diakaki et al [41][42][43] and Paradela et al [44] at the time that the present thesis was written show discrepancies up to 7%.…”

“…On the other hand, the 237 N p(n, f ) cross-section is equally important, since it is frequently used as a reference reaction in feasibility and design studies regarding advanced nuclear systems. In addition, the latest time-of-flight data by Paradela et al [44] and Diakaki et al [41], both obtained at n TOF, revealed a discrepancy of the order of 7% at the first chance fission plateau, which the present work attempted to solve.…”

The fission experimental programme at the CERN n_TOF facility: status and perspectives

“…An additional measurement was also performed in EAR-1 by employing the FIC detection setup, covering incident neutron energies between 150 keV and 10 MeV. The cross section measured with the PPAC setup [69] was found to be systematically higher, by 4-6% in the plateau of first-chance fission, than the FIC measurement [124] and evaluations of the major nuclear data libraries, a somewhat unexpected result shown in Fig. 52.…”

“…In order to verify and improve these results, the measurement of the 241 Am(n,f) cross section has recently been repeated with Micromegas detectors in Fig. 52 The 237 Np(n,f) cross section measurement was performed during the first phase of operation in EAR-1 using the PPAC [69] and the FIC [124] detection setups. The measurements had a 4-6% discrepancy in the 1-6 MeV region (inset) therefore the measurement was repeated in EAR-1 and EAR-2 with the "tilted PPAC" and Micromegas detectors, respectively the second experimental area, taking advantage of the higher neutron flux and of the much more favourable signal-tobackground ratio in the new measuring station for the background related to the α-decay of this relatively short-lived actinide.…”