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Measurements of the 241 Am(n,2n) reaction cross section have been performed at the Joint Research Centre (JRC) Geel in the frame of a collaboration between the European Commission (EC) JRC and French laboratories from CNRS and the Commissariatà L'Energie Atomique (CEA) Cadarache. Raw material coming from the Atalante facility of CEA Marcoule has been transformed by JRC Karlsruhe into suitable 241 AmO 2 samples embedded in Al 2 O 3 matrices specifically designed for these measurements. The irradiations were carried out at the 7-MV Van de Graaff accelerator. The 241 Am(n,2n) reaction cross section was determined relative to the 27 Al(n,α) 24 Na standard cross section. The measurements were performed in four sessions, using quasi-monoenergetic neutrons with energies ranging from 8 to 21 MeV produced via the 2 H(d,n) 3 He and the 3 H(d,n) 4 He reactions. The induced activity was measured by standard γ -ray spectrometry using a high-purity germanium detector. Below 15 MeV, the present results are in agreement with data obtained earlier. Above 15 MeV, these measurements allowed the experimental investigation of the 241 Am(n,2n) reaction cross section for the first time. The present data are in good agreement with predictions obtained with the TALYS code that uses an optical and fission model developed at CEA.

Measuring and modeling (n, n ) cross section is chal-68 lenging leading to large uncertainties. Therefore it features 69 prominently in the High Priority Request List (HPRL) 70