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Radioactive 55Fe is formed as a result of neutron activation of stable iron by (n,γ) nuclear reaction. It decays by electron capture to 55Mn with the half-life of 2.7 years. Since in the primary decay process only undetectable neutrinos are emitted the activity determination is based on the measurement of secondary x-ray radiation (average energy 5.9 keV) and Auger-electrons (average energy 5.2 keV) that are created as a consequences of the filling of the hole of captured electron. Radioactivity is usually measured with a proportional counter or using liquid scintillation counting. In the 1950s and 1960s, a significant quantity of 55Fe ended up in stratosphere as a result of the nuclear weapons tests carried out in the atmosphere. In the stratosphere, the 55Fe deposited as a global fallout. The half-life of 55Fe is so short that it has all already decayed. 55Fe is a typical activation product radionuclide in nuclear power plants. It is primarily formed from the iron of the primary circuit. As a result of corrosion iron mobilized into primary circuit coolant water from which it is trapped into purification systems, e.g. ion exchange resins. Radioactive iron has also ended up in the environment from the nuclear power plant accidents. Since the low energy of radiation generated by 55Fe it is not of major radiological risk concern.
The aim of this work is to analyze 55Fe from spent ion exchange resins from the purification of nuclear power plant process waters. For to the measurement of 55Fe radioactivity by liquid scintillation counting iron must be separated from other radionuclides, especially from other radioactive activation and corrosion products.