Study of the radiation damage of Nd-Fe-B permanent magnets.

Nd-Fe-B permanent magnets are highly desirable for use in the insertion devices of synchrotron radiation sources due to their high remanence, or residual magnetic induction, and intrinsic coercivity. However, the radiation environment within high-energy electron storage rings necessitates the determination of the degree of radiation sensitivity as well as the mechanisms of radiation-induced demagnetization. A 0.5% change in the residual induction due to radiation damage cannot be tolerated in these devices. Sample Nd-Fe-B permanent magnets were irradiated at the Advanced Photon Source (APS) with bending magnet x-rays up to an absorbed dose of approximately 280 Mrad (1 Mrad = 10 kGy). Sample magnets were also irradiated with 60 Co {gamma}-rays up to an absorbed dose of 700 Mrad at the National Institute of Standards and Technology's (NIST) standard gamma irradiation facility. Changes in the residual induction were found to be within the experimental uncertainties for both the x-ray and {gamma}-ray irradiations. Sample Nd-Fe-B permanent magnets were then irradiated at Oak Ridge National Laboratory's (ORNL) Californium User Facility for Neutron Science with fast neutrons up to a total fast fluence of 1.61 x 10{sup 14} n/cm{sup 2} and with thermal neutrons up to a total thermal fluence of 2.94 x 10{sup 12} n/cm{sup 2}. The fast-neutron irradiation with a {sup 252}Cf spontaneous fission source revealed significant changes in residual induction of the sample magnets