CaF2 Physical properties of CaF2(Eu) Density [g/cm3] 3.18 Melting point [K] 1691 Thermal expansion coefficient [K-1] 19.5 x 10-6 Cleavage plane <111> Hardness (Mho) 4 Hygroscopic no Wavelength of emission maximum [nm] 435 Lower wavelength cutoff [nm] 395 Refractive index at emission maximum 1.47 Primary decay time [vs] 0.94 Afterglow (after 6ms) [%] < 0.3 Light yield [photons/MeVy 19 x 103 Photoelectron yield [% of NaI(Tl)] (for y-rays) 50 General description CaF2(Eu) is a transparent material used for detecting y-rays up to several hundred keV and for detecting charged particles. Because of its low Z-value, the material's photofraction is relatively small which prohibits its use in y-ray spectrometry at higher energies. However, the low Z-value makes CaF2(Eu) an ideal material for the detection of b-particles because of the small amount of backscattering. 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. CaF2(Eu) has a very low vapor pressure, allowing it to be used in a wide variety of vacuum applications. It is insoluble in water and most organic solvents, permitting radioactive samples in solution to be placed in direct contact with the crystal. 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 435 nm is well matched to bialkali photocathode photomultiplier tubes. CaF2(Eu) transmits visible light well, but it has a sharp absorption band at 400 mm which partly overlaps with the scintillation emission band. This causes some self absorption of the scintillation light. For an optimal energy resolution, a crystal thickness of a few centimeters is therefore recommended. Fig. 1 shows the scintillation emission spectrum. Fig. 2 shows a pulse height spectrum of 30 keV x-rays emitted by 129l measured with a CaF2(Eu) scintillator. When a 241Am a-source is used, the 5.5 MeV alpha peak appears at an equivalent y-ray energy of about 1 MeV, indicating approximately 20% light yield per MeV for alpha-particles relative to y-rays. The decay time of CaF2(Eu) for y-ray excitation is 0.94 ms. The scintillation intensity changes with temperature as shown in Fig. 3. At 300K, the slope of the curve is approx. 0.3%K-1. The material shows little afterglow, usually less than 0.3% after 3 ms. [ Scintillator options available ] Organic Products | Inorganic Scintillation Products | Crystal Products Bicron RMP | Optics and Oxides | Crismatec | Product Search/Faq Company Profile | News | Contact Us | NE Technology | Home