## 1 Introduction  
The ENEA Research Center in Frascati housed the Frascati Tokamak Upgrade (FTU), a high-magnetic-field tokamak dedicated to research on radio-frequency plasma heating [1, 2]. This facility is currently undergoing decommissioning to make space for the new Divertor Tokamak Test (DTT), which will investigate alternative divertor configurations relevant to DEMO, the demonstration fusion power plant. As part of the Radiological Characterization Plan, analyses of steel components have been conducted to identify and quantify radionuclides resulting from neutron activation processes. Gamma-emitting radionuclides are readily identified using conventional gamma spectrometry. In contrast, beta-emitting radionuclides such as \({}^{55}\)Fe and \({}^{63}\)Ni require complete separation from the sample matrix and other radionuclides due to over-lapping beta energy spectra, which complicate direct measurement. Both \({}^{55}\)Fe and \({}^{63}\)Ni are products of neutron activation:\({}^{55}\)Fe (t\({}_{1}\)/\({}_{2}\) = 2.7 years) is primarily formed through the reactions \({}^{54}\)Fe(n,\(\gamma\))\({}^{55}\)Fe and \({}^{56}\)Fe(n,2n)\({}^{55}\)Fe. It decays via electron capture to stable \({}^{55}\)Mn, emitting Auger electrons and low-energy X-rays (notably 5.89 keV, with 16.9% intensity). Due to the low energy of these emissions, detection using low-energy gamma/X-ray detectors or gas flow proportional counters is possible, but these methods typically yield low counting efficiencies (<1%) compared to gamma spectroscopy [3]. \({}^{63}\)Ni is a pure beta emitter with a maximum beta energy of 66.95 keV and a long half-life of 100.1 years. It is generated via \({}^{62}\)Ni(n,\(\gamma\))\({}^{63}\)Ni and \({}^{63}\)Cu(n,p)\({}^{63}\)Ni reactions. In steels, the presence of Ni in significant concentrations results in a corresponding presence of \({}^{63}\)Ni. This radionuclide is crucial for clearance and waste acceptance due to its prevalence in reactor components. Trace amounts of Ni and Cu, and thus \({}^{63}\)Ni, may also be found in other reactor materials such as graphite, concrete, lead, and aluminum alloys [4; 5]. The measurement of \({}^{63}\)Ni is also challenging due to its low beta energy, with detection methods such as windowless gas flow proportional counters or ion-implanted silicon detectors yielding limited efficiencies (ranging from 2.6% to 20%) [6]. While Inductively Coupled Plasma Mass Spectrometry (ICP-MS) has been considered for radionuclide determination, it is not suitable in this context for either \({}^{55}\)Fe or \({}^{63}\)Ni. Their high specific activities (8.7 \(\times\) 10\({}^{13}\) Bq/g for \({}^{55}\)Fe and 2.1 \(\times\) 10\({}^{12}\) Bq/g for \({}^{63}\)Ni) result in detection limits well above those required for clearance. Moreover, the presence of the decay product \({}^{55}\)Mn significantly interferes with \({}^{55}\)Fe analysis, further limiting the applicability of mass spectrometry. Liquid Scintillation Counting (LSC) is therefore the preferred technique due to its high counting efficiency--up to 95% for low-energy beta emitters. Accurate LSC measurement of \({}^{55}\)Fe and \({}^{63}\)Ni requires prior mineralization of the sample using strong acid mixtures, followed by chemical separation steps. Several separation techniques have been documented in the literature, including chelating agents, anion exchange chromatography, solvent extraction, hydroxide precipitation, and, for Ni, complexation with dimethylglyoxime (DMG), followed by precipitation or organic extraction of the Ni-DMG complex [7; 8]. Chelation chromatography and hydroxide precipitation can be effective but often require combination with additional methods for adequate separation [6]. In the case of FTU steel samples, the activity due to neutron activation is extremely low (e.g., <2 mBq/g of \({}^{55}\)Fe in blanket components) [3]. As a result, substantial quantities of steel must be processed to reach the Minimum Detectable Activity Concentration (MDC) required for clearance.