Radiation Effects in Cells

With respect to radiation protection, the relation between radiation dose and damage, in particular the effects of radiation in cells, is of the greatest importance 

Cells contain about 70% water, and the radiation is largely absorbed by interaction with the water molecules and formation of ions, free radicals and excited molecules. The ions may react at ionizable positions of the DNA (e.g. phosphate groups). Radicals, such as OH and H, and oxidizing products, such as H2O2, may be added at unsaturated bonds or they may break the bonds between two helices. Excited molecules may transfer the excitation energy to the DNA and also cause breaks. A great number of different products of DNA damage have been identified. 

On the other hand, living cells contain natural radical scavengers, and as long as these are present in excess of the radiolysis products, they are able to protect the DNA. However, when the concentration of radiolysis products exceeds that of the scavengers, radiation damage is to be expected. This leads to the concept of a natural threshold for radiation damage which should at least be applicable for low LET values and low radiation intensities, e.g. for low local concentrations of ions and radicals. The scavenging capacity may vary with the age and the physical conditions of the individuals considered. 

With respect to the damage, the dose rate (i.e. the time during which a certain dose is transmitted to the body) is of great importance. This is illustrated by the following example A low-LET dose of 3 Gy produces 3000 single-strand breaks and 100 double-strand breaks in every cell of a human body. If this dose is transmitted within a short time of several minutes, the damage in the cells cannot be repaired and may result in death. However, if the same dose is spread over a period of about a week, only aberrations in the chromosomes are observed. 

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Goldman, M., An overview of high LET radiation effects in cells, in The Health Effects of Plutonium and Radium (W. S. S. Jee, ed.), pp. 751-766, J. W. Press, Salt Lake City, Utah (1976). 

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