Physics and Engineering of Radiation Detection

11.3. Passive Dosimetry 635

11.3.DTrackEtchDosimetry

Up until now we have been talking about the problems associated with radiation
damage to the materials. There is one instance where this damage can be exploited
to determine the dose delivered by the radiation. The process is fairly simple and
starts with letting the material absorb radiation for an extended period of time.
After the exposure the material is etched with a suitable solution, which reveals the
damaged zones ortracksof particles. The number of these tracks and their geometry
are a measure of the particle fluence and can therefore be used to estimate the dose.
Track etch detectors are usually made of plastics in the form of polymer foils.
Since these materials are fairly inexpensive, they are widely used for personal and
environmental radiation monitoring.
Estimation of dose from track etch detectors is based on the principle that the
damage caused by radiation is directly related to the linear energy transfer orLET.
Therefore the dimensions of the track bear direct relationship to the stopping power
of the radiation. And since stopping power is related to the atomic number of the
incident particles, the track dimensions are proportional to the atomic number as
well. A particle entering the material deposits its energy as it traverses the material
as shown in Fig.11.3.4. The damaged zone is generally a deformed cone but can
also have sharp boundaries and other shapes. Depending on the thickness of the
material and the energy and type of radiation the incident particle may or may not
get fully stopped.

Incident Radiation

(a)

(b)

Etched Track

Figure 11.3.4: (a) Damage caused by in-

cident radiation to a track etch dosime-

ter. (b) The damaged track after chem-

ical etching of the material.