Fluorescent X-ray analyzer

Details Fluorescent X-ray analyzer Fluorescent X-ray analyzer

1999-10-20

2002-01-08

Church, Craig E. (Department: 2882)

X-ray or gamma ray systems or devices

Specific application

Fluorescence

C378S148000

Reexamination Certificate

active

06337897

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a fluorescent X-ray analyzer and, more particularly, to the fluorescent X-ray analyzer of a type provided with a collimator for restricting the field of view so that fluorescent X-rays and/or scattering X-rays generated from sources other than a sample piece being analyzed will not reach a detecting means.
2. Description of the Prior Art
Generally in a fluorescent X-ray analyzer utilizing parallel beams, as shown in
FIG. 19
, a sample piece
1
fixedly supported on a sample table is generally radiated with primary X-rays
3
generated from an X-ray tube
4
to excite the sample piece
1
. The sample piece
1
so excited generates fluorescent X-rays
5
which are subsequently guided through a collimator
10
A to a solar slit
7
to extract the fluorescent X-rays
5
in the form of parallel beams. The fluorescent X-rays
5
emerging from the solar slit
7
are subsequently monochromatized by a monochromator
8
according to spectrum of different wavelengths corresponding to elements contained in the sample piece
1
with a detector
9
consequently detecting the monochromatized X-rays.
The collimator
10
A disposed between the sample piece
1
and the solar slit
7
is employed for the following reason.
Since the primary X-rays
3
emanating from the X-ray tube
4
irradiate not only the sample piece
1
to be analyzed, but also the sample table
2
, the absence of the collimator results in that as shown in
FIG. 20A
, not only the fluorescent X-rays generated from the sample piece
1
, but also a large amount of disturbing rays such as fluorescent X-rays and/or scattering X-rays generated from a portion
2
a
of the sample table
2
adjacent and surrounding the sample piece
1
impinges upon the detector
9
. For this reason, the disturbing rays eventually constitute a background with respect to the spectrum of the fluorescent X-rays emanating from the sample piece
1
, accompanied by reduction in the S/N ratio.
In contrast thereto, the use of the collimator
10
A results in that as shown in
FIG. 20B
, the field of view, or coverage, of the detector
9
is restricted to a portion
2
a
of the sample table
2
surrounding the sample piece
1
. Specifically, this portion
2
a
of the sample table
2
encompassed by the collimator
10
A shown in
FIG. 20B
, although constituting a source of the disturbing rays, is limited to an area smaller than the portion
2
a
covered by the detector
9
when no collimator
10
A is used, and therefore, the most of the disturbing rays are intercepted by the collimator
10
A and does not reach the detector
9
, resulting in improvement of the S/N ratio.
The collimator
10
A discussed above is of a structure including, as shown in
FIG. 19
, an oblong plate member having a plurality of, for example, three field-limiting apertures
12
a,
12
b
and
12
c
of varying diameters defined therein in a row conforming to a direction of sliding motion of the collimator
10
A shown by the arrow Y The apertures
12
a
to
12
c
are selectively brought into alignment with the path of travel of the fluorescent X-rays
5
towards the solar slit
7
one at a time depending on the size of a target area of the sample piece
1
to be measured.
However, as shown in
FIG. 20B
, there is a certain distance L between the collimator
10
A and the sample piece
1
. Accordingly, even though one of the apertures, for example, the aperture
12
a
of a diameter substantially equal to the size of the sample piece
1
is selected, the “eye” of the detector
9
looking at the sample piece
1
through the selected aperture
12
a
is such that even the disturbing rays emanating from that portion
2
a
closely exteriorly surrounding the sample piece
1
are apt to pass through the selected aperture
12
a
and then to be incident upon the detector
9
, eventually resulting in incapability of improving the S/N ratio.
If in an attempt to prevent the disturbing rays from entering the detector, one of the apertures which is of a diameter smaller than the size of the sample piece
1
is selected, the intensity of the fluorescent X-rays passing through the selected aperture will decrease, resulting in reduction in sensitivity of detection.
In order to alleviate the above discussed problems, the Japanese Patent No. 2,674,675 discloses the use of such a collimator
10
B as shown in FIG.
21
. The suggested collimator
10
B comprises a plurality of, for example, three tubes
15
a
to
15
c
having varying inner diameters each corresponding to the size of a target area of the sample piece
1
to be measured and, also, varying lengths with the largest length chosen for the smallest inner diameter of the tube and the smallest length chosen for the largest inner diameter of the tube such that when one of the tubes
15
a
to
15
c
is selected, the smaller the inner diameter of the tube, the closer the tube is to the sample piece
1
. In such case, if one of the tubes
15
a
to
15
c
in the collimator
10
B is properly selected according to the particular size of the sample piece
1
to be analyzed, the “eye” of the detector
9
looking at the sample piece
1
through the selected tube is such as to encompass only the sample piece
1
and, therefore, the disturbing rays emanating from an area other than the sample piece
1
can be effectively intercepted. Therefore, with no need to reduce the diameter of the corresponding aperture down to a value smaller than the size of the sample piece
1
, any possible entry of the disturbing rays emanating from the area other than the sample piece
1
to the detector through the solar slit
7
can be effectively minimized, accompanied by improvement in S/N ratio without the sensitivity of detection being decreased. However, the use of the collimator
10
B has been found having such a problem that as shown in
FIG. 22
, when the fluorescent X-rays
5
emanating from the sample piece
1
are partially cut off by, for example, the tube
15
a,
a portion
5
a
of the fluorescent X-rays
5
emanating from the sample piece
1
tend to impinge upon an inner wall surface
16
a
of the tube
15
a,
resulting in generation of disturbing rays
30
, such as fluorescent X-rays and/or scattering X-rays, from the inner wall surface
16
a
which will eventually enter the detector through the solar slit
7
. Accordingly, the S/N ratio cannot yet be improved sufficiently. Also, respective longitudinal axes of those tubes
15
a
to
15
c
must extend parallel to the solar slit foil and, thus, a high processing precision is required to manufacture the collimator
10
B, accompanied by reduction in workability.
On the other hand, in the prior art fluorescent X-ray analyzer, as shown in
FIG. 21
, the sample piece
1
is irradiated by the primary X-rays
3
with the direction of an axis of the X-ray source
4
inclined relative to the sample piece
1
, so that the fluorescent X-rays
5
generated from the sample piece
1
while the X-ray source
4
is positioned as close as possible to the sample piece
1
to cause the latter to receive an increased radiation intensity can enter the detector. The radiation intensity of the primary X-rays
3
towards the target area of the sample piece
1
to be measured means the total radiation intensity of the primary X-rays
3
towards the entire target area of a sample surface
1
a
to be measured. As a result of the simulated test conducted to determine a pattern of distribution of radiation intensity of the primary X-rays
3
over an imaginary irradiation plane including the sample surface
1
a
and its plane extension, inclination of the direction of the axis of the X-ray source
4
has resulted in that as shown by a curve B in
FIG. 23
, distribution of the radiation intensity was not maximized at a location C where the radiation center axis of the X-ray source
4
extends to the imaginary irradiation plane, but was maximized at a location M displaced in a direction conforming to the direction of inclination of the X-ray source
4
, thus re

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