Material issues relating to high power spallation neutron sources
M Futakawa, J-PARC Center, Japan Atomic Energy Agency, Japan

Neutrons are used for innovative research in scientific and engineering fields, i.e. fuel cell, hydrogen embrittlement, protein structure, medicine, etc. High power pulsed-spallation neutron sources are being operated at the Materials and Life Science Experimental Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC) in Japan and the Spallation Neutron Source (SNS) in the US. In both facilities, liquid mercury was selected as a target material to produce pulsed-neutrons by spallation reaction because of its high-neutron yield and efficient self-cooling performance.
When protons bombard mercury, the thermal shock results in pressure wave propagation, leading to aggressive cavitation and damage on the solid wall of the target vessel. The cavitation phenomenon becomes a crucial issue to increase the power in the mercury target for the pulsed spallation neutron source.
In order to mitigate the cavitation damage, two kinds of approaches have been applied: hardening of vessel-wall and softening of mercury.