We have measured the radiation dose in simple heterogeneous phantoms and compared our results with those obtained by various methods of computation. Dose data were obtained both within and distal to simulated regions of lung in order to test the ratio of tissue-air ratios (TAR), Batho, and equivalent TAR methods. These procedures are used routinely in manual and computer-aided planning of radiation therapy, but have been validated primarily for cobalt-60 radiation. Tests performed with 6- and 15-MV x rays reveal that incorrect doses can be computed within or near to a low-density medium, particularly when the field size is small. In these cases, electronic equilibrium is not achieved in the lateral direction, thereby violating an implicit assumption of all the above calculation methods. We quantify the errors in dose calculation for simple slab phantoms, and support our interpretation with a Monte Carlo simulation in which the energy transported by charged particles away from sites of x-ray interactions is considered directly.
Liquid products from the SRC-II processing of a high volatile bituminous coal were distilled into narrow boiling range fractions with average boiling points ranging up to 800 K. Liquid density, thermal conductivity, and viscosity were measured at temperatures to 505 K, and specific heat was determined to 600 K. Other property determinations included molecular weight, pour point, elemental analyses, water content and solubility, and hydrocarbon types. Both organic oxygen content and water solubility showed a pronounced maximum for the fraction having an average boiling point of 470 K and significantly Influenced density. A secondary distillation on six different fractions spaced over the entire boiling range yielded heart cuts spanning 4-26 K that were used for measurement of surface tension, heat of vaporization, and vapor pressure at temperatures to 755 K. Property data for all the fractions are compared with other published data and existing property correlations.
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