U.P.B. Sci. Bull., Series D, Vol. 74, Iss. 1, 2012 ISSN 1454-2358 DETERMINATION OF DIFFICULT TO MEASURE NUCLIDES IN SPENT RESINS Ruxandra TOMA 1 , Ilie PRISECARU 2 , Cristian DULAMA 3 This paper presents a method to determine Strontium – 90 in liquid samples by extracting Strontium 90 from the sample with the Eichrom resin, Sr-Spec, and using the Deconvolution Method in order to eliminate the interferrences due to other radionuclides. Due to its pure beta emission, Strontium 90 cannot be measured directlz bz radiometric methods, and it requires radiochemical separation from the matrix and determination bz liquid scintillation counting afterwards. The experiments were performed at the Nuclear Research Institute, Piteşti, Romania and the method provided by Eichrom to extract Stronntium 90 from the sample was adapted to the laboratory’s resources. Keywords: Strontium 90, deconvolution, radioactive waste. 1. Introduction The Radiological characterization represents one of the basic processes in radioactive waste management activities, through which it can be achieved the goal of a high quality final product realization for disposal. In order to properly characterize the radioactive waste packages it is required to know the amounts and concentration of specific radionuclides in the waste package. Many of these specific radionuclides are difficult to measure from outside of the package, as they are alpha and beta emitting radionuclides, and they require laborious and complex radiochemical separation methods, which are not practical for large amounts of waste packages originating from the same waste stream [1]. The difficult-to-measure nuclides of primary interest are those with very long half-lives which will persist in a disposal site long after the period of institutional control. Their declaration is often important for the assessment of the consequences to health and safety for future uses of the disposal site. The information about the activity concentration and total activity are also required for the transport of radioactive materials [2]. 90Sr can be produced by neutron fission in nuclear reactor and weapons testing and released to environment and it is one of important radionuclides in the views of radiation protection, environmental monitoring, radioecology, and radioactive waste management due to its relative high radioactive level in 1 Eng., University POLITEHNICA of Bucharest, Faculty of Power Engineering, Nuclear Engineering Department, Bucharest, Romania, email: tomar@router.citon.ro 2 Prof., University POLITEHNICA of Bucharest, Faculty of Power Engineering, Nuclear Engineering Department, Bucharest, Romania, e-mail: prisec@gmail.com. 3 Phys., Institute for Nuclear Research, Radioprotection Laboratory, Pitesti, Romania, e-mail: cristian.dulama@nuclear.ro.