How is irradiation used in sterilisation?

Sterilisation uses Irradiation in the form of gamma when sterilisation through heat is not possible. Objects are sterilised through irradiation by first being wrapped in plastic paper to stop bacteria from entering, then the object is placed near a radioactive isotope that emits gamma radiation, and the isotope is inside a lead shield to protect workers from radiation. And when the lead shield is removed gamma radiation irradiates the object, and the gamma radiation kills any present bacteria