Variability in quartz OSL signals caused by measurement uncertainties: Problems and solutions

Abstract

We simulated the variability in measured quartz optically stimulated luminescence (OSL) signals and dose response curves (DRCs) caused by measurement uncertainties, including counting statistics and instrumental irreproducibility. We find that these measurement errors can give rise to large variations in the observed luminescence signal and contribute to among-aliquot or among-grain scatter in DRCs and equivalent dose (De) values. Different measurement systems (i.e., luminescence readers) may have different counting statistics properties and, hence, may exhibit differing extents of variation in the observed OSL signal, even for the same sample. Our simulation shows that the random measurement uncertainties may result in some grains or aliquots being ¿saturated¿ (that is, the measured natural signal is consistent with, or lies above, the saturation level of the measured DRC) and that the rejection of these ¿saturated¿ grains may result in a truncated De distribution, with De underestimation for samples with natural doses close to saturation (e.g., twice the characteristic saturation dose, D0). We propose a new method to deal with this underestimation problem, in which standardised growth curves (SGCs) are established and the weighted-mean natural signal (Ln/Tn) from all measured grains is projected on to the corresponding SGCs to determine De. Our simulation results show that this method can produce reliable De estimates up to 5D0, which is far beyond the conventional limit of ¿2D0 using the standard SAR procedure. AbstractWe simulated the variability in measured quartz optically stimulated luminescence (OSL) signals and dose response curves (DRCs) caused by measurement uncertainties, including counting statistics and instrumental irreproducibility. We find that these measurement errors can give rise to large variations in the observed luminescence signal and contribute to among-aliquot or among-grain scatter in DRCs and equivalent dose (D e ) values. Different measurement systems (i.e., luminescence readers) may have different counting statistics properties and, hence, may exhibit differing extents of variation in the observed OSL signal, even for the same sample. Our simulation shows that the random measurement uncertainties may result in some grains or aliquots being 'saturated' (that is, the measured natural signal is consistent with, or lies above, the saturation level of the measured DRC) and that the rejection of these 'saturated' grains may result in a truncated D e distribution, with D e underestimation for samples with natural doses close to saturation (e.g., twice the characteristic saturation dose, D 0 ). We propose a new method to deal with this underestimation problem, in which standardised growth curves (SGCs) are established and the weighted-mean natural signal (L n /T n ) from all measured grains is projected on to the corresponding SGCs to determine D e . Our simulation results M A N U S C R I P TA C C E P T E D ACCEPTED MANUSCRIPT 2 show that this method can produce reliable D e estimates up to ...

Single-Grain Quartz OSL Characteristics: Testing for Correlations within and between Sites in Asia, Europe and Africa

“…Furthermore, since nearly half of the quartz grains have very low D 0 values (~30-50 Gy), it may result in "truncated" D e distributions (and, hence, D e underestimation) for samples with natural doses >100 Gy [21]. As a result, caution should be taken when dating samples with a large proportion of early saturation grains (e.g., [9][10][11]46]).…”

“…Firstly, D 0 estimates are usually imprecise when only a few regenerative data (e.g., 5-7) and a relatively narrow dose range (e.g., <2D 0 ) are measured. Li et al [21] demonstrated that the D 0 estimates are influenced significantly by measurement uncertainties and also the measurement strategy (such as the number and range of regenerative doses applied). Another issue with D 0 is that it only works when all the DRCs follow a single saturating exponential function, and it becomes problematic when there are many grains follow different growth patterns, such as double exponential or exponential plus linear.…”

“…Previous studies have focused on the relationship between D e estimates and the variability of a particular OSL characteristic for single grains, e.g., luminescence sensitivity [1,7,15,20], shape of OSL decay curve [1,6,7,15,19,20], and measurement uncertainties (including counting errors and instrument irreproducibility errors) [21]. However, none of these studies have systematically investigated correlations between multiple luminescence behaviors.…”

Review of the Post-IR IRSL Dating Protocols of K-Feldspar

“…The first cycle is to measure the natural signal (Ln/Tn) and the second cycle to measure the signal (Lc/Tc) of a regenerative dose, which is here termed The empirical 2D 0 limit was initially proposed for quartz [8]. A recent study argued that the D e underestimation beyond the 2D 0 limit of quartz was caused by the rejection of the 'saturated' aliquots or grains which resulted in a truncated D e distribution [93]. Instead of the conventional 'mean D e ' method, Li et al [93] proposed a 'mean L n /T n ' method to overcome this problem.…”

“…A recent study argued that the D e underestimation beyond the 2D 0 limit of quartz was caused by the rejection of the 'saturated' aliquots or grains which resulted in a truncated D e distribution [93]. Instead of the conventional 'mean D e ' method, Li et al [93] proposed a 'mean L n /T n ' method to overcome this problem. The 'mean L n /T n ' method applies the mean of re-normalized natural signal (L n /T n ) to calculate the final D e , thus no grains or aliquots would be abandoned when their natural signals lie above the saturation level of the growth curve.…”