Biological dosimetry of solar radiation for different simulated ozone column thicknesses.

During the Spacelab mission D-2, in the experiment RD-UVRAD, precalibrated biofilms consisting of dry monolayers of immobilised spores of Bacillus subtilis (strain Marburg) were exposed, for defined intervals, to extraterrestrial solar radiation filtered through an optical filtering system, to simulate different ozone column thicknesses. After the mission, the biofilms were processed and optical densities indicative of any biological activity were determined for each exposure condition by image analysis. For the different simulated ozone column thicknesses, biologically effective irradiances were experimentally determined from the biofilm data and compared with calculated data using a radiative transfer model and the known biofilm action spectrum. The data show a strong increase in biologically effective solar UV irradiance with decreasing (simulated) ozone concentrations. The full spectrum of extraterrestrial solar radiation leads to an increment of the biologically effective irradiance by nearly three orders of magnitude compared with the solar spectrum at the surface of the Earth for average total ozone columns.

Recent results of the joint ESA-DARA/IBMP experiments Biokosmos "Seeds".

Comparison of experimental data obtained from short (SDEF) and long duration exposure flights (LDEF) have recently led to results which will be significant for longer and/or repeated sojourn of man in space. Under orbital conditions biological stress and damage are induced in test subjects by cosmic radiation, especially the high energetic, densely ionizing component of heavy ions. Plant seeds were successful model systems for a biotest in studying the physiological damages and mutagenic effect caused by ionizing cosmic radiation in particular stem cells. Dosimetrically, the subdivision into charge- and Let-groups reveals the contribution of the intermediate group (LET = 350-1000 MeV/cm) due to the medium heavy ions (Z = 6-10). Their relative contribution increases with the lower inclination of the orbit of LDEF-1; on the other hand, the total fluence becomes higher with longer duration of the flight. The observed endpoints of the biological radiation damage hint at a correlation with particle dose rate rather than with the dose; additionally, data on shielding effects inside and outside the space craft and its exposure were gained from the different SDEF- and LDEF-missions.

Long-Term Dosimetry of Solar UV Radiation in Antarctica with Spores of Bacillus subtilis.

The main objective was to assess the influence of the seasonal stratospheric ozone depletion on the UV climate in Antarctica by using a biological test system. This method is based on the UV sensitivity of a DNA repair-deficient strain of Bacillus subtilis (TKJ 6321). In our field experiment, dried layers of B. subtilis spores on quartz discs were exposed in different seasons in an exposure box open to solar radiation at the German Antarctic Georg von Neumayer Station (70 degrees 37'S, 8 degrees 22'W). The UV-induced loss of the colony-forming ability was chosen as the biological end point and taken as a measure for the absorbed biologically harmful UV radiation. Inactivation constants were calculated from the resulting dose-response curves. The results of field experiments performed in different seasons indicate a strongly season-dependent trend of the daily UV-B level. Exposures performed at extremely depleted ozone concentrations (October 1990) gave higher biologically harmful UV-B levels than expected from the calculated season-dependent trend, which was determined at normal ozone values. These values were similar to values which were measured during the Antarctic summer, indicating that the depleted ozone column thickness has an extreme influence on the biologically harmful UV climate on ground.

Experiment "Seeds" on Biokosmos 9. Dosimetric part.

The aim of the experiment "Seeds" on the Sowjetic satellite Biokosmos 9 was the observation of mutagenic effects caused at special loci of seeds of Arabidopsis thaliana and assigned to particles of the Cosmic radiation. Two types of exposure units were flown: A low-shielding unit Type I, mounted at the surface of the satellite (1.4 g/cm2 shielding) and, for comparison, an identical item inside (16 g/cm2 shielding), using nuclear emulsion as track detectors. A Type II unit, flown inside (18g/cm2 shielding) was mounted with AgCl track detectors. The layout will be briefly described. A first set of dosimetric data from the physical evaluation of the experiment will be presented. The subdivision into charge- and LET-groups shows a rather high contribution of the intermediate LET-group (350-1000 MeV/cm) due to medium heavy particles (Z = 6-10) and to enders of light (p, alpha) particles.

Biokosmos 8 experiment: dosimetric measurements with AgCl track detectors behind low shielding.

Monocrystalline sheets of AgCl nuclear track detectors, mounted on top of a detector package, covered by a thin light-filter of 15 micrometers-thick Kapton-foil, were flown in the outside facilities of the Biokosmos 8 Mission. The aim of this lay-out was to record low energy protons and heavy ions, including SAA particles, from the unshielded cosmic radiation. The tracks recorded turned out to be strongly faded. The possible reasons, high temperature (>60 degrees C at the detector surface indicated by temperature markers) or too high temporary intensities of the filtered sunlight, are discussed on the basis of simulation experiments. The report briefly describes: (1) Characteristics of the AgCl-detectors. (2) The lay-out of the experiment, postflight handling and results. (3) Simulation experiments on the ground with respect to the observed fading. (4) A new lay-out proposed for a future analogous experiment with AgCl-detectors.

LET spectra of cosmic-ray nuclei for near earth orbits.

Measurements of cosmic-ray LET spectra were part of the radiobiological space research programs during the Spacelab 1 (SL-1) and the D1 missions. We analyzed CR-39 plastic nuclear track detectors of the Advanced Biostack experiment of SL-1 and of the Dosimetric Mapping and Carausius morosus experiments in the BIORACK on D1. The particle tracks in the CR-39 were detected and measured by an automatic scanning and measuring system. An in-flight calibration was derived from track measurements of minimum ionizing oxygen and iron nuclei and of stopping nuclei as a function of the residual range. LET spectra measured at different locations in the space shuttle are presented and discussed for both missions. A model describing the effects of the geomagnetic field of the earth on charged cosmic-ray particles and the shielding by matter is used to calculate LET spectra for the two missions and for typical space station orbits at low inclinations. A comparison of measured LET spectra and LET spectra calculated for different flight parameters shows that besides geomagnetic shielding the shielding by matter is most important in comparison to solar modulation and to variation of particle flux with flight altitude. Model calculations must be improved and must consider more detailed sectored shielding by matter and the influence of trapped radiation. The last item is of importance in the case of low-inclination orbits.

Life sciences: radiobiological advanced biostack experiment.

The radiobiological properties of the heavy ions of cosmic radiation were investigated on Spacelab 1 by use of biostacks, monolayers of biological test organisms sandwiched between thin foils of different types of nuclear track detectors. Biostacks were exposed to cosmic radiation at several locations with different shielding environments in the module and on the pallet. Evaluations of the physical and biological components of the experiment to date indicate that in general they survived the spaceflight in good condition. Dosimetric data are presented for the different shielding environments.

Advanced biostack: experiment 1 ES 027 on Spacelab-1.

The radiobiological properties of the heavy ions of cosmic radiation were investigated on Spacelab 1 by use of biostacks, monolayers of biological test organisms sandwiched between thin foils of different types of nuclear track detectors. Biostacks were exposed to cosmic radiation at several locations with different shielding environments in the module and on the pallet. Evaluations of the physical and biological components of the experiment to date indicate that in general they survived the spaceflight in good condition. Dosimetric data are presented for the different shielding environments.

Assignment of particle tracks to spores of Bacillus subtilis on silver chloride detectors.

In Biostack III B, flown in the Apollo-Soyuz Test Project, AgCl detectors were used to study ionizing effects of HZE particles on spores of Bacillus subtilis or eggs of Artemia salina. The tracks of these particles inside the detectors are used to extrapolate the path of the particle near the biological objects which are fixed at the detector surface. The closest distance to the geometric centre of the object, the so-called impact parameter, is determined with a mean accuracy of 0.3 micrometers for 1 micrometers spores. From knowledge of the lateral distribution of the energy transferred by primary and secondary ionization effects of the particle, the energy deposit and its localization at the objects can be determined. We describe some technical aspects of a video-electronic scanning system, Quantimet 720, which has been adjusted to the particular requirements of these experiments. The main improvements achieved are increased precision of coordinate measurements, objective focusing of the microscopic image combined with measurements of the density profile of particle tracks, and finally speeding up of the measurements by automatic data transfer.

Radiobiological results of the Biostack experiment on board Apollo 16 and 17.

After penetrating the Biostack capsule, some of the HZE particles hit the biological objects carried: bacterial spores (Bacillus subtilis), seeds (Arabidopsis thaliana and Vicia faba), and shrimp eggs (Artemia salina). The different biological objects were affected by heavy ions in widely varying ways. A broad range of radiobiological investigations has been carried out in regard to the objects' response to HZE particles. The most sensitive biological objects in the Biostack experiments proved to be the shrimp eggs. The development of 500 eggs hit by heavy cosmic ions was investigated. This differed significantly from the flight controls (eggs flown in the Biostack but not hit by heavy ions) and from the ground controls. From this it has been concluded that penetration on the part of a single heavy ion may injure the encysted blastula. This damage was found to influence gastrula formation and even the hatching process of the nauplius. Abnormalities (increased by a factor of 10) in the orthonauplius were observed during the development of the hit eggs; they consisted, for example, of shortened extremities or an abnormal thorax or abdomen. In addition, eggs of Tribolium confusum and Carausius morosus, which were included in Biostack 2 (Apollo 17), have been investigated, and the influence of single heavy ions on the development process of these highly organized insects has been studied.

AgCl detectors in the Biostack II experiment aboard Apollo 17.

Two layers of AgCl detectors with a total surface of 90 cm2 were flown. Tracks of nuclei, from light (Z>4) up to the heaviest were recorded and could be distinguished by their geometrical trackwidths. The tracks were divided into five groups of atomic numbers, and their abundance was measured. Also the number of surviving nuclear stars was counted. 22.5 cm2 of the detector surface were covered with eggs of Artemia salina. The detectors could be developed without removing the eggs, so that the spots hit could be determined directly. The radiation effect on these eggs is being investigated.

Solid state AgCl detectors for nuclear tracks with on- and off-response at choice: applications to life sciences.

A new concept of trackforming solid state detectors is presented. These detectors record and accumulate tracks of ionizing particles which can be revealed if they are irradiated with yellow light during the passage of the particle through the detector; otherwise the tracks are dropped by fading. Tracks stabilized by yellow light are stable for months. The detectors consist of thin layers of 200-300 micrometers of Cd-doped AgCl crystals, supported by a thin plate of quartz glass. The invisible latent tracks in these detectors are revealed at microscopically visible size by ultraviolet light. The sensitivity of the crystals against particles of different specific energy transfer depends upon the concentration of Cd; these have rather good thresholds, which permit selective recording in a well-known manner. These AgCl(Cd) crystals have a unique property amongst trackforming detectors; their response can be switched on and off at choice, for instance by electronic triggering of the stabilizing accompanying yellow light. This allows a time assignment of particle tracks, or restriction to tracks of desired particles. Examples of tracks and of applications in cosmic ray research, heavy ion physics, radiobiology and dosimetry are given.

The Biostack experiment on Apollo 16.

The object of the Biostack experiment is to study the biological effects of high ZE particles of cosmic radiation in order to obtain information on the mechanism of these particles in biological matter. For this purpose individual local evaluation methods have been developed which allow one to identify each biologically effective particle and to correlate the individual hitting particle with the biological effect produced. The Biostack experimental package contains a series of monolayers of selected biological objects (Bacillus subtilis spores, Arabidopsis thaliana seeds, Vicia faba radiculae, Artemia salina eggs) with each layer sandwiched between several different cosmic ion track detectors (nuclear emulsions, cellulose nitrate, polycarbonate). By this arrangement a variety of biological effects due to a single penetrating particle can be analysed. Influence on cellular and tissue development, nuclear damages, and mutation induction are the main investigated effects. These space flight findings will be completed by results of balloon flight and accelerator experiments.