Radiopurity of an archaeological Roman lead cryogenic detector

Archaeological Roman lead (Pb) is known to be a suitable material for shielding experimental apparata in rare event searches. In the past years the intrinsic radiopurity of this material was investigated using different technologies. In this work we applied the latest advancements in cryogenic techniques to study the bulk radiopurity of a 1 cm${}^3$ sample of archaeological Roman Pb. We report the lowest ever measured limit on ${}^{210}$Pb content in Roman Pb, with a concentration lower than 715 μBq/kg. Furthermore, we also studied ${}^{238}$U and ${}^{232}$Th impurity concentrations. Our values concur with independent measurements reported in literature.