Photomultiplier reaction time

Depending on their positioning the dynodes are referred to as being head-on or side-on . Commercial scanners mostly employ side-on secondary electron multipliers where, as the name implies, the radiation impinges from the side — as in Figure 19. Their reaction time is shorter than for head-on photomultipliers because the field strength between the dynodes is greater. 

Johnson et al. (1962) measured the quantum yield of Cypridina luciferin in the luciferase-catalyzed reaction for the first time, using a photomultiplier calibrated with two kinds of standard lamps. The measurement gave a value of 0.28 0.04 at 4°C in 50 mM sodium phosphate buffer, pH 6.5, containing 0.3 M NaCl. The quantum yield... 

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 laser beam highly focused by a microscope into a solution of fluorescent molecules defines the open illuminated sample volume in a typical FCS experiment. The microscope collects the fluorescence emitted by the molecules in the small illuminated region and transmits it to a sensitive detector such as a photomultiplier or an avalanche photodiode. The detected intensity fluctuates as molecules diffuse into or out of the illuminated volume or as the molecules within the volume undergo chemical reactions that enhance or diminish their fluorescence (Fig. 1). The measured fluorescence at time t,F(t), is proportional to the number of molecules in the illuminated volume weighted by the... 

Per-Anders Persson et al, "A Technique for Detailed Time-Resolved Radiation Measurements in the Reaction Zone of Condensed Explosives , 4thONRSympDeton(1965), 602-08. Preliminary experiments with nonporous 60/40-RDX/TNT and NMe (N it ro me thane) using a fast photomultiplier and high-speed oscilloscope are described. The technique permitted recording... 

In principle, absorption spectroscopy techniques can be used to characterize radicals. The key issues are the sensitivity of the method, the concentrations of radicals that are produced, and the molar absorptivities of the radicals. High-energy electron beams in pulse radiolysis and ultraviolet-visible (UV-vis) light from lasers can produce relatively high radical concentrations in the 1-10 x 10 M range, and UV-vis spectroscopy is possible with sensitive photomultipliers. A compilation of absorption spectra for radicals contains many examples. Infrared (IR) spectroscopy can be used for select cases, such as carbonyl-containing radicals, but it is less useful than UV-vis spectroscopy. Time-resolved absorption spectroscopy is used for direct kinetic smdies. Dynamic ESR spectroscopy also can be employed for kinetic studies, and this was the most important kinetic method available for reactions... 

Light emission was recorded with an IP 21 R.C.A. photomultiplier tube in the range 3000-7000 A. Interference filters (spectral bandwidth A A = 100-140 A.) showed that the light emission of the pic darret arises from the same emitter as that from the slow reaction—probably excited formaldehyde (16). The pic darret appears as a clear pulse on the record of light intensity vs. time (Figure 1). 

In the photolysis of ozone, only emission from 02(1A9) can be detected,70 and the absence of 02(1S,+) is now understood in terms of the considerable reactivity of 02(123+) with ozone61 (see Sect. V-B-l). has been detected in the vacuum UV photolysis products of 0277 although absolute measurements of the excitation efficiency have not, so far, proved practicable. The limits of sensitivity of the photomultiplier detector to 1.27 [x emission suggest that reaction (19) could proceed perhaps 20 times more rapidly than reaction (20) work is at present in progress in an attempt to measure k12 directly. 

As described above, recent advances in accelerator technology have enabled the production of very short electron pulses for the study of radiation-induced reaction kinetics. Typically, digitizer-based optical absorbance or conductivity methods are used to follow reactions by pulse radiolysis (Chap. 4). However, the time resolution afforded by picosecond accelerators exceeds the capability of real-time detection systems based on photodetectors (photomultiplier tubes, photodiodes, biplanar phototubes, etc.) and high-bandwidth oscilloscopes (Fig. 8). Faster experiments use streak cameras or various methods that use optical delay to encode high temporal resolution, taking advantage of the picosecond-synchronized laser beams that are available in photocathode accelerator installations. 

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