Mesures des sections efficaces totale et (n,2n) sur 241Am
Vendredi 27/11/2009, 14:30
salle des conseils (bat. 100), Institut de Physique Nucléaire, Orsay

Several measurements of neutron induced reaction cross sections on 241Am have been performed at the JRC-IRMM in Geel, Belgium, in the frame of a collaboration between the EC Joint Research Centres IRMM and ITU and French laboratories from CNRS and CEA. Raw material coming from the Atalante facility of CEA Marcoule has been transformed by JRC-ITU Karlsruhe into suitable 241AmO2 samples embedded in Al2O3 and Y2O3 matrices. They were specifically designed for activation and Time-Of-Flight measurements.

The irradiations for the 241Am(n,2n)240Am reaction cross section measurement were carried out at the 7 MV Van de Graaff accelerator using the activation technique. The measurements were performed in four sessions, using quasi mono-energetic neutrons with energies ranging from 8 to 21 MeV produced via the D(d,n)3He and the T(d,n)4He reactions. The 241Am(n,2n) reaction cross section was determined relative to the 27Al(n,alpha)24Na standard cross section and was investigated for the first time above 15 MeV. The experimental results were used to parameterize new theoretical calculations of the (n,2n) cross section with the TALYS code.

A different sample of the same isotope 241Am has been measured in transmission and capture experiments in the resolved resonance region at the neutron Time-Of-Flight facility GELINA. The transmission measurement was performed in two campaigns, the second one after a recent upgrade of the whole data acquisition system. The performances of the new acquisition system, especially concerning its better flexibility for the off-line data reduction, were investigated. A preliminary analysis of the resonance parameters tends to confirm the recent evaluation to a higher value for the cross section at the bottom of the resonances.

The capture measurement was achieved following the transmission one and using the same sample, but its data reduction and analysis are not part of this PhD work. A new design of C6D6 detectors for capture based on a truncated 5-sided pyramid shape has been studied, especially concerning its total gamma efficiency and its neutron sensitivity.

Contact : Valerie POYETON


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