Ionizing radiation is damaging to DNA, but is there such a thing as a safe dose below which no DNA damage could occur? I'm not asking about a minimum safe dose overall, just whether or not there's an amount of ionizing radiation so small that the cell wouldn't even "notice" it if it were absorbed. Suppose I have, say, a fertilized egg cell on a petri dish. Would a single stray x-ray photon absorbed by the cell be enough to destroy it before it could reproduce? Is most DNA damage from x-rays due to the action of single photons, or from multiple ones being absorbed at the same time?