Quantum detect

In a model proposed by Lewis [228] the effect of the excited state of retinal on the conformational state of the protein is considered to be the first step of the excitation mechanism. Charge redistribution in the retinal by excitation with light would have the consequence of vibrationally exciting and perturbing the ground state conformation of the protein, i.e., excited retinal would induce transient charge density assisted bond rearrangements (e.g., proton translocation). Subsequently, retinal would assume such an isomeric and conformational state so as to stabilize maximally the new protein structure established. In this model, 11-m to trans isomerization would not be involved in the primary process, but would serve to provide irreversibility for efficient quantum detection. It was also proposed that either the 9-m-retinal (in isorhodopsin) or the 11-m-retinal (in rhodopsin) could yield the same, common... 

C. W. Helstrom, Quantum Detection and Estimation Theory, Academic, New York, 1976. 

MicroChannel plates are becoming widely used in spectroscopy and two dimensionaj imaging at EUV (100 - 1000 A) and soft X-ray wavelengths (10 - 100 A) for astronomy and microscopy. Although bare microchan-nel plates have low sensitivity (5% - 10% quantum detection efficiency) in this spectral region, use of photocathodes can increase substantially (to 30%-40%) microchannel plate performance. This, combined with the high spatial resolution (<50/rm), fast time response (<300 ps), and large effective area (up to 100 mm diameter) achievable with microchannel plates make the latter a very attractive and versatile tool. We discuss the properties of microchannel plates, photocathode materials, and various microchannel plate detector readout schemes that have been used for soft X-ray and EUV detection. 

Investigations (51., 52) of the variation of quantum efficiency as a function of the Csl layer thickness show that (Figure 7) the quantum detection o efficiency, for wavelengthso under 100A, is nearly constant for layers above 1000A in thickness. Below 1000A thick, the QDE fails off, due to the increasing transmission of the photocathode layer. 

Figure 6. Quantum detection of efficiency of Csl-coated MC Ps and flat samples, as a function of wavelength. Key —. Reference 48 (10°) —, Reference 49 (20 and 23°) — and —. Reference 17 Reference 15 (8°) and o. Reference 47.

Figure 8. Quantum detection efficiency of Cslcoatings as a function of grazing angle of incidence. Key , X = 67 A (48) and, X = 44 A (17).

The quantitative determination of X-ray intensities with a photon energy up to 150 keV can be realized by three types of detectors semiconductor-based detectors which call for efficient cooling, ionization chambers which have a low quantum detection efficiency (< 50%), and detectors based on luminescent materials. The latter type of detector is of interest here, because it is realized by the combination of a luminescent material with a photodiode. 

To form an image, the transmitted X-rays must be detected and their energy converted into a usable signal. Quantum detection efficiency, rj, describes the fraction of the X-rays incident on the detector, that... 

These operations must be optimized if the detector is to provide high-quality images at appropriate dose levels. Detectors are characterized by their quantum detection efficiency,sensitivity,spatial resolution properties, noise, dynamic range, and linearity of response. 

As discussed in Chap. 1, quantum detection efficiency, r ( ), describes the fraction of the X-rays falling on the detector, that interact with it, producing at least some signal. Some calculated values of tj for... 

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