Photo counting

The detection of photoelectrons is a doubly-stochastic Poisson process wherein the light intensity fluctuates and causes a random modulation in discrete number of measured photoelectrons, which are themselves subject to intrinsic fluctuations in the shot-noise limit. Suppose there are n photoelectrons counted in an integration time G, the mean photo-count is... 

Due to the pulsed radiation output of the LINAC the detectors and the detector electronics have to handle very high counting rates in very short periods. Therefore the detectors have to work in a mode, where the detector output is integrated for one or several beam pulses. For that purpose the crystals are coupled to photo- diodes. Their currents are read out and analysed by the electronic board, which has been developed for this special application. 

Here the sum runs over all possible initial states and the operator describes the interaction of the electrons and the radiation field with wave vector q and polarization A. In Eq. (1) it has been assumed that the detector selectively counts photo electrons with energy E, wave vector k, and spin polarization The corresponding final... 

The thickness of a Mossbauer sample affects not only the strength of the Mossbauer signal but also the intensity of the radiation arriving at the detector because the y-rays are inherently attenuated by the sample because of nonresonant mass absorption caused by the photo effect and Compton scattering as mentioned earlier. The counting rate C in the detector decreases exponentially with the density of the absorber,... 

Nuclear scattering is counted by two avalanche photo diode (APD) detectors. The detector for NIS (Fig. 9.1) is located close to the sample. It counts the quanta scattered in a large solid angle. The detector for NFS is located far away from the sample. It counts the quanta scattered by the nuclei in the forward direction. These two detectors follow two qualitatively different processes of nuclear scattering ... 

Table 4. Analysis of metabolites of photo-cis-chlordane in blue-gill as analyzed by TLC (silica gel GF-254, 0.25 mm) followed by X-ray autoradiography and scintillation counting (16).

He/Ne laser focussed into a small tapered hole in a pellet of the plastic. The flux density achieved at the focus was about 1000 Watts/cma. The scattered radiation was examined using a double spectrometer and photon-counting detection. A very fine spectrum, superior even to that of Maklakov and Nikitin (see Table 1), was recorded photo-electrically. Schaufele pointed out that a band atAv= 109cm-1 forecast previously by Tadokoro et aL (15) was not observed at first but in a note added in proof he mentions that a feature may be genuine at 98 2 cm-1. A band had already been observed at Av= 110cm-1 by instrument developers at the Cary Instrument Co. since Szymanski (16) shows a spectrum of isotactic polypropylene, recorded at Monrovia, Calif., on a laser sourced Cary 81 spectrometer, as an example of recent advances in Raman spectroscopy. 

Moldavan A (1934). Photo-electric technique for the counting of microscopical cells. Science 80 188-189. 

In a passive detector developed by the National Radiological Protection Board (Wrixon et al., 1988), the etched pits in the detectors are filled with scintillator fluid. After exposure to radon, the detector is irradiated with an alpha source, and the resulting scintillations counted with a photo-multiplier tube. In this way, track density over 1 cm2 of detector can be measured in a few seconds. Passive detectors used in the UK National Survey were sensitive down to 20 kBq m-3 h of accumulated exposure, equivalent to a radon concentration of 5 Bq m-3 measured over 4000 h exposure. 

After amplification, the signals from the photo- and Auger electrons were fed to the time-measuring device, a time-to-digital converter (see Fig. 4.47). To reduce the total dead time of the device, the Auger electrons which had a lower counting... 

For an experimental investigation, we could make use of a magic camera that could photograph individual argon atoms and take a million photographs of the contents of the box. The camera would be performing a time average of the motion of the atoms in the box.3 With a million photos and only four atoms in the box, it is likely that we would find some photos with all the atoms on the left side of the box. How would we interpret this result A reasonable interpretation would be in terms of probability. We could count the pictures that showed all four atoms on the left side of the box (consistent with our definition of the final state of the reverse Joule process) and divide it by the total number of pictures, where the four atoms could be anywhere in the box (consistent with the initial state). This ratio... 

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