The thin layer activation (TLA) technique has been applied to study the surface erosion of D9 stainless steel (D9 SS) by producing a thin layer (~430µm) of ⁵⁶Co activity using 15 MeV proton beam. The cumulative ablation thickness of 90µm in D9 SS, observed against total deposited laser energy of ~20kJ, is reported here. The minimum detection limit was found to be ~50 nm in the measurement of surface loss of material by TLA technique. No surface loss could be detected when D9 SS was exposed to laser fluence pre-requisite for its efficient decontamination.