Barium fluoride detector

As with BGO, barium fluoride needs no activator. At first sight, the material appears to offer little advantage over other scintillators. The low light output means that the resolution of barium fluoride detectors is particularly poor. Its only real advantage lies in the fact that the luminescence has two components, a rather slow one with a decay time of 630 ns and an extremely fast one with only 0.6 ns lifetime. The fast emission is in the ultraviolet and needs an appropriately sensitive light detector. Barium... 

Piezoelectricity links the fields of electricity and acoustics. Piezoelectric materials are key components in acoustic transducers such as microphones, loudspeakers, transmitters, burglar alarms and submarine detectors. The Curie brothers [7] in 1880 first observed the phenomenon in quartz crystals. Langevin [8] in 1916 first reported the application of piezoelectrics to acoustics. He used piezoelectric quartz crystals in an ultrasonic sending and detection system - a forerunner to present day sonar systems. Subsequently, other materials with piezoelectric properties were discovered. These included the crystal Rochelle salt [9], the ceramics lead barium titanate/zirconate (pzt) and barium titanate [10] and the polymer poly(vinylidene fluoride) [11]. Other polymers such as nylon 11 [12], poly(vinyl chloride) [13] and poly (vinyl fluoride) [14] exhibit piezoelectric behavior, but to a much smaller extent. Strain constants characterize the piezoelectric response. These relate a vector quantity, the electrical field, to a tensor quantity, the mechanical stress (or strain). In this convention, the film orientation direction is denoted by 1, the width by 2 and the thickness by 3. Thus, the piezoelectric strain constant dl3 refers to a polymer film held in the orientation direction with the electrical field applied parallel to the thickness or 3 direction. The requirements for observing piezoelectricity in materials are a non-symmetric unit cell and a net dipole movement in the structure. There are 32-point groups, but only 30 of these have non-symmetric unit cells and are therefore capable of exhibiting piezoelectricity. Further, only 10 out of these twenty point groups exhibit both piezoelectricity and pyroelectricity. The piezoelectric strain constant, d, is related to the piezoelectric stress coefficient, g, by... 

The principal materials used for pyroelectric detectors are members of the TGS group, lithium tantalate, strontium barium niobate, ceramics members of the lead zirconate titanate (PZT) group and, more recently, films of the polymers polyvinyl fluoride (PVF) and polyvinylidene fluoride (PVFj). 

The pyroelectric detectors now being manufactured in quantity use either LiTaOj or a ceramic based on PZT modified to enhance its pyroelectric properties [8.43]. Strontium Barium Niobate (SBN) [8.44] and polyvinylidene fluoride films [8.36a, d] are also used. The use of polymer films could expand as the understanding of these films increases. 

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