Proposal and experiments of non-destructive analytical method for ancient bronze mirrors with mapping of magnetic fields

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In this study, we have proposed a new method to detect week magnetic fields due to magnetic impurities such as Fe and Ni in ancient bronze mirrors. We developed a magnetic scanning system in combination with a highly sensitive magnetic measurement system using a superconducting interference device called a SQUID and a XY table. Using the system, we demonstrated scanning of a ancient bronze mirror with 82 mm in diameter and 8 mm in thickness, and we obtained residual magnetic field mapping of about 100 nT at maximum. In this result, we have confirmed that this method is useful as a non-destructive observation for bronze mirrors. We also expect the developed system is promising for evaluation of week residual fields in some other antiquities.