The Petkau effect is an early counterexample to linear-effect assumptions usually made about radiation exposure.
It was found by Dr. Abram Petkau at the Atomic Energy of Canada Whiteshell Nuclear Research Establishment, Manitoba and published in Health Physics March 1972.
[2] Petkau had been measuring, in the usual way, the radiation dose that would rupture a simulated artificial cell membrane.
[3] Then, almost by chance, Petkau repeated the experiment with much weaker radiation and found that 0.7 rad delivered in 11+1⁄2 hours (1 millirad/min = 0.61 mSv/h) also ruptured the membrane.
[7] Thus, Petkau's original 1972 experiment apparently revealed the potential effects of ionizing radiation on cells without natural radioprotective mechanisms in place.