What Is Radiation and How Is It Detected and Measured?
Radiation is energy travelling through space or matter, either as electromagnetic waves or as fast-moving particles. The type that matters most for dosimetry and for the products on this site is ionising radiation — radiation with enough energy to knock electrons off atoms, which is exactly what allows it to be detected and what makes dose measurement necessary. Detecting it generally means letting it interact with a material and then reading the lasting trace of that interaction. Track-etch plastics such as CR-39 (PADC) do this by recording damage trails that become visible only after chemical etching.
Ionising vs non-ionising radiation
The practical dividing line is whether a single quantum or particle carries enough energy to ionise atoms.
| Ionising | Non-ionising | |
|---|---|---|
| Nature | Particles (alpha, beta, neutron) or high-energy photons (X-rays, gamma) | Lower-energy electromagnetic waves, e.g. radio, visible light |
| Effect on matter | Strips electrons from atoms | Mainly excites or heats, does not ionise |
| Typical monitoring | Dosimeters, track detectors, survey meters | Field-strength or power measurements |
| Relevance here | Radon and neutron dosimetry | Not the focus of track-etch detection |
Alpha particles, beta particles, neutrons, X-rays and gamma rays are all ionising. Radon is a radioactive gas that decays into alpha-emitting progeny, and neutrons are uncharged particles produced in nuclear environments — both are ionising and both are measured with track detectors.
Why dose is measured, and in what units
Ionising radiation deposits energy in tissue, so monitoring is about estimating that deposited energy rather than simply counting particles. The quantities you will meet:
- Activity — how many nuclear decays per second, in becquerels (Bq). Radon gas concentration is often quoted in Bq per cubic metre.
- Absorbed dose — energy deposited per unit mass, in gray (Gy).
- Equivalent and effective dose — absorbed dose weighted for the type of radiation and the tissue involved, in sievert (Sv). This is the number used for protection limits and for comparing exposures.
Dose matters because biological harm scales with deposited energy, not with the number of particles passing through. A single alpha particle deposits far more energy along its short path than a gamma ray does, which is why alpha-emitting radon progeny are a concern indoors.
How track-etch detection works
Track-etch detection is a passive method: the detector sits in place, accumulates damage, and is read later. The mechanism, as used in TASTRAK PADC (CR-39) plastic:
- Exposure — an ionising particle or recoil nucleus passes through the plastic and breaks chemical bonds along its path, leaving a narrow damaged trail.
- Etching — the plastic is treated with a chemical etchant. Damaged material dissolves faster than undamaged material, so each trail opens into a visible pit or track.
- Counting and analysis — tracks are counted, usually automatically, and the track density is converted into a dose or concentration using calibration factors.
The key property is that the plastic only responds to radiation that deposits enough energy to create an etchable trail, which is why the same material family serves radon measurement and neutron dosimetry.
Radon vs neutron dosimetry in practice
Both use track-etch plastic, but the exposure setup and the interpretation differ.
- Radon measurement — the detector is exposed in a defined volume, often with a filter or diffusion chamber, so that radon gas (or its progeny) reaches the plastic. The result is a long-term average radon concentration over the deployment period, typically months.
- Neutron dosimetry — neutrons are uncharged and do not ionise directly, so they are detected via recoil nuclei or nuclear reactions that produce charged particles. The detector is paired with a converter material, and the track count is related to neutron dose.
In both cases the detector is passive, integrating over time, which is why track-etch methods suit long-term monitoring rather than instant readout.
Where to find detectors and accredited measurement
Track Analysis Systems Ltd (TASL) manufactures dosimetry-grade TASTRAK PADC (CR-39) plastic and supplies TASL Image systems for radon measurement, neutron dosimetry and nuclear technology. The company states it is ISO-accredited in laboratories across Europe, HSE accredited in the UK and NVLAP accredited in the USA, with worldwide sales in over 80 countries. For a specific monitoring need, the practical route is to check the relevant accreditation for your country and confirm the deployment period and reporting format with the supplier or an authorised agent.