Photomultiplier tubes spectral sensitivity

In the chemiluminescent detection of nitrogen oxides, a constant source of ozone reacts with a metered air sample containing nitric oxide. Fontijn et al. suggested that this method could also be used for ozone detection by using a constant nitric oxide source for reaction with ozone in the air sample. The ozone-nitric oxide reaction is carried out at reduced pressure, to avoid quenching the chemiluminescent reaction. Detection of the emission in the spectral r on involved (600-3,000 nm) requires using a near-infrared-sensitive photomultiplier tube. The noise of such a photomultiplier tube is reduced by cooling it to about - 20 C. ... 

Fig 5. Spectral sensitivity curves for quartz prism monochromator, (a) With EMI 6256 photomultiplier tube (6) with EMI 9558 Q photomultiplier tube. 

The detection system of a spectrophotometer is a light sensitive photomultiplier tube. Operation of this device is described in detail in Chapter 3 and is not, therefore, discussed here. In instruments with a broad spectral range it is usually necessary to use two different photomultipliers, one most sensitive between 200 and 600 nm and a second sensitive to... 

Barrier-layer cells and photomultipher tubes have both been used for photodetection in atomic absorption spectroscopy. The use of barrier-layer cells of course is limited by their sensitivity and the diflBculty encountered in amplifying their output. They will suflBce where determination of the alkali elements is desired only. For most other work photomultiplier tubes are necessary. These are available for a broad spectral... 

Photomultipliers used within a range of 200 to 650 nm serve as detectors. Only recently broadband photomultipliers with a spectral sensitivity of 185-850 nm have appeared on the market1). In the range above 650 nm the photocell operating up to 1100 nm or the photoresistance responding up to 2500 nm are used. Occasionally attempts have been made to apply flame ionisation detectors to thin-layer chromatography 8 10). In this case, however, it is necessary to carry out the chromatography on rods, or strips or tubes coated with adsorbents. 

Light emitted by the samples is registered by a general purpose side-on photomultiplier tube (Hamamatsu 1P28, the spectral response from 185 to 700nm, the peak sensitivity at 450 nm),and recorded independently for each of eight cells by a multichannel recorder (Hewlett Packard 7418A)... 

A very important parameter of every photomultiplier tube is the spectral sensitivity of its photocathode. For best results, the spectrum of the scintillator should match the sensitivity of the photocathode. The Cs-Sb surface has a maximum sensitivity at 440 nm, which agrees well with the spectral response of... 

The spectra were not corrected for the spectral variation in the excitation source and photomultiplier tube sensitivity. Background scattered light was zeroed electronically before the acquisition of the fluorescence of 4-methylcoumaro-[222]cryptand. Absorption spectra were obtained using Perkin Elmer Lambda 7 UV/VIS Spectrophotometer. 

FIGURE 6-12. Spectral sensitivities of the R106 and R166 photomultiplier tubes. [From A. Walsh, Physical Aspects of Atomic Absorption, ASTM-STP 433 (1968). Used by permission of the American Society for Testing Materials.]... 

The spectral response of a photomultiplier tube varies with the coating materials used on the photocathode. Spectral responses of various photomultiplier tubes are given in Table 6-3. Chapter 6 also includes a general discussion of photomultiplier phototubes. The 1P28 tube (S-5 response) is sensitive from 2000 to 6500 A and is frequently used for atomic absorption spectroscopy. The Hamamatsu R106 also has an S-5 response but uses a silica window to lower the usable short wavelength response to about 1700 A. The S-20 response of the RCA 4459 permits measurements to 8500 A and is very useful for most of the alkali metals. 

Rgura IX) The spectral sensitivity curve of a Hamamatsu R955 photomultiplier tube. 

Silicon diodes are more sensitive than vacuum phototubes but less sensitive than photomultiplier tubes (see curve fin Figure 7-27). Photodiodes have spectral ranges from about 190 to llOOnm. 

The specimen holders are designed to expose an average of 65 mm x 65 mm of specimen to the heat source. The photometric system consists of a vertically mounted light source and a photocell. The photocell consists of a photomultiplier tube with a spectral response which is considered to be close to that of the human eye. In line with the photomultiplier tube is connected a sensitive amplifier and chart recorder or PC. The amplifier has provision for accurately measuring light transmittance down to 0.001% and it can be extended down to 0.00001% by a... 

The advantages of Fourier transform spectrometry over the use of a scanning monochromator (often referred to as dispersive spectrometry) is fully valid only when the detector noise is independent of the power of the radiation incident on the detector. When the detector is photon shot-noise limited [as it generally is for a photomultiplier tube (PMT), and often is for other sensitive detectors used in the near-infrared, visible, and ultraviolet spectral regions], the noise level is proportional to the square root of the incident power. For a boxcar spectrum, this means that shot noise is proportional to the square root of the number of resolution elements in the spectrum, This disadvantage therefore precisely offsets Fellgett s advantage when continuous broadband sources are employed. It should also be... 

Similarly, the number of photons detected can be increased by modestly increasing the spectral bandwidth on the emission side. However, again this will have a corresponding effect on spectral resolution. In the most sensitive of instruments the detector, invariably a photomultiplier tube, is cooled to reduce noise and thus improve the signal-to-noise levels. 

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