Dynamic field on 40-MeV. mu. /sup +/ traversing magnetized iron

Previous experiments have demonstrated the existence of large dynamic magnetic fields that act on positive heavy ions traversing magnetized iron. These studies have been extended to the limit of ionization and to v/c = 0.68 by using spin-polarized muons. The angular precession of the spin of ..mu../sup +/ particles which traversed magnetized-iron plates and stopped in aluminum was measured. Decay positrons were detected at 0/sup 0/, 90/sup 0/, and 270/sup 0/. Relative phases of the corresponding muon-spin-rotation spectra were obtained as a function of the magnetization direction in the iron. After subtracting the phase shift resulting from the saturation magnetization in the iron and the fringing fields, the experimental result for the dynamic field ..delta..B = -0.5 +- 2.6 kG is obtained, in agreement with theoretical expectations for very fast totally stripped ions.