Patent Number: 051329972
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray spectroscopic analyzing apparatus having a source of X-rays for radiation onto a sample to be analyzed. 2. Description of the Prior Art As an apparatus for achieving an elemental analysis of a sample to be analyzed, a fluorescent X-ray analyzing apparatus has been known which comprises a source of X-rays, for example, an X-ray tube, for radiating an excitation X-ray beam towards a sample to be analyzed, and a fluorescent X-ray detector for detecting the intensity of fluorescent X-rays coming from the sample to determine elements contained in the sample, In this type of fluorescent X-ray analyzing apparatus, a low-order beam having a relatively high intensity is spectroscopically selected from a spectrum of the X-rays emitted from the X-ray tube and is used as the excitation X-rays. With the prior art fluorescent X-ray analyzing apparatus, it has been found that no element of the sample having a wavelength component lower than that of the low-order beam cannot be spectroscopically determined. Accordingly, where the sample contains the same element as that contained in a target material of the X-ray tube, the spectroscopic determination of such element is not possible. By way of example, if the target material is made of tungsten (W), and so long as a WL.beta..sub.1 beam (.lambda.=1.2818 .ANG., E=9.671 keV) having a relatively high intensity is employed for the excitation X-ray beam, the determination of the presence of tungsten in the sample is not possible even though the sample in fact contain tungsten. This is because the wavelength at the absorption edge peculiar to tungsten is shorter than the wavelength of the WL.beta..sub.1 beam. This is also true of other elements than tungsten. By way of example, arsenic cannot be spectroscopically analyzed with the prior art fluorescent X-ray analyzing apparatus because the wavelength (.lambda.=1.045 .ANG.) at the absorption edge peculiar to arsenic is shorter than the wavelength of the WL.beta..sub.1 beam. Apart from the foregoing prior art, a total reflection fluorescent X-ray analyzing method is also well known in which a primary X-ray beam is radiated so as to be incident upon a sample to be analyzed at a minute angle of incidence so that fluorescent X-rays reflected from a surface region of the sample can be analyzed for the elemental determination. In the practice of this prior art fluorescent X-ray spectroscopic analyzing method utilizing the total reflection, a monochromatic light is employed for the primary X-ray beam. However, where the monochromatic light is employed, it has often been observed that the spectroscopic analysis tends to result in a measurement error depending on preset values of parameters used during the analysis. SUMMARY OF THE INVENTION Accordingly, the present invention has for its important object to provide an improved X-ray spectroscopic analyzing apparatus effectively utilizable for the analysis of an element having a wavelength at the absorption edge which is shorter than that of the low-order beam of relatively high intensity contained in the spectrum of the excitation X-rays. Another important object of the present invention is to provide an improved X-ray spectroscopic analyzing apparatus of the type referred to above, which can be effectively utilized in the practice of the fluorescent X-ray analyzing method using the total reflection with a minimized measurement error, thereby to improve the reliability of the elemental determination. In order to accomplish the foregoing objects, in accordance with the present invention, there is provided a X-ray spectroscopic analyzing apparatus which comprises a source of X-rays, a first analyzing crystal for diffracting the X-rays from the X-ray source, and a second analyzing crystal for diffracting the X-rays from the X-ray source and also for passing therethrough a diffracted X-ray component from the first analyzing crystal. The first and second analyzing crystals are so disposed and so positioned as to permit the diffracted X-ray components of different wavelengths to travel along a single path towards a sample to be analyzed. On an optical path extending between the X-ray source and the sample, a filtering means for cutting a portion of the X-rays which has a wavelength shorter than a predetermined wavelength. Preferably, the X-ray spectroscopic analyzing apparatus of the above described construction may be provided with a shutter means for selectively causing one of the diffracted X-ray components to be incident upon the sample to be analyzed. According to one aspect of the present invention, since the use has been made of the two analyzing crystals, one of the two analyzing crystals may be used to diffract a low-order beam of X-ray having a relatively high intensity and the other of the two analyzing crystals may be used to diffract a continuous X-ray beam having a predetermined wavelength or a high-order beam of X-ray having a relatively low intensity. Therefore, an excitation X-ray beam comprised of the low-order beam and an X-ray beam component having a wavelength shorter than that of the low-order beam can be obtained. Also, according to another aspect of the present invention, the use of the two X-ray beam components used for the elemental analysis as discussed above makes it possible to average measurement errors attributable to preset values of various parameters and, therefore, any possible measurement error can be minimized advantageously.