632 Chapter 11. Dosimetry and Radiation Protection
Some of the advantages of OSL dosimetry are listed below. We have made com-
parison with TL dosimetry only since functionally it is closest to the OSL dosimetry.
Faster Processing: OSL dosimetry requires light to retrieve the dose infor-
mation. This process is significantly faster and more efficient as compared to
heating the TLDs.Higher Precision:Since the light used to retrieve the dose information can be
controlled much more precisely than the heat, therefore the dose measurements
fro OSL dosimeters are much more accurate than their TLD counterparts.High Dynamic Range:OSL dosimeters are much more sensitive to very low
and very high doses as compared to TLDs. Typical crystals can be used from
about 1mradup to several thousandrads.Multiple Readouts: Most of the energy stored in a TLD material gets re-
leased upon heating, leaving no possibility of re-reading the material. This
is not the case with OSL dosimeters since they release only a fraction of the
absorbed energy when optically stimulated. Hence an OSL dosimeter can be
read out a number of times, which reduces the uncertainty in the results.Shapes and Forms: OSL crystals can be formed in a variety of forms and
shapes. They can even be produced in the form of fibers and powders.Mechanical Stability:OSL materials are highly stable with respect to large
variations in temperature and humidity.Looking at the list above, it is quite evident that OSL materials have many
desirable characteristics. Therefore since the realization of their potential, OSL
dosimeters are becoming more and more popular.
B.1 WorkingPrincipleandOSLCurve
It has been observed that most TL materials, at least to some extent, possess OSL
characteristics. This points to the possibility that the underlying energy retrieval
mechanism for the two types of stimulation should be similar. In other words, in
both cases the energy storage mechanism is the same. However there have been some
experiments, which have pointed to the fact that a fairly intact TL glow curve can be
obtained from the same material after optical stimulation (see Fig.11.3.3). On this
finding it has been argued that the two storage mechanisms should be intrinsically
different. It should, however, be pointed out that, as pointed out earlier, the energy
released by optical luminescence is very small as compared to thermal luminescence.
In fact, it is only a fraction of the energy stored by the material. Therefore the
argument that they are intrinsically different does not hold.
Just like glow curve for TL materials, one can also obtain OSL curve from OSL
materials. A typical OSL curve is shown in Fig.11.3.3. It is apparent that the OSL
curve has a much faster decay time than glow curve making the reading process
much faster.