About track detectors
In 1978, while investigating the properties of CR-39™* plastic, the radiation research group at Bristol University taped a sample of the plastic from a spectacle lens to a window pane to observe the effect of sunlight on the material. The material they used, CR-39™*, has the chemical composition Poly Allyl Diglycol Carbonate (PADC). When the sample was etched, it was found to have recorded the tracks of alpha-particles due to traces of uranium and thorium in the glass. The ease with which the small number of tracks could be recognised and measured showed PADC to be an ideal material for low-level counting and, to pursue such research, the Track Analysis Group was formed.
To obtain high-quality material formulated specifically for track detection, the group experimented in producing its own PADC plastic at Bristol. To exploit the sales enquiries which followed their success, TASL was formed in 1983, and has now been producing TASTRAK™, its brand name for PADC manufactured specifically for nuclear track detection, routinely since 1985.
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*CR-39 is a trademark of PPG industries.
How do plastic track detectors work?
TASTRAK™ PADC, commonly known as CR-39, is a Dosimetry Grade plastic with the ability to record tracks of electrically charged nuclear particles. An important property of TASTRAK™ PADC is that it is highly selective in its recording of nuclear tracks. Thus, the plastic is insensitive to visible light and does not record X-rays, gamma-rays or tracks of beta-particle electrons, but is highly effective in the recording of alpha-particles at natural energies, protons with energies up to around 9 MeV, heavy ions and fast ions generated in laser-plasma interactions. These features are illustrated below, using alpha-particles as an example.
|Ionisation damage along an alpha-particle track in TASTRAK™ PADC plastic. When etched in a strong alkali, the surface of the plastic is etched away, but at the same time, preferential etching occurs along the trail of damage.
|Simulated vertical section of the growth of etch track along the trail of a 218Po alpha-particle with range 40 µm and dip angle 55° in TASTRAK™ plastic. Etching is at 98°C in 6.25 M NaOH.
|Photo-micrographs of etch tracks corresponding to the degree of etching shown in (b), (c) and (d).
|See corresponding video of growth of etch track