Development status of low activation ternary Au–In–Cd alloy decoupler for a MW class spallation neutron source: 1st Production of Au–In–Cd alloy

Abstract

The Japan Spallation Neutron Source (JSNS) at the Japan Proton Accelerator Research Complex (J-PARC) has been developed as a 1-MW spallation neutron source. Ag–In–Cd (AIC) alloy was used as the decoupler material in two decoupled moderators, which allowed high decoupling energies of 1eV to be achieved for the first time in a MW-class spallation neutron source. Although the AIC decoupler is superior in neutronic performance, it has the disadvantage of high residual radioactivity resulting from the production of Ag-110m (T1/2 (half-life)=250d) and Ag-108m (T1/2=418yr). A Au–In–Cd alloy has been proposed as a solution to this problem, as the neutronic performance of this alloy is sufficiently high for it to act as a decoupler. By diffusion of Cd into Au at a maximum temperature of 1123K, we successfully produced this ternary Au–In–Cd alloy. Then, we confirmed the compositional uniformity of the alloy by energy-dispersive X-ray (EDX) analysis. The thermal conductivity, Young’s modulus, and stress at 0.2% strain of the Au–In–Cd alloy were 87.7W/m/K, 80GPa, and 160MPa, respectively. These results demonstrated the possibility of using this alloy as a decoupler. Further study of the Au–In–Cd alloy is in progress.