Radiation transducers

Lead zirconate [12060-01 -4] PbZrO, mol wt 346.41, has two colorless crystal stmctures a cubic perovskite form above 230°C (Curie point) and a pseudotetragonal or orthorhombic form below 230°C. It is insoluble in water and aqueous alkaUes, but soluble in strong mineral acids. Lead zirconate is usually prepared by heating together the oxides of lead and zirconium in the proper proportion. It readily forms soHd solutions with other compounds with the ABO stmcture, such as barium zirconate or lead titanate. Mixed lead titanate-zirconates have particularly high piezoelectric properties. They are used in high power acoustic-radiating transducers, hydrophones, and specialty instmments (146). 

Invariably in modern instruments, the information of interest is encoded and processed as an electrical signal. The term transducer is used to indicate the type of detector that converts quantities, such as light intensity, pH, mass, and temperature, into electrical signals that can be subsequently amplified, manipulated, and finally converted into numbers proportional to the magnitude of the original quantity. All the detectors discussed here are radiation transducers. 

As indicated in Figure 7-, b, there arc two general types of radiation transducers. One type responds to photons, the other to heat. All photon transducers (also called phoforli ciric or quantum detectors) have an active surface (hat absorbs radiation. In some types. 

Instruments for measuring the absorption of ultraviolet. visible, and near-infrared radiation are intide up ol one or more (I) sources, (2) wavelength selectors, (3) sample containers. (4) radiation transducers, and (.5) signal processors and readout devices. The design and peifoi mance of components (2). f4). and (5) were described in considerable tletail in Oiapier 7 and thus arc not discussed further here. We will, however, consider briefly the characteristics of sources and sample containers for the region of l9l) to nm. 

FIGURE 18-9 Raman spectrometer with fiber-optic probe. In (a) a microscope objective focuses the laser radiation onto excitation fibers that transport the beam to the sample. The Raman scattering is collected by emission fibers and carried to the entrance slit of a monochromator or to the entrance of an interferometer. A radiation transducer, such as a photomultiplier tube, converts the scattered light Intensity to a proportional current or pulse rate (b) end view of the probe (c) end view of collection libers at entrance slit of monochromator. The colored circles represent the input fiber and the uncoiored circles the collection fibers. (Adapted from R. L. McCreery. 

A General Designs of Optical Instruments 164 7B Sources of Radiation 166 7C Wavelength Selectors 175 7D Sample Containers 190 7E Radiation Transducers 191 7F Signal Processors and Readouts 202 7G Fiber Optics 202 7H Types of Optical Instruments 203 71 Principles of Fourier Transform Optical Measurements 204 Questions and Problems 212... 

For a good discussion of optical radiation transducers of all rypes, including thermal detectors, see E. I.. Dereniak and G- D. Growe. Optical Radmiion Detecion. New York Wiley, 1984. 

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