Petkau effect
Encyclopedia
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.
Petkau had been measuring, in the usual way, the dose that would rupture a particular cell membrane
. He found that 3500 rad
s delivered in 2¼ hours (26 rad/min = 15.5 Sv/h) would do it. Then, almost by chance, he tried again with much weaker radiation and found that 0.7 rads delivered in 11½ hours (1 millirad/min = 0.61 mSv/h) would also destroy the membrane. This was counter to the prevailing assumption of a linear relationship between total dose or dose rate and the consequences.
The radiation was of ionizing nature, and produced negative oxygen
ion
s. Those ions were more damaging to the membrane in lower concentration
s than higher (a somewhat counterintuitive result in itself) because in the latter, they more readily recombine with each other instead of interfering with the membrane. The ion concentration directly correlated with the radiation dose rate and the composition had nonmonotonic consequences.
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
exposure. It was found by Dr. Abram Petkau at the Atomic Energy of Canada Whiteshell Nuclear Research Establishment, Manitoba
Manitoba
Manitoba is a Canadian prairie province with an area of . The province has over 110,000 lakes and has a largely continental climate because of its flat topography. Agriculture, mostly concentrated in the fertile southern and western parts of the province, is vital to the province's economy; other...
and published in Health Physics March 1972.
Petkau had been measuring, in the usual way, the dose that would rupture a particular cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
. He found that 3500 rad
Rad (unit)
The rad is a unit of absorbed radiation dose. The rad was first proposed in 1918 as "that quantity of X rays which when absorbed will cause the destruction of the malignant mammalian cells in question..." It was defined in CGS units in 1953 as the dose causing 100 ergs of energy to be absorbed by...
s delivered in 2¼ hours (26 rad/min = 15.5 Sv/h) would do it. Then, almost by chance, he tried again with much weaker radiation and found that 0.7 rads delivered in 11½ hours (1 millirad/min = 0.61 mSv/h) would also destroy the membrane. This was counter to the prevailing assumption of a linear relationship between total dose or dose rate and the consequences.
The radiation was of ionizing nature, and produced negative oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s. Those ions were more damaging to the membrane in lower concentration
Concentration
In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...
s than higher (a somewhat counterintuitive result in itself) because in the latter, they more readily recombine with each other instead of interfering with the membrane. The ion concentration directly correlated with the radiation dose rate and the composition had nonmonotonic consequences.