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  • 1990-1994  (9)
  • 1
    Electronic Resource
    Electronic Resource
    Protection of DNA from high LET radiation by two OH radical scavengers, tris (hydroxymethyl) aminomethane and 2-mercaptoethanol (1993)
    Springer
    Radiation and environmental biophysics 32 (1993), S. 21-32 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The effect of high linear energy transfer (LET) radiation on DNAin vitro, both in protective and non-protective environments was investigated. Two hydroxyl radical scavengers, tris(hydroxymethyl) aminomethane and 2-mercaptoethanol, were compared for their ability to protect SV40 DNA from radiation damage over a wide LET range. At comparable OH scavenging capacities, significant differences were found between these protective agents, indicating that other, radical scavenger-dependent processes affected the extent to which the DNA was protected. In general, a decrease in single-strand breaks (SSBs) relative to double-strand breaks (DSBs) was observed as LET increased. This effect was more pronounced when a radioprotector was present. Comparison of the relative biological efficiency (RBE) of radiation damage as LET increased showed a peak of DSB production in the mid-LET range. These data agree with measurements made by Christensen et al. (1972). An explanation for this increase in DSB production efficiency has been proposed based on the particle track structure of high-LET radiation.Correspondence to: G. Taucher-Scholz
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01213127
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  • 2
    Electronic Resource
    Electronic Resource
    Heavy ion induced membrane damage: Hemolysis of erythrocytes and changes in erythrocyte membrane fluidity (1994)
    Springer
    Radiation and environmental biophysics 33 (1994), S. 233-241 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Human erythrocytes were irradiated with heavy ions of energies between 4 and 18 MeV/u having linear energy transfer (LET) values between 92 and 14000 keV/µm. Hemolysis has been studied as a macroscopic parameter for membrane damage and changes of the fluidity as a more microscopic parameter. The membrane fluidity changed in a characteristic dose-dependent manner as detected by electron spin resonance employing 12-doxylstearic acid methyl ester spin label (SL 12). Lysis cross sections and RBE values were determined from dose effect curves. The results demonstrate a high hemolytic efficiency of heavy ions compared to X rays. With increasing LET values the measured relative biological efficiency (RBE) values increase continuously. In the complete LET range the cross sections formed one common curve as function of LET and no saturation effects are observed. This is in direct contrast to other biological endpoints such as cell inactivation or DNA damage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01212679
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  • 3
    Electronic Resource
    Electronic Resource
    Combination of static-field gel electrophoresis and densitometric scanning for the determination of radiation-induced DNA double-strand breaks in CHO cells (1994)
    Springer
    Radiation and environmental biophysics 33 (1994), S. 111-124 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract An experimental setup using static-field gel electrophoresis (SFGE) was developed to determine radiation-induced DNA double-strand breaks (DSBs) in CHO-K1 cells after exposure to X-rays or heavy charged particles. The fraction of DNA eluted into the gel matrix depends on the quantity of DSBs introduced. In agreement with a recent report, SFGE and pulsed-field electrophoresis were found to be equally sensitive in DSB detection. With radiolabeled DNA from cell cultures, the absolute amount of DNA migrating out of agarose plugs into the gel was quantified by determining the radioactivity in the gel lane. Alternatively, relative measurements of the amount of DNA released into the gel were achieved with a standardized protocol for both SFGE and a subsequent densitometric scanning of photographic negatives from gels stained with ethidium bromide. After calibration with the radioactive method, the fractions of DNA retained could be calculated directly from the data obtained with the densitometric assay to set up classical dose-effect curves. This procedure was validated for its application with heavy ions using an 500 MeV/u lead beam.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01219335
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  • 4
    Electronic Resource
    Electronic Resource
    LET, track structure and models (1992)
    Springer
    Radiation and environmental biophysics 31 (1992), S. 161-180 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Summary Swift heavy ions when penetrating through matter strip off those electrons having a smaller orbital velocity than the ion velocity. The remaining electrons screen the nuclear charge yielding an effective charge. The effective charge of the ions interacts predominately with the target electrons causing excitation and ionizations of the target atoms. Using the Bethe Bloch formula for the energy loss combined with the Barkas formula for effective charge, the energy loss values as well as unrestricted and restricted linear transfer can be calculated within a few percent of accurancy. From the primary energy loss only a small fraction of 10% or less is transformed into excitation. The major part of the energy loss is used for the ionization of the target atoms and the emission of the corresponding electrons with a high kinetic energy. These electrons form the track around the trajectory of the primary ion in which two thirds of the primary energy is deposited by collisions of primary, secondary and later generations of electrons with the target molecules. In the electron diffusion process the energy is transported from the center of the track into the halo. The radial dose decreases with the square of the radial distance from the center. The diameter of the track is determined by the maximum range of the emitted electrons, i.e. by the maximum energy electrons. All ions having the same velocity i.e. the same specific energy produce electrons of the same energy and therefore tracks of the same diameters independent of the effective charge. But the dose inside the track increases with the square of the effective charge. Track structure models using this continuous dose distributions produce a better agreement with the experiment than models based on microdosimetry. The critical volume as used in microdosimetry is too large compared to the size of the DNA as critical structure inside the biological objects. Track structure models yield better results because the gross-structure of the track i.e. its lateral extension and the thin down toward the end of the track is included in these calculations. In a recent refinement the repair capacity of the cell has been included in a track structure model by using the complete shouldered x-ray survival curve as a template for the local damage produced by the particle tracks. This improved model yields presently the best agreement with the experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01214825
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  • 5
    Electronic Resource
    Electronic Resource
    Calculations of heavy-ion track structure (1994)
    Springer
    Radiation and environmental biophysics 33 (1994), S. 91-109 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract A Monte Carlo model is presented to study details of the energy deposition inside tracks of heavy charged particles in water vapor. The input data for most of the calculations based on the binary encounter approximation are double-differential cross sections for electron emission after heavy-ion impact. The paths of the liberated electrons are simulated, taking into account elastic scattering, ionization, and excitation. Each basic interaction of an electron or heavy ion is treated individually. Radial dose distributions and specific energy deposition are calculated for projectiles from protons to uranium in the energy range from one to several hundred megaelectron volts per unified atomic mass unit. Good agreement with measurements in tissue-equivalent gas and propane is obtained for light and medium-heavy projectiles, whereas for heavy projectiles such as uranium, deviations around a factor of 2–3 are observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01219334
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  • 6
    Electronic Resource
    Electronic Resource
    Irradiation increases proteolysis in erythrocyte ghosts: A spin label study (1992)
    Springer
    Radiation and environmental biophysics 31 (1992), S. 117-121 
    Details
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Summary X- and gamma-irradiation of human erythrocyte membranes (250–1000 Gy) was found to decrease the ratio of weakly to strongly immobilized signal height of membrane-bound maleimide spin label (Mal-6). Subsequent incubation of spin-labeled membranes at ambient temperature (21 °C) induced a progressive increase in this ratio, faster for membranes irradiated with low doses which was hampered by protease inhibitors. These results demonstrate that ionizing radiation stimulates proteolysis of erythrocyte membrane proteins by membrane-associated proteases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01211209
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  • 7
    Electronic Resource
    Electronic Resource
    Delta-electron emission in fast heavy ion — atom collisions: observations of new phenomena and breakdown of common scaling laws (1992)
    Springer
    The European physical journal 22 (1992), S. 713-721 
    Details
    ISSN: 1434-6079
    Keywords: 34.50.Fa ; 34.80.Kw
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Double differential cross sections for the emission of Delta-electrons have been measured in fast uranium-rare gas collisions. The well-known Binary Encounter peak reveals unexpected structures for certain observation angles and its intensity increases towards smaller angles, which is in contradiction to results and scaling laws obtained by experiments with light ion impact. The observed dependencies are fairly well described by recent calculations in the framework of IA and CTMC. From systematic experimental as well as theoretical studies we can derive that the potential of the partially stripped projectile ion gives rise to rainbow and glory scattering of the target electron in the field of the projectile. The rainbow scattering is observed in the laboratory frame as pronounced interference structures, whereas the glory scattering is responsible for the steep increase of the cross sections for binary-encounter electrons towards small laboratory ejection angles. The observed effects have a dramatic influence on the commonq 2 scaling laws derived from experiments with light ions. Furthermore, since the binary-encounter electrons ejected at forward angles have approximately twice the projectile velocity, these new phenomena have an important influence on the electronic stopping power of heavy ions and therefore have to be taken into account for the investigation of radiation damage by these ions e.g. in biological matter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01437253
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  • 8
    Electronic Resource
    Electronic Resource
    δ-Electron emission in fast, highly-charged heavy ion-atom collisions (1991)
    Springer
    The European physical journal 21 (1991), S. S301 
    Details
    ISSN: 1434-6079
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426333
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  • 9
    Electronic Resource
    Electronic Resource
    5th Leipzig symposium on biotechnology december 10-13, 1990 (1991)
    Berlin : Wiley-Blackwell
    Acta Biotechnologica 11 (1991), S. 183-183 
    Details
    ISSN: 0138-4988
    Keywords: Life Sciences ; Life Sciences (general)
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/abio.370110224
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