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Safety_Series_025_1968 - gnssn - International Atomic Energy ...

Safety_Series_025_1968 - gnssn - International Atomic Energy ...

This publication is no

This publication is no longer validPlease see http://www.ns-iaea.org/standards/In reality the state of matters is not so simple and many otherfactors are involved which change the final result.It should be borne in mind that RBE is a radiobiological conceptand that in protection work quality factors are used (see section 1.1.5).Recommended values for the relationship between QF and LET aregiven in Table II.TABLE II. RECOMMENDED VALUES FOR THERELATIONSHIP BETWEEN QF AND LETLETk eV /fim in water3. 5 or less 13 .5 - 7 1 - 27 - 2 3 2 - 523 - 53 5 ' 1053 - 175 10 - 201. 2. 1. 4. Phenomena of radiation injuryRadiation injury is a complex process. The living cell is a verycomplex entity of intricate structure where a complicated series ofevents continually takes place. Radiation acts randomly on differentparts of this system. The relative importance of the part impairedby the radiation determines whether or not the cell is injured ordestroyed. For this reason the first apparent stage of radiationinjury must be sought in changes of the important macro-molecules.1 .2 .1 .4 .1 . Effects on m acro-m olecules of proteins and nucleicacids. A whole range of. biologically important substances, such asenzymes, proteins and nucleic acids, are decomposed in vitroby relatively large doses of radiation. In certain cases direct actionis exerted on the intra-m olecular bonds; in others, however, theaction is indirect through the medium of radicals. In this latter way12

This publication is no longer validPlease see http://www.ns-iaea.org/standards/some enzymes are inactivated. In the case of nucleic acids, modificationshave been observed to occur in certain characteristics,viscosity for example, even after the radiation has ceased. Themajority of macro-molecules forming important cellular constituentsare, however, quite resistant in vivo. This is particularly true ofproteins and of some enzymes, which at the same time are quitesensitive in dilute solution in vitro. On the other hand, the nucleoproteinmetabolism in the cell seems to be modified even by smallradiation doses. The end effect of radiation, it should be borne inmind, is a highly complex event as altered individual componentsinteract, causing new qualitative changes.1.2. 1 .4 .2 . Bacteriophage as models for understanding radiationeffects. Bacteriophage are in essence m acro-m olecules of proteinand nucleic acid. They have a complicated structure but are able tomultiply only in the presence of a living bacterial cell. Outside thecell they have no metabolism of their own. Their genetic apparatusis very complicated. They are able to multiply inside the host celland may be used as a model for the replication of some sub-cellularstructures, e.g. the chromosomes, ribosomes etc. All these c ir ­cumstances suggest the possibility of using phage as models of thefundamental biological action of radiations.When phage are irradiated either outside or inside the bacterialcell, they are inactivated to a degree which depends on the size ofthe dose. Generally the mean inactivation dose is in the range of105 rads. If host cells are heavily irradiated and then infected withnon-irradiated phage, they are still able to support phage growth.The nucleoprotein of the phage itself must be affected by the radiationin order to stop effectively the multiplication of the phage. A veryinterestingfact can be observed when several inactivated phage infectthe same cell. Under such conditions, the phage can recombine theirintact parts within the host cell and form a new phage capable ofreplication. This is a remarkable way of repair of radiation injuryon the molecular level.1. 2 . 1. 4. 3. Morphological changes in the cell. After irradiation acharacteristic change may occur both in-the cell nucleus and in thecytoplasm. In the dividing nucleus, chromosome breaks occur followedby normal or abnormal recombination of the broken ends(aberrations). If these changes take place in gonadal cells, hereditarychanges simulating mutations may ensue. Sometimes after ir-13

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