Curved-crystal spectrometer

Fig. 7-12. The curved-crystal spectrometer of Adler and Axelrod, showing a polished ore specimen in position. (1) Microscope stage (2) polished ore sample (3) crystal support block (4) Geiger counter and scatter slits. (Courtesy of Adler and Ayelrod and the U. S. Geological Survey.)...

The apparatus as modified for x-ray emission spectrograph is also shown in Figure 11-1. The proportional counter may be used alone (pulse-height analysis Section 2.13) or a curved-crystal spectrometer can be employed to achieve better resolution. Analytical results were comparable to those quoted above, but localization of the area analyzed was considerably less sharp than the micron-diameter spot achieved in differential absorptiometry. 

In a WDS, the X-radiation coming from the specimen is filtered by means of a curved crystal spectrometer, which employs diffraction to separate the X-rays according to their wavelength. A typical arrangement for the spectrometer is shown in Figure 5.5. 

An optical diagram of a Johansson curved-crystal spectrometer is given in Fig 9. F.ach spectrometer of an x-ray qnantometer may be equipped with optimum crystal-detector combinations for specific determinations in a wide variety of matrixes, including steel, aluminum, copper-base materials, ores, cement, and slags—in both liquid and solid states. 

Fig. 9. Optical diagram of Johansson curved-crystal spectrometer...

Neutron capture as well as charged particle reactions produce in general very dense y-ray spectra. The high resolution electron [MAM78] and curved crystal spectrometers [K0C80] at ILL in Grenoble present excellent... 

Detail tests on nuclear models require not only a knowledge of energy, spin and parity of many levels, but also the determination of transition multipolarities and branching ratios. Precise intensities are thus needed. The well shielded anti-Compton spectrometer offers a rather simple solution especially for accurate angular distribution measurements. When the spectra are very complex, like in the case of final doubly odd nuclei, intensities cannot be determined without use of high resolution instruments. The curved crystal spectrometer provides a powerful solution at, unfortunately, non negligible cost. 

Fig. 1. Principle of the set-up for the pion mass experiment consisting of the cyclotron trap with a gas cell and a curved-crystal spectrometer equipped with a two-dimensional position-sensitive X-ray detector. The focusing condition for a wave length A reflected under the Bragg angle Ob is R-sin B, where R is the (horizontal) radius of curvature. Typical values for R and the diameter of the spherically bent crystals are 3 m and 100 mm...

Estimates of shifts of spectra in curved crystal geometries are often calculated for an ideal detector located on the Rowland circle. However, the detection surface is usually fiat and therefore cannot lie on the Rowland circle. Detectors located on a fixed length detector arm will additionally travel off the Rowland circle as the Bragg angle is scanned unless the crystal curvature is simultaneously scanned (which raises problems of stress hysteresis). Conventional shifts calculated for detection on the Rowland circle do not agree with shifts at a flat extended detector and this systematic error can be 100-200 ppm for any Johann curved crystal spectrometer. We have incorporated fiat surface detectors located off the Rowland circle into the general theory [18,17]. 

The use of a Johann-type curved crystal spectrometer and an electron beam ion trap allow us to obtain X-ray specta of the Lyman-a lines of medium Z... 

Collimators are not needed for curved crystal spectrometers where shts or pinholes are used instead nor are they needed for energy dispersive spectrometers. 

Figure 8.20 Schematic of the optical path in a curved crystal spectrometer. [Courtesy of PANalytical, Inc., The Netherlands (www.panal3ftical.com).]...

Recently, Izawa et al. studied the chemical effect of the L /L. X-ray intensity ratio of molybdenum compounds by electron and proton bombardment. The X-ray spectra were measured with a curved crystal spectrometer (Johansson type, ADP crystal). and are representative of variable and invariable peaks, respectively. 

Benka et al. studied K X-ray spectra of solid and gaseous fluorine compounds by bombarding with 80 MeV Ar " ions and with 48 MeV Mg ions. The satellite and hypersatellite spectra were measured with a curved crystal spectrometer. The spectra obtained by bombarding with 80 MeV Ar for various alkali metal and alka-... 

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