Direct determination of dose-to-water using a water calorimeter
A flexible, temperature-regulated, water calorimeter has been constructed which consists of three nested cylinders. The innermost ''core'' is a 10 x 10 cm right cylinder made of glass, the contents of which are isolated from the environment. It has two Teflon-washered glass valves for filling, and two thermistors are supported at the center by glass capillary tubes. Surrounding the core is a ''jacket'' that provides approximately 2 cm of air insulation between the core and the ''shield.'' The shield surrounds the jacket with a 2.5-cm layer of temperature-regulated water flowing at 5 l/min. The core is filled with highly purified water the gas content of which is established prior to filling. Convection currents, which may be induced by dose gradients or thermistor power dissipation, are eliminated by operating the calorimeter at 4 /sup 0/C. Depending upon the power level of the thermistors, 15--200 ..mu..W, and the insulation provided by the glass capillary tubing, the temperature of the thermistors is higher than that of the surrounding water. To minimize potential errors caused by differences between calibration curves obtained at finite power levels, the zero-power-level calibration curve obtained by extrapolation is employed. Also the calorimeter response is corrected for the change in power level, and therefore thermistor temperature, that follows the resistance change caused by irradiation. The response of the calorimeter to 4-MV x rays has been compared to that of an ionization chamber irradiated in an identical geometry. For nitrogen-saturated water, the grand mean of the calorimeter-to-ion chamber (Cal/Ion) dose ratio for five experiments conducted over a period of six months is 1.006 +- 0.001.
- Research Organization:
- Department of Therapeutic Radiology, Yale University, New Haven, Connecticut 06510
- OSTI ID:
- 6246730
- Journal Information:
- Med. Phys.; (United States), Journal Name: Med. Phys.; (United States) Vol. 14:5; ISSN MPHYA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
CALIBRATION
CALORIMETRIC DOSEMETERS
DOSEMETERS
DOSIMETRY
GAMMA DOSIMETRY
HYDROGEN COMPOUNDS
MEASURING INSTRUMENTS
OXYGEN COMPOUNDS
RADIATION DOSE DISTRIBUTIONS
WATER
X-RAY DOSIMETRY