A new standard cylindrical graphite-walled ionization chamber for dosimetry in 60Co beams at calibration laboratories

• A new cylindrical ionization chamber was developed to be used as a reference dosimeter.
• The characterization tests were performed according to the IEC 60731 standard.
• All tests presented results within its recommended limits.
• The correction factors were determined using the EGSnrc Monte Carlo code.
• This dosimeter presents potential use as a primary standard dosimeter.

60Co sources are used mostly at dosimetry laboratories for calibration of ionization chambers utilized for radiotherapy dosimetry, mainly in those laboratories where there is no linear accelerator available. In this work, a new cylindrical ionization chamber was developed and characterized to be used as a reference dosimeter at the Calibration Laboratory of the IPEN. The characterization tests were performed according to the IEC 60731 standard, and all tests presented results within its recommended limits. Furthermore, the correction factors for the wall, stem, central collecting electrode, nonaxial uniformity and the mass-energy absorption coefficient were determined using the EGSnrc Monte Carlo code. The air kerma rate determined with this new dosimeter was compared to the one obtained with the IPEN standard, presenting a difference of 1.5%. Therefore, the new ionization chamber prototype developed and characterized in this work presents potential use as a primary standard dosimeter at radiation metrology laboratories.