Concepts of Microdosimetry and their Applicability to Radiation Protection Problems in Manned Space Missions
Abstract
A distinct and characteristic feature of ionizing radiation is its discontinuous interaction with matter. The energy imparted to the exposed material is due to discrete random events with stochastic fluctuating energy depositions. These fluctuations result in a highly non-uniform microdistribution of the transmitted energy and the subsequent radiation products. The current dosimetric quantities, such as the absorbed dose, D, or the Linear Energy Transfer, LET, are merely the statistical averages of the actual energy deposits and may deviate from these by orders of magnitude. The deviations are most substantial for small volumes, for small doses, or for densely ionizing radiations.
Biological effects of ionizing radiation depend on the energy deposited in volumes as small as individual cells or subcellular structures. Differences in the biological effectiveness of different types of ionizing radiation at equal values of absorbed dose can only be understood if the microstructure of the different spatial energy-deposition patterns are taken into account.
The characteristic feature of the ambient radiation field in space with its broad spectrum of different radiation quality makes it neccessary to take account of the stochastical nature of energy deposition. Microdosimetry provides the concepts that are required to quantify the microscopic distributions and the spatial correlation of energy deposits in small volumes and for radiations of different quality. Microdosimetric approaches have led to a deeper understanding of the underlying primary mechanisms of the interaction of ionizing radiation with biological structures.
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