图1－1 XRF仪器的外观特征

光源：

X射线光源：白色X射线。即具有各种波长的X射线，可分析前面所列范围的所有元素。放射性同位素光源：放射出的射线亦在X射线范围，但能量是固定的。因此只能分析部分元素，仪器的体积可以很小，最新型的相当于一个计算器的大小。

同步辐射光源：光源的能量更大，对后续的二次射线检测很有利，所以分析精度更高，但 仪器造价很昂贵。 2 分析原理 When the atoms in a sample material are irradiated with high-energy primary x-ray photons, electrons are ejected in the form of photoelectrons. This creates electron 'holes' in one or more of the orbits, converting the atoms into ions - which are unstable（Figure 1－2(1)）.

Figure 1－2 XRF分析原理(1)

To restore the atoms to a more stable state, the holes in inner orbits are filled by electrons from outer orbits. Such transitions may be accompanied by an energy emission in the form of a secondary x-ray photon - a phenomenon known as \－1(2)).

Figure 1－2 XRF分析原理(2)

The various electron orbits are called K, L, M, etc., where K is closest to the nucleus. Each corresponds to a different energy level - and the energy (E) of emitted fluorescent photons is determined by the difference in energies between the initial and final orbit for the individual transitions(Figure 1－3).

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Figure 1－3 Electron orbits K, L, M,

Characteristic x-ray emissions result in an energy spectrum that is a \－4). So we can determine the element kinds in the sample. And also the intensities of the peaks in the spectrum are roughly proportional to the concentrations of the constituent elements.

Figure 1－4 Characteristic x-ray emissions result

3 仪器构成

波长色散型XRF：WAVELENGTH DISPERSIVE XRF (WDS-XRF)

通过分析样品在入射X射线作用下产生的二次X射线(荧光射线)的波长，来定性或定量分析样品的元素组成及含量。

能量色散型XRF: ENERGY-DISPERSIVE XRF （EDS－XRF） 通过分析样品在入射X射线作用下产生的二次X射线(荧光射线)的能量，来定性或定量分析样品的元素组成及含量。 WDS-XRF and EDS-XRF(图1－5)

图1－5 XRF工作流程框图

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4 WDS-XRF Wavelength dispersive XRF uses a crystal to separate the various wavelengths: for every angle of incident radiation(入射辐射), the only wavelength reflected to the detector is the one that conforms to Bragg’s formula: n? = 2d sin ?

where ? is the wavelength of the x-ray radiation produced by the sample; d is a constant characteristic of every crystalline substance (i.e. the x-ray crystal); and ? is the angle on incidence of the x-radiation on the sample. The crystals and their planes often used are as follow（表1－2）.

表1－2 常用的分光晶体

How to determine the wavelength（图1－6）: Detector is rotating when doing the wavelength determination, also the crystal is rotating by half speed. So, by changing the angle of the crystal, you can select any wavelength for specific elements of interest.

Different crystal can be used determine different elements. When doing measurement, we often need to change crystals for the various elements, finally we can yield results in any form desired: qualitative, ratio, quantitative, graphic, etc.

The relationship between the range of analyzing element and the crystals, and the 2 theta scanning range（表1－3）.

图1－6 波长测定示意图

表1－3 The relationship between the range of analyzing element and the crystals

Element range Ti22－U92 Al19－ Ti22 Mg12 Na11 、F9 、Mg12

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crystals LiF EDDT ADP TAP 2?scanning ranges 5°－90° 35°－145° 0°－+3° 5°－+3° Analyzing Procedure: Every element has a strongest X ray wavelength. In order to determine it, first we should measure the intensity of that wavelength.

For example, strongest Line and their 2? position for Ni, Fe, & Ru, when detected by different crystal（表1－4）.

表1－4 Strongest Line and their 2? position for Ni, Fe, & Ru

In order to make the determination more accurate, we should also measure their accompanying peaks（表1-5）.

表1－5 Ni, Fe的K系特征

Analyzing Procedure（图1－7）:

图1－7 分析程序框图

小结

? WDS was introduced in the early 1950s.

? WDS spectrometer systems employ diffraction by a single crystal to separate characteristic wavelengths emitted

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