Physics & STEM Education
Teaching Radiation You Can See
Most classroom radiation tools give students a number on a meter. CR-39 gives them something better: a permanent, physical record of individual particles. When a charged particle strikes the polymer it breaks molecular bonds, and chemical etching turns that latent damage into a visible track. Students don't just read that radiation happened — they look at where each particle went, from what direction, and how deep.
That makes CR-39 a uniquely tangible way to teach ionizing radiation, particle energy, and counting statistics. It is also a less visceral display of radiation damage than many demonstrations, which suits it well to classroom use from high school through university.
Why it works in class
Four Reasons CR-39 Belongs in the Lab
Radiation You Can See
Each particle leaves a permanent, individual track — not an abstract count on a display.
Passive & Inert
The chip itself is inert plastic. The controlled steps are the source and the heated-NaOH etch, set by your safety officer.
Low Cost per Student
Standard chips start at $1/cm2, so a whole section can each have their own detector.
Scales to the Class
From a single demo chip to bulk class sets, with domestic lead times that fit the semester.
Experiment ideas
Concepts You Can Teach, by Level
CR-39 supports exercises from a one-period demonstration to a term-long advanced project. A few starting points, matched to what each one makes visible.
| Exercise | Level | What students observe / learn |
|---|---|---|
| Alpha exposure & track viewing | High school / AP, intro college | Ionizing radiation is real and discrete; each alpha leaves one track (the Learning Radiation Kit uses a thorium-tungsten alpha source). |
| Direction & penetration study | Intro college | Track angle and depth reveal the direction of impact and how far particles penetrate the polymer. |
| Exposure-time vs track-density | Intro / intermediate | Counting statistics and dose accumulation — compare exposure time, etch time, and observed track density. |
| Energy from track morphology | Intermediate / advanced | Relate track diameter and shape to particle energy; introduce moderation (e.g. energies reduced through a material). |
| Neutron demonstration | Advanced | Boron-coated chips detect thermal/epithermal neutrons via the 10B(n,α)7Li reaction. |
| SEM + AI analysis project | Advanced / capstone | Full-chip automated counting and particle-type classification, backed by a peer-reviewed method. |
For step-by-step handling, etching, and imaging guidance, point students to the CR-39 best-practice page. Advanced sections can extend into automated AI track analysis.
How it compares
CR-39 vs Geiger Counter vs Cloud Chamber
Each classic radiation demo teaches something different. CR-39's distinctive value is a permanent, per-particle record students can keep and measure.
| Attribute | CR-39 Track Detector | Geiger Counter | Cloud Chamber |
|---|---|---|---|
| What students see | Permanent etched track per particle | A count rate / clicks | Transient vapor trails |
| Permanent record | Yes — chip can be kept and re-measured | No | No |
| Per-particle detail | Direction, depth, energy from morphology | None | Path shape, live |
| Setup / consumables | Source + heated NaOH etch + microscope | Powered instrument, minimal setup | Dry ice / alcohol, continuous |
| Cost per student | Low ($1/cm2 chips) | One shared instrument | One shared setup |
| Best for teaching | That radiation is discrete, directional, and measurable | Count rate and shielding | Live visualization of tracks |
Educator questions
Teaching with CR-39 FAQ
How do you teach radiation with CR-39?
Expose a CR-39 chip to a radiation source, etch it in heated sodium hydroxide, and view the result under a microscope or, for dense exposures, with the unaided eye. Each charged particle leaves a permanent etched track, so students measure radiation directly instead of trusting a black-box counter reading. BSI's Learning Radiation Kit packages this as a classroom demonstration using an alpha source.
Is CR-39 safe for students to handle?
The detector itself is a passive plastic chip and is inert to handle. The safety controls depend on the radiation source used and the etching workflow, which involves heated sodium hydroxide (NaOH). The instructor and the institution's radiation-safety officer should specify source handling and etching procedures for the class.
What do students actually see on a CR-39 detector?
After etching, students see individual particle tracks — pits and cones left where charged particles damaged the polymer. The tracks reveal the direction of impact and depth of penetration, and their size and shape relate to particle energy. This makes abstract ideas like ionizing radiation and particle energy concrete and observable.
Do I need a microscope to use CR-39 in class?
A basic optical microscope is enough for most teaching-level exercises, and heavily exposed chips can show visible damage to the unaided eye. For advanced student projects, BSI can also discuss SEM large-area mapping and AI-assisted track analysis, which is documented in a peer-reviewed publication.
Can I order class sets or get a ready-made classroom kit?
Yes. Standard CR-39 chips start at $1/cm2 with bulk class-set discounts, and the Learning Radiation Kit ($75) is a turnkey option for classroom demonstrations. BSI is a domestic manufacturer, so instructors can plan around the semester calendar. See the CR-39 for teaching labs page for class-set ordering.
Plan your next lab
Bring Visible Radiation into Your Classroom
Start with the turnkey Learning Radiation Kit, or order CR-39 class sets sized to your section. Tell us your course level, section size, and experiment and we'll recommend quantity, format, and handling guidance.
More for educators: university teaching labs · automated AI track analysis · published research