Indirect and direct measurement of thermal neutron acceleration by inelastic scattering on the 177Lu isomerG. Bélier1, O. Roig1, V. Méot1, J. Aupiais2, J.-M. Daugas1, Ch. Jutier2, G. Le Petit2, A. Letourneau3, F. Marie3 and Ch. Veyssière4
1 CEA/DIF/DPTA Service de Physique Nucléaire, BP. 12, 91680 Bruyères-le-Châtel, France
2 CEA/DIF/DASE Service de Radio-analyse, Chimie et Environnement, BP. 12, 91680 Bruyères-le-Châtel, France
3 CEA/DSM/DAPNIA Service de Physique Nucléaire, CE Saclay, 91191 Gif-sur-Yvette, France
4 CEA/DSM/DAPNIA Service d'Ingénierie des Systèmes, CE Saclay, 91191 Gif-sur-Yvette, France
Published online: 21 May 2008
When neutrons interact with isomers these last can be de-excited. In such a reaction the outgoing neutron has an energy greater than the ingoing one. This process is referred as Inelastic Neutron Acceleration or Super-elastic Scattering. Up to now this process was observed for only two nucleus, 152mEu and 180mHf by measuring the number of fast neutron produced by isomeric targets irradiated with thermal neutrons. In these works the energies of the accelerated neutrons were not measured. This report presents an indirect measurement of inelastic neutron acceleration on 177mLu, based on the burn-up and the radiative capture cross sections measurements. Since at thermal energies the inelastic scattering and the radiative capture are the only processes that contribute to the isomer burn-up, the inelastic cross section can be deduced from the difference between the two measured quantities. Applying this method for the 177Lu isomer with different neutron fluxes we obtained a value of 258 (58) barns, and determined that there is no integral resonance for this process. In addition the radiative capture cross section on 177gLu was measured with a much better accuracy than the accepted value. Since the acceleration cross section is quite high a direct measurement of this process was undertaken, sending thermal neutrons and measuring the fast neutrons. The main goal now is to measure the outgoing neutron energies in order to identify the neutron transitions in the exit channel. In particular the K conservation question can be addressed by such a measurement.
© CEA 2008