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

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Nuclear Science

Background:

• The International Commission on Radiation Units and Measurements (ICRU) Report 90 increased the recommended uncertainty for the absorbed dose to air (Wair) from 0.15% to 0.35%.
• Accurate Wair values are fundamental for precise radiation dosimetry and dose calibration in various applications, including radiotherapy and radiation protection.

Purpose of the Study:

• To develop an absolute measurement system for determining the absorbed dose to air (Wair) with reduced uncertainty using 60Co gamma rays.
• To establish a more accurate Wair value for electrons, addressing the increased uncertainty in current recommendations.

Main Methods:

• Employed a graphite calorimeter and a graphite-wall ionization chamber for absolute Wair determination.
• Calculated Wair as the ratio of energy deposition to the number of ion pairs created in a defined air volume.
• Utilized 60Co gamma rays as the radiation source for the measurements.

Main Results:

• Determined the Wair value to be 33.91 eV with a relative standard uncertainty of 0.08 eV (k=1).
• The obtained Wair value is in excellent agreement with the ICRU Report 90 recommended value of 33.97 eV.
• Achieved a measurement uncertainty of 0.23% for Wair, which is among the lowest reported in recent studies.

Conclusions:

• The developed absolute measurement system successfully determined Wair with a significantly reduced uncertainty.
• The system's low uncertainty makes it a valuable tool for advancing radiation dosimetry standards.
• The proposed system has the potential for future applications in measuring Wair in high-energy electron beams.