Study on the Differences in Measurement Results of Radiation Dose Rate From Cirus Teletherapy System with 60Co Source in Off Condition Using 4 Different Surveymeters

Study on the differences in measurement results of radiation dose rate from Cirus Teletherapy system with 60Co
source in off condition using 4 different surveymeters have been carried out. This study was conducted to determine the
feasibility of performance, measurement of uncertainty and the uniformity of measurement results of 4 different types of surveymeter. The instruments used to measure gamma radiation dose rate has calibration factors ranging from 0.923 to 1.010. Two surveymeters (A and B) have a measurement unit in Sievert/hour (Sv/h) and two others (C and D) has a measurement unit in Rontgen/hour (R/h). Cirus teletherapy system used as research objects have radiation source of 60Co with activity of 233.63 TBq as of June 1, 1999. Retrieval of research data was conducted during the system was in off conditions and focused on one point in the front of the container that has the highest gamma radiation dose rate. Data were collected at a distance of 5 cm and 100 cm from the surface of the container front and repeated for 10 times for each measurement point. The results showed that all surveymeters have response and nearly has the same performance. The background was ranged from 0.000 to 0.231 μSv/h. The uncertainty at a distance of 5 and 100 cm was at a ranges (1.93 to 5.55)% and (1.00 to 10.39)%, respectively. The surveymeter B has the best precision because it has advantages 2 decimal digits behind the comma for the same amount of dose rate. Whereas Surveymeter D shows the differences in the measurement at the distance of 100 cm to 5 cm by 63% compared to other three surveymeters (<2%), so the performance and uniformity of these surveymeters were not good. From these results we are expecting that radiation workers should choose one type of surveymeter with the most appropriate and suitable so that the calculation of the limitation of radiation doses for workers/general public can be done properly in accordance with regulation in Perka BAPETEN No. 6/2009 and No. 4/2013.