Rare earth regenerator material particle, rare earth regenerator material particle group, and cold head, superconducting magnet, examination apparatus, and cryopump using the same

摘要

A rare earth regenerator material particle and a regenerator material particle group having a high long-term reliability, and a superconducting magnet, an examination apparatus, a cryopump and the like using the same are provided. A rare earth regenerator material particle contains a rare earth element as a constituent component, and in the particle, a peak indicating a carbon component is detected in a surface region by an X-ray photoelectron spectroscopy analysis.