The radioactive contamination around a cyclotron

Although cyclotrons are known mainly as closed radiation sources, a considerable radioactive contamination may appear in their surrounding. At the isochronous cyclotron in Juelich the different forms of the radioactive contamination were studied, occuring at different places, on the surface of the structural elements, around the accelerator and target system, and in the connected radiochemical laboratory. The isotropic composition and the activity of the collected samples was determined by using Ge(Li)- and Si(Li) spectrometers. Different contamination monitors were tested with this radioactive sources. Whether they are sensitive enough to correspond to the requirements of the international recommendations and the national regulations concerning the limits of the radioactive contamination. It was found that around the cyclotron often appears surface contamination of varying isotope composition with a surface activity above 0.37 kBq/cm2. The sensitivity of the contamination monitors is generally between 30 - 300 Bq, depending on the decay mode of the investigated isotope(s). The counting rate of the monitors might strongly decrease by the incomplete geometry or by the possible absorbent layers. The calibration of the contamination monitors for practicle purposes is generally difficult and may be only approximately valid, so to determine by them the condition of 'free from contaminants' - satisfying the requirements for an uncontrolled area - is practically impossible. (Author)