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Jacques Bezuidenhout Stellenbosch University South Africa

Measuring low concentrations of naturally occurring uranium by analysing the 351.9 keV gamma ray peak of 214 Pb. Jacques Bezuidenhout Stellenbosch University South Africa. Naturally Occurring Radioactive Nuclides. - Earth’s sciences - Exploration - Environmental monitoring

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Jacques Bezuidenhout Stellenbosch University South Africa

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  1. Measuring low concentrations of naturally occurring uranium by analysing the 351.9 keV gamma ray peak of 214Pb. Jacques Bezuidenhout Stellenbosch University South Africa

  2. Naturally Occurring Radioactive Nuclides - Earth’s sciences - Exploration - Environmental monitoring - Classification of soil and rocks - Fossil areas - Mining areas

  3. Gamma ray surveys(in situ)

  4. Primordial nuclides Uranium (238U), Thorium (232Th) and Potassium (40K)

  5. 214Pb (351.3 keV) Counts 40K (1460.8 keV) 214Bi (1764.5 keV) 208Tl (2614.5 keV) Energy (keV) Method A Typical Laboratory Gamma Ray Spectrum

  6. Uranium decay 238U gamma lines

  7. Uranium decay Gamma ray emitting daughters of uranium

  8. Method • 1. Sampling • - More than a 100 samples • - Polypropylene pill containers of 100 ml • - Sample mass ranging from 0.110 kg to 0.180 kg. • 2. Measuring System • - NaI(Tl) detector (7.62 x 7.62 cm) coupled to a scintiSPEC MCA • - Surrounded by 15 cm thick lead shielding • 3. Calibration and measurements • - Efficiency calibration was done with 40K, 238U and 232Th reference materials. • - Energy calibration was done from 0.3 to 2.7 MeV. • 4. Region of Interest (ROI) • - Four counting windows or ROI were selected. • - Equation of Rybach (1971, 1988) was adapted for four regions

  9. Method Net count rate in the ROI: ROI’s is i = 0, 1, 2, and 3 (351.3 keV, 1460.8 keV, 1764.5 keV and 2614.5 keV Calibration standards is j = 1, 2 and 3 of 40K, 238U and 232Th. The isotopes n = 1, 2 and 3 of 40K, 238U and 232Th. The net count rate Ri,j: Linear system of i x n (4 x 3) simultaneous equations

  10. 214Pb (351.3 keV) Counts 40K (1460.8 keV) 214Bi (1764.5 keV) 208Tl (2614.5 keV) Energy (keV) Method A Typical Laboratory Gamma Ray Spectrum

  11. Method Solved efficiencies

  12. Method Solve AU’, AK, AU and ATh Measuring uncertainties Detection limits

  13. Results 212Pb peak vs. 214Bi peak R2 = 0.9789

  14. Results 212Pb peak vs. 214Bi peak Coefficient of correlation: 0.9789 Average Statistically uncertainties: 214Pb => 7.1 Bq/kg 214Bi => 4.4 Bq/kg The natural background less than 3 counts/second. Average detection limits: 214Pb => 9.6 Bq/kg 214Bi => 36.8 Bq/kg Samples within detection limits: 214Pb => 76.6% 214Bi => 31.2% 214Pb peak results in shorter acquisition or more accurate uranium concentration

  15. Future - In Situ measurements - Fossil areas - 234Pa measurements - 232Th measurements

  16. Uranium decay γ-emitters

  17. Baviaansberg Palaeoshoreline

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