Thermal-spike lifetime from picosecond-duration preequilibrium effects in hyperfine magnetic fields following ion implantation

The effective hyperfine magnetic fields acting on short-lived excited nuclear states (27<t<127ps) have been measured for ∼7.5MeV Ir and Pt ions immediately after implantation into iron hosts at room temperature. The observed field strengths decrease with the lifetime of the probe state and are consistent with the hyperfine field being absent for about 6 ps after implantation. As the hyperfine field is quenched while the local temperature exceeds the Curie temperature, these results give a direct measurement of the thermal-spike lifetime.