BaF₂ Barium Fluoride Scintillation Detectors

1Overview

BaF₂ is the workhorse of fast-timing nuclear physics. No common inorganic scintillator is faster. The crystal emits two distinct scintillation components: a fast UV band at 220 nm with a decay constant of just 800 ps, and a slower component at 310 nm with a decay constant of approximately 630 ns. The fast component is what sets BaF₂ apart. It enables coincidence timing resolutions of 150 ps (FWHM) at 1 MeV per detector, a figure that competes with specialized organic scintillators while retaining the high effective atomic number and stopping power of an inorganic crystal.

The crystal is non-hygroscopic, eliminating the hermetic sealing complexity required for NaI(Tl), LaBr₃, and similar materials. It is mechanically stable and straightforward to handle. The principal trade-off is light yield: the fast component contributes roughly 5% of the output relative to NaI(Tl), and the slow component brings the total to about 16%. For spectroscopic resolution, this is a limitation. For timing applications, the photon statistics of the fast component are more than adequate, and the low background count rate of BaF₂ (no internal radioactive isotopes) is an asset in coincidence experiments.

Choose BaF₂ when the requirement is sub-nanosecond timing, when spectroscopic energy resolution is secondary, and when a non-hygroscopic crystal is preferred. For applications demanding both fast timing and good energy resolution, consider pairing BaF₂ with a ScintIQ LaBr₃(Ce) or CeBr₃ stop detector.

2Specifications

Readout note: Detection of the fast 220 nm component requires a PMT with a quartz (fused silica) entrance window. Standard borosilicate glass windows absorb below approximately 280 nm and will suppress the fast component. ScintIQ BaF₂ detectors include a quartz-window PMT by default. If your application uses only the slow 310 nm component (where full timing performance is not required), a borosilicate-window tube is acceptable.

3Timing Performance

The 800 ps decay constant of BaF₂'s fast component is unique among inorganic oxide or halide scintillators. To put this in context: NaI(Tl) decays in 230 ns; CeBr₃ in roughly 18 to 25 ns; BaF₂ in under 1 ns. This is a difference of more than two orders of magnitude relative to NaI(Tl), and a factor of 20 to 30 even versus the fast lanthanide halides.

The consequence for coincidence timing is direct. A single ScintIQ BaF₂ detector with a quartz-window PMT and a constant-fraction discriminator (CFD) will deliver approximately 150 ps FWHM timing resolution at 1 MeV. Coincidence timing resolution between two such detectors (the figure of merit in positron lifetime spectroscopy) follows from the single-detector value; exact coincidence resolution depends on the electronics chain, PMT transit-time spread, and CFD settings.

Component separation for PSD and coincidence gating

The fast and slow components of BaF₂ are well separated in time, with a ratio of approximately 800 ps to 630 ns (a factor of roughly 800). This separation is large enough that a simple timing gate can isolate the fast component for coincidence purposes, while integrating only the slow component in a wider gate. This is the basis for pulse-shape-based neutron/gamma discrimination in BaF₂ detectors (see Section 4).

4Pulse-Shape Discrimination

BaF₂ supports neutron/gamma pulse-shape discrimination (PSD). The mechanism relies on the ratio of light emitted in the fast UV component versus the slow component. Neutron-induced nuclear recoils and gamma-induced electron recoils produce different fast-to-slow ratios, allowing digital or analog charge-comparison circuits to separate the two populations. The discrimination is described in the source specification as "well possible."

BaF₂-based PSD is complementary to the approach used in CLYC or CLLBC (which exploit Ce³⁺ and core-valence luminescence components). BaF₂ PSD is suited to high-rate physics environments where the speed of the detector outweighs the PSD figure of merit compared with dedicated dual-mode crystals. For applications where neutron/gamma separation is the primary specification, contact Berkeley Nucleonics to discuss CLYC or CLLBC alternatives.

5Typical Applications

• Positron lifetime spectroscopy (PALS): BaF₂ is the standard material for start and stop detectors in positron annihilation lifetime systems. The 511 keV annihilation photons produce fast, well-defined pulses at 220 nm, enabling ps-level lifetime resolution in materials science, defect studies, and polymer physics.
• Fast coincidence timing: Any coincidence experiment requiring sub-nanosecond time resolution. Includes nuclear decay scheme measurements, time-of-flight (TOF) systems, and prompt gamma timing.
• High-energy physics (HEP) calorimetry (legacy and specialized): BaF₂ was used in major HEP detectors for its combination of fast timing and moderate stopping power. Custom large-format crystals are available for ongoing or new experiments.
• Medical physics timing: Time-of-flight PET (TOF-PET) research applications, particularly where very fast timing is being studied at the crystal level. Production TOF-PET systems typically use LYSO for its superior light yield, but BaF₂ is relevant for frontier timing R&D.
• Nuclear structure and reaction physics: Fast-timing arrays for measuring nuclear level lifetimes in the picosecond-to-nanosecond range.
• Neutron/gamma discrimination: Applications requiring PSD in fast, high-rate environments where the speed of BaF₂ is more important than PSD figure of merit.
• Synchronization and trigger detectors: As a fast start trigger in multi-detector arrays alongside slower, higher-resolution materials (e.g., LaBr₃, HPGe).

6Available Configurations

ScintIQ BaF₂ detectors are built to order. Standard and custom configurations are available across a range of crystal sizes, housing types, and readout options. The table below describes the general configuration options. Contact Berkeley Nucleonics for specific sizes, custom geometries, or system-level integration.

7Request a Quote

ScintIQ BaF₂ detectors are configured to your timing and geometry requirements. To request a quote or discuss your application, reach Berkeley Nucleonics directly.