Measurement of Residual Radioactivity of Machine Elements and Concrete on the Cyclotron Decommissioning

The AVF cyclotron was decommissioned at the CYRIC (Cyclotron and Radioisotope Center) of Tohoku University for installing a new cyclotron. With this decommissioning, we sampled the main part of machine elements such as accelerator box, acceleration electrodes, magnet yoke, and the concrete of the cyclotron vault which had been strongly activated for about 20 years operation. We measured the residual radioactivities of these samples with a high pure Ge detector and identified the nuclides of 22Na, 46Sc, 51Cr, 54Mn,59Fe, 56Co, 58Co, 60Co, 65Zn, 134Cs, 152Eu from the gamma-ray spectra and half-lives. The peak counts per unit time (cps) were converted into radioactivities per unit mass (Bq/g) with the Ge peak efficiency In addition, we measured the spatial dose distribution in the cyclotron room and the surface dose of electromagnet with a Nal (Tl) survey meter. These results will be useful for the future accelerator decommissioning.