Radiological characterization of targets from the ISOLDE facility at CERN

The European Laboratory for Particle Physics (CERN, Geneva) has been operating accelerators for high-energy physics both on Swiss and French territory for 50 years. Due to the interaction of the particle beams with matter, part of the accelerator structure and its surroundings become radioactive. Once at the end of their operational lifetime, these materials are defined as waste. The elimination of radioactive waste towards the final repositories in France and Switzerland requires the determination of the radionuclide inventory. The radioactive nuclides generated in accelerators are different from those identified in reactors. With very few exceptions there are no fission products and alpha emitters. One of the requirements for acceptance of an item of waste in a repository is an estimate of the residual long-lived radioactive nuclides with their specific activity. The list should be exhaustive and include also those nuclides which are difficult to be experimentally detected. Different methods for the evaluation of the radionuclide inventory are currently under investigation at CERN. This paper describes the application of one method, the so-called fingerprint method, to a specific case of radioactive waste, the one of the targets of the ISOLDE facility. Both advantages and limitations of the method are highlighted. In the present study, the fingerprints are calculated both with Monte Carlo methods and gamma spectroscopy and they are applied to a large collection of targets.