CaF2(Eu) is a transparent material used for detecting gamma rays up to several hundred keV and for detecting charged particles. Because of the low atomic number, the material's photofraction is relatively small which prohibits the use in gamma ray spectrometry at higher energies. However, the low atomic number makes CaF2(Eu) an ideal material for the detection of beta particles because of the small amount of backscattering. Due to its refractive index of 1.47, which is close to that of most PMT windows and optical coupling compounds, a high light collection efficiency can be obtained. Furthermore, the emission maximum at 435nm is well matched to bialkali photocathode photomultiplier tubes.
CaF2(Eu) is not hygroscopic and is relatively inert. It has a sufficiently high resistance to thermal and mechanical shock, and it is easily fabricated into a variety of detector geometries.
Thin layers of 0.004” thick CaF2(Eu) have been used with 2x2” NaI(Tl) to make phoswiches. These are capable of separating α, β and γ.
Small pieces 10mm x 10mm x thickness at 500um up to large ones 3” diameter x 3” and more
|Melting point [K]||1691|
|Thermal expansion coefficient [C-1]||19.5 x 10-6|
|Wavelength of emission max. [nm]||435|
|Lower wavelength cutoff [nm]||395|
|Refractive index @ emission max||1.47|
|Primary decay time [ns]||940|
|Light yield [photons/keVγ]||19|
|Photoelectron yield [% of NaI(Tl)] (for γ-rays)||50|