646 Chapter 11. Dosimetry and Radiation Protection
The disadvantages of diamond dosimeters include the following.
Dose Rate Dependence: Diamond dosimeters show some dependence on
dose rate.
Polarization:If diamond dosimeters are not in a radiation field they tend to
become polarized. Therefore to minimize this effect they must be irradiated
before being deployed.11.4.C Plastic Scintillator Dosimeter
A scintillator is a material that produces light when irradiated. The detectors based
on such materials are called scintillation detectors. We have discussed these materi-
als and the different types of detectors based on them in the chapter on scintillation
detectors. The interested reader is encouraged to read through the relevant sections
of that chapter to understand how such devices work.
Scintillators are available in many shapes and forms but for dosimetry purposes
the most popular are plastic scintillators. A typical plastic scintillator dosimeter
consists of a plastic scintillator, an optical fiber to carry the light photons, and a
PMT to count the photons. Sometimes another fiber and a PMT is added to the
setup to measure and subtract the background light. In the following we list some
advantages of plastic scintillators.
Small Size:Typical dimensions of plastic scintillator dosimeters are less than
1 mm^3 , which makes them suitable for medical dosimetry.
Temperature Stability: Plastic scintillators show very good temperature
stability and therefore the response of dosimeters does not change significantly
with drifts in temperature.
Good Spatial Resolution:Due to their small size, plastic scintillator dosime-
ters show excellent spatial resolution.
Good Energy Response:The linear energy response of these devices makes
them highly suitable for use in radiation therapy applications.
Radiation Hardness:The response of plastic scintillators does not deterio-
rate significantly with irradiation.
Good Isotropy:The isotropy of plastic scintillator dosimeters is comparable
to that of diamond detectors.
Large Dynamic Range:The large dynamic range makes them suitable for
use in diverse radiation environments.
Water Equivalence:The composition of plastic scintillators is approximately
equivalent to water. This makes them suitable for phantom measurements in
clinical dosimetry.
Perhaps the biggest disadvantage of plastic scintillator dosimeters is that they are
highly susceptible to background Cherenkov light. This can be overcome by using
a background subtraction counter, which requires another set of fibers and PMT.
However the development of highly efficient light guides and PMTs has made the
task simpler than before. Consequently these dosimeters are now gaining popularity.