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Infrared Radiofluorescence (IR-RF) of K-Feldspar: An Interlaboratory Comparison Cover

Infrared Radiofluorescence (IR-RF) of K-Feldspar: An Interlaboratory Comparison

Geochronometria
Volume 48 (2021): Issue 1 (January 2021)
By: Madhav K. Murari,  Sebastian Kreutzer,  Marine Frouin,  Johannes Friedrich,  Tobias Lauer,  Nicole Klasen,  Christoph Schmidt,  Sumiko Tsukamoto,  Daniel Richter,  Norbert Mercier and  Markus Fuchs  
Open Access
|Dec 2021

Figures & Tables

Fig. 1

Spectra for sunlight and solar simulator of lexsyg at Giessen measured with the spectrometer while for Risø device, a computer-generated gaussian profile centered at 395 nm plotted for UV-LED (395 nm). The spectrometer is a combination of a spectrograph (Shamrock-163) and a CCD camera (Newton 920 BU) manufactured by Andor, an Oxford Instruments company. To facilitate easy comparison, spectra are normalized to the maximum intensity. Spectra for sunlight and solar simulator were measured with the same spectrometer settings, and light intensity was reduced using the neutral density filter ND 10B.

Fig. 2

A) and B) are ternary diagrams for elemental concentration obtained from the SEM analysis. A total of 137 grains for sample LUM1225 and 198 grains for sample GI326 were examined. The ternary diagram shows the atomic weight percentage of potassium (K), combined calcium and sodium (Ca+Na), and aluminum (Al) for each grain. Al was kept as a common element in each feldspar. C) SEM images of randomly selected grains.

Fig. 3

A) and B) show the dose recovery for a given dose of 10 ks (660 Gy) for samples GI326 and LUM1225 measured on lexsyg research at Giessen. Dose was recovered using the vertical sliding method (Murari et al., 2018). The dose rate of used device was 0.066 Gy · s−1 (calibrated on 01.02.2016). Each aliquot for both samples resulted in a dose recovery difference between ca 1.6 % and 7.6 % from unity. Both plots have same units for x-axes and y-axes.

Fig. 4

The instrumental background counts for each device are shown in boxplots. The scatter in background counts is measured for three aliquots. Background counts for each device are normalized to the device dose rate. The background levels for the lexsyg research device at Bordeaux (6840 ± 160 cts · s−1 · Gy−1) and the Risø device at Hannover (17,858 ± 250) were on the lower side compared to the average background counts (33,932 ± 6729 cts · s−1 · Gy−1 excluding outlier of Leipzig and lowest background of Bordeaux device). One aliquot out of three from Leipzig shows 1,47,691 cts · s−1 · Gy−1, which is exceptionally high and can be considered an outlier. Further, the background level for the newly installed lexsyg research devices at Leipzig (~43,000 cts · s−1 · Gy−1; excluding one outlier; manufactured in 2014) and Oxford (~45,000 cts · s−1 · Gy−1; manufactured in 2014) is elevated as compared to the average background. (Note: the detection method for the Risø system is different from the lexsyg research device, for more details, see main text).

Fig. 5

The behaviour of natural (RFnat) and regenerated (RFreg) IR-RF curves for a modern sample for all devices. Most of the devices show a noticeable difference between RFnat and RFreg IR-RF signal except for those at köln and Oxford.

Fig. 6

A) A typical behaviour of IR-RF signals for RFnat and RFreg. B) Dose estimation by sliding the RFreg onto the RFnat signal. C) Boxplot shows the scatter in dose values for individual devices, estimated using vertical sliding of the RFnat signal onto the RFreg signal.

Fig. 7

Dose distribution of all measurements for the Triassic sandstone sample (~250 Ma). The dose value ranges from ca 1000 Gy to ca 1700 Gy for the lexsyg research devices except for one outlier (2798.8 Gy) for the device at Freiberg. The dose value for the Risø device is 1080 ± 150 Gy, which is also comparable to the average dose value obtained for the lexsyg research devices. The dashed line indicates the central value, here the weighted mean of the values on a log scale. The grey polygon displays the area of ±2 standard estimates around the central value.

Fig. 8

A) and B) A typical behaviour of Initial rise for IR-RF measurements on Triassic sandstone sample GI326. IR-RF data was normalized to its maximum IR-RF value and smoothed. Every device showed an initial rise in the signal before decaying monotonically. An equivalent dose corresponding to the initial rise point was approximated from the smoothed data as there was a significant amount of noise in the original data. C) Boxplot shows the scatter in estimated dose values for individual devices for 5 aliquots (except Freiberg which has 3 aliquots). The average value of dose for initial rise was equivalent to 19.01 ± 4.24 Gy, and it was slightly lower (15.8 ± 2.3 Gy) for the Risø device. Further, the first IR-RF point for all lexsyg research devices stays at ~3 % lower than its maximum IR-RF point while it was ~6% for the Risø device.

Fig. 9

A) IR-RF signal from the modern analog sample LUM1225, mounted with silicon oil on the cups. B) IR-RF signal when the same sample is mounted with aluminum adhesive tape (Tesa company), heat resistant up to 140 °C. The Al tape prevents grain loss or further lateral dispersion of grains on the sample carrier during the measurement. However, the RFnat intensity is always higher than RFreg for both cases.

Fig. 10

A series of photos from A to C showing the change in sample geometry. A sticker was placed in a sample cup with markings of three arrows. The arrows’ different positions clearly show the movement of the cup when the arm moves from one position to another. The IR-RF curves blue, yellow, and red are the repeated measurements of RFreg of the same aliquot. The sample was bleached for 7 h with the solar simulator followed by a pause of 2 h before measurement of RFreg. All three repeated regenerated RFreg curves do not show any significant change in shape and intensity. The overlapping three repeated RFreg curves confirm that the rotation geometry change has no significant effect on the IR-RF signal.

Fig. 11

Early saturation of the geological sample. A) and B) show two measurements of IR-RF before and after a pause. Green-coloured IR-RF for a dose equivalent to 4,290 Gy is recorded just after bleaching of the sample for 7 h, and red-coloured IR-RF is recorded after the pause of several days. The units of the y-axes are similar for both figures.

Samples used for the intercomparison IR-RF measurements_

Sample codeSample preparationGrain size [μm]Sediment typeExpected age [a]MethodReference
LUM1225Hannover150–200Beach dune sand0Quartz OSL doseKunz et al. (2010)
GI326Giessen160–200Sandstone108StratigraphyRöhling et al. (2018)

Solar simulator spectra settings for each LED normalized to the Bordeaux solar simulator settings_

LEDs wavelength [nm]Bordeaux [mW · cm−2]Bayreuth [mW · cm−2]Freiberg* [mW · cm−2]Giessen [mW · cm−2]Köln [mW · cm−2]Leipzig [mW · cm−2]Oxford [mW · cm−2]
36510869968
46263533555553849
52554453047473342
59037312132322329
62511596641001007090
85096805384835875

Device parameters used for the interlaboratory comparison measurements_

LaboratoryDevice [manufacturing year]PMTFilterSource dose rate [Gy · s−1]Calibration dateBleaching power density [mW · cm−2]Bleaching time [h]
BordeauxLexsyg [2012]H7421-50D850/400.065 ± 0.00604.04.20153756.00
BayreuthLexsyg [2011]H7421-50HC857/30*0.051 ± 0.00218.08.20163137.20
FreibergLexsyg [2013]H7421-50D850/400.055 ± 0.00307.10.201420810.80
GiessenLexsyg [2013]H7421-50D850/400.066 ± 0.00201.02.20163266.89
KölnLexsyg [2011]H7421-50D850/400.053 ± 0.00527.08.20153266.90
LeipzigLexsyg [2014]H7421-50D850/400.058 ± 0.00401.08.20162289.86
OxfordLexsyg [2014]H7421-50D850/400.057 ± 0.00327.11.20172937.67
HannoverRisø [2017]H7421-50D900/100*0.116 ± 0.00601.10.20201000#0.42#

The applied IR-RF protocols_

StepsTreatmentComment
##Protocol for background measurement
1.Preheat (70 °C for 900 s)Temperature stabilization
2.IR-RF (70 °C for 1 ks)Background measurement
##IR-RF Protocol for sample measurement
1.Preheat (70 °C for 900 s)Temperature stabilization
2.IR-RF (70 °C for 10 ks)IR-RF Natural (RFnat)
3.Bleach (70 °C, varying time)*8.1 kJ · cm−2 equivalent to Bordeaux
4.Pause (2 h)To avoid phosphorescence after bleach
5.IR-RF (70 °C for 65 ks)IR-RF Regenerated (RFreg)
##IR-RF dose recovery measurement protocol at Giessen
1.Bleaching (70 °C, 7 h)8.1 kJ · cm−2 equivalent to Bordeaux
2.Pause (2 h)To avoid phosphorescence after bleach
3.Preheat (70 °C for 900 s)Temperature stabilization
4.IR-RF (70 °C for 10 ks)IR-RF dose to be recovered
5.Pause (2 h)–
6.Preheat (70 °C for 900 s)Temperature stabilization
7.IR-RF (70 °C for 15 ks)15 ks IR-RF signal to recover given dose of 10 ks [step 4]
8.Bleaching (70 °C, 7 h)8.1 kJ · cm−2 equivalent to Bordeaux
9.Pause (2 h)To avoid phosphorescence after bleach
10.Preheat (70 °C for 900 s)Temperature stabilization
11.IR-RF (70 °C for 50 ks)IR-RF regenerated curve

The observations made on all devices for background, initial rise, bleaching of the modern analog dune sand sample LUM1225 and the sandstone sample GI326 which was ~250 Ma old_

##Initial rise IR-RF dose [Gy]Modern sample [LUM1225]Old sample [GI326]
LabsDevice [manufacturing year]+Background [cts · s−1 · Gy −1]RFreg [0 Gy]RFnat [~1200 Gy] *Δ IR-RF [%]#Equivalent IR-RF dose [Gy]IR-RF Dose [Gy]
BordeauxLexsyg [2012]6840 ± 160(n = 3)3.1 ± 0.524.4 ± 8.9(n = 5)4.2 ± 1.536.3 ± 7.6(n = 5)1539 ± 438(n = 5)
BayreuthLexsyg [2011]26627 ± 406(n = 3)3.5 ± 1.420.9 ± 0.6(n = 5)5.1 ± 1.759.5 ± 8.1(n = 5)1115 ± 49(n = 5)
FreibergLexsyg [2013]35417 ± 456(n = 3)3.2 ± 0.818.9 ± 0.9(n = 3)0.8 ± 0.521.3 ± 1.8(n = 3)1599 ± 591(n = 6)
GiessenLexsyg [2013]29912 ± 183(n = 3)2.9 ± 0.418.1 ± 1.3(n = 5)1.3 ± 1.818.6 ± 9.7(n = 5)1259 ± 179(n = 5)
KölnLexsyg [2011]32788 ± 91(n = 3)2.9 ± 0.318.6 ± 0.4(n = 5)0.2 ± 0.412.9 ± 3.1(n = 5)1234 ± 30(n = 5)
Leipzig++Lexsyg [2014]43185 ± 62(n = 2)2.9 ± 0.317.8 ± 3.8(n = 5)2.2 ± 1.330.7 ± 7.9(n = 5)1199 ± 383(n = 5)
OxfordLexsyg [2014]44567 ± 1598(n = 3)3.0 ± 0.317.7 ± 2.0(n = 5)0.1 ± 0.515.1 ± 1.4(n = 5)1163 ± 176(n = 5)
HannoverRisø [2017]17858 ± 306(n = 3)2.6 ± 0.515.8 ± 2.3(n = 5)1.3 ± 0.620.2 ± 2.2(n = 5)1081 ± 117(n = 5)
DOI: https://doi.org/10.2478/geochr-2021-0007 | Journal eISSN: 1897-1695
Journal RSS Feed
Language: English
Page range: 105 - 120
Submitted on: Feb 28, 2021
|
Accepted on: Sep 6, 2021
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Published on: Dec 18, 2021
Published by: Sciendo
In partnership with: Paradigm Publishing Services
Publication frequency: 1 issue per year
Keywords:
IR-RF,
interlaboratory-comparison,
K-feldspar,
dosimetry,
dating
Related subjects:
Geosciences,
Geosciences, other

© 2021 Madhav K. Murari, Sebastian Kreutzer, Marine Frouin, Johannes Friedrich, Tobias Lauer, Nicole Klasen, Christoph Schmidt, Sumiko Tsukamoto, Daniel Richter, Norbert Mercier, Markus Fuchs, published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

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