Photoelectric detection

Finished zinc and zinc aHoys are usuaHy analyzed for metals other than zinc by emission spectroscopy and the zinc determined by difference. ASTM method E 27 describes a technique using a dissolved sample and photographic detection. The internal standard is the zinc line at 267.0 nm. However, procedures using soHd samples are generaHy preferred and photoelectric detection often replaces optical detection. Samples are cast and machined on the surface where the arc is stmck. Up to 15 elements can be determined in a few minutes by modem automatic spectrometers. ASTM gives wet chemical methods for metals other than zinc (79). 

A modern laser Raman spectrometer consists of four fundamental components a laser source, an optical system for focusing the laser beam on to the sample and for directing the Raman scattered light to the monochromator entrance slit, a double or triple monochromator to disperse the scattered light, and a photoelectric detection system to measure the intensity of the light passing through the monochromator exit slit (Fig. 7). 

Photoelectric detection is incorporated in all modern Raman instruments. 1. Photomultipliers... 

Fig. 2-2, Room-temperature absorption coefficients and cross sections of NO by photoelectric detection A = 590-960 A absorption coefficients to base e for 1 atm of gas at 273°K (from Metzger and Cook309 with permission).

FIGURE 3. Absorption cross sections for CO by photoelectric detection with an instrumental band pass of 0.025 nm. Absorption cross section is to the base e 1 Mb = 10 8c(n2 (from Myer and Samson with permission). 

FIGURE 4b. Absorption coefficients of CO by photoelectric detection with an instrumental band width of 0.05 nm. Absorption coefficient is to the base e for 1 atm of gas at 2730k (from Huffman et al. with permission). 

FIGURE 6. Molar absorptivity of CO2 by photoelectric detection, defined as (bc) log- o where b is the path length in cm and c is the concentration in moles/1iter. Reprinted with permission from J.W. Rabalais et al., Chem. Rev., 71, 73 (1971). Copyright by the American Chemical Society. 

FIGURE 7. Extinction coefficient, k, for CO by photoelectric detection with an effective instrumental resolution of about 0.4 nm. Extinction coefficient determined through the relation Iq/1 = exp (k ns.). Curve (1) estimated extinction coefficient, curve (2) measured values, see reference 42 (from Shemansky permission). 

Photographic emulsions and photoelectric detection devices can be used as detectors for electromagnetic radiation between 150 and 800 nm. Among the photoelectric devices, photomultipliers are the most important but new solid state devices have become a useful alternative. 

The silicon intensified target (SIT) vidicon has a number of unique properties which make it a valuable detector for atomic spectroscopy. The SIT vidicon provides two-dimensional photoelectric detection with high sensitivity and rapid signal readout. Time resolution can be obtained in a time-resolved (real time) mode on the millisecond scale and in a time-gated (equivalent time) mode on the submicrosecond scale. 

Fluctuations in electronic excitation-sources (described in Sec. 11.2), together with sample irregularities, constitute the major sources of error in emission spectroscopy. Modern spectrometers provide excellent stability and precision, and new sources like the ICP discharge and the controlled-waveform spark discharge have reduced many of the previous limitations. Photoelectric detection generally provides precision superior to that of photographic methods. 

Smoke detectors (photoelectric) Detects smoldering fires Low cost Easily contaminated Indoor use... 

Walters has designed a complete system for time-resolved spectroscopy that is useful for transients from 0.2 to 90 /xsec over a wavelength range of 1000 A per exposure, using either photographic or photoelectric detection. The system utilizes a rotating mirror with photocell synchronization. 

Peaks at 5.9 and 6.5 keV, originating from photoelectric detection of Mn K-L2,3 (Ka) and Mn K-M23 (K S), broadened by the statistical factors that affect the detection process as discussed above. 

F. Valentin, Photoelectric Detection of the Raman Effect, Compt. rend. 244, 1915-1917, 1957. 

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