Use of Miniature Glass Rod Dosimeters in Radiation Ecology

A system is discussed for radiation dose measurements in ecological studies with 1 x 6 mm silver—activated metaphosphate glass rods. The miniature size of the dosimeters, their low cost, simplicity of use, and wide range of sensitivity make them especially well suited for use in radiation ecology. The system measures radiation dose by the principle of radiophotoluminescence, whereby ionizing radiation entering the glass matrix reduces ionic silver to its ground state. This change is directly proportional to dose and is easily measured in a fluorometer which can be calibrated to give the actual dose that was received by the rods. Two important radioecological applications are (1) the measurement of exposure, and (2) the measurement of absorbed dose in media of interest such as tissue, soil, and water. Air exposure can be measured at particular locations around gamma irradiation facilities or above an infinite plane source (radioactive fallout on soil or radionuclides mixed with soil). Glass rods used to measure the exposure above the radioactive White Oak Lake bed showed that the exposure rate at five feet is reduced to only one half of the dose rate at the soil surface. Cotton rats tagged with glass rod dosimeters on White Oak Lake bed had an absorbed dose rate of approximately 2.8 rads/day in mid—June of 1962, but the dose rate decreased to 1.5 rads/day by mid—December. This decrease in dose rate was attributed to the gradually rising water table which filtered low energy photons and caused a corresponding decrease of the dose rate above the soil surface. The miniature fluorods were successfully implanted in acorns, in an on living plants, and in soil. Many other applications are possible in radiation ecology including the use of glass rods to monitor wildlife.