1. Field of the Invention
The present invention generally relates to a fluorescent X-ray analyzing apparatus and, more particularly, to the fluorescent X-ray analyzing apparatus capable of being used selectively as a wavelength dispersive type and an energy dispersive type.
2. Description of the Prior Art
The fluorescent X-ray analyzing apparatus is well known as an instrument for analyzing elements contained in an area of interest of a sample by applying primary X-rays to such area interest to excite the target area and subsequently detecting, by means of a detecting means, fluorescent X-rays emitted from the area of interest as a result of excitation thereof. The detecting means are currently available in two types; wavelength dispersive type and energy dispersive type. The area of interest of the sample referred to hereinabove and hereinafter is intended to encompass at least a portion of a surface of the sample at an arbitrary site on the sample and its nearby deep structure. At least a portion of the sample surface referred to above is to be understood as including the entire surface of the sample.
The wavelength dispersive type detecting means although having an excellent wavelength resolving power characteristically recurs a relatively large length time to measure the intensity of the fluorescent X-rays. On the other hand, the energy dispersive type detecting means has a wavelength resolving power less than that exhibited by the wavelength dispersive type detecting means, but has a feature in that intensities of the fluorescent X-rays over a broad range of wavelengths can be simultaneously measured. Accordingly, where broad wavelength distribution characteristics are desired to be examined in a short length of time, the energy dispersive type detecting means can be advantageously utilized therefore, but where a precise fluorescent X-ray analysis, that is, a high-resolution fluorescent X-ray analysis over a relatively narrow range of wavelength is desired to be performed, the wavelength dispersive type detecting means can be advantageously utilized therefore. Thus, if the energy dispersive type detecting means and the wavelength dispersive type detecting means are used one at a time depending on the purpose of analysis, the efficient analysis can be done. Also, if a qualitative analysis is carried out by the use of the energy dispersive type detecting means and the subsequent qualitative analysis of elements of interest is carried out by the use of the wavelength dispersive type detecting means, a quick and accurate fluorescent X-ray analysis can be performed with respect to totally unknown samples.
An X-ray analyzing apparatus employing both the wavelength dispersive type detecting means and the energy dispersive type detecting means for detecting the X-rays has been well known in the art. By way of example, the X-ray analyzing apparatus disclosed in the Japanese Laid-open Patent Publication No. 5-281163 includes, as shown in FIG. 16, an X-ray tube 4 for radiating primary X-rays 3 towards a sample 1 supported on a sample support 2 to excite the sample 1, a divergent Soller slit for collimating secondary X-rays 5 emitted from the sample 1 as a result of excitation thereof, a spectroscope 8 for analyzing the collimated secondary X-rays which is subsequently detected by a detector 9. The X-ray analyzing apparatus disclosed in the above mentioned publication and shown in FIG. 16 makes use of an energy dispersive type detector 12 for detecting the secondary X-rays 5 emitted from the sample 1.
The Japanese Laid-open Patent Publication No. 10-206356 discloses such a fluorescent X-ray analyzing apparatus as shown in FIG. 17. The fluorescent X-ray analyzing apparatus shown in FIG. 17 is so designed and so configured that the fluorescent X-rays 5 emitted from the sample 1 on the sample support 2 when the sample 1 is excited by the primary X-rays 3 emitted from the X-ray tube 4 can be detected by the detector 9 after having passed through the spectroscope 8. The spectroscope 8 used therein is supported for movement between an operative position, in which as shown by the solid line in FIG. 17 the spectroscope 8 is aligned with the path of travel of the fluorescent X-rays 5, and a retracted position in which the spectroscope 8 having been moved in a direction shown by the arrow A is retracted from the path of travel of the fluorescent X-ray 5.
Accordingly, when the spectroscope 8 is moved to the retracted position, the energy dispersive type detector 12 is brought in position to detect the fluorescent X-rays 5.
However, in the case of the X-ray analyzing apparatus shown in FIG. 16, the angle between the first path of travel 81 of the fluorescent X-rays, extending between the sample 1 and the spectroscope 8, and the surface of the sample 1, that is, the angle .theta.1 of emergence of the fluorescent X-rays 5 to be detected by the wavelength dispersive type detector 9 differs from the angle between the second path of travel 82 of the fluorescent X-rays, extending between the sample 1 and the energy dispersive type detector 12, and the surface of the sample 1, that is, the angle .theta.2 of emergence of the fluorescent X-rays 5 to be detected by the energy dispersive type detector 12. In other words, in order to enhance the strength of the energy dispersive type detector 12 as high as possible while because the energy dispersive type detector 12 has a small light receiving area the intensity of the fluorescent X-rays incident upon the energy dispersive type detector 12 tends to be low, the angle of emergence of the fluorescent X-rays to be detected by the energy dispersive type detector 12 is chosen to be large.
On the other hand, in the X-ray analysis, the intensity of X-rays to be measured depends on the angle of emergence and the correlation therebetween is complicated. Accordingly, where the angle .theta.1 of emergence for the wavelength dispersive type detector and the angle .theta.2 of emergence for the energy dispersive type detector are different from each other as discussed above, the intensity of the fluorescent X-rays measured by the wavelength dispersive type detector and that by the energy dispersive type detector cannot be correlated with each other. Moreover, even though compensation for the difference in angle of emergence is made, the correlation between the X-ray intensities with respect to the angle of emergence depends also on the composition of the sample and is thus complicated. Therefore, the compensation cannot be made accurately and, because of this uncertainty, the analyzing accuracy cannot be increased.
Also, if the sample has a rough surface full of minute surface irregularities, distribution characteristics of the X-ray wavelengths vary even though the angles of emergence are equal to each other when the spectroscope and the detector aim at the same area of interest of the sample from different directions, resulting in respective results of measurement which cannot be correlated with each other unless modified in any way.
In contrast thereto, in the case of the fluorescent X-ray analyzing apparatus shown in FIG. 17, the first path of travel 81 of the fluorescent X-rays and the second path of travel 82 of the fluorescent X-rays lie on the same path and the angle of emergence for the energy dispersive type detector and the angle of emergence for the wavelength dispersive type detector remain the same at the angle .theta.1. Accordingly, the intensity of the X-rays detected by the energy dispersive type detector and that by the wavelength dispersive type detector can be correlated with each other if they are multiplied by a predetermined sensitivity coefficient peculiar to the respective detecting system that does not depend on the sample.
However, since the energy dispersive type detector generally has a small light receiving area such as observed in a semiconductor detector (SSD) having a relatively excellent energy resolving power, the sensitivity will lower unless the energy dispersive type detector 12 is positioned close to the sample 1. Although in the fluorescent X-ray analyzing apparatus equipped with only the energy dispersive type detector the energy dispersive type detector can be positioned close to the sample 1 since no spectroscope is employed therein, the energy dispersive type detector 12 employed in the fluorescent X-ray analyzing apparatus shown in FIG. 17 cannot be positioned close to the sample 1 since in the fluorescent X-ray analyzing apparatus of FIG. 17 the spectroscope 8 is disposed between the sample 1 and the energy dispersive type detector 12. Accordingly, during detection by the use of the energy dispersive type detector, the sensitivity tends to lower and, particularly where the fluorescent X-rays emitted from a minute area of the sample are desired to be detected, no sufficient sensitivity required for the analysis cannot be secured.
Also, the conventional fluorescent X-ray analyzing apparatus that can be used as the wavelength dispersive type and the wavelength dispersive type one at a time has the following problem. In order to increase the accuracy of the quantitative analysis and the qualitative analysis, a so-called semiquantitative analysis is generally carried out prior to the analysis to determine varieties of and approximate contents of elements of interest contained in the sample. Unless respective results of detection given by the wavelength dispersive type detecting means and the energy dispersive type detecting means during the semiquantitative analysis are properly combined and used, neither the qualitative analysis nor the quantitative analysis can be performed quickly and accurately.
As hereinabove discussed, according to the prior art, the fluorescent X-ray analyzing apparatus that can be used as either a wavelength dispersive type or an energy dispersive type is incapable of performing a quick and accurate analysis.