Resolving power, crystal spectrometer

WDSs have excellent resolving power, and the peak-to-background ratio of each line is much higher than can be achieved with a crystal detector. With a suitable crystal of large lattice spacing it is possible to detect and count X-rays as soft as boron K or even beryllium K , and this type of spectrometer is widely used when... 

The resolution of crystal spectrometers is traditionally expressed as the resolving power, which is the inverse of the energy resolution ... 

Figure 12 2 Resolving power and energy resolution of a crystal spectrometer as a function of X-ray energy (data used n - I, d = 0.2 nm, A0 = j°).

The resolving power of a neutron crystal spectrometer is given (based on Eqs. 14.49 and 14.50) by... 

Nowadays, pulsed, frequency tripled Nd YAG UV lasers (355 nm) are usually employed for MALDI experiments with a repetition rate of 1000 Hz in commercial instruments for sufficient data acquisition. In MALDI-IMS, the resolving power for application strongly depends on the sample preparation step (e.g., matrix crystal size), stepper motor accuracy, and laser spot sizes. To achieve MALDI-IMS to a practical resolution, the laser spot size of 20 pm is usually used. Therefore, the time needed to obtain images from a sample depends on the number of analyzed spots, the repetition rate of the laser (Hz), and the data collecting and processing speed of computers. For example, imaging a whole-body mouse or rat section with current commercially available MALDI mass spectrometers equipped with lasers operating at 1 kHz would take 2-4 h. 

Fig. 5. A schematic illustration of an angle-resolved photoemission experiment An incident photon, with wavevector p and polarization E, strikes the sample with polar incidence angles (61p, p) relative to the crystal axes. In practice the light source is generally fixed relative to either the crystal or the detector. However, the ability to vary the photon polarization from synchrotron sources provides a powerful tool for obtaining information on the symmetries of electronic states. By moving the analyzer or the sample (depending on the details of the experimental apparatus), photoelectrons leaving the surface at polar angles (6, ) are collected by the spectrometer the component of their crystal momentum, k, parallel to the sample surface is strictly conserved, allowing accurate determination of the two-dimensional band structure.

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