BSI Products — Education
LEARNING
RADIATION KIT
See the effects of radiation with your own eyes. Using CR-39 thermoset polymer and Th-232 alpha sources, students can observe exactly where alpha particles hit, their approximate energy, and direction of travel.
Kit Price
$100
Per Kit
Contact for bulk / classroom pricing+ BSI Processing
Contact for Pricing
All 14 detectors
In the Classroom
Lab Activity Ideas
Activity 01
Dose vs. Exposure Time
Use the varied-time holder to expose detectors for different lengths of time at a fixed distance. Students count the tracks on each one and plot count against exposure time, and the result is a straight line. Thorium-232's half-life is more than 14 billion years, so the source's activity doesn't measurably change during the experiment, and doubling the exposure doubles the tracks. It's a clean way to introduce activity, dose, and why some sources are effectively constant.
Activity 02
The Inverse-Square Law
Load the varied-distance holder and expose detectors at several spacings from the thorium rod. The rod emits alpha particles in every direction, so the farther out a detector sits, the more area that flux is spread across, and track density falls off with the square of the distance. Students count tracks per microscope field at each position, plot density against distance, and test the fit to 1/r². It's a direct, visual demonstration of the inverse-square law from an isotropic source.
Activity 03
Reading Track Shape and Direction
Not every track looks the same under the microscope. A particle that strikes the detector head-on etches a round pit, while one that arrives at a glancing angle leaves an elongated ellipse aligned with its path. Students photograph or sketch tracks, sort them by shape, and use the orientation of the ellipses to work out where the source sat relative to the detector, reconstructing a particle's direction of travel from the evidence it left behind.
Extensions
Shielding
Put a sheet of paper, kitchen foil, or plastic wrap between the rod and a detector. Even thin materials cut the track count sharply, and students can compare which ones stop the alphas completely.
Control / Background
Keep one detector sealed and away from the rods for the same period. The few tracks it collects come from natural background radiation, mostly radon, which builds in a lesson on experimental controls.
Counting Statistics
Have students count tracks in several different fields of view on the same detector. Counts vary from field to field because decay is random, and comparing that spread to √N shows students how to put error bars on their results.
Tip: plan how you'll split the 14 detectors before you start. All 14 are processed together.
The Science
Radiation You Can Actually See
When a high-energy particle impacts CR-39 polymer, it breaks chemical bonds along its path, allowing for preferential etching during post-exposure processing. These etched tracks can then be observed and characterized under a microscope — or with enough exposure, seen with the unaided eye.
The kit uses 2% thorium-tungsten rods as the alpha source. These rods contain thorium-232, a primordial nuclide with a half-life exceeding 14 billion years — longer than the estimated age of the universe. Its extraordinary stability makes it safe to handle while still producing measurable alpha emissions.
The alpha particles emitted are energetic helium ions at approximately 4.1 MeV — over 160 million times more energetic than their thermal motion at rest. At this energy they carry a charge of +2e and travel at roughly 0.4% the speed of light. Once slowed to rest they capture electrons and become ordinary helium atoms.
The kit's two 3D-printed holders let students vary distance and exposure time independently, turning a single experiment into a controlled investigation of inverse-square attenuation and track density.
Kit Contents
CR-39 is sensitive to energetic protons, alpha particles, heavier ions, and fast neutrons. The Th-232 rods produce 4.1 MeV alpha particles — ideal for track formation in CR-39.
In Practice
Kit and Results
2 3D-printed holders, 2 thorium-tungsten rods, 14 pieces of CR-39
Assembled kit
CR-39 after 7-day contact exposure and developing etch
50× optical microscope image — 7-day exposure at 0.6" distance
Processing Options
Send to BSI or Do It Yourself
After exposure, CR-39 must be developed in NaOH solution and imaged under a microscope. BSI offers full-service processing, or you can purchase the DIY equipment for in-house analysis — recommended for those teaching the module across multiple classes year after year.
Full Service
BSI Processing
BSI develops, images, and characterizes all 14 CR-39 particle track detectors in your kit and provides you with digital images. All 14 must be processed simultaneously.
DIY Option 1
Development Kit
BSI provides a chemical development kit to process CR-39 particle track detectors yourself. Includes a hot plate with heating instructions. Sodium hydroxide (NaOH) must be purchased separately.
DIY Option 2
Microscope System
Reconditioned optical microscope with ocular camera and computer interface. Includes a new laptop loaded with imaging and image analysis software for track counting and characterization.
Advanced AI-based analysis tools available at additional cost — differentiates particle types, arrival angles, and energies with full distribution displays. Custom analysis software available for research applications.
Get Started
Ready to Order?
Contact BSI to purchase a kit, arrange BSI processing of your exposed detectors, or discuss DIY equipment options for classroom or lab use.