Plutonium Biokinetics in Human Body A. Luciani - Kit-Bibliothek - FZK

Annex
Quantities used in Radiological Protection
and Internal Dosimetry
The interaction of the ionizing radiations with the biological matter determine a release of
energy that changes the physical characteristics of atoms and molecules and may thus sometimes
damage cells and tissues. When a damage to cells occurs two effects are possible:
1. The cell can get unable to survive or to reproduce;
2. It can be able to live and reproduce but in a modified form.
These two different effects of the interaction of ionizing radiation have important
consequences for the whole organism the cells belong to.
In the first case if the damage has caused a significant loss of cells the relating tissue will be
likely characterized by a decrease of its own functions. The probability of causing such harm will
be zero at small doses but will increase quickly above a certain level of dose, called dose threshold.
Above such threshold the severity of the damage too will increase with the dose. This type of effect
due to the ionizing radiation is currently called “deterministic”.
In the second case the clone produced by the cell, still alive but subdued to modification
owing to the ionizing radiation interaction, may show malignant consequences, after a variable
delay called latency period. The probability of a cancer increases with the dose but the severity of
the cancer is not affeted by the level of the dose. This kind of effect is called “stochastic”. It is
currently assumed that the stochastic effect have no dose threshold and that the probability of
occurrence is roughly proportional to the dose, particularly for doses smaller than the dose threshold
for deterministic effect. In the particular case in which the damage occurred in a cell for the
transmission of the genetic information, the effect may result in defects in the progeny of the
exposed persons. This particular type of stochastic effect is called “hereditary”.
The system of radiation protection has the primary goal of preventing the occurrence of
deterministic effects and of limiting the effect of the stochastic effects to an acceptable level; this
means that professional activities with exposure to ionizing radiations should not be characterized
by a risk higher than other professional activities currently considered “safe”.
In order to control the exposure to ionizing radiation quantities have been expressively
designed and developed by ICRP for radiation protection purposes. The quantities were developed
by ICRP since different years [58] up to a wide and deep review and update work presented in the
Publication 60 [26].
The fundamental quantity in radiation protection is the absorbed dose D given by:
D = d
dm
155
equation A.1
where d is the energy of the ionizing radiations absorbed by the matter of mass dm. The SI
unit for the absorbed dose is J kg -1 and its special name is “gray” (Gy). The absorbed dose is defined