Radiationhyphen;induced changes in the magnetization of sintered Ndhyphen;Fehyphen;B permanent magnets are known to vary widely among specimens produced by different manufacturers. Samples of Ndhyphen;Fehyphen;B MAGNEQUENCH magnets, which are made from melthyphen;spun ribbons, have not been studied and show a much reduced sensitivity to neutron irradiation than do sintered Ndhyphen;Fehyphen;B magnets. All melthyphen;spun ribbonhyphen;based MAGNEQUENCH magnets, i.e., epoxyhyphen;bonded, hothyphen;pressed, and diehyphen;upset magnets, show essentially the same slow decrease in magnetic remanence with neutron dose. Measurements of the openhyphen;circuit remanenceBr/Brthinsp;0at various times during the irradiation show a decay of only 1.5percnt; of the preirradiated value for the MAGNEQUENCH magnets after 1 h of irradiation, or a dose of 1.4times;1016neutrons/cm2, compared to a 4.6percnt; drop in remanence for the best sintered Ndhyphen;Fehyphen;B magnet (Sumitomo 30H) with the same irradiation dose. Moreover, after 5.3 h of irradiation, the remanence drops by only 3percnt; for the MAGNEQUENCH magnets. Magnets made from melthyphen;spun ribbons are thus the least sensitive to neutron irradiation so far measured for Ndhyphen;Fehyphen;B permanent magnets, but are somewhat more sensitive than samariumhyphen;cobalt magnets.
展开▼
