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Environmental dose rate determination using a passive dosimeter: Techniques and workflow for α-Al2O3:C chips

Sebastian Kreutzer
Sebastian Kreutzer
, 
Loïc Martin
Loïc Martin
, 
Guillaume Guérin
Guillaume Guérin
, 
Chantal Tribolo
Chantal Tribolo
, 
Pierre Selva
Pierre Selva
 et 
Norbert Mercier
Norbert Mercier
   | 21 févr. 2018
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Article Category: Regular Articles
Publié en ligne: 21 févr. 2018
Pages: 56 - 67
Reçu: 26 juil. 2017
Accepté: 17 janv. 2018
DOI: https://doi.org/10.1515/geochr-2015-0086
Mots clés
© 2017 S. Kreutzer., published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Fig. 1

Photos of the α-Al2O3:C field equipment. Shown are the homemade bleaching unit (left inset) equipped with a high power blue LED, the chip container (field dosimeter tube), the sample carriers used for luminescence measurements and α-Al2O3:C chips.
Photos of the α-Al2O3:C field equipment. Shown are the homemade bleaching unit (left inset) equipped with a high power blue LED, the chip container (field dosimeter tube), the sample carriers used for luminescence measurements and α-Al2O3:C chips.

Fig. 2

Typical green stimulated OSL shine-down curve recorded at 70°C with a green stimulation power density of 50 mW cm–2. Before measurement, the chip was heated to 350°C for 10 min and afterwards irradiated for 4 s (ca. 816 μGy) under the closed source. The curve shows a slow decay of the signal, reaching a stable background of ca. 40,000 cts s–1 after ca. 200 s. In contrast, the inset shows a GSL background of the equipment without sample carrier of ca. 6,000 cts s–1 (green curve) and a PMT background (no stimulation) of ca. 100 cts s–1. Background measurement temperature: 70°C.
Typical green stimulated OSL shine-down curve recorded at 70°C with a green stimulation power density of 50 mW cm–2. Before measurement, the chip was heated to 350°C for 10 min and afterwards irradiated for 4 s (ca. 816 μGy) under the closed source. The curve shows a slow decay of the signal, reaching a stable background of ca. 40,000 cts s–1 after ca. 200 s. In contrast, the inset shows a GSL background of the equipment without sample carrier of ca. 6,000 cts s–1 (green curve) and a PMT background (no stimulation) of ca. 100 cts s–1. Background measurement temperature: 70°C.

Fig. 3

GSL and TL curves recorded during the reproducibility test. The plot order follows the sequence listed in Table 3 (steps 2,4,5,6). Each plot contains 50 curves. All curves were recorded on one particular sample carrier and α-Al2O3:C chip. The first TL curve (A, red curve) shows that the chip received a small dose after its resetting in an external furnace at 900°C. All particular curves are overlapping, and the signals are highly reproducible.
GSL and TL curves recorded during the reproducibility test. The plot order follows the sequence listed in Table 3 (steps 2,4,5,6). Each plot contains 50 curves. All curves were recorded on one particular sample carrier and α-Al2O3:C chip. The first TL curve (A, red curve) shows that the chip received a small dose after its resetting in an external furnace at 900°C. All particular curves are overlapping, and the signals are highly reproducible.

Fig. 4

Stability of the GSL emission over a series of 50 cycles consisting each of a thermal resetting, irradiation for 4 s (ca. 816 μGy), GSL measurement at 70°C, a second resetting and a GSL background measurement. Results are summarised in a histogram. The intensity varies by only 0.2% (cv) reflecting a high system reproducibility.
Stability of the GSL emission over a series of 50 cycles consisting each of a thermal resetting, irradiation for 4 s (ca. 816 μGy), GSL measurement at 70°C, a second resetting and a GSL background measurement. Results are summarised in a histogram. The intensity varies by only 0.2% (cv) reflecting a high system reproducibility.

Fig. 5

Typical dose response curve for determining the irradiation time correction. Shown is the mean for one aliquot with five repetitions each. The red numbers in brackets indicate the effective irradiation time after correction.
Typical dose response curve for determining the irradiation time correction. Shown is the mean for one aliquot with five repetitions each. The red numbers in brackets indicate the effective irradiation time after correction.

Fig. 6

Results of the irradiation cross-talk estimation. The round circle represents the sample carousel with its sample positions. The result for each position is the mean of three measurements, the colours code the equivalent radiation cross-talk in seconds. The inset within the circle shows the individually obtained results for each position. For the irradiation cross-talk correction, the fitted polynomial function (red line) was used. For details see main text.
Results of the irradiation cross-talk estimation. The round circle represents the sample carousel with its sample positions. The result for each position is the mean of three measurements, the colours code the equivalent radiation cross-talk in seconds. The inset within the circle shows the individually obtained results for each position. For the irradiation cross-talk correction, the fitted polynomial function (red line) was used. For details see main text.

Fig. 7

Dose values in ascending order, as measured during the irradiation cross-talk estimation (upper plot) and the corresponding cumulative relative standard deviation (RSD, lower plot). Each circle shows the mean for three measurements similar to the values presented in Fig. 6, but in ascending order. The dashed red line indicates the value at which the RSD becomes positive. The black horizontal lines (dashed, solid) indicate the here defined minimum detection level and minimum determination level. For further details see main text.
Dose values in ascending order, as measured during the irradiation cross-talk estimation (upper plot) and the corresponding cumulative relative standard deviation (RSD, lower plot). Each circle shows the mean for three measurements similar to the values presented in Fig. 6, but in ascending order. The dashed red line indicates the value at which the RSD becomes positive. The black horizontal lines (dashed, solid) indicate the here defined minimum detection level and minimum determination level. For further details see main text.

Fig. 8

Gamma-dose rates obtained in this study compared to the values published by Miallier et al. 2009 for four (natural) reference sites. Error bars show 1σ uncertainties. The solid line indicates unity, the dashed lines deviation by 10% from unity. For three out of the four sites the γ-dose rates agree within 10% of unity. However, within 2σ all values are in accordance with each other.
Gamma-dose rates obtained in this study compared to the values published by Miallier et al. 2009 for four (natural) reference sites. Error bars show 1σ uncertainties. The solid line indicates unity, the dashed lines deviation by 10% from unity. For three out of the four sites the γ-dose rates agree within 10% of unity. However, within 2σ all values are in accordance with each other.

Fig. 9

Coefficient of variation (A) and TL peak shift vs. De (B) for the analysed field dosimeters (n = 63). Please note that in contrast to Section 5 – Application example, De values are given in s instead of Gy, i.e. Cv is not the same. The left plot (A) shows the inter-aliquot scatter (cv up to ca. 18%) for each analysed sample (n = 21). Each circle represents three chips from one sample. Circles with a red coloured frame highlight aliquots for which a significant TL peak shift (cf. inset) was observed. However, the right plot (B, each circle one aliquot, n = 63) shows no correlation between the peak shift and the obtained De. For further details see main text.
Coefficient of variation (A) and TL peak shift vs. De (B) for the analysed field dosimeters (n = 63). Please note that in contrast to Section 5 – Application example, De values are given in s instead of Gy, i.e. Cv is not the same. The left plot (A) shows the inter-aliquot scatter (cv up to ca. 18%) for each analysed sample (n = 21). Each circle represents three chips from one sample. Circles with a red coloured frame highlight aliquots for which a significant TL peak shift (cf. inset) was observed. However, the right plot (B, each circle one aliquot, n = 63) shows no correlation between the peak shift and the obtained De. For further details see main text.

Ratios of the dose (D) absorbed in the Al2O3:C chips to the infinite matrix dose (Dmatrix) for the three sediments: Sand, CC and DK. For calculations, the U- and Th-series were at secular equilibrium.

SedimentSeriesD/DmatrixSE (D/Dmatrix)MeanSE(Mean)
SandU-series0.9380.0610.9310.052
Th-series0.9330.056
40K0.9210.040
CC

Carbonated sediment rich in clay;

U-series0.9210.0710.9380.041
Th-series0.9510.032
40K0.9400.021
DK

Sediment rich in organic matter

U-series0.9380.0400.9390.041
Th-series0.9280.045
40K0.9510.038

Composition (in mass %) and densities of the three sediments used for determining the fraction of dose absorbed by the chips, relative to the infinite matrix dose values. Sand: sand sediment; CC: carbonated sediment rich in clay; DK: sediment rich in organic matter.

SedimentDensity(g cm–3)Chemical composition
Sand1.8SiO2(100%)
CC

Carbonated sediment rich in clay;

1.8O (52.91%), Si (27.71%), Al (8.81%), Fe (7.00%), K (1.55%), Na (0.20%), Mg (0.46%), P (0.11%), S (0.05%), Cl (0.001%), Ca (0.448%), Ti (0.61%), Mn (0.10%)
DK

Sediment rich in organic matter

1.6O (38.30%), C (29.00%), Ca (9.70%), Si (5.40%), Cl (4.10%), P (3.30%), Mg (2.20%), K (1.90%), N (1.20%), F (0.50%), Na (1.90%), Al (1.00%), S (0.70%), Ti (0.10%), Fe (0.70%)

Sequence used for determining an accumulated dose in an α-Al2O3:C chip. The LEDs power was set to 50 mW cm–2 and the regenerated dose was 816 μGy. For the three OSL signals, the integration limits were between 0–10 s (0–500 mJ cm–2).

# TreatmentObservation
1 GSL@70°C for 10 s with 50 mW cm–2Natural signal
2 TL to 300°C (5 K/s)
3 Irradiation (closed ß-source for 4 s, ca. 816 μGy)
4 GSL@70°C for 10 s with 50 mW cm–2Regenerated signal
5 TL to 300°C (5 K/s)
6 GSL@70°C for 10 s with 50 mW cm–2Background signal
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