What is neutron-sensitized CR-39?
Standard CR-39 with a thin converter coating of an element that undergoes an (n, p/d/t/α) reaction. The reaction products are charged particles that etch into the polymer as visible tracks.
Neutron-Sensitive Track Detectors
Neutron-Sensitized CR-39
CR-39 is a thermoset polymer used in nuclear particle tracing and calorimetry as a solid-state nuclear track detector (SSNTD). On its own it records charged particles — but neutrons are uncharged and leave no direct track. By coating the chip with an element that undergoes an (n, charged-particle) reaction, BSI sensitizes CR-39 to neutrons in specific energy ranges. Comparing the coated and uncoated faces then reveals both the energy and the flux of incoming neutrons.
BSI manufactures these detectors in the United States and validated boron-coating performance in a peer-reviewed paper on boron nitride coatings for CR-39.
At a glance
Passive Neutron Detection, Coated to Order
A passive, powerless neutron detector: no high voltage, no electronics in the field, and a permanent etched record you can re-read under a microscope.
Neutron-Sensitized
$6 / in2
Boron-coated 1-inch-square panes; standard boron-coated CR-39 from $3/cm2.
Coatings
B / Li / N
Natural boron, natural lithium, or nitrogen, matched to your neutron energy range.
Neutron Energy
Thermal → Fast
Coatings for thermal/epithermal; proton-recoil methods for intermediate and fast neutrons.
Analysis
SEM + AI
Optical or SEM large-area mapping with AI track counting, or process it yourself.
How it works
Turning a Charged-Particle Detector Into a Neutron Detector
Neutrons carry no charge, so they leave no track in bare CR-39. A converter coating changes that: when a neutron is captured, it releases a charged particle that CR-39 can record.
How does a boron coating detect neutrons?
Through the 10B(n,α)7Li capture reaction. A thermal or epithermal neutron absorbed in the boron layer emits an alpha particle, which strikes the CR-39 and leaves a track that survives chemical etching.
Why do you need a reference pane?
A coated pane records both neutron-induced and ambient alpha tracks. An uncoated reference pane placed nearby measures the ambient alpha background, so subtracting it isolates the true neutron signal. Order at least as many uncoated panes as coated.
Which coatings are available?
Natural boron, natural lithium, and nitrogen. Each is applied with a non-toxic, water-soluble adhesive that dissolves in the developing solution and does not affect the etch rate — so the coating never distorts the track record.
What about fast neutrons?
Capture coatings target thermal and epithermal neutrons. For intermediate and fast neutrons, proton-recoil techniques apply — BSI has recorded 14 MeV neutron-induced proton-recoil tracks in CR-39. Contact us to match a method to your spectrum.
How are exposed panes analyzed?
Return exposed panes and BSI etches, images, and counts them with optical or SEM large-area mapping plus AI classification tools — the methodology in our peer-reviewed SEM/AI paper.
Match the coating
Coating, Reaction & Neutron Energy
Which converter suits which part of the neutron spectrum, and how the signal is read.
| Coating | Capture reaction | Neutron energy | Signal in CR-39 |
|---|---|---|---|
| Natural boron | 10B(n,α)7Li | Thermal / epithermal | Alpha tracks (vs. uncoated reference) |
| Natural lithium | 6Li(n,α)3H | Thermal / epithermal | Alpha + triton tracks |
| Nitrogen | 14N(n,p)14C | Thermal / epithermal | Proton-recoil tracks |
| Uncoated (reference) | — | — | Ambient alpha background for subtraction |
| Uncoated (proton recoil) | Elastic n–p scattering | Intermediate / fast | Recoil-proton tracks (e.g. 14 MeV) |
Coating selection and reference-pane counts depend on your source and geometry. Contact BSI while planning your neutron application so the detector set matches the measurement.
Processing & analysis
Send It to Us, or Process It Yourself
BSI processing service
BSI will gladly process your exposed CR-39 panes using our optical or SEM analysis equipment and procedures, including AI analysis and counting tools. Pricing is quoted per job based on pane count and the analysis you need.
Optical track analysisPer job quote
SEM large-area mapping + AI countingPer job quote
Neutron-sensitized 1 in2 pane$6 each
Request a quote through the ordering page and describe your source, geometry, and pane count.
Build your own lab
Prefer to process in-house? BSI offers classes on processing and analyzing your own panes and can supply the equipment. A reconditioned optical processing setup runs about $2,000 and typically includes:
- A temperature-controlled hot plate with associated chemicals and glassware
- A reconditioned optical microscope with an ocular electronic camera
- A laptop computer
- Commercial and custom software
- Common laboratory equipment and computer supplies
BSI can provide a full reconditioned system at this price, integrate equipment into your existing lab, or supply all-new gear with factory warranties at roughly twice the cost. Contact us for a custom assembly plan and quote.
Proven on real sources
Validated Against AmBe and 14 MeV Neutrons
Uncoated CR-39, AmBe
Uncoated CR-39 exposed to 30 days of a 10 mCi Am-Be neutron source shows recoil-proton neutron tracks — the ambient-alpha reference case.
Boron-Coated CR-39, AmBe
Boron-coated CR-39 exposed to the same 30 days of 10 mCi Am-Be shows both neutron and alpha-particle tracks — the added 10B(n,α) signal over reference.
14 MeV + AI Detection
SEM imaging captures 14 MeV neutron-induced proton-recoil and U-238 fission-fragment tracks, labeled automatically by BSI's AI detection pipeline.
Frequently asked questions
Neutron-Sensitized CR-39 FAQ
How much does neutron-sensitized CR-39 cost?
Boron-coated 1-inch-square panes are $6.00 each. Standard boron-coated CR-39 is priced at $3/cm2 with bulk discounts above 100 units. Custom sizes, coatings, and lithium or nitrogen converters are quoted on request — see the ordering page.
How many detectors should I order?
Because neutron measurement relies on subtracting the ambient alpha background, order at least as many uncoated reference panes as coated panes. Tell BSI your source and geometry and we will recommend a set.
Does the coating change the etching process?
No. The converter is applied with a non-toxic, water-soluble adhesive that dissolves in the developing solution and does not affect the etch rate, so coated and uncoated panes etch identically for direct comparison.
Is this the same CR-39 sold on the main product page?
Yes — it is BSI's standard optical-grade CR-39 (PADC) with an added neutron-converter coating. For the full detector overview, sizes, and analysis service, see the main CR-39 page and the passive neutron detection page.
Next step
Plan Your Neutron Measurement
Contact BSI while you are designing the experiment. Tell us the source, neutron energy range, and geometry, and we will recommend coatings, reference panes, and an analysis path — or place an order directly.