It is required to measure air density correction factor at the time of absorbed dose calibration or measurement. In general, thermometer and barometer are widely used for air density correction. However, this can be done using the radioactive check device with better accuracy. The measurements of air density correction were performed by using the radioactive check device, Unidos electrometer, and 0.6 cc Farmer-type ion chamber of PTW under the different environmental conditions. Above experiments were repeated with thermometer and barometer. By comparing the two methods, they were within the difference of 0.2 L/o. The overall uncertainty for the dose found in thermometer and barometer was 1.2.- 1.6 %, depending upon either one step or two, whereas the overall uncertainty for the radioactive check device was 1.02
! %. This method may reduce the possible error which could occur when thermometer and
barometer are not calibrated at regular basis.
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