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Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. Because it is a gas, it can seep into buildings through floors, foundations, and gaps, where it can accumulate to levels that matter for health. The practical way to know whether a building has a problem is to measure it: short-term detectors give a quick indication, while long-term detectors (commonly passive track-etch plastics such as CR-39/PADC) give the reliable average needed to decide on mitigation. This article explains the mechanism, the main measurement options, how a test is run, and how to read the result.

What radon is and why it is measured

Radon forms as uranium and radium in soil and rock decay. It is chemically inert as a gas, so it moves through the ground and into the air rather than binding to surfaces. Indoors, it can concentrate when ventilation is low and the building sits over radon-producing ground.

The health concern is long-term exposure. Radon decay produces radioactive particles that can be inhaled; prolonged exposure raises the risk of lung cancer, and the risk is greater for smokers. This is why measurement, not guesswork, drives decisions: two similar houses on the same street can differ substantially because of soil, construction, and how the building is used.

How radon is detected and measured

Different methods trade speed against accuracy.

Track-etch detectors are widely used because they are passive (no power needed), integrate exposure over months, and are analysed in a laboratory. TASL, a Bristol-based company, manufactures dosimetry-grade TASTRAK PADC (CR-39) plastic and supplies TASL Image systems for reading such detectors, alongside radon measurement services. Its detectors are used in radon measurements, neutron dosimetry, and nuclear technology, and the company states ISO-accredited laboratories in Europe, HSE accreditation in the UK, and NVLAP accreditation in the USA.

How a radon test is carried out

A typical long-term test follows this sequence:

1. Placement. Detectors are set in occupied rooms, typically the lowest lived-in level, away from drafts, direct heat, and exterior walls where practical. Placement matters because radon concentration varies within a building.
2. Exposure period. The detector is left in place for the measurement period — long-term tests run for several months to average out daily and seasonal variation.
3. Retrieval and analysis. The detector is returned to a laboratory, where track-etch plastic is etched and the tracks are counted, or the analysis method appropriate to the detector is applied.
4. Reporting. The result is expressed as a radon concentration, allowing comparison against the relevant reference level.

The key point is that the exposure period and placement determine what the number means. A short test tells you about that window; a long test tells you about the average you are actually living with.

Interpreting results and deciding what to do

Compare the reported concentration against the action level that applies where you are — these are set by national authorities and differ by country, so check the current local figure rather than assuming one. If the reading is at or above the applicable level, the next step is mitigation: sealing entry routes, improving sub-floor ventilation or installing a radon sump, and increasing general ventilation. Because radon varies over time and between rooms, a single borderline result may warrant a confirmatory long-term measurement before committing to structural work.

Where to go next

If you need detectors or analysis, look for a laboratory with relevant accreditation and a documented measurement protocol, and confirm the exposure period and reporting format before you start. TASL's site provides information on TASTRAK PADC plastic, TASL Image systems, radon detectors and services, plus publications and downloads, and lists authorised agents for different regions.

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

1. Exposure. The plastic is deployed in the environment or workplace. Each qualifying particle that crosses it creates a latent damage trail.
2. 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.
3. 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

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.

TASL is Track Analysis Systems Ltd, a Bristol, UK-based company that specialises in radon measurement, neutron dosimetry, and the manufacture of dosimetry-grade TASTRAK PADC plastic — the material commonly known as CR-39. It supplies both the detector material and the analysis systems used to read it, so it sits at two points in the chain: making the track-detecting plastic and providing the hardware, software, and laboratory services that turn an exposed detector into a measurement result. That combination makes it relevant if you need radon detectors, neutron dosimetry, or a track-etch analysis capability rather than just a raw material supplier.

What TASL actually supplies

The site groups its offering into a few clear areas:

• TASTRAK PADC (CR-39) — dosimetry-grade nuclear track-detecting plastic, described as the core material for radon detectors and neutron dosimetry.
• TASL Image systems — the analysis side, used for radon measurements, neutron dosimetry, and nuclear technology applications.
• Neutron dosimetry — a dedicated application area alongside radon.
• Radon measurements and radon services — detector supply plus laboratory analysis, rather than material alone.
• Supporting material — publications, downloads, and a list of authorised agents.

The distinction worth noting: TASTRAK is the plastic, TASL Image is the readout/analysis route, and the radon and neutron services are the applied end of both.

How the track-etch chain works

CR-39 records damage trails when charged particles pass through it. Those trails are far too small to see directly, so the workflow is:

1. Expose the TASTRAK detector in the environment being monitored — a radon detector in a building, or a dosimeter worn or placed where neutrons are present.
2. Etch the plastic under controlled chemical conditions so the latent tracks enlarge into visible pits.
3. Image and analyse the etched surface, counting and classifying tracks to derive a dose or concentration.

TASL's role spans steps 1 and 3: it makes the plastic that determines what gets recorded, and provides the TASL Image systems that convert the etched tracks into numbers. The accuracy of the final result depends on both — the plastic grade and the analysis method have to match.

Radon vs neutron use

Both applications rely on the same underlying property of PADC — it permanently records particle tracks — but the detector configuration and the analysis calibration differ.

Accreditations and reach

If you are choosing a supplier for regulated or commercial dosimetry work, the quality signals matter. TASL states it holds:

• ISO accreditation in laboratories across Europe
• HSE accreditation in the UK
• NVLAP accreditation in the USA
• Worldwide sales in over 80 countries across 5 continents
• Winner of the 2013 Queen's Award for Enterprise — Innovation

Those accreditations are the practical reason a laboratory or commercial operator would pick an established supplier over generic CR-39: the material grade and the analysis method are tied to recognised quality systems.

When TASL is the right fit

TASL is likely relevant if you:

• Need dosimetry-grade CR-39 rather than general-purpose plastic, because track quality and background affect low-level measurements.
• Want a complete route from detector to analysed result, including the imaging system or a laboratory service.
• Are working in radon monitoring or neutron dosimetry where accreditation and traceability are required.
• Need authorised agents or local support — the site lists agents, which matters for international deployment.

It is less relevant if you only need a one-off radon test with no interest in the detector technology, or if you are looking for a material unrelated to nuclear track detection.

Practical starting points

The site's own navigation points to where to go next: TASTRAK PADC for the material, TASL Image systems for analysis hardware and software, Neutron Dosimetry and Radon Measurements / Radon Services for the applied offerings, and Publications and Downloads for technical detail. Contact and Authorised agents are the routes for pricing, lead times, and regional supply — the site itself does not publish prices, so those have to be requested directly.

CR-39 is a transparent thermoset plastic — chemically polyallyl diglycol carbonate (PADC) — used as a solid-state nuclear track detector. When ionizing particles such as alpha particles or neutrons (via recoil protons) pass through it, they leave latent damage trails that can be enlarged by chemical etching and then counted. It is chosen for radon measurement and neutron dosimetry because it is sensitive to these particles while producing a low background signal. The practical catch is that not all CR-39 is equal: dosimetry-grade material is manufactured and handled to strict tolerances, because detector quality directly affects how reliably tracks can be etched and counted.

The track-etch principle

CR-39 does not produce an electrical signal the way a Geiger counter does. Instead it stores radiation damage permanently in the plastic:

1. Damage. An incoming charged particle breaks chemical bonds along its path, leaving a narrow latent track.
2. Etching. The plastic is immersed in a chemical etchant (typically a hot alkaline solution). Etchant attacks the damaged material faster than the surrounding bulk plastic, so each latent track opens into a visible pit or cone.
3. Counting. The etched tracks are counted — manually under a microscope or automatically with an image-analysis system — and the track density is converted into a radiation dose or concentration.

Because the tracks persist, the detector integrates exposure over time rather than measuring an instantaneous rate. That makes it well suited to long-term radon surveys and cumulative neutron dose monitoring.

Why CR-39 is used instead of other detectors

The trade-off is that CR-39 gives you a cumulative track count, not real-time data, and the result depends on controlled etching and counting conditions.

Typical applications

• Radon measurement. CR-39 is used in passive radon detectors placed in buildings for weeks to months. Alpha particles from radon decay leave tracks that are etched and counted to estimate radon concentration.
• Neutron dosimetry. In neutron fields, recoil protons from neutron collisions create tracks, allowing cumulative neutron dose to be assessed.
• Nuclear technology and research. The same track-detecting property supports particle identification and other nuclear measurement work.

TASL (Track Analysis Systems Ltd), a Bristol-based specialist, manufactures dosimetry-grade TASTRAK PADC plastic — described on its site as CR-39 — and supplies it for radon measurements, neutron dosimetry, and nuclear technology, alongside the TASL Image system for analysing the etched tracks.

Practical considerations

• Dosimetry-grade quality. The material must be manufactured and processed to consistent standards; impurities or inconsistent thickness degrade track quality and reproducibility.
• Controlled etching. Etchant concentration, temperature, and time all affect track size and shape, so etching is a calibrated step, not a rough dip.
• Counting method. Tracks can be counted manually or by automated image analysis. Automated systems improve throughput and consistency for large batches.
• Accreditation context. TASL states it is ISO-accredited in laboratories across Europe, HSE-accredited in the UK, and NVLAP-accredited in the USA — relevant if you need results from an accredited measurement route.

If you are specifying CR-39 for a project, the key questions are the grade of the plastic, the etching and counting protocol, and whether the laboratory providing the result holds the accreditation your application requires.

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.

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:

1. Exposure — an ionising particle or recoil nucleus passes through the plastic and breaks chemical bonds along its path, leaving a narrow damaged trail.
2. 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.
3. 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.