[en] The holistic approach to analyzing tissue effects that are initiated primarily at the level of cells, thus leads to new questions in radiation biology, which still need to be answered. Only with the help of the tools of microdosimetry applied at the level of cells, can the sequence of biological responses perpetuating from the atomic-molecular level to the more complex levels of biological organization be integrated into assessing risk to the whole organism. This is important for radiation protection and uncovers the potential for beneficial effects also in terms of a reduced incidence of malignant diseases following low dose irradiation. (orig.)

[en] Single-event spectra have been measured for ⁶⁰Co γ-radiation and filtered 200 kV X-rays for spherical and cylindrical volumes of sub-cellular size. For the measurements a novel wall-less proportional counter was developed which in a simple manner may be converted into a wall-counter. Measurements of the gas amplification of this counter yielded new values for the gas parameters A and B permitting the estimation of the multiplication of proportional counters at high electric potential on the collecting electrode. It further showed that the minimum effective diameter to be used is 0.1 μm if measurements of radiation with a low LET are made. The energy deposition with the highest probability was approximately 0.17 KeV/μm for the ⁶⁰Co radiation and approximately 0.65 KeV/μm for the X-radiation. (orig./BJ)

No abstract available

[en] It is shown that three parameters are necessary to characterize energy absorption of a certain radiation in small volumes: the shape and size of the volume, its cross-section to the radiation in question, and the absorbed energy. The cross-section in relation to the radiation is bigger than the geometrical cross-section because of δ-ray production. Measurement of the radiation defined cross-section and its relation to the geometrical cross-section is proposed. A new measure describing the absorbed energy is defined which is based on the mean local energy density and is called ''Linear Energy Absorption'' (LEA). It is shown that the LEA is equal to the track length averaged LET for any volume shape, if the ionizing particles are ideally straight lines crossing the volume. In cases where this idealization does not hold, the LEA is, in general, bigger than the track length averaged LET and gives the correct value for the mean energy absorbed inside of the volume per unit length. The LEA should therefore be used as the biologically significant average of LET spectra. (author)

[en] High doses of ionizing radiations are known to bear the risk of cancer to the exposed individual. In order to appreciate potential carcinogenesis from low doses also, the action of ionizing radiation in the human body has to be considered in holistic approach: energy depositions to individual cells trigger effects within a hierachical structure of interacting levels of biological systems, consisting consecutively of atoms, molecules, cells and organ tissue. The present paper describes the cell dose concept which is an essential factor in assessing the risk due to the ionizing radiation to the cells and tissues. Low dose of ionizing radiation induces adaptive response in individual cells which could be linked to the action of molecular radicals. Enzyme activities in bone marrow cells and bilayer lipid membranes and radicals are directly related to radiation effects. Temporary improvements of the detoxification of molecular radicals also improve the cellular defence. The risk analysis calls for more attention as it is important for radiation protection and other beneficial effects due to low doses of irradiation. (author). 18 refs

[en] The contributions of a poster session from a clinical radiotherapy conference are discussed. The contributions were concerned with radiation quality, RBE measurements, dosimetry and neutron spectra with particular respect to the biologically and clinically significant description of the radiation quality of fast neutron and high LET radiations. The usefulness of a quantity, y*, describing the saturation corrected dose average lineal energy was discussed. It was concluded that microdosimetric models need to be refined with regard to a more precise description of radiobiological mechanisms. In clinical radiation, a physical quantity describing radiation quality remains an unsolved problem. (U.K.)

[en] Only a complete description of biological systems allows the assessment of health risks due to ionizing radiations at environmental levels (Feinendegen, 1990). The smallest functional entity in biological systems appears to be the living cell. At first the risk of a cell to a radiation stimulus and the severity of this stimulus has to be ascertained. These are physical parameters, which depend on the type of radiation and the dose. Furtheron, the kind and probability of the cell reaction to radiation stimuli has to be determined. This is a biological parameter, which depends on the condition of the cell at the time of exposure. This parameter is not invariant, since defence and repair mechanisms are available to the cell. Only if the response of cells is known as a function of radiation quality and its condition at the time of the exposure, the assessment of concequences for a cell system (organ or organism) may be attempted. Due to the variability of cell responses to ionising radiation events, a linear relation between dose and effect may not be generally valid at the system level. (orig.)

[en] Results are presented for some basic physical parameters of low energy monoenergetic electrons (20eV-2keV) in several important gases (CH₄, CO₂, A, N₂ and tissue-equivalent gas of Rossi and Failla). Specifically the results are detailed measurement of: a) the mean energy required to form an ion pair - W-value, b) electron transmission functions and electron range - R₉₅. The physical principles of the apparatus used to obtain the above results is briefly outlined, and an estimation of the error in the results is made. Comparison between these experimental results and the work of other experimental and theoretical groups is discussed. The W-value is found to increase with lowering primary electron energy for all gases measured. The reported W-values do not show the 'bump' observed by Waker and Booz (2) both for CH₄ and tissue-equivalent gas. The electron range (R₉₅) measurements are in general agreement with the experiments of Cole (3) for air, but below 100eV the present results tend to be below that of Cole. The present results fit well with the recent calculations of Rsub(ext) of Terrissol and Patau (13) for water, and above 500eV the reported data is slightly higher than the theoretical results of Berger (11) for the Rsub(csda) in water

[en] A new operational quantity is suggested, H⁰(d), that is the dose equivalent in the cavity of a hollow sphere of the same composition and external diameter as the ICRU sphere. The parameter d corresponds to the wall thickness of such a hollow phantom, d=25 mm being its recommended value for environmental monitoring of penetrating radiations. The proposed quantity is invariant to the direction of incident radiation. Its relation to the effective dose equivalent is not less advantageous than that of the ambient dose equivalent. The feasibility of the experimental realisation of H⁰(25) has been demonstrated. (author)

[en] Monte Carlo simulated proton- and alpha-particle tracks in water vapor were used to develop an analytical function for calculating number distributions of ionizations induced in spherical sites. For charged particles crossing the site, Fermi-like functions were used to approximate the ionization distributions. Ionization event distributions due to particles passing outside the site were approximated with an exponentially decreasing function. The function parameters were calculated for protons and alpha particles in the energy range 0.3-5.0 MeV/amu and for site diameters of 1 to 1000 nm. The quality of fit obtained is very good for the particles, energy range and site diameters considered. (orig.)