DEVELOPMENT OF ABSOLUTE MEASUREMENT SYSTEM FOR ��AIR IN 60CO GAMMA RAYS

In the ICRU Report 90, the uncertainty of the recommendation for ${{W}}_{{air}}$ was changed from 0.15 to 0.35%. The purpose of this study is to develop an absolute measurement system for ${{W}}_{{air}}$ in electrons with lower uncertainty using 60Co gamma rays. ${{W}}_{{air}}$ was determined by the ratio of the energy deposition to the number of ion pairs created in a given volume of air using a graphite calorimeter and a graphite-wall ionisation chamber. The obtained value for ${{W}}_{{air}}$ was 33.91 eV with a relative standard uncertainty of 0.08 eV (k = 1), and was in good agreement with the recommended value of the ICRU Report 90 (33.97 eV). Additionally, the uncertainty for ${{W}}_{{air}}$ obtained in this investigation is 0.23% and is comparable with that reported by Burns et al., which is the lowest uncertainty in recent studies determining ${{W}}_{{air}}$ In the future, the proposed system can be used to measure ${{W}}_{{air}}$ in high-energy electron beams.