Rapid nuclear event determination by caesium-137, stroncium-90 and plutonium activity and atomic ratios T2.2-P16 A. Puzas*, D. Baltrūnas, B. Lukšienė, R. Gvozdaitė, A. Gudelis, R. Druteikienė, R. Davidonis, Š. Buivydas, V. Remeikis Institute of Physics of Center for Physical Sciences and Technology, LITHUANIA *[email protected] Problem Global nuclear test fallout, the large scale nuclear accidents at the Chernobyl nuclear power plant (NPP) in 1986 and at the Fukushima Daiichi NPP in 2011 caused a widespread dispersion of technogenic radionuclides all over the world. These events have proven that radionuclides can reach territories from the source even at a distance of thousand kilometres under favourable meteorological conditions and can be detected by radionuclides “finger prints” which depend on their source. In this work a rapid comprehensive method considering optimisation of man-hours of work, materials and including activities such as radiochemistry, alpha-, beta-, mass- and gamma-spectrometry techniques combined together for radionuclide determination and assessment source is demonstrated. Equipment Four different techniques for measurements of soil samples: • alpha spectrometry - for plutonium-238 and plutonium-239,240 determination, • inductively coupled plasma mass spectrometry (ICP-MS) - for plutonium-239 and plutonium-240, • gamma-spectrometric system – for caesium- 137, • beta counter – for strontium-90. Conclusion 1. A one gamma spectrometer is not enough for more than three samples set rapid 137 Cs determination as only a one sample is measured per time. 2. Alpha spectrometer can measure 8 samples simultaneously, thus, it is optimal to measure 8 samples as a one sample set for rapid 238 Pu, 239,240 Pu determination. 3. ICP-MS technique lets to measure 239 Pu, 240 Pu isotopes significantly faster than alpha spectrometry. 4. APEX IR sample introduction system for ICP-MS stabilizes plutonium isotopic signals s by 67%, thus, shorter analysis time could be used. 5. According to 137 Cs/ 90 Sr, 137 Cs/ 239,240 Pu, 238 Pu/ 239,240 Pu and 240 Pu/239Pu activity and atomic ratios it was assessed that global fallout and Chernobyl accident sources prevail. 6. It is shown that less than 48h (+24h for sampling) is enough for a rapid radionuclides analysis. Sample preparation & measurement Three soil samples set was taken. Time used to collect samples and to start samples preparation and measurement – 24 h. Caesium-137: soil samples were prepared in plastic containers of the standard geometry for gamma spectrometry measurement. The reference standards with radionuclides ( 57 Co, 139 Ce, 113 Sn, 85 Sr, 137 Cs, 54 Mn and 65 Zn) free of the coincidence-summing effects were used for the efficiency calibration. The gamma spectrometer was equipped with the HPGe coaxial gamma-X-ray detector (GMX-series with a 0.5 mm thickness Be window) made by Ortec (USA). The relative efficiency of the detector was 33 %, the energy resolution at 1332.5 keV was 1.8 keV. All samples were counted for the fixed time of 50,000 s. The detection limit for 137 Cs is 0.185 Bq. Additionally, activity concentration of 37 Cs was measured in the IAEA-TEL-2014-03 reference soil sample for analytical quality control. Work total – 3 x 13 h of measurement = 36 h. Strontium-90 was extracted by acid leaching of ashed soil samples. We determined 90 Sr using methods based on 90 Y separation from samples by di-2-ethylhexylphosphoric acid (HDEHP) extraction. The ashed soil samples were dissolved in 1 mol/L HCL, and 90 Y was extracted with 10% HDEHP at pH 1.0–1.2. 90 Y was back- extracted with 3 mol/L HNO 3 and precipitated as a hydroxide. The chemical yield of 90 Y was determined using the known amount of inactive Y. Y precipitates were suction filtered onto a membrane filter. The precipitate and a filter were dried at 60°C, weighed and placed in a copper planchet for counting. Work total - (3 x 1.5 h) of preparation, 8 h of counting simultaneously = 14 h. Plutonium was extracted by acid leaching from the soil matrix and purified using the anion- exchange (Bio-Rad AG-1×8 100-200 mesh, Bio Rad Company) method followed by the extraction chromatography technique. Initially, samples were dried at 500°C for 2h, then left for 12h in 700°C to burn organic part of soil. The analytical procedure has been reported in [1]. Work total - 14h of drying and ashing, 3 x 1.5h preparation, 25h of alpha- and 1h of ICP-MS measurements = 44.5 h. Man-working hours in total – 94.5 h + 24 h of sampling. The analysis results ; References: 1. A. Puzas et al. J Radioanal Nucl Chem (2015) 303:751–759. A man-hour plan and timetable hours 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 Caesium-137 Strontium-90 238 Pu, 239,240 Pu (alpha spectrometry) 239 Pu, 240 Pu (ICP-MS) p.s. There should be +20% of time to be added for sample handling. preparation is done with alpha spectrometry together. Fig. 1. Air mass trajectories from suspected nuclear event place modeled. We assume an nuclear event registered by seismic stations that pointed out to Kaliningrad district governed by Russian Federation (Fig. 1). Samples collection begins right after 72h. Three samples from undisturbed meadow soils were collected right under the trajectories where the air masses with the possible plume traveled. The samples preparation started just right after collecting them. The analysis results are presented in Table 1. p.s. 137 Cs/ 239+240 Pu global fallout value for 2015 is 29±3, typical global fallout value of 240 Pu/ 239 Pu is 0.180. Sample Specific activity, Bq/kg 238 Pu/ 239,240 Pu Specific activity, Bq/kg 239,240 Pu 238 Pu 90 Sr 137 Cs 240 Pu/ 239 Pu 137 Cs /90 Sr 137 Cs /239+240 Pu 2` Dir. Vilkaviškis 0.13 0.007 0.05 1.9 6.1 0.194±0.009 3.2 46.9 9 Dir. Molėtai 0.2 0.007 0.04 2.7 5.6 0.194±0.009 2.1 28.0 10 Dir. Jurbarkas 0.14 0.035 0.24 3.5 5.8 0.189±0.013 1.7 41.4 Table 1. The analysis results.