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

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 1 eV 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-110 m ( T _1/2 (half-life) = 250 d) and Ag-108 m ( T _1/2 = 418 yr). 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 1123 K, 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 87.7 W/m/K, 80 GPa, and 160 MPa, respectively. These results demonstrated the possibility of using this alloy as a decoupler. Further study of the Au–In–Cd alloy is in progress.