Investigation of the optically stimulated luminescence dating method ...

OSL from quartz 37
associated with the natural signal. The sensitivity corrected natural OSL signal (open
circle) is slightly lower than the corrected regenerated circles. This is owing to the fact
that the regenerative dose employed in the experiment was slightly higher than the natural
dose.
Knowledge of the influence of thermal treatments (both in nature and in the laboratory) on
the luminescence efficiency has revolutionised optical dating technology over the last few
years. It can finally be pointed out, however, that an exact mechanism explaining
sensitivity changes in quartz remains to be established. Some relevant studies of this
matter are those by Zimmerman (1971), Aitken (1998), Wintle and Murray (1999), Chen
and Li (2000), Vartanian et al. (2000) and Bailey (2001, 2002).
OSL signal (counts / 0.16 s)
12000
11000
10000
9000
8000
7000
0 1 2 3 4 5 6 7 8 9 10
Measurement Cycle
, X 3
0 1 2 3 4 5 6 7 8 9 10
Figure 2.11: Illustration of monitoring the sensitivity change by the use of the OSL response to a small test
dose given after every OSL measurement. The sample is the same as in Figure 2.10. After the natural
signal was removed, the aliquot was put through a repeated identical cycle of irradiation (~11 Gy),
preheat (10 s at 160°C) and OSL measurement (40 s 470 nm at 125°C). After each principal OSL
measurement, a small test dose (~2.4 Gy) was administered and the corresponding OSL response recorded
(after a 160°C cut heat; see Chapter 3). Shown in the graph on the left are the absolute intensities of the
main OSL signals (squares) and test dose OSL signals (diamonds; note that for clarity, these values have
been multiplied by three). The change in sensitivity is clear, and is closely followed by the test dose signals.
The signals appropriate to the natural OSL signal are represented by the open symbols. The right hand
figure shows the result when allowance is made for the sensitivity change, which is accomplished by
normalising each OSL measurement to its appropriate sensitivity. The effectiveness is clearly illustrated
by the fact that all points now lie on the dashed line representing the average. Note that the natural datapoint
falls slightly under the line, as the naturally accumulated dose in the quartz grains of this aliquot
was a slightly lower than the dose of ~11Gy used in the repeat cycles.
Sensitivity Corrected OSL
4
3
Measurement Cycle