What Is Track Analysis and How Does It Work for Radon and Neutron Dosimetry?
Track analysis is the process of counting and measuring the microscopic damage tracks that ionising radiation leaves in a solid detector, typically after chemical etching has enlarged them enough to be seen. It is used for radon measurement and neutron dosimetry because passive detectors such as CR-39/PADC plastic accumulate a permanent record of individual particle interactions, and reading that record gives an estimate of exposure. The approach suits long-term, low-level monitoring where electronic instruments would be impractical, but the result depends on controlled etching and consistent image analysis.
The detector material: TASTRAK PADC (CR-39)
Track Analysis Systems Ltd (TASL) manufactures dosimetry-grade TASTRAK PADC plastic, commonly known as CR-39, and supplies it as nuclear track-detecting plastic for radon detectors, neutron dosimetry and nuclear technology applications. The material is the sensing element: when an alpha particle or neutron-induced recoil passes through it, it leaves a narrow trail of molecular damage. That damage is invisible at first, which is why the etching step matters.
How the track etch principle works
- Exposure. The plastic is deployed in the environment or workplace. Each qualifying particle that crosses it creates a latent damage trail.
- Chemical etching. The plastic is treated with a chemical etchant under controlled conditions. Etching removes material faster along the damaged trail than from the undamaged surface, so each latent trail opens into a visible pit or track.
- Track formation. The resulting tracks are permanent features that can be counted and measured. Their number relates to the number of particles; their size and shape carry information about the particle type and energy.
The key mechanism is differential etch rate: damage along the particle path etches faster than the bulk plastic, converting a nanoscale trail into an optically detectable feature.
Applying track analysis to radon and neutron dosimetry
Radon measurement
Radon decays into alpha-emitting progeny. Alpha particles that reach the detector surface produce etchable tracks, so counting tracks per unit area over a known exposure period provides the basis for a radon concentration estimate. TASL supplies radon detectors and radon measurement services built on this principle.
Neutron dosimetry
Neutrons are uncharged and do not directly ionise the plastic, so detection relies on neutron interactions that produce charged recoil particles or reaction products capable of leaving tracks. TASL provides neutron dosimetry using TASTRAK plastic, with the same underlying readout approach: expose, etch, analyse.
Typical workflow from exposure to result
| Stage | What happens | Why it matters |
|---|---|---|
| Detector preparation | Dosimetry-grade TASTRAK PADC is cut and mounted | Consistent material reduces background variation |
| Exposure | Detector is deployed for the monitoring period | Track density accumulates in proportion to exposure |
| Etching | Controlled chemical treatment enlarges latent tracks | Etch conditions set track size and counting reliability |
| Image analysis | TASL Image™ systems count and measure tracks | Automated analysis improves throughput and repeatability |
| Reporting | Track data are converted to dose or concentration | Requires calibration and quality control |
TASL's TASL Image™ systems are the automated readout component for radon measurements, neutron dosimetry and nuclear technology applications.
Quality and accreditation considerations
Track analysis results are only as reliable as the controls around them. TASL states it is ISO-accredited in laboratories across Europe, HSE accredited in the UK and NVLAP accredited in the USA, and that its products have worldwide sales in over 80 countries across 5 continents. For anyone selecting a track analysis supplier or interpreting results, the practical checks are:
- Accreditation scope — confirm the specific measurement (radon, neutron dose) is covered, not just the laboratory generally.
- Calibration traceability — track-to-dose or track-to-concentration conversion should rest on documented calibration.
- Etching and analysis consistency — batch-to-batch control of etch conditions and image analysis settings.
- Background and detection limits — relevant when monitoring low radon levels or low neutron doses over long periods.
TASL was a winner of the 2013 Queen's Award for Enterprise-Innovation, and its published materials, downloads and publications list are available for those wanting detail on methods and performance.