X-ray or gamma ray systems or devices – Specific application – Fluorescence
Reexamination Certificate
2000-03-08
2001-11-06
Dunn, Drew (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Fluorescence
C378S049000
Reexamination Certificate
active
06314158
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a data processor to be used in fluorescent x-ray spectroscopy, and in particular to a data processor for carrying out a quantitative analysis by making use of results of an x-ray fluorescence analysis.
In the field of fluorescent x-ray spectroscopy, quantitative analyses by using the so-called fundamental parameter (FP) method are recently coming to be widely carried out. This method of analysis is characterized wherein the contents of the elements in a sample are determined on the basis of both the measured intensity of fluorescent x-ray emitted from the sample and a theoretically calculated x-ray intensity value. When such a method of analysis is used, many parameters are necessary for calculating the theoretical x-ray intensity. Examples of such parameters include the accelerating voltage of current for the primary x-rays applied from an x-ray tube to the sample, the contents of all elements contained in the sample, their physical constants such as the atomic numbers and wavelengths of fluorescence, the angle of incidence of the primary x-rays onto the sample and the angle of measured fluorescent x-rays from the sample. The x-ray intensity theoretically calculated on the basis of these parameters is that of the fluorescent x-rays as they are generated on the surface of the sample. The measured intensity, on the other hand, is obtained after the fluorescent x-rays generated on the surface of the sample reaches a detector and is thereby converted into electrical energy pulses. For this reason, the theoretically obtained x-ray intensity and the measured intensity do not always agree as a matter of course. For this reason, what is commonly being done is to preliminary make measurements on a standard sample of which the composition is known, to calculate and store the ratio between the measured and theoretical intensities for each element (usually referred to as the “element sensitivity”) and to carry out the usual steps of quantitative analysis while making appropriate adjustments by using such element sensitivities.
In fluorescent x-ray spectroscopy, it is desired to make the degree of vacuum inside the analysis chamber as high as possible because any gas which is present along the optical path of the primary x-rays between the x-ray tube and the sample and that of the fluorescent x-rays generated on the surface of the sample between the sample and the detector acts to absorb the x-rays to attenate the intensity. When the sample is a liquid or in a powder form and is easy to scatter around and if it is difficult to maintain a vacuum environment inside the analysis chamber, it is inevitable to carry out the analysis either in an atmospheric environment or in an environment of helium or some other appropriate kind of gas.
If measurements are taken under such a condition, x-rays are attenuated both between the x-ray tube and the sample and between the sample and the detector. In other words, the measured intensity values include the effects of x-ray absorption while theoretically calculated values are those of the intensity on the sample surface without taking the effects of attenuation by absorption into account.
In view of the above, the standard sample had to be measured under different conditions such as in vacuum, under the atmospheric condition and in helium and to prelimarily obtain the element sensitivities as measured under different conditions from the results of such measurements. For the quantitative analysis of a given sample with an unknown composition, a theretical calculation had to be carried out by using a correct element sensitivity corresponding to the environment in which the measurement was taken. It now goes without saying that this routine is troublesome and cumbersome because it involves obtaining many element sensitivities and storing many sensitivity data.
This problem is particularly important with lighter elements with small molecular values because fluorescent x-rays emitted from such light elements are particularly susceptible to absorption by an environmental gas. If the measurement must be taken in an atmospheric environment or in helium, for example, the intensity of the x-rays reaching the detector may be quite weak and a trustworthy analysis cannot be expected to result if an inaccurate element sensitivity must be used.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a data processor for fluorescent x-ray spectroscopy with which the troubles for obtaining element sensitivities can be eliminated and the accuracy of analysis can be improved.
A data processor for fluorescent x-ray spectroscopy with which the above and other objects can be attained is characterized wherein theoretical x-ray intensity values from a standard sample with a known composition and an unknown sample with an unknown composition are calculated by using a formula which incorporates the effect of x-ray absorption by an environmental gas which may be present inside the analysis chamber. Thus, the element sensitivity calculated on the basis of the result of measurement on a standard sample according to this invention is a value which is independent of the environmental condition inside the analysis chamber when the measurement was taken.
Explained more in detail, a data processor for fluorescent x-ray spectroscopic measurement functions such that theoretical x-ray intensity expected to be obtained by measurement on a standard sample with known composition is calculated by using a formula which incorporates the effects of the environmental condition inside the analysis chamber, that is, the possible effects of x-ray attenuation if the interior of the analysis chamber is not in a vacuum condition. Element sensitivity values are obtained from such calculated intensity and the result of an actual measurement on the standard sample. When an unknown sample with unknown composition is to be analyzed similarly by fluorescent x-ray spectroscopy, a theoretical x-ray intensity value is calculated, say, by initially using estimated values as parameters and using the formula incorporating the effects of the environmental condition inside the analysis chamber on the attenuation of the x-rays. Actually measured intensity and theoretically obtained intensity values are compared and the parameters are changed, if their difference is larger than a specified maximum allowable limit value, and this process may be repeated any number of times until it becomes satisfactorily small, or less than a specified allowable limit. The composition of the unknown sample is obtained from the theoretically calculated intensity, actually measured intensity and the element sensitivity which was earlier obtained.
REFERENCES:
patent: 5978442 (1999-11-01), Kuwabara
patent: 6173036 (2001-01-01), Hossain et al.
Kuwabara Shoji
Nishino Makoto
Shiota Tadahiro
Coudert Brothers
Dunn Drew
Shimadzu Corporation
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