Slow scintillation time constants in NaI(Tl) for different interacting particles

•Scintillation time constants in NaI(Tl) from ns up to 300 ms have been studied.•Slow scintillation strong dependence on the exciting particle is reported.•Four crystals have been characterized showing similar, but not the same, behavior.

Very large thallium doped sodium iodide crystals operated underground and in very low background environment in the context of a dark matter search experiment have been used to determine scintillation components in the tens of ms range in the light pulse induced by different interacting particles: γ/μ and α.