RESUMEN
Various types of proton-irradiated lead-bismuth eutectic (LBE) samples from the MEGAPIE prototype spallation target were analyzed concerning their content of (148)Gd, (173)Lu, and (146)Pm by use of α- and γ-spectrometry. A radiochemical separation procedure was developed to isolate the lanthanide fraction and to prepare thin samples for α-ray measurement. The results prove a substantial depletion of these three elements in bulk samples, whereas accumulation on the LBE/steel-interfaces was observed. The amount of material accumulated on surfaces was roughly estimated by relating the values measured on the sample surfaces to the total surface of the inner target walls. The amount of (148)Gd, (173)Lu, and (146)Pm was then quantified by summing up the contributions from every sample type. The results show a reasonable agreement with theoretical predictions. The obtained results are of utmost importance for the evaluation of the performance of high-power spallation targets, especially concerning the residual nuclide production, the physicochemical behavior of the produced radionuclides during operation, and in terms of an intermediate or final disposal.
RESUMEN
A spallation ultra-cold neutron source--UCN source--is scheduled to start operation at PSI in 2006 using up to 2 mA 590 MeV protons from the ring cyclotron. It will be operated in a pulsed mode with an average current of 20 microA. For safe maintenance, during operation as well as handling, transport and storage of the UCN target assembly after its lifespan, detailed knowledge about the activation induced by the impinging protons and secondary radiation fields is required. The Monte Carlo transport code MCNPX was coupled with the European Activation System--EASY--to calculate the residual nuclide production in the UCN target assembly. The nuclide inventory is finally used to design the shielded exchange flask that is needed to safely remove and transport the UCN target assembly after its lifespan to a hotcell for dismantling.