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BaF2
Properties of BaF2
General description Barium fluoride (BaF2) is presently the fastest known scintillator. Due to its subnanosecond decay time, it can be used for very fast timing, such as is required for positron life time studies, time of flight, Positron Emission Tomography (PET) or certain high energy or nuclear physics applications. Using special electronics together with dynode readout of photomultiplier tubes, time resolutions for 1 MeV y-rays around 100 ps are possible. BaF2 scintillation crystals combine fast timing with a high efficiency due to its high density (4.9 g/cm3) and high Z value. BaF2 has several scintillation emission bands. The fast scintillation light is emitted in the UV in bands centered at 220 and 195 nm. The decay time of the fast component varies between 600 and 800 ps. 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. Usually silicone oils or compounds are used. The self absorption of the material is very low so that the use of large scintillation crystals is possible. Next to the fast emission components, BaF2 also emits a relatively slow scintillation component in a band centered at 310 nm. The decay time of this component has an average value of 630 ns. Using quartz photomultiplier tubes for the detection of the scintillation light, about 20% of photoelectrons is produced by the fast component whereas 80% originates from the slow component (y-rays). The total number of photoelectrons detected with a PMT from a BaF2 crystal is about 2 x 103 / MeV. The ratio between the intensity of the fast and the slow scintillation components of BaF2 depends on the ionizing power of the absorbed particle. a-particles hardly produce any fast component. This feature allows you to discriminate y-rays, protons, deuterons and a-particles using a pulse shape discrimination technique. The scintillation intensity of the fast component is independent of temperature between 100 and 400 K. The slow component, in contrast, decreases in intensity with increasing temperature. Fig. 2 shows the intensity of the fast and the slow scintillation components as a function of temperature. The intensity of the slow component decreases approximately 1.1% K-1 between 250 K and 325 K (-23 and 52°C). BaF2 is not hygroscopic and is relatively radiation hard. Radiation doses of 105 Gray (107 rad) do not cause any severe damage to its scintillation characteristics.
Organic Products | Inorganic Scintillation Products | Crystal Products |
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