Alpha-Track Radon Measurement
Radon Detection with CR-39
Radon is a radioactive gas that, along with its short-lived progeny, decays by emitting alpha particles. That makes it a natural fit for CR-39 — a solid-state nuclear track detector that permanently records alpha particles as etchable tracks in a plastic chip. Leave a detector in place, and every alpha it registers adds to a running, physical tally of exposure.
BlankSlate Innovation manufactures CR-39 detectors in the United States and offers a ship-back analysis service that counts and characterizes the resulting tracks. Because CR-39 integrates over the whole exposure, it is suited to long-term radon measurement and research applications, including home radon detection and dosimetry.
The physics
How CR-39 Detects Radon
Radon detection with CR-39 is a passive, four-step process. There is no power, no pump, and no electronics in the detector itself — just a plastic chip that keeps a permanent record.
01
Alpha Emission
Radon-222 and its short-lived progeny (such as Po-218 and Po-214) decay by emitting alpha particles into the surrounding air.
02
Latent Tracks
Each alpha that strikes the CR-39 breaks molecular bonds along its path, leaving latent damage in the polymer.
03
Chemical Etching
Etching in heated NaOH preferentially enlarges the damaged sites into pits that are countable under a microscope.
04
Integrated Readout
Track density scales with the integrated radon exposure over the deployment period — an average, not a single snapshot.
For imaging and counting, exposed chips can be read under an optical microscope or sent to BSI for SEM large-area mapping and AI-driven track analysis, which counts across the full chip and separates genuine tracks from surface artifacts.
Choosing a method
Alpha-Track vs Other Radon Methods
Different radon detectors answer different questions. Alpha-track detectors like CR-39 are integrating devices, which is their key strength for long-term measurement.
| Attribute | CR-39 Alpha-Track | Activated Charcoal | Electronic Monitor |
|---|---|---|---|
| Measurement type | Integrating over the exposure | Short-term adsorption | Continuous / logged |
| Typical duration | Days to months | A few days | Real-time, ongoing |
| Power required | None (passive) | None (passive) | Yes |
| How it is read | Etch + microscopy / AI counting | Gamma counting in a lab | On-device electronics |
| Permanent physical record | Yes — the etched chip | No | Data log only |
| Best suited to | Long-term averages, research, dosimetry | Quick screening | Live monitoring |
Quantitative conversion from track density to a radon concentration depends on detector geometry, exposure time, and calibration. BSI can discuss the calibration and analysis appropriate to your measurement goal — contact us with your application.
Detectors + analysis
What BSI Provides
US-Made Detectors
CR-39 chips from $1/cm2, in standard sizes or custom geometries to fit your fixture or chamber. BSI is a domestic manufacturer.
Ship-Back Analysis
Send exposed chips for SEM large-area mapping and AI track counting — full-chip counts with artifact rejection.
Waterborne Isotopes Too
For alpha-emitting radioisotopes in drinking water, see the related Radioisotopes in Water Test.
Common questions
CR-39 Radon Detection FAQ
Can CR-39 detect radon?
Yes. CR-39 is a solid-state nuclear track detector that registers alpha particles. Radon-222 and its short-lived progeny emit alpha particles, and each alpha that strikes the polymer leaves a latent track that becomes visible after chemical etching. Because the detector accumulates tracks for the whole time it is exposed, CR-39 is well suited to integrated radon measurement rather than a single instantaneous reading.
How do alpha-track detectors measure radon?
An alpha-track detector is left passively in the measurement location. Alpha particles from radon and its progeny damage the plastic along their paths. After the exposure period, the chip is etched in heated sodium hydroxide (NaOH) to enlarge the latent damage into countable tracks, and the track density on the surface scales with the integrated radon exposure over that period.
How long do you expose a CR-39 radon detector?
Because CR-39 integrates exposure, it is typically deployed over an extended period — days to months — to average out short-term fluctuations in radon concentration. The right duration depends on your goal and expected concentration; BSI can advise on exposure planning and on the etching and analysis needed to interpret the result for your application.
Can I send exposed CR-39 chips to a lab for analysis?
Yes. BSI offers a ship-back analysis service: send your exposed CR-39 chips and the SEM large-area mapping pipeline plus AI-driven track classifier returns a full-chip track count with source-versus-noise discrimination that separates genuine tracks from surface artifacts. BSI both manufactures the detectors and performs the analysis.
What is the difference between CR-39 and a charcoal radon test?
Activated-charcoal kits adsorb radon over a short window (typically a few days) and are read by gamma counting, giving a short-term snapshot. CR-39 alpha-track detectors record alpha tracks over the full exposure and are read by etching and microscopy, making them an integrating detector suited to longer-term measurement and to research settings that need a permanent physical record.
Get started
Measure Radon with US-Made CR-39
Order alpha-track detectors, request analysis of exposed chips, or both. Tell us your measurement goal, location, and exposure plan and we'll recommend detector size, quantity, and the etching and analysis to match.
Related: automated AI track analysis · radiation in water testing · American CR-39 manufacturer