Development and implementation of a measurement system for PTW water phantom in the determination of absorbed dose to water

At Secondary Standard Dosimetry Laboratory (SSDL) in Venezuela is the only one in the country that performs calibrations of dosimetry systems with an IAEA water phantom. However, SSDL has a PTW water phantom, for which there is no procedure for the calibration of dosimetry systems. Therefore, a methodology was developed for its validation using a cobalt-60 equipment, a secondary standard, an IAEA water phantom and a PTW phantom. The adapter for ionization chamber type NE 2561 was studied and designed to protect it from water. The methodology consisted of calculate of absorbed dose rate to water in IAEA water phantom and PTW water phantom. Subsequently, the absorbed dose rates to water were compared between both phantoms and finally, the validation of the new procedures and their respective uncertainties was performed. The adapter of ionization chamber was built with PMMA material. Comparisons between absorbed dose rates to water showed that there is no difference between the two phantoms. The absorbed dose rate to water was calculated with the procedure updates along with their associated uncertainties, obtaining =0.13482 ± 0.00292 Gy/min. Finally, the validation obtained a value of less than 0.7%, which means that the implementation of the new procedures for the calibration of dosimetry systems is valid and applied at the SSDL-Venezuela.