# An Assessment of the Impact of Gypsum Deposit Development on Changes in the Radiation Environment
## 2 Materials and Methods
### Analytical Procedures
The fired sample was transferred to a Teflon cup and moistened with distilled water, and 1 cm\({}^{3}\) of the \({}^{232}\)U isotope indicator was added (the accuracy of introducing the indicator into the sample should not be worse than 3%). Then, 40 cm\({}^{3}\) of HF and 10 cm\({}^{3}\) of HClO\({}_{4}\) were added, covered with a Teflon lid, and heated until HClO\({}_{4}\) vapors appeared. The HF treatment was repeated 2 more times, each time cooling the cup before adding the acid and evaporating until HClO\({}_{4}\) began to smoke. After decomposition was complete and the solution cooled, the edges of the cup and the lid were washed with water and evaporated again until thick white HClO\({}_{4}\) vapors appeared with the cup open. This operation was repeated twice more. The solution was finally evaporated to wet salts. The salts were dissolved by boiling in 50 cm\({}^{3}\) of 7 M HNO\({}_{3}\). If there was an insoluble residue, it was filtered through a 9 cm diameter \"blue ribbon\" filter and washed 3 times with hot 7 M HNO\({}_{3}\) in portions of 5-10 cm\({}^{3}\). The solution containing uranium isotopes was transferred to a separatory funnel, a 30% solution of freshly purified TBP in toluene was added (aqueous and organic phase ratio of 4:1), and the radionuclides were extracted for 5 min. After the separation of the phases, the mother liquor (lower layer) was poured back into the beaker, and the organic extract was washed for 1 min, first 2 times with an equal volume of 7 M HNO\({}_{3}\) and then 1 time with an equal volume of a solution of 0.25 M HNO\({}_{3}\) in 0.04 M HF. The mother liquor and washings were discarded. Then, the re-extraction of uranium isotopes was carried out by washing the organic phase for 1 min 3 times with an equal volume of distilled water. The combined aqueous re-extract was evaporated to dryness, treated with 5 cm\({}^{3}\) of concentrated HNO\({}_{3}\) to remove traces of organic substances and evaporated to dryness again. The dry residue containing uranium isotopes was dissolved in 10 cm\({}^{3}\) of a 2% soda solution with heating, filtered through a \"blue ribbon\" filter and transferred to an electrolytic cell. The filter and beaker were washed with 5 cm\({}^{3}\) of electrolyte and added to the main solution. The electrodeposition of uranium isotopes was carried out on a stainless steel substrate for 30 min at a constant current of 2 A. The substrate (disk) was cleaned with fine sandpaper and wiped with acetone immediately before use. After electrolysis, the disk was washed with distilled water and dried in air. The resulting preparation (counting sample) was measured on an alpha spectrometer with an uncertainty of 10-15%. The total uncertainty of the analysis was defined as st + sys(statistical + systematic), the errors of U measurement are given individually, and the extraction deficit of \({}^{232}\)U was 40-50%. The conversion of \({}^{238}\)U activity concentrations into U concentrations was carried out by using a calculation method. Gamma spectrometric measurements were carried out as described previously [28] (see Supplementary Materials, Text S1). The radionuclides \({}^{137}\)Cs, \({}^{226}\)Ra, \({}^{232}\)Th and \({}^{40}\)K were determined on a low-background semiconductor gamma-spectrometer (ORTEC, Perkin Elmer, Inc., Shelton, CT, USA), based on a coaxial germanium detector of high purity (HPGe; GEM10P4-70) with a pulse signal processor (SBS-75) and Gamma-pro software (Baltic Scientific Instruments, Riga, Latvia. [[https://timet.by/wp-content/uploads/2023/08/analytical-software-gammapro.pdf](https://timet.by/wp-content/uploads/2023/08/analytical-software-gammapro.pdf)]([https://timet.by/wp-content/uploads/2023/08/analytical-software-gammapro.pdf](https://timet.by/wp-content/uploads/2023/08/analytical-software-gammapro.pdf)) (accessed on 9 June 2025). The resolution of the gamma-spectrometer along the line of 1.33 MeV (\({}^{60}\)Co) was 1.75 keV, and the relative efficiency was 15%.