Conductimetric Dosimetry: A Calorimetric Method for Measuring High-Intensity Pulsed Radiation

A calorimetric method for measuring the absorbed dose received by an aqueous solution from a 15-MeV linear accelarator, has been developed. A quartz conductivity cell with two parallel, circular platinum electrodes, filled with a 0.01 M phosphate buffer of pH 7, is placed coaxially behind a collimator confining a circular electron beam of about half the electrode diameter. When the cell receives a burst of electrons, the absorbed energy causes a temperature rise in the irradiated electrolyte which in turn results in an increase in electrical conductivity, corresponding to a temperature coefficient of about 2%/°C. The conductivity change is measured in a sensitive bridge circuit and recorded. Since, due to the short irradiation time of 2 seconds or less, the temperature rise is quasi-adiabatic, no thermal insulation is required. Doses as low as 1 krad can be measured with a standard deviation of 3%. Errors due to radiation chemical reactions could be excluded, but a correction for the energy absorption in the platinum was necessary. The conductimetric dosimeter agreed with the Fricke dosimeter within experimental random errors.