Development of the mini ionization chamber for high dose monitoring on line inside a gamma irradiation facility

A cylindrical ionization chamber of 0.9 cm³ has been developed for monitoring high doses on line during the sample irradiation at a static position in a ⁶⁰Co gamma industrial plant, with about 25.9 PBq (700 kCi). Nitrogen gas at pressure of 1 bar was utilized to fill the ionization chamber and to determine an appropriate configuration to be used as a detector for high dose measurements. The first detector tests were carried out using a ⁶⁰Co Gammacell with about 0.26PBq (7 kCi) and dose rates of 0.6, 1.8 and 2.6 kGy/h. These dose rates were reached with lead absorbers. A good linearity of the detector was found between dose and accumulated charge, independently of the different dose rates caused by lead absorbers. The developed ionization chamber showed suitable to be used as a dosimeter on line for doses between 1 to 6 kGy at a ⁶⁰Co Gammacell independently of the spectrum degradation caused by absorbers between 50 to 90%.