Energy resolution crystal spectrometer

Recently, Bergmann et al. (37) measured the A -capture x-ray spectra of Fe metal and FcjO, with high-energy-resolution crystal spectrometer and compared them with the x-ray excited spectra for Mn metal and MnO. Unfortunately they did not evaluate the K0/Ka ratio, but demonstrated the difference in the peak shapes for K0 spectra between two excitation modes. Considering these facts, future experimental studies on the K0 /K a ratio for 3d elements should be performed with high-resolution spectrometers, or at least with careful data analysis of the SSD spectra. 

Fig. 4. Portion of the 165Ho(a,3ny)166Tm spectrum observed with the on-line bent crystal spectrometer and with a good resolution germanium detector in the inset (the corresponding region is represented with open circles). Transitions are identified by their approximate energy in keV.

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. 

Table 1. Calculated electromagnetic energies and line widths of the antiprotonic transitions measured with the crystal spectrometer. The energy resolution AEexp of the Bragg spectrometer was determined from narrow transitions of antiprotonic noble gases. Ob stands for the Bragg angle...

A different method became available with modern meson factories, where the characteristic X-radiation from exotic atoms can be studied under optimized conditions and with reasonable count rates. Such experiments require the use of high-intensity external beam lines together with a particle concentrator like the cyclotron trap and a high-resolution low-energy crystal spectrometer. 

The calculated results are qualitatively in agreement with the experimental data, except for CrOa. The experimental value for CrOa is larger than unity, while the calculated one is smaller. In the case of MnOa, the theoretical value agrees with the measured value of Mukoyama et al. [26], but smaller than the experimental value of Tamaki et al [18]. It should be noted that the experimental studies of Tamaki et al [18] and Brunner et al [22] were performed with poor-energy-resolution Si(Li) detectors. On the other hand, a double crystal spectrometer with high energy resolution was used by Mukoyama et al [26]. In the latter experiment, the K(3" and /C/ 2,5 peaks were observed separately from the peak, as shown in... 

The utility of this kind of spectrometer is based on two properties (1) the excellent energy resolution of the Si(Li) counter (Sec. 7-8), which is far better than that of any other type of proportional counter, and (2) the ability of the MCA to perform rapid pulse-height analysis (Sec. 7-9). The latter feature makes this spectrometer very much faster than a single-channel crystal spectrometer. The MCA can measure the intensities of all the spectral lines from the sample in about a minute, unless elements in very low concentrations are to be determined. 

In a crystal spectrometer the intensity of the fluorescent radiation from the sample is greatly reduced before it reaches the counter by (a) the collimator, which is necessary for good resolution but which blocks all rays except those nearly parallel to the collimator axis, and (b) the crystal, which diffracts very inefficiently. Neither of these losses exists in the energy-dispersive spectrometer, so that the fluorescent radiation incident on the counter can be quite intense. 

Summary. The various differences between wavelength-dispersive and energy-dispersive spectrometry have been described in this chapter. All in all, wavelength dispersion by a crystal spectrometer is superior, chiefly because of its better resolution for most elements of interest, for the quantitative determination of several elements in a complex sample with high accuracy. Energy dispersion has a special place in microanalysis, in portable spectrometers, or wherever fast, semi-quantitative analyses are required. 

Filter instruments offer good intensity at modest energy resolutions and crystal analyser instruments offer good resolution with modest intensities. While a ciystal analyser instrument is conceivable at a continuous source (such an instrument would be a specialised form of the triple axis spectrometer ( 3.4.1) [17]) none have yet been constructed to exploit the advantages of low final energies. 

In this Appendix we derive the analytical expression for the energy resolution of a low-bandpass spectrometer like TOSCA ( 3.1) (also known as crystal analyser spectrometers) and describe two key features of the design ( 3.2), time focussing ( 3.2.1) and the Marx principle ( 3.2.2) that improve the resolution at high and low energy transfer respectively. 

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

It should be pointed out that the X-ray detector used with the crystal spectrometer need not have an extremely good energy resolution, because it is the resolution of the analyzing crystal that determines the spectroscopic capabilities of the system, not that of the detector. The X-ray counter may be a proportional counter or a Si(Li) detector. 

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