Velocity dependence of transient hyperfine field at Pt ions rapidly recoiling through magnetized Fe

The velocity dependence of the transient hyperfine magnetic field acting at nuclei of ${}_{}{}^{196}{}_{}{}^{}\mathrm{Pt}$ ions rapidly recoiling through thin magnetized Fe was investigated at a number of recoil velocities. The state of interest ($2_1^{+}$) was populated by Coulomb excitation using beams of 80- and 120-MeV ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ and 150- and 220-MeV ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ ions. The $2_1^{+}$→$0_1^{+}$ $\gamma$-ray angular distribution precession measurements were carried out in coincidence with backscattered projectiles. From these results, the strength of the transient field acting on Pt ions recoiling through magnetized Fe with average velocities in the extended range $2.14\le 〈\frac{v}{v_0}〉\le 4.82$ ($v_0=\frac{c}{137}$) was found to be consistent with a linear velocity dependence and to be incompatible with the specific $v^{0.45\pm 0.18}$ dependence which has been previously reported to account well for all ions in the mass range from oxygen through samarium. This seemingly singular behavior for Pt and other ions in the Pt mass vicinity is discussed.