Photomultiplier maximum sensitivity

Phosphorus-containing pesticides la 254 Phosphorus insecticides lb 83 Phosphorus pesticides lb 32 Photochemical activation lb 13 Photochemical reactions lb 15,17 Photodiodes la 24,29 Photo effect, external la 24 -, internal la 24, 29 Photo element la 24,29 Photography, exposure times la 137 -, instmmentation la 137 Photomultiplier la 25ff -, disadvantages la 27 -, energy distribution la 26 -, head on la 27 -, maximum sensitivity la 28 -, side on la 27 -, spectral sensitivity la 28 -, window material la 28 Photocells la 25 Phloxime lb 116... 

A Perkin-Elmer MPF-2A Fluorescence Spectrophotometer was used to determine the excitation and emission wavelengths required for achieving maximum fluorescence intensity for the pesticides studied. The MPF-2A contained a 150 watt xenon arc and an excitation monochromator with a grating blazed at 300 nm as the excitation unit a Hamamatsu R 777 photomultiplier tube (sensitivity range 185 - 850 nm) and an emission monochromator grating blazed at 300 nm as the emission detection unit. A DuPont Model 848 Liquid Chromatograph was used for HPLC (Figure 2). The accessory injection device included a Rheodyne Model 70-10 six-port sample injection valve fitted with a 20 y liter sample loop. A Whatman HPLC column 4.6 mm x 25 cm that contained Partisil PXS 1025 PAC (a bonded cyano-amino polar phase unspecified by the manufacturer) was used with various mobile phases at ambient temperature and a flowrate of 1.25 ml/minute. 

In the present technique, organo-nitrate compounds are first trapped into a collection tube that contains a proprietary sampling material. The desorbed material is then catalytically converted to NO2 upon exposure to pulse heated platinum wire. Chemiluminescence is then produced by the reaction of NO2 with luminol. The detection system uses a gas-liquid reaction leading to light emission with a maximum at 425 nm. This wavelength corresponds to the maximum sensitivity for most photomultiplier tubes. The biggest problem... 

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... 

Photomultiplier tubes (PMTs) are the most commonly used detectors, various types are available for different applications. In general they are sensitive in the range from 200 to 600 nm, with maximum sensitivity obtained in the 300—500 nm range. Red-sensitive PMTs are also available for investigations beyond 600 nm. The PMT housings are sometimes cooled to temperatures as low as —40 °C to minimize temperature-dependent noise. 

Emission from dimols of singlet oxygen may be detected by photomultipliers used for measurement of chemiluminescence from hydrocarbon polymers with a maximum spectral sensitivity at 460 nm. The above scheme, however, requires the presence of at least one molecule of hydrogen peroxide in close vicinity to the two recombining peroxyl radicals and assumes a large heterogeneity of the oxidation process. 

Excellent summaries of the various response curves available with commercial photomultipliers can be found in commercial sales publications and review articles [5.11] and we will not repeat such data in detail here. One response summary for classical photoemitters is given in Fig. 5.20 [5.11]. Note that the maximum yield is in the order of 0.3 electron per incident photon, with the higher efficiencies and broader response generally obtained with more complex materials. Note also that the IR-sensitive S-1 surface has by far the poorest quantum efficiency over the visible spectrum. Summaries of the general advantages and applications of each generic surface are given in [5.1, 11]. 

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