# An Assessment of the Impact of Gypsum Deposit Development on Changes in the Radiation Environment
## 2 Materials and Methods
### Analytical Procedures  
The desorption of uranium from BAU-A-grade coal in water samples was carried out under laboratory conditions in the laboratory of environmental radiology of the N. Laverov Federal Center for Integrated Arctic Research of the Ural Branch of the Russian Academy of Sciences (Arkhangelsk, Russia), which complies with the accreditation criteria for testing laboratories established in ISO/IEC 17025 [26]. The laboratory has a wide range of reference radionuclide sources for equipment calibration and quality control procedures for measurements. Activated carbon with the remaining water was filtered with a Buchner funnel with a diameter of 90 mm and a \"white ribbon\" filter. The sorbent was dried in a drying cabinet at a temperature of 105 \({}^{\circ}\)C. The dried carbon with precipitated isotopes was placed in a 250 mL beaker, filled with hot 5% soda solution and thoroughly mixed with a stirrer for 3 h. After that, the resulting mixture was filtered with a vacuum filtration funnel through a \"white ribbon\" filter with a diameter of 90 mm, and the carbon was additionally washed several times with distilled water. Then, the carbon was discarded, and the filtrate was brought to pH 1-2 with hydrochloric acid and boiled for 30 min in a beaker under a watch glass. After the solution cooled, 1 mL of ferric chloride solution was added to it and mixed, and iron hydroxides were precipitated with a 30% aqueous ammonia solution. The hydroxides thus obtained were filtered with a \"blue ribbon\" filter and dissolved in 70 mL of a 7 M HNO3 solution. At this stage, there occurred separation from the interfering isotopes \({}^{210}\)Po (5.305 MeV) and \({}^{226}\)Ra (4.777 MeV), as well as from iron due to the very low coefficient of their transfer from the HNO3 solution to tributyl phosphate (TBP). Next, the uranium isotopes were extracted with 15 mL of a 30% tributyl phosphate solution in toluene in a  
Figure 2: General layout of the study area showing (**a**) water, sediment and soil sampling locations; (**b**) locations of ambient dose equivalent rate and radon flux density measurement points. separatory funnel using a stirrer for 5 min. The lower part of the solution was discarded, and the upper extract was washed twice for 1 min with 15 mL of 7 M HNO\({}_{3}\). At this stage, separation from \({}^{230}\)Th (4.685 MeV) took place, since in a 30% TBP solution, uranium extraction occurs more than 10 times more efficiently than thorium. Next, to prepare for the re-extraction of uranium isotopes from tributyl phosphate, the extract was washed with a solution of a complexing agent (0.04 M HF in 0.25 M HNO\({}_{3}\)) for 1 min. The re-extraction of uranium isotopes from TBP was performed by stirring it 3 times in portions of 15 mL with distilled water for 1 min each. The combined aqueous re-extract (45 mL) was evaporated to dryness in a quartz crucible, the dry salts were treated with 5 mL of concentrated HNO\({}_{3}\) and evaporated again, and the dry residue was dissolved in 20 mL of 2% Na\({}_{2}\)CO\({}_{3}\) with heating. The resulting solution was poured into a Teflon cell for electrolysis. Deposition was carried out on a stainless steel disk with a diameter of 34 mm for 30 min at a current of 2 A. A platinum electrode was used as an anode. The disk was washed with distilled water and dried, and activity was measured with a Multirad-AS alpha spectrometer (NPP DOZA, Moscow, Russia). Bottom sediment samples were dried in a BINDER E28 drying oven at 105 \({}^{\circ}\)C. A sample used as a tracer solution with known activity of the internal standard \({}^{232}\)U was also added to a 10 g sample of each bottom sediment sample. The method for extracting uranium isotopes after complete decomposition was described in a previous study [27]. A 10 g sample was placed in a porcelain crucible and fired at 500 \({}^{\circ}\)C until the organic matter was completely burned out.