Barium fluoride (BaF2) has an emission component with subnanosecond decay time that yields very fast timing. It is a scintillator showing two wavelengths of emission (310 nm and 295 nm). The emission at 220nm has an emission with sub nanosecond decay time interesting for timing applications. Using special electronics, time resolutions around 200 ps are possible for small detector geometries.
There are several other scintillators that also have excellent timing capabilities. These are BrilLanCeTM 380 and 350 (LaBr3:Ce and LaCl3:Ce) and LYSO scintillators.
To detect the fast scintillation light, it is necessary to use a photomultiplier tube with a quartz entrance window. Furthermore, the optical coupling compound must have a good transparency for UV light. BaF2 is not hygroscopic, but condensing moisture can pit its surface. It is relatively radiation hard.
small cross-sections; 1"x1", 1.5"x1.5", 2"x2"
|Melting point [K]||16.27|
|Thermal expansion coefficient [C-1]||18.4 x 10-6|
|Wavelength of emission max. [nm]||310 / 220(195)|
|Lower wavelength cutoff [nm]||135|
|Refractive index @ emission max||150(310nm) 1.54(220nm)|
|Primary decay time [ns]||630 (slow) / 0.6-0.8 (fast)|
|Light yield [photons/keVγ]||10 (slow) / 1.8 (fast)|
|Photoelectron yield [% of NaI(Tl)] (for γ-rays)||16 (slow) / 3 (fast)|