Investigation of the optically stimulated luminescence dating method ...

– CHAPTER 1 –
ESSENTIALS OF LUMINESCENCE DATING
1.1. General principles of luminescence dating
Luminescence dating belongs to the category of the so-called radiation dosimetric dating
methods, which are based on the time-dependent accumulation of radiation damage in
minerals. Other members belonging to this family of dating methods are, for instance,
fission-track dating and electron spin resonance dating. The radiation damage is the result
of the exposure to a low-level of ionising radiation that is omnipresent in nature. The
longer a mineral is exposed to this fluence of radiation, the greater the radiation damage.
The intensity of the radiation damage is consequently a measure for the total dose (the
total amount of energy absorbed from the ionising radiation) the mineral has received over
a certain period of time.
In luminescence dating, the intensity of the radiation damage is detected as a small
amount of light, which is called luminescence. The radiation damage, and hence the latent
luminescence signal, can be removed, or set to zero, by exposure to heat or light. For
ancient pottery, for instance, the ‘zeroing’ took place during manufacturing, when it was
baked in an oven. In the context of sediment dating, the zeroing event was the exposure to
daylight during erosion, transport and deposition of the mineral grains. This zeroing
through exposure to sunlight is also called bleaching. Once the zeroing agent is no longer
operative, the luminescence signal can start to build up again. For instance, in the case of
sedimentary mineral grains, the clock starts ticking anew when they are shielded from the
sunlight by burial under other grains deposited on top of them.
The latent luminescence signal can also be released in the laboratory using the same
zeroing agents, heat or light. At this point, however, the luminescence signal that is being
emitted will be recorded. If the signal is set free by applying heat, the resulting
luminescence is called thermoluminescence (TL). If the measured signal results from
exposure of the mineral grains to a beam of light, the emitted luminescence is termed
optically stimulated luminescence (OSL).