1Overview
CsI(Tl) is a cubic single crystal with no cleavage, grown from high-purity cesium iodide feedstock and doped with thallium at a tightly controlled 0.10–0.12 mole%. Its density of 4.51 g/cm³ provides good stopping power across a broad gamma and X-ray energy range. The emission maximum at 550 nm falls squarely in the sensitivity band of standard silicon photodiodes, bialkali photomultiplier tubes with green-extended cathodes, and modern SiPM devices. This spectral match makes CsI(Tl) one of the most versatile scintillators for compact, cost-effective detector designs.
Unlike NaI(Tl), CsI(Tl) is only slightly hygroscopic. Crystals in a sealed or lightly protected housing tolerate standard laboratory environments without hermetic sealing. The wide useful temperature range (−40 °C to +125 °C) supports field-deployable and downhole applications where thermal cycling is routine. CsI(Tl) was selected as the active material in numerous international calorimeter projects including MUST, Chimers, and HIRA, partly because of its mechanical robustness and the uniformity of its thallium distribution.
Choose CsI(Tl) when photodiode or SiPM readout is preferred over PMT, when the detector must survive mechanical shock or thermal variation, or when a slightly hygroscopic crystal is acceptable in exchange for higher density and a green-yellow emission peak. For applications requiring deep-UV readout or sub-microsecond timing, consider CsI (undoped) or BaF2 instead.
2Specifications
Physical and Optical Properties
| Parameter | Value |
|---|---|
| Crystal composition | CsI(Tl) |
| Physical form | Single crystal |
| Crystal class | Cubic, no cleavage |
| Density | 4.51 g/cm³ |
| Maximum emission wavelength | 550 nm |
| Decay time | 600 ns and 3.4 µs (two components) |
| Refractive index at emission maximum | 1.79 |
| Photoelectron yield (bialkali PMT) | 45% relative to NaI(Tl) |
| Optical attenuation length | > 1 m |
| Thallium doping concentration | 0.10–0.12 mole% |
| Hygroscopicity | Slightly hygroscopic |
| Storage condition (bare crystal) | < 50% relative humidity |
| Useful temperature range | −40 °C to +125 °C |
3Mechanical and Thermal Properties
| Parameter | Value |
|---|---|
| Thermal conductivity | 0.13 W·m⁻¹·K⁻¹ |
| Thermal expansion coefficient | 51 × 10⁻&sup6; K⁻¹ |
| Specific heat | 201 J/kg·K |
| Apparent elastic limit | 5.58 MPa |
| Young's modulus | 5.3 GPa |
| Shear modulus | 6.24 GPa |
| Bulk modulus | 12.7 GPa |
| Maximum thermal gradient (small cm-scale crystals) | 10 °C/min |
| Maximum thermal gradient (larger crystals) | Depends on crystal size (verify) |
4Crystal Quality and Energy Resolution
ScintIQ CsI(Tl) crystals are grown using a controlled process that maintains a highly homogeneous thallium concentration throughout the full crystal volume. Uniform doping is the primary determinant of energy resolution and response homogeneity in CsI(Tl): spatial variation in Tl concentration produces light yield gradients that degrade spectral peak width. Every crystal is individually selected on light output and resolution before shipment.
The reflective wrapping is certified to maximize light collection. This combination of growth control, crystal selection, and optimized wrapping delivers consistent, reproducible energy resolution across production lots. CsI(Tl) crystals produced under these controls have been used in large-array calorimeter systems where inter-crystal uniformity is critical.
Typical energy resolution at 662 keV: verify against delivered crystal test reports. As a reference, the master material table indicates CsI(Tl) light yield of approximately 45% relative to NaI(Tl) on a bialkali PMT; actual resolution figures depend on crystal dimensions, readout device, and coupling method.
5Typical Applications
- Charged particle detection and nuclear physics calorimetry (MUST, Chimers, HIRA and similar arrays)
- General gamma and X-ray counting with silicon photodiode or SiPM readout
- Compact, battery-operated radiation monitors where PMT high voltage is impractical
- Medical and industrial imaging detectors requiring a 500–600 nm emission match
- Environmental radiation monitoring instruments
- Field-portable isotope identifiers (RIID) in thermally demanding environments
- Aerospace and downhole logging applications requiring a wide operating temperature range
- Phoswich detector stacks (paired with a fast front layer for particle discrimination)
6Available Configurations
ScintIQ CsI(Tl) crystals are supplied as bare polished crystals, wrapped crystals, or assembled detector modules. Specific dimensions, maximum achievable sizes, and housing types are configured to order. Contact Berkeley Nucleonics to confirm availability for your target geometry.
| Option | Details |
|---|---|
| Crystal shapes | Cylinder, rectangular slab, trapezoidal (phoswich), and custom geometries (verify availability) |
| Maximum dimensions | Depends on crystal geometry; verify with BNC applications team |
| Wrapping | Certified reflective wrapping to maximize light output; hermetic encapsulation available |
| Readout coupling | Photomultiplier tube (PMT), silicon photodiode, SiPM array |
| Entrance window | Aluminum, beryllium, or glass (application-dependent; verify) |
| Housing | Aluminum or stainless steel; EMI shielding options available (verify) |
| Integrated electronics | Compatible with ScintIQ bMCA, bPAD, and TOPAZ-HR readout modules |
7Request a Quote
Talk to a ScintIQ Engineer
Custom crystal dimensions, readout pairings, and large-array pricing are available on request. Berkeley Nucleonics applications engineers can advise on crystal selection, housing design, and integration with ScintIQ electronics modules.
Email: info@berkeleynucleonics.com
Phone: 800-234-7858
Web: berkeleynucleonics.com/products/custom-scintillation-detectors/