Investigation of the optically stimulated luminescence dating method ...

OSL from quartz 33
The uncertainties associated with the lifetimes are usually large, which might explain,
beside sensitivity changes (see Section 2.7), some of the differences between the lifetimes
obtained by various authors. It can also not be excluded that some differences arise due to
the fact that different components of the OSL signal, or different combinations of them,
were considered in these studies. Using the linear modulation technique, Singarayer and
Bailey (2003) were able to carry out more detailed investigations on the thermal stability
of the different components of the OSL signal. They found that the different components
exhibited different thermal stabilities, with the so-called fast, medium and S1 component
(and possibly also the S3 component; see section 2.5 and Figure 2.10) being sufficiently
stable for dating sediments on Quaternary timescales. For the fast component, for
instance, they found a lifetime of 310 Ma at 20°C, which is comparable to the estimates
given in Table 2.2. On the whole, however, it can be concluded that the parts of the quartz
OSL signal that are nowadays usually employed for dating, are sufficiently stable to
permit dating over the entire time range of the Quaternary, with an upper limit determined
by signal saturation, rather than thermal fading.
Signal E (eV) s (s -1 ) τ20°C (a) Reference
OSL 1.84 2 * 10 15 6 * 10 8 Smith et al. (1990a)
OSL 1.65 2.7 * 10 13 2.8 * 10 7 Huntley et al. (1996) †
OSL 1.59 2.8 * 10 12 2.1 * 10 7 Spooner and Questiaux (2000)
OSL 1.66 1 * 10 13 1.1 * 10 8 Murray and Wintle (1999a) ‡
325°C TL 1.69 1 * 10 14 3.0 * 10 7 Wintle (1975)
325°C TL 1.60 5.7 * 10 12 1.7 * 10 7 Spooner and Questiaux (2000)
Table 2.2: Some reported values of trap parameters E (trap depth) and s (frequency factor), and
calculated lifetimes at 20°C for quartz. All values were obtained using isothermal decay methods. The
table is by no means exhaustive. †: In their experiments, Huntley et al. (1996) identified four traps; the
data tabulated here are those for the trap with the largest contribution to the total initial luminescence. ‡:
Murray and Wintle (1999a) found three OSL components; the values given in the table are for the major
component of the initial OSL decay in both natural and laboratory irradiated samples, after sensitivity
correction. It can be added that only the values obtained by Murray and Wintle (1999a) are corrected for
sensitivity changes occurring during the measurements (see Section 2.7).