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The Application of Full Spectrum Analysis to NaI(Tl) Gamma Spectrometry for the Determination of Burial Dose Rates

Minqiang Bu
Minqiang Bu
, 
Andrew S. Murray
Andrew S. Murray
, 
Myungho Kook
Myungho Kook
, 
Jan-Pieter Buylaert
Jan-Pieter Buylaert
 und 
Kristina J. Thomsen
Kristina J. Thomsen
   | 31. Dez. 2021
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Online veröffentlicht: 31. Dez. 2021
Seitenbereich: 161 - 170
Eingereicht: 15. Feb. 2019
Akzeptiert: 28. Okt. 2019
DOI: https://doi.org/10.2478/geochr-2020-0009
Schlüsselwörter
© 2019 Minqiang Bu et al., published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Fig. 1

Drift correction reference spectrum KUTh mix, and drift-corrected spectra from 40K, 238U and 232Th calibration standards and background.
Drift correction reference spectrum KUTh mix, and drift-corrected spectra from 40K, 238U and 232Th calibration standards and background.

Fig. 2

Illustration of the agreement of a calculated fitted spectrum with the original sample spectrum, together with fitting residuals in each channel.
Illustration of the agreement of a calculated fitted spectrum with the original sample spectrum, together with fitting residuals in each channel.

Fig. 3

(a–c) Minimum detection limits (MDLs) for activities of 40K, 238U and 232Th, respectively, defined as random uncertainty approaching 30%, when random uncertainty is expressed as a function of expected activity (AEXP); (d–f) Comparison of measured 40K, 238U and 232Th activity concentration (AMEAS) and expected activity concentration (AEXP), showing the accuracy of measurement and FSA analysis. The error bars in panels (d-f) shows the random uncertainty.
(a–c) Minimum detection limits (MDLs) for activities of 40K, 238U and 232Th, respectively, defined as random uncertainty approaching 30%, when random uncertainty is expressed as a function of expected activity (AEXP); (d–f) Comparison of measured 40K, 238U and 232Th activity concentration (AMEAS) and expected activity concentration (AEXP), showing the accuracy of measurement and FSA analysis. The error bars in panels (d-f) shows the random uncertainty.

Fig. 4

Normalized deviations between those activity concentrations for 40K, 238U and 232Th (a–c), and total (β + γ) dose rates (d) determined by the NaI(Tl) spectrometer and those determined by an HPGe spectrometer, for 20 geological samples. The shaded regions represent ±5% deviation in panels (a–c), and ±4% deviation in panel (d). The standard deviation for 20 data in each subpanel show a high measurement precision on NaI(Tl) spectrometer. All error bars in panel (a-c) and in panel (d) are derived from the total uncertainties of ACNaI and ACHPGe, and total uncertainties of DRNaI and DRHPGe, respectively.
Normalized deviations between those activity concentrations for 40K, 238U and 232Th (a–c), and total (β + γ) dose rates (d) determined by the NaI(Tl) spectrometer and those determined by an HPGe spectrometer, for 20 geological samples. The shaded regions represent ±5% deviation in panels (a–c), and ±4% deviation in panel (d). The standard deviation for 20 data in each subpanel show a high measurement precision on NaI(Tl) spectrometer. All error bars in panel (a-c) and in panel (d) are derived from the total uncertainties of ACNaI and ACHPGe, and total uncertainties of DRNaI and DRHPGe, respectively.

Fig. 5

Activity concentrations (a-c) and total dose rate (d) of a natural sample (LD962) counted with different counting time on NaI(Tl spectrometer. The horizontal dashed line in the centre of shaded region in each subpanel represents the activity concentration (a-c) and total dose rate (d) from HPGe spectrometer. All error bars in panel (a-c) and in panel (d) denote the total uncertainties of ACNaI, and total uncertainties of DRNaI, respectively.
Activity concentrations (a-c) and total dose rate (d) of a natural sample (LD962) counted with different counting time on NaI(Tl spectrometer. The horizontal dashed line in the centre of shaded region in each subpanel represents the activity concentration (a-c) and total dose rate (d) from HPGe spectrometer. All error bars in panel (a-c) and in panel (d) denote the total uncertainties of ACNaI, and total uncertainties of DRNaI, respectively.

Fig. 6

Dependence of relative total dose rate uncertainty on counting time, for a sample containing 235, 8.6, and 8.3 Bq·kg−1 of 40K, 238U and 232Th, respectively and a total dose rate of 1.09 Gy·ka−1.
Dependence of relative total dose rate uncertainty on counting time, for a sample containing 235, 8.6, and 8.3 Bq·kg−1 of 40K, 238U and 232Th, respectively and a total dose rate of 1.09 Gy·ka−1.

Average ratios of ACNaI/ACHPGe and DRNaI/DRHPGe (n = 20).

Average ratio
40K 0.995 ± 0.005
238U 0.984 ± 0.005
232Th 1.005 ± 0.006
Total dose rate 0.993 ± 0.004

Updated 40K, 238U and 232Th activity concentration per ppm for dose rate derivation.

Radionuclide Activity concentration (Bq·kg−1) Uncertainty (Bq·kg−1)
40K 317 3
238U 12.922 0.025
232Th 4.061 0.029

Comparison of MDLs (Bq·kg−1) from different studies.

Nuclide NaI(Tl) spectrometer (Sample weight: 0.23 kg) HPGe spectrometer (Sample weight: 0.25 kg)
FSA (This study) 3-Window (Bu et al., 2018) (Murray et al., 2018)
40K 4.8 21 0.6
238U 0.4 4.0 0.04
232Th 0.3 2.1 0.03
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