Neutrons and the Oxygen Effect: Corroboration of the Greater Effectiveness at High LET for Sensitization by Oxygen at Low Concentrations

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Abstract
Another comparison was made between the sensitivity of cells at low O2 concentration to 290 kV X-rays or 14 MeV neutrons. The K values for O2 with young sporelings of the fern Osmunda regalis were 35 .+-. 5 .mu.M for X-rays, and 23 .+-. 7 .mu.M for neutrons. The former value is higher than those reported for other cells. The trend toward a lower value for neutrons is consistent with 2 of 3 previous comparative mesurements. This consensus of experimental evidence indicates that the comonent of the dose from neutrons, which demonstrates an O2 effect, tends to show more affinity for sensitization by O2 in the competitive-type reaction which leads to fixation of damage than does the X-ray dose. This qualitative feature should be considered in proposed mechanisms for the reduction in OER [oxygen enhancement ratio] with an increase in ionization density, and these are discussed.

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