Decommissioning procedures for an 11 MeV self-shielded medical cyclotron after 16 years of working time

The present article describes the decommissioning of a compact, self-shielded, 11 MeV medical cyclotron. A Monte Carlo simulation of the possible nuclear reactions was performed in order to plan the decommissioning activities. In the course of the cyclotron dismantling, cyclotron components, shields, and floor concrete samples were measured. Residual activities were analyzed with a Ge(Li) detector and compared with simulation data. Doses to staff involved in the decommissioning procedure were monitored by individual TL dosimeters. The simulations identified five radioactive nuclides in shields and floor concrete: ⁵⁵Fe and ⁴⁵Ca (beta emitters, total specific activity: 2.29 × 10⁴ Bq kg^-1) and ¹⁵²Eu, ¹⁵⁴Eu, ⁶⁰Co (gamma emitters, total specific activity: 1.62 × 10³ Bq kg^-1). Gamma-ray spectrometry confirmed the presence of gamma emitters, corresponding to a total specific activity of 3.40 × 10² Bq kg^-1. The presence of the radioisotope ¹²⁴Sb in the lead contained in the shield structure, corresponding to a simulated specific activity of 9.38 × 10³ Bq kg^-1, was experimentally confirmed. The measured dose from external exposure of the involved staff was