Chemistry Reference
In-Depth Information
1.
Removing and preparing a representative sample of the solid.
2.
Heating the sample with a conventional heat source or a laser and
measuring the intensity of the luminescence emitted by the sample.
3.
Relating the intensity of the thermoluminescence emitted to the
amount of ionizing radiation absorbed by the solid since it was last
hot. This is usually done by irradiating the sample with a well-
calibrated source of ionizing radiation, then measuring the lumi-
nescence it emits after the irradiation, and finally comparing this
value with the value measured in stage 2.
4.
Calculating the average annual amount of ionizing radiation to
which the solid was exposed over time. With the data at hand, the
following relatively simple formula yields the time elapsed since the
solid was last at a high temperature:
total amount of accumulated radiation
amount of radiation accumulated per year.
thermoluminescence age
=
Both the thermoluminescence and optically stimulated luminescence tech-
niques are suitable for dating past heating events over a timespan ranging
FIGURE 20
Thermoluminescence dating.
Thermoluminescence (TL) is light
emitted when electrically nonconductive solids, such as stone or pottery, are
heated to high temperature although below their incandescence point. The inten-
sity of the light emitted is related to the amount of energy the material absobed
when exposed to surrounding ionizing radiation. The thermoluminescence
emitted when a stone or a piece of pottery is heated therefore indicates the
length of time since the solid was last heated to high temperature. An experi-
mental setup, required to heat up a sample so that thermoluminescence is
emitted and can be detected, is illustrated
(a)
. A recorded graph
(b)
usually pro-
vides the range of temperatures at which the material is heated and the inten-
sity of the light emitted at each temperature. From these two values, the length
of time elapsed since the material was at high temperature can be calculated.
