Calibration of radiation protection area monitoring instruments in Sudan

RADIATION PROTECTION IN THE RELEASE OF PATIENTS RECEIVING 131I TREATMENT

Radiation measurements were made to support radiation protection decisions and instructions concerning the release of patients receiving 131I treatment in Sudan. In hyperthyroidism, administered activity ranged from 370 to 1110 MBq (average: 817.8 MBq), and air-absorbed dose rate at 1 m in front of the patients varied from 20 to 66 μGy h-1 (average: 47.0 μGy h-1). For thyroid cancer patients, the administered activity ranged from 3700 to 7400 MBq (average: 4816.2 MBq), and the air-absorbed dose rate at 1 m in front of the patients ranged from 3 to 55 μSv h-1 (average: 19.2 μSv h-1). On average, the contamination activity was highest in the patients' clothes: 11.0 Bq cm-2, followed by the toilet: 6.6 Bq cm-2 and the front bed: 2.9 Bq cm-2. The estimated release times from the confinement were well with the radiation safety criteria, whereas instruction are given concerning precaution times to limit radiation exposure to family members and co-worker.

TEMPORAL DEPENDENCE OF THE RADIATION MONITORING INSTRUMENTS FOR AREA MONITORING USED AT RADIODIAGNOSTIC AND INTERVENTION FACILITIES

Area monitoring is a fundamental test at radiodiagnostic facilities to maintain an acceptable level of radiation exposure for employees and members of the public. Experimental measurements were taken in an ionising radiation calibration laboratory. Four area monitor instruments were used. Dose and dose rate measurements were measured in integrated and rate operating modes. The results show that precautions are necessary where the area monitor uses exposure times of ≤2 s. When taking measurements in rate mode for times ≤2 s, the area monitors evaluated show a tendency to underestimate dose rate, the inaccuracy was 41 %, and varied between 34 and 45 % for different energies. It is highly recommendable to work in integrated mode, inaccuracy varied from 2 to 35 %. For measurements taken with exposure times of ≥3 s, the average inaccuracy was 15 % and the range was between 2 and 41 %.

Slănic-Prahova low background calibration facility

The reduced background of 2 nSv h(-1) of the Slănic-Prahova Low Background Radiation Laboratory allowed installing a calibration stand for low-dose-rates dosimetry. The stand is provided with (60)Co, (137)Cs and (241)Am low activity sources. A Physikalisch-Technische Bundesanstalt-calibrated AUTOMESS 6150 AD-6 dose rate meter with a 6150 AD-b/H external probe was used to check to what extent this stand could serve as a low background calibration facility. A detailed analysis of possible uncertainties in measuring dose rates evidenced an extended uncertainty related to the certified calibration as well as instrument readings of about 3 % for a confidence level of 95 %. In these conditions, the experimentally determined dose rates for all three gamma ray sources and for source-to-probe distances varying between 0.3 and 2.0 m confirmed a good correlation between the calculated and measured dose rates. At the same time, dose rates perfectly obey to an inverse squared distances law.