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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 37 (1999), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: We determined the impacts of irrigated vegetable agriculture on ground water quality in a 29 km2 portion of the Wisconsin central sand plain (WCSP). Vegetable fields cover 22% of the study area and are used for growing potatoes, sweet corn, snap beans, peas, field corn, and soybeans. We found that contaminant plumes from fields underlay about 54% of the area. Plumes were 3 to 〉16 m thick and in places occupied the entire aquifer thickness. Impacted ground water retained the chemical signature observed under fields, and compared with unimpacted ground water, had elevated NO3-N (median 13.7 mg L−1 impacted vs. 0.5 for unimpacted) and Cl (median 23 vs. 2.0 mg L−1) and 1.4 to 2.5 times the Ca, Mg, K, Na, and SO4. NO3-N detections exceeded 10 mg L−1 in 58% of impacted monitoring wells compared with none of the unimpacted wells. Evidence of denitrification was observed, but rarely. Residues of the pesticides alachlor, atrazine, carbofuran, metolachlor, and metribuzin were detected, but usually at summed concentrations of 〈1 μg L−1 outside of fields. The maximum observed sum of pesticide residues was 8 μg L−1. Not all potential pesticide residues were detectable by the analytical method.Agricultural impacts limit the aquifer's value as a source of potable water, because wells are unable to tap unimpacted ground water through much of the area. Results of this study are generally applicable to other humid sandy areas in the north-central United States and elsewhere. Impacts might be more severe elsewhere because the agricultural land use is frequently denser and ground water flowpaths are longer.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 529-531 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A bunch length monitor for ultrashort (90 fs to 1 ps) electron bunches using a coherent synchrotron radiation detection techniques has been developed in a collaboration between the Thomas Jefferson National accelerator Facility (Jefferson Lab) and the University of Virginia. The noninvasive, high-resolution, high-sensitivity, low-noise monitor employs a state-of-the-art "bandpass" GaAs Schottky whisker diode operated at room temperature. This letter presents the monitor's performance. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Radiation and environmental biophysics 36 (1997), S. 59-66 
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract A simplified method for the calculation of mammalian cell survival after charged particle irradiation is presented that is based on the track structure model of Scholz and Kraft [1, 2]. Utilizing a modified linear-quadratic relation for the x-ray survival curve, one finds that the model yields linear-quadratic relations also for heavy ion irradiation. If survival is calculated as a function of specific energy, z, in the cell nucleus – thus reducing the stochastic fluctuations of energy deposition – the increase in slope of the survival curve and therefore the coefficient β z can be estimated with sufficient accuracy from the initial slope, α z . This permits the tabulation of the coefficients α z for the particle types and energies of interest, and subsequent fast calculations of survival levels at any point in a mixed particle beam. The complexity of the calculations can thereby be reduced in a wide range of applications, which permits the rapid calculations that are required for treatment planning in heavy ion therapy. The validity of the modified computations is assessed by the comparison with explicit calculations in terms of the original model and with experimental results for track-segment conditions. The model is then used to analyze the influence of beam fragmentation on the biological effect of charged particle beams penetrating to different depths in tissue. In addition, cell-survival rates after neutron irradiation are computed from the slowing-down spectra of secondary charged particles and are compared to experimental observations.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Radiation and environmental biophysics 34 (1995), S. 101-106 
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Radiation-induced DNA double-strand breaks (DSBs) were measured in Chinese hamster ovary cells (CHO-K1) using an experimental protocol involving static-field gel electrophoresis following exposure to various accelerated ions. Dose-effect curves were set up, and relative biological efficiencies (RBEs) for DSB induction were determined for different radiation qualities. RBEs around 1 were obtained for low energy deuterons (6–7 keV/µm), while for high energy oxygen ions (20keV/µm) an RBE value slightly greater than 1 was determined. Low energetic oxygen ions (LET=250 keV/µm) were found to show RBEs substantially below unity, and for higher LET particles (≥31 y≥-250 keVµm) RBEs for DSB induction were generally found to be smaller than 1. The data presented here are in line with the generally accepted view that not induced DSBs, but rather misrepaired or unrepaired DNA lesions are related to cellular inactivation.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Radiation and environmental biophysics 37 (1998), S. 47-51 
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Chinese hamster ovary (CHO) cells and thermoluminescent detectors (TLD-700) were used for physical and biological verification of heavy ion treatment planning. Experiments were performed in a cylindrical water phantom, in some cases with lung and bone equivalent material in front of the target volume. The results confirm the possibility of using thermoluminescent detectors for a quantitative verification of dose distributions. CHO cells can be used at least for qualitative dose verification.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-2099
    Keywords: Key words Normal tissue ; Minipig ; Lung ; Heavy particles ; Carbon ionsIntroduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract  The response of pig lungs to irradiation with 12C-ions was assessed in two experiments to validate the procedures for heavy ion therapy planning at the Gesellschaft für Schwerionenforschung (GSI) and to explore their range of applicability. In both experiments, the target volume (spread-out Bragg peak, SOBP) was planned to be a 4 cm long cylinder with a diameter of 4 cm. Doses in the SOBP were prescribed to be equivalent to 5×4 Gy, 5×5.5 Gy and 5×7 Gy of x-rays in the first experiment, and to 5 fractions of 7 Gy and 9 Gy in the second experiment. The lung response in the first experiment was less than expected on the basis of earlier experiments with photons. Pneumonitis reaction and chronic fibrotic changes were observed outside the prescribed high-dose region. In the second experiment, the effects were more pronounced than had been expected on the basis of the first experiment. Changes were most intense in the high-dose region, but were also seen throughout the lung along the beam channel. Moreover, significant skin reactions were observed at the beam entrance site in all animals and – less pronounced – at the beam exit site in 3 of the 6 animals. In conclusion, the complex irradiation geometry of the pig lung, the changes of body weight between the two experiments, and insufficient accounting for a change in the relative biological effectiveness (RBE) computation led to substantial deviations of the observed reactions from expectations, the reasons for which could be identified in a subsequent analysis. The less pronounced lung reaction in the first experiment was due to an overestimation of RBE in a preliminary version of the algorithm for its determination. The extension of the fibrotic reaction resulted from the smear-out of the high-dose region due to density variations in tissue structures, respiratory movement, and limited positioning accuracy. The skin reactions at the entrance port reflect the different treatment geometry in the two experiments. The one unexplained observation is the mild skin reaction that was observed in the second experiment at the beam exit site.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Radiation and environmental biophysics 38 (1999), S. 229-237 
    ISSN: 1432-2099
    Keywords: Key words Ions ; Tumor therapy ; RBE ; Track structure ; Treatment planning ; Carbon beam
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract  The elevated relative biological effectiveness (RBE) of heavy ions like carbon is the main reason for their use in radiotherapy and is due to the microscopic distribution of dose inside each particle track. High local doses produce lesions that are expected to have a diminished possibility of repair. Thus, RBE depends on track structure and on the biological repair capacity of the tissue that is affected by the irradiation. For tumor treatment planning with heavy ions, the beam quality and the tissue sensitivity have to be taken into account. Using the dependence of radial dose distribution on particle energy and atomic number on the physical side and x-ray dose response for the repair capacity on the biological side, the response to particle irradiation can be calculated in the local effect model (LEM) and used for treatment planning. This article traces the route from electron emission as the basis of track structure to the RBE calculation and the application in treatment planning.
    Type of Medium: Electronic Resource
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