U.S. patent application number 09/826846 was filed with the patent office on 2001-10-25 for fluorescent x-ray analyzing apparatus and secondary target device disposed therein.
This patent application is currently assigned to SHIMADZU CORPORATION. Invention is credited to Kuwabara, Shoji.
Application Number | 20010033635 09/826846 |
Document ID | / |
Family ID | 18631139 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010033635 |
Kind Code |
A1 |
Kuwabara, Shoji |
October 25, 2001 |
Fluorescent x-ray analyzing apparatus and secondary target device
disposed therein
Abstract
A fluorescent X-ray analyzing apparatus includes a secondary
target device therein. The secondary target device includes a
target main body, and an X-ray blocking member for preventing an
irradiation of primary X-rays from a X-ray source to a sample. The
target main body is formed of plural target members in which
secondary target materials are formed on at least target surfaces
facing a central axis, and the target members are arranged
concentrically to have different distances from the central axis.
Accordingly, the primary X-rays do not pass through a space between
the target members, and are irradiated only at the target surfaces
of the target members. The secondary X-rays from the target
surfaces pass through the space between the target members, and
reach the sample.
Inventors: |
Kuwabara, Shoji;
(Ibaraki-shi, JP) |
Correspondence
Address: |
KANESAKA AND TAKEUCHI
1423 Powhatan Street
Alexandria
VA
22314
US
|
Assignee: |
SHIMADZU CORPORATION
|
Family ID: |
18631139 |
Appl. No.: |
09/826846 |
Filed: |
April 6, 2001 |
Current U.S.
Class: |
378/45 ; 378/124;
378/143 |
Current CPC
Class: |
G01N 23/20 20130101 |
Class at
Publication: |
378/45 ; 378/124;
378/143 |
International
Class: |
G01N 023/223 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 21, 2000 |
JP |
2000-120307 |
Claims
What is claimed is:
1. A secondary target device for transferring primary X-rays
generated at a primary X-ray source to a sample as secondary
X-rays, comprising: a target main body including a plurality of
target members having target surfaces facing a central axis linking
between the primary X-ray source and the sample, and secondary
target materials formed on the target surfaces, said plurality of
target members being disposed concentrically with respect to the
central axis to be spaced apart from each other, each of the target
members having a length in a direction along the central axis and a
disposition interval relative to a target member adjacent thereto
to satisfy a first condition for allowing the primary X-rays to
enter the target surface and a second condition for allowing the
secondary X-rays generated at the target members by incidence of
the primary X-rays to enter the sample, and an X-ray blocking
member disposed on the central axis for blocking an irradiation of
the primary X-rays from the primary X-ray source to the sample.
2. A secondary target device according to claim 1, wherein in said
first condition, an effective solid angle of observing one target
surface of one target member from the primary X-ray source
coincides with an effective solid angle of observing a space
between said one target member and an adjacent target member
located inside said one target member from the primary X-ray
source, and in the second condition, an effective solid angle of
observing the target surface of said one target member from the
sample coincides with an effective solid angle of observing the
space between said one target member and said adjacent target
member from the sample.
3. A secondary target device according to claim 2, wherein said
target members are arranged have front and back edges facing the
X-ray source and the sample, respectively, said front and back
edges of the target members being disposed parallel to each
other.
4. A secondary target device according to claim 3, wherein said
target members are spaced apart from each other with different
distances.
5. A secondary target device according to claim 4, further
comprising at least one support member for connecting the target
members to be spaced apart from each other.
6. A secondary target device according to claim 5, wherein said
target surfaces are arranged parallel to the central axis.
7. A fluorescent X-ray analyzing apparatus, comprising: a primary
X-ray source for generating primary X-rays, a secondary target
device for receiving the primary X-rays and providing fluorescent
X-rays to a sample, said secondary target device including a target
main body located near the primary X-ray source, and an X-ray
blocking member disposed on a central axis linking between the
primary X-ray source and the sample to prevent the primary X-rays
from the primary X-ray source from being irradiated to the sample,
said target main body including a plurality of target members
having target surfaces facing the central axis and secondary target
materials formed on the target surfaces, said plurality of target
members being disposed concentrically with respect to the central
axis to be spaced apart from each other, each of the target members
having a length in a direction along the central axis and a
disposition interval relative to a target member adjacent thereto
to satisfy a first condition for allowing the primary X-rays to
enter the target surface and a second condition for allowing the
secondary X-rays generated at the target members by incidence of
the primary X-rays to enter the sample, and an X-ray detector for
detecting fluorescent X-rays generated from the sample.
8. A fluorescent X-ray analyzing apparatus according to claim 7,
wherein in said first condition, an effective solid angle of
observing one target surface of one target member from the primary
X-ray source coincides with an effective solid angle of observing a
space between said one target member and an adjacent target member
located inside said one target member from the primary X-ray
source, and in the second condition, an effective solid angle of
observing the target surface of said one target member from the
sample coincides with an effective solid angle of observing the
space between said one target member and said adjacent target
member from the sample.
9. A fluorescent X-ray analyzing apparatus according to claim 8,
further comprising a first shielding member surrounding said
periphery of the target members, said first shielding member having
opening sections on the central axis, one of the opening sections
limiting an area of irradiating the secondary X-rays in the
sample.
10. A fluorescent X-ray analyzing apparatus according to claim 9,
further comprising a second shielding member surrounding the X-ray
source for irradiating the primary X-rays to the target
members.
11. A fluorescent X-ray analyzing apparatus according to claim 8,
further comprising at least one of a collimator for directly
irradiating the primary X-rays to the sample and a filter for
absorbing a part of the primary X-rays, one of said secondary
target device, the collimator and the filter being disposed on the
central axis.
12. A fluorescent X-ray analyzing apparatus according to claim 11,
further comprising a driving device for disposing one of the
secondary target device, the collimator, and the filter on the
central axis.
Description
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
[0001] The present invention relates to a secondary target device
which generates secondary X-rays called fluorescent X-rays by
irradiating X-rays (primary X-rays) generated from an X-ray source,
and a fluorescent X-ray analyzing apparatus in which the
fluorescent X-rays generated from the secondary target device are
irradiated to a sample, and fluorescent X-rays generated from the
sample are used to carry out a qualitative and quantitative
analysis.
[0002] In a fluorescent X-ray analysis, a wavelength and an
intensity of characteristic X-rays generated from a sample by
irradiating X-rays to the sample are measured, to thereby carry out
a qualitative and quantitative analysis of elements in the sample.
In the fluorescent X-ray analysis, there have been known a direct
irradiation method in which X-rays (primary X-rays) generated from
an X-ray source are directly irradiated to a sample, and a
secondary target method which uses a secondary target.
[0003] In the direct irradiation method, primary X-rays generated
from an X-ray tube are directly irradiated to the sample, and
fluorescent X-rays generated from the sample are detected by an
X-ray detector, such as a semiconductor detector. In the direct
irradiation method, since it is possible to analyze a wide range of
elements, the direct irradiation method is suitable for a detection
of unknown micro-elements.
[0004] On the other hand, the secondary target method improves a
limit of detecting micro-elements by making excited X-rays
monochromatic, and in the secondary target method, primary X-rays
are irradiated to the secondary target formed of a material which
differs from an anode target of an X-ray tube, to thereby generate
fluorescent X-rays including characteristic X-rays which are
inherent to the secondary target, so that continuous X-rays
included in the primary X-rays are decreased. Therefore, a
signal-to-noise (S/N) ratio of the fluorescent X-rays from the
sample is improved, to thereby improve the limit of detecting the
micro-elements.
[0005] In the fluorescent X-ray analyzing apparatus, it has been
desired to have a wide applicability for both detection of an
unknown micro-element and highly sensitive analysis of a specific
micro-element, and there has been proposed an analyzing apparatus
which can perform both analyses by the direct irradiation method
and by the secondary target method by switching these methods.
[0006] Conventionally, as a structure for switching the analysis by
the direct irradiation method and the analysis by the secondary
target method, there has been used a secondary target device and a
fluorescent X-ray analyzing apparatus, wherein a secondary target
is disposed at a position diverting from a straight line connecting
between an X-ray source and a sample in the secondary target device
so as not to directly irradiate primary X-rays from an X-ray tube
to the sample, so that only secondary X-rays from the secondary
target are irradiated to the sample, and in case the primary X-rays
are directly irradiated to the sample, an orientation of the X-ray
source is changed.
[0007] In the secondary target device and the fluorescent X-ray
device described above, although the direct irradiation method and
the secondary target method are achieved by one apparatus, there
have been the following problems. Namely, since a moving mechanism
for rotating the X-ray source is necessary, the apparatus becomes a
large size. Also, since an X-ray irradiating condition (irradiation
angle and irradiation position) by the direct irradiation method
does not always coincide with an X-ray irradiating condition by the
secondary target method, there is a problem in an accuracy of a
correspondence between the measured data by both methods.
[0008] Also, there has been proposed a secondary target device and
a fluorescent X-ray device as disclosed in Japanese Patent
Publication (KOKAI) No. 10-325814, in which a secondary target is
disposed on a straight line connecting between an X-ray source and
a sample. In a case of using the secondary target and a case of
directly irradiating primary X-rays, irradiated X-rays are switched
while an orientation of the X-ray source is fixed.
[0009] In the conventional secondary target device and the
fluorescent X-ray analyzing apparatus, as described above, there
are problems, such as an increase of the size of the apparatus, and
an accuracy problem in the correspondence between the measured data
due to the difference between the X-ray irradiating conditions with
respect to the sample.
[0010] Also, in the proposed apparatus described above, since the
irradiated X-rays can be switched while the orientation of the
X-ray source is fixed, a hollow section of the secondary target is
formed into a tapered form in which an opening section at an X-ray
source side is large and an opening section at a sample side is
narrowed. Therefore, primary X-rays from the X-ray source can be
irradiated with a large effective solid angle to the secondary
target, but an effective solid angle of the secondary target
observed from the sample is reduced, and an angle of observing the
sample from the secondary target is shallow, so that enough
secondary X-rays can not be irradiated to the sample, resulting in
difficulty in obtaining a high measurement sensitivity.
[0011] Also, in both conventional apparatus and proposed apparatus,
since the secondary X-rays expand on a surface of the sample in a
relatively large range, it is difficult to limit an irradiation
area on the surface of the sample by the secondary X-rays into a
very small area, so that these apparatuses can not be applied to an
analysis of a minute portion.
[0012] Accordingly, the present invention has been made to solve
the aforementioned problems, and an object of the invention is to
provide a secondary target device in which X-ray irradiating
conditions in switching the irradiated X-rays are held constant, to
thereby irradiate enough secondary X-rays with respect to a sample
and to irradiate the secondary X-rays to a minute portion of the
sample.
[0013] Another object of the invention is to provide a fluorescent
X-ray analyzing apparatus, in which X-ray irradiating conditions in
switching the irradiated X-rays are held constant and enough
secondary X-rays are retained to thereby improve a detection
sensitivity, and to improve a sensitivity of analyzing the minute
portion of the sample.
[0014] Further objects and advantages of the invention will be
apparent from the following description of the invention.
SUMMARY OF THE INVENTION
[0015] To achieve the aforementioned objects, in the present
invention, an X-ray irradiating condition in case of switching
irradiated X-rays is maintained to be constant by disposing an
X-ray source, a target main body, and a sample on a straight line,
and further, in the structure described above, an effective solid
angle of observing a target surface from the X-ray source and an
effective solid angle of observing the target surface from a sample
irradiation position are substantially enlarged, so that enough
secondary X-rays are irradiated to the sample. Accordingly, a high
detection sensitivity can be obtained in a fluorescent X-ray
analyzing apparatus.
[0016] Also, in substantially enlarging the effective solid angles,
the secondary X-rays irradiated from a plurality of target surfaces
are condensed to an irradiation area of the sample, and an
irradiation of the secondary X-rays to an area other than the
irradiation area is limited, so that the secondary X-rays are
irradiated to a minute portion of the sample. Accordingly, a
sensitivity of analyzing the minute portion is increased in the
fluorescent X-ray analyzing apparatus. Incidentally, the effective
solid angle is a solid angle of observing a predetermined region or
surface from a certain point, and in the secondary target device
and the fluorescent X-ray analyzing apparatus of the invention, the
effective solid angle is formed by treating the target surface as
the predetermined region surface.
[0017] Therefore, in the target device of the invention, the X-ray
source, a sample irradiation position, the target main body having
a plurality of target members, and an X-ray blocking member for
blocking an irradiation of primary X-rays to the sample irradiation
position are arranged on a straight line.
[0018] In the target main body, the straight line connecting the
X-ray source and the sample irradiation position constitutes a
central axis, and the plurality of target members is arranged at
positions having different distances from the central axis. In each
of the target members, a secondary target material is provided on
at least a surface of the target member opposed to the central
axis, and the surface described above constitutes a target surface.
Incidentally, the secondary target material can be provided on a
rear surface of the target member which is not opposed to the
central axis, or the entire target member can be formed of the
secondary target material, or the target member can be a structure
in which the secondary target material is provided on a front
surface of an X-ray shielding material as a base or substrate.
[0019] The target members can be structured in cylindrical forms,
in which a plurality of the target members is disposed on
respective circumferences of concentric circles having the straight
line connecting the X-ray source and the sample irradiation
position as the central axis. Also, as long as the target members
have different distances from the central axis, the target members
are not limited to the cylindrical shapes, and may be polygonal
shapes, or the target members may have a structure in which the
target members are disposed only in predetermined diametral
directions from the central axis. Also, the target members may be
disposed continuously, or separated or dispersed.
[0020] In setting the straight line connecting the X-ray source and
the sample irradiation position as the central axis, a plurality of
the target members is disposed around the diametral direction of
the central axis. In case of switching the irradiated X-rays, an
X-ray irradiating condition by a direct irradiation method and an
X-ray irradiating condition by a secondary target method can be
made the same. Incidentally, a disposition of plural target members
on the respective circumferences of the concentric circles is an
example of the disposition of plural target members around the
diametral direction of the central axis.
[0021] In this structure, there is formed an effective solid angle
of observing the target surface of the target member from the X-ray
source or the sample irradiation position. Incidentally, in case
the target members are respectively disposed in a direction of a
normal line from the central axis to be space away from each other
with a predetermined interval therebetween, the effective solid
angle constitutes an angle of observing a surface, which is formed
in a range of a predetermined distance from a center and extends in
a form of a concentric circle, from a certain point. However, in
the present invention, the shape is not limited to the concentric
circle, and may be selected according to the shapes of the target
members and the target surfaces, or the disposition location
thereof.
[0022] In the secondary target device of the invention, in order to
effectively irradiate the secondary X-rays to the sample while the
irradiation of the primary X-rays to the sample is being prevented,
the primary X-rays from the X-ray source are required not to pass
through a space between the target members and irradiated only to
the target surfaces of the target members. Also, the secondary
X-rays from the target surfaces are required to pass through the
space between the target members and reach the sample irradiation
position.
[0023] In order to fulfill the above requirements, in the
structures of the target main body of the invention, a length of
each target member in the central axis direction and a disposition
interval in the diametral direction between the adjacent target
members are required to satisfy the first condition regarding the
primary X-rays and the second condition regarding the secondary
X-rays. Here, the first condition constitutes a condition in which
an effective solid angle of observing the target surface from the
primary X-ray source coincides with an effective solid angle of
observing the space between the adjacent target members in the
target surface side, and the second condition constitutes a
condition in which an effective solid angle of observing the target
surface from the sample irradiation position coincides with an
effective solid angle of observing the space between the adjacent
target members from the sample irradiation position in the target
surface side.
[0024] Since the target members have the structures as described
above, the primary X-rays can be irradiated to the target surfaces
without being blocked by the adjacent target members, and the
secondary X-rays generated at the target surfaces can reach the
sample irradiation position without being blocked by the adjacent
target members, to thereby form the effective solid angles of the
respective target members. Also, by arranging a plurality of the
target members as described above, the respective effective solid
angles can be consolidated to have a large effective solid angle
which is enlarged as a whole.
[0025] Also, in the present invention, the X-ray blocking member is
disposed on the central axis. The X-ray blocking member is provided
for preventing the primary X-rays generated from the X-ray source
from being irradiated to the sample irradiation position, and the
X-ray blocking member assures the irradiation of the secondary
X-rays to the sample irradiation position.
[0026] Further, the fluorescent X-ray analyzing apparatus of the
invention constitutes a fluorescent X-ray analyzing apparatus with
the target device of the invention, and the fluorescent X-ray
analyzing apparatus of the invention is formed of an X-ray source
for generating X-rays, a secondary target device of the invention,
and an X-ray detector for detecting fluorescent X-rays generated
from a sample.
[0027] In the fluorescent X-ray analyzing apparatus of the
invention, by using the target device of the invention, the X-ray
irradiating condition in case of switching the irradiated X-rays
can be maintained to be constant, and at the same time, a detecting
sensitivity can be improved by obtaining enough secondary X-rays
irradiated to the sample.
[0028] Also, according to the target device of the invention, by
condensing the secondary X-rays with respect to the sample
position, the sensitivity of analyzing the minute portion can be
increased.
[0029] In analyzing the minute portion, it is structured that a
shielding member having an opening section, which limits an area of
irradiating the secondary X-rays in the sample, on the central axis
is provided between the secondary target device and the sample
irradiation position. Thus, an irradiation of the secondary X-rays
to areas other than the area, to which the secondary X-rays are
irradiated, is limited to condense the secondary X-rays to the
sample position, to thereby increase the sensitivity of analyzing
the minute portion.
[0030] Also, one or both of a collimator for directly irradiating
the primary X-rays to the sample and a filter for absorbing a part
of the primary X-rays are provided, and there is disposed a driving
device for disposing one of the secondary target device, the
collimator and the filter on the central axis. The collimator, the
filter, or the secondary device is switchably disposed on the
straight line connecting between the X-ray source and the sample by
the driving device. Accordingly, in case the collimator is
disposed, the primary X-rays can be directly irradiated to the
sample, and in case the filter is disposed, X-rays with specific
wavelengths in the primary X-rays can be irradiated. Also, in case
the secondary target device is disposed, by generating fluorescent
X-rays including characteristic X-rays inherent to the secondary
targets, continuous X-rays contained in the primary X-rays can be
decreased, and a signal-to-noise (S/N) ratio of the fluorescent
X-rays from the sample can be improved, to thereby carry out the
highly sensitive detection of the micro-elements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a view for schematically explaining a target
device and a fluorescent X-ray analyzing apparatus of the
invention;
[0032] FIG. 2 is a schematic view for showing an example of a
target main body of the invention;
[0033] FIG. 3 is a schematic sectional view of target members of
the invention;
[0034] FIG. 4 is a schematic view for explaining paths in which
primary X-rays and secondary X-rays pass;
[0035] FIGS. 5(a) through 5(c) are schematic views for explaining a
first example of the target member of the invention;
[0036] FIGS. 6(a) through 6(c) are schematic views for explaining
an example of holding second target materials of the invention;
[0037] FIG. 7 is a schematic view for explaining a mechanism of
switching irradiated X-rays;
[0038] FIG. 8 is a schematic view for explaining another example of
a target main body applied to the secondary target device of the
invention;
[0039] FIGS. 9(a) through 9(e) are schematic views for explaining a
still another example of the target main body applied to the
secondary target device of the invention; and
[0040] FIGS. 10(a) and 10(b) are schematic views for explaining a
still further example of the target main body applied to the
secondary target device of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0041] Hereunder, embodiments of the present invention will be
explained with reference to the attached drawings.
[0042] FIG. 1 is a view for schematically explaining a target
device and a fluorescent X-ray analyzing apparatus of the
invention.
[0043] A secondary target device 2 includes a target main body and
an X-ray blocking member 20, and is disposed on a central axis C
(shown by a single-dotted line in the FIG. 1) connecting between an
X-ray source 3 and a sample irradiation position 4. The secondary
target device 2 generates secondary X-rays 32 by receiving primary
X-rays 31 from the X-ray source 3, and irradiates the secondary
X-rays 32 to a sample S disposed at the sample irradiation position
4. Also, a fluorescent X-ray analyzing apparatus 1 includes the
target device 2 and an X-ray detector 6 for detecting a
characteristic X-ray 33 generated from the sample S by irradiation
of the secondary X-rays 32, to thereby measure a wavelength and a
strength or intensity of the characteristic X-ray 33, so that the
apparatus 1 carries out a qualitative and quantitative analysis of
elements in the sample S.
[0044] The target main body 10 includes a plurality of target
members 11 including 11a, 11b, 11c, 11d, 11e and 11f, and the
target members 11a through 11f are disposed radially by
respectively changing distances from the central axis C. In the
target members 11a through 11f, at least target surfaces thereof
facing the central axis C are provided with secondary target
materials. On the central axis C, there is disposed the X-ray
blocking member 20, which prevents the primary X-rays 31 generated
in the X-ray source 3 from reaching the sample irradiation position
4, and only the secondary X-rays 32 generated at the target
surfaces are irradiated to the sample S.
[0045] Incidentally, the X-ray source 3 is formed of, for example,
a heater radiating thermoelectrons and an anode target which
generates the primary X-rays 31 by collisions with the
thermoelectrons, and the anode target may be formed of a material,
such as rhodium (Rh), chromium (Cr), copper (Cu), molybdenum (Mo),
and tungsten (W). Also, the target members 11 may be made of a
material corresponding to the desired characteristic X-ray, such as
aluminum (Al), copper (Cu), germanium (Ge), yttrium (Y) and tin
(Sn).
[0046] Further, in the X-ray source 3 and the target main body 10,
there are disposed shielding members 5', 5 for shielding the
primary X-rays 31 and the secondary X-rays 32. The shielding member
5' provided in the X-ray source 3 has an opening section 5a through
which the central axis C passes in order to radiate the primary
X-rays 31 generated in the X-ray source 3 toward a sample S side.
Also, the shielding member 5 provided in the target main body 10
has an opening section 5b through which the central axis C passes
to irradiate the primary X-rays 31 only to the target members 11
such that the primary X-rays 31 are not irradiated to the sample S,
and an opening section 5c through which the central axis C passes,
to condense the secondary X-rays 32 generated in the target members
11 to the sample irradiation position 4. At the same time, the
shielding member 5 provided in the target main body 10 shields the
secondary X-rays 32 such that the secondary X-rays 32 do not reach
the X-ray detector 6.
[0047] Incidentally, the X-ray blocking member 20 and the shielding
members 5, 5' can be formed of an X-ray shielding material, such as
lead (Pb).
[0048] FIG. 2 is a schematic view for showing a first example of
the target main body. The target main body 10 in the first example
includes the target members 11a through 11f, which have cylindrical
shapes with different diameters and are disposed in the forms of
concentric circles around the central axis C. The X-ray blocking
member 20 is disposed at a center position of the target main body
10.
[0049] The target members 11a through 11f are required to satisfy a
predetermined disposition relationship in order to effectively
irradiate the primary X-rays to the target members 11a through 11f
and the secondary X-rays to the sample. Hereinafter, this
positional relationship of the target members will be explained
with reference to FIG. 3.
[0050] FIG. 3 is a schematic sectional view of the target members
11, and two adjacent target members 11m and 11n are shown as an
example. Each of the target members 11m and 11n has a length l in a
direction of the central axis C, and a target surface 11A of the
target member 11m is disposed at a position away from the central
axis C for a space or length dm in the diametral direction. The
target surface 11A of the target member 11n is disposed at a
position away from the central axis C for a space dn in the
diametral direction. The target members 11m and 11n are spaced
apart from each other for a disposition interval dmn in the
diametral direction. Also, the target members 11m and 11n have side
ends located away from a center 3a of the X-ray source 3 for a
distance D1 on the central axis C, and the opposite side ends
located away from a center 4a of the sample irradiation position 4
for a distance D2 on the central axis C. The target surfaces 11A of
the target members 11m and 11n are disposed parallel to the central
axis C.
[0051] An angle .alpha. on a sectional surface including the
central axis C in case the target surface 11A of the target member
11m is seen from the center 3a of the X-ray source 3, is determined
by an angle formed between one end of the target member 11m at an
X-ray source 3 side and the other end of the target member 11m at a
sample irradiation position 4 side, and the angle .alpha. forms an
effective solid angle a with respect to observing surfaces around
the central axis C observing from the X-ray source 3. Here, in
order to effectively irradiate the primary X-rays 31 to the target
surface of the target member 11m, the adjacent target member 11n is
required to be disposed outside the angle .alpha. (effective solid
angle a), so that the target 11n does not block the primary X-rays
31. Also, it is necessary that the primary X-rays 31 do not
directly reach the sample S.
[0052] Also, as in the angle .alpha., an angle .beta. on the
sectional surface including the central axis C in case the target
surface 11A of the target member 11m is seen from the center 4a of
the sample irradiation position 4, is determined by an angle
between the one end of the target member 11m at the X-ray source 3
side and the other end of the target member 11m at the sample
irradiation position 4 side. The angle .beta. forms an effective
solid angle b with respect to observing surfaces around the central
axis C observing from the sample irradiation position 4.
[0053] Here, in order to allow the secondary X-rays 32 generated in
the target surface 11A to reach the sample irradiation position 4
effectively, it is necessary to dispose the adjacent target member
11n outside the angle .beta. (effective solid angle b), so that the
target member 11n does not block the secondary X-rays 32.
[0054] The length l of the target member 11 in the direction of the
central axis C, and the disposition interval dmn between the target
members 11m and 11n are set to satisfy the above conditions.
Incidentally, the angle .alpha. (effective solid angle a), the
angle .beta. (effective solid angle b) can be determined
geometrically by the length l, the disposition interval dmn, and
the distances D1 and D2.
[0055] An effective solid angle A observing the target members 11
from the X-ray source 3 is formed by combining the effective solid
angles a, respectively formed between the two adjacent target
members, among the plural target members 11a through 11f. Here, by
arranging the adjacent target members to be located outside the
angle .alpha. of observing each target surface, the effective solid
angle A can be a solid angle of observing a diameter of the target
member 11a provided at the outermost circumference except a solid
angle portion of the X-ray blocking member 20 disposed on the
central axis C.
[0056] Also, an effective solid angle B of observing the target
members 11 from the sample irradiation position 4 is formed by
combining the effective solid angles b, which are respectively
formed between the two adjacent target members, among the plural
target members 11. Here, by arranging the adjacent target members
to be located outside the angle .beta. of observing each of the
target surfaces, the effective solid angle B can be an angle of
observing the diameter of the target member 11a provided at the
outermost circumference except the solid angle portion of the X-ray
blocking member 20 disposed on the central axis C.
[0057] Next, paths through which the primary X-rays and the
secondary X-rays pass will be explained with reference to FIG.
4.
[0058] The X-ray source 3 generates the primary X-rays 31 in a
certain intensity distribution (for example, an intensity
distribution 31a shown in FIG. 4), and the primary X-rays 31 are
emitted from the opening section 5a of the shielding member 5'
toward the secondary target main body 10 side. Incidentally, the
shielding member 5' of the X-ray source 3 prevents leakage of the
primary X-rays toward areas other than the secondary target main
body 10 side. The primary X-rays 31 radiated from the X-ray source
3 pass through the opening section 5b of the shielding member 5'
surrounding a periphery of the target members 11, and are
irradiated to the target surfaces 11A of the target member 11.
[0059] The primary X-rays 31, which have passed through the opening
section 5b, pass through a space between the adjacent target
members 11m and 11n, and are irradiated to the target surface 11A
of the target member 11m. By setting the length l of the target
member and the disposition interval dmn or the like to satisfy the
aforementioned conditions, the target surface 11A is effectively
irradiated without being blocked by the target member 11n.
[0060] In the target surface 11A, by an excitation due to the
irradiated primary X-rays 31, in the certain intensity distribution
(for example, intensity distributions 32a and 32b shown in FIG. 4),
the secondary X-rays 32, which have a spectrum inherent to the
second target material, are generated. By setting the length l and
the disposition interval dmn or the like to satisfy the above
conditions, among the generated secondary X-rays 32, X-rays to be
transferred to the sample irradiation position 4 are directed to
the sample irradiation position 4 without being blocked by the
target member 11n.
[0061] Furthermore, the secondary X-rays 32 generated in the target
surface 11A are narrowed down by the shielding member 5, the inner
diameter of which is narrowed toward the sample irradiation
position 4 direction, and are irradiated to the sample irradiation
position 4 through the opening section 5c. A distribution curve
shown in a right end section of FIG. 4 schematically shows an
intensity distribution of the secondary X-rays which reach the
sample irradiation position 4. By using the shielding member 5, the
inner diameter of which is narrowed, the secondary X-rays 32 are
allowed to pass through the opening section 5c with a small
diameter, so that a range of an irradiation area of the secondary
X-rays 32 can be narrowed, to thereby increase an analyzing
sensitivity. Incidentally, broken lines and an arrow line in the
distribution curve respectively show a limitation range and the
irradiation area by the shielding member 5 of the target members
11. In a structure which is not provided with the shielding member
5 of the target members 11, the secondary X-rays are irradiated at
the sample irradiation position 4 in a large range, so that the
analyzing sensitivity is decreased.
[0062] Therefore, the shielding member 5 of the target members 11
prevents the primary X-rays from irradiating to areas other than
the secondary target device 2 side, and at the same time, the
shielding member 5 of the target member 11 condenses the secondary
X-rays 32 toward the sample radiation position 4.
[0063] Next, examples of the target member will be explained with
reference to FIGS. 5(a) through 5(c). FIG. 5(a) is a first example
of the target member, and is formed by adhesion or vapor deposition
of a secondary target material 11C on both surfaces of a substrate
or base 11B made of an X-ray shielding material. The substrate 11B
has a thickness which prevents the primary X-rays from passing
therethrough. Also, the secondary target material 11C has
preferably a film thickness which can provide enough fluorescent
X-rays excited from the secondary target material by the primary
X-rays, and which can provide the maximum fluorescent X-rays. Also,
the thickness of the secondary target material 11C is preferable
selected such that the fluorescent X-rays generated from the X-rays
shielding materials of the substrate are fully absorbed therein.
Further, it is desirable that the film thickness of the secondary
target material 11C is considered as a bulk.
[0064] It is enough that the secondary target material 11C is
provided on at least one surface of the target member 11, to which
the primary X-rays are irradiated, and a surface where the primary
X-rays are not irradiated can constitute a substrate surface. In a
second example shown in FIG. 5(b), the secondary target material
11C is provided only on one surface of the target member 11. Also,
as in a third example shown in FIG. 5(c), there can be adopted a
structure formed of only the secondary target material 11C without
using the substrate or base.
[0065] Examples of holding the secondary target members will be
explained with reference to FIGS. 6(a) through 6(c). In an example
of holding the secondary target materials shown in FIG. 6(a), a
plurality of secondary target members 11 is held by a single
supporting member 21, and the supporting member 21 formed of the
X-ray shielding material is provided to pass through a center of
the respective secondary target members 11. In a holding example
shown in FIG. 6(b), a plurality of secondary target members 11 is
held by two supporting members 21a and 21b, and the supporting
members 21a and 21b formed of the X-ray shielding material pass
through a center of the respective secondary target members 11 with
a predetermined angle therebetween. The supporting members 21, 21a,
and 21b may be formed in a shape of a wire with a small diameter,
and the irradiation of the primary X-rays to the target surface is
made a very small to be ignored.
[0066] Also, in a holding example shown in FIG. 6(c), a plurality
of secondary target members 11 is held by a plate-like supporting
member 22, and grooves or slits 23 are formed in one side of the
plate-like supporting member 22 made of the X-ray shielding
material such that the grooves 23 are provided with intervals
therebetween, which are the same as the disposition intervals
between the secondary target members 11. By inserting the secondary
target members 11 into the grooves 23 at positions such that the
supporting member 22 passes through the center of the secondary
target members 11, the secondary target members 11 can be held by
the supporting member 22. The thickness of the supporting member 22
can be made thin sufficiently with respect to the effective solid
angle, and the supporting member 22 becomes substantially parallel
to a direction of irradiating the primary X-rays. Thus, prevention
of the irradiation of the primary X-rays to the target surface can
be made very small to be ignored. Incidentally, plural sheets of
supporting members 22 may be arranged to cross each other at the
center position of the secondary target members 11 by using the
plural sheets of the supporting members 22.
[0067] Next, the fluorescent X-ray analyzing apparatus of the
invention has a structure such that the secondary X-rays and the
primary X-rays are switched for irradiation to the sample. FIG. 7
is a schematic view for explaining a mechanism of switching the
irradiated X-rays. In FIG. 7, in addition to the secondary target
device 2 of the invention, there are disposed a collimator 7 which
irradiates the primary X-rays to the sample directly, and a filter
8 for absorbing a part of the primary X-rays. The collimator 7 and
the filter 8 can be switched by a driving mechanism 9.
Incidentally, one or both of the collimator 7 and the filter 8 may
be provided.
[0068] The driving mechanism 9 moves the secondary target device 2,
the collimator 7, and the filter 8 on the central axis C connecting
between the X-ray source 3 and the sample irradiation position 4.
In case a direct excitation by the primary X-rays is carried out by
directly irradiating the primary X-rays to the sample S, the
collimator 7 is disposed on the central axis C. Also, in case
X-rays with specific wavelength are irradiated to the sample S by
absorbing a part of the primary X-rays, or in case of using a
primary X-ray filtering method where a background of an object
element is decreased, the filter 8 is disposed on the central axis
C.
[0069] Also, in case the secondary target device 2 is disposed, by
generating fluorescent X-rays including characteristic X-rays
inherent to the secondary target, continuous X-rays contained in
the primary X-rays are decreased, and the signal-to-noise (S/N)
ratio of the fluorescent X-rays from the sample is improved, to
thereby achieve a highly sensitive detection of the
micro-elements.
[0070] Next, other examples of the target member applied to the
secondary target device of the invention will be explained with
reference to FIG. 8 through FIG. 10(b). Incidentally, the target
member shown in FIG. 2 constitutes a first example.
[0071] As shown in FIG. 8, in a second example of a target member,
a shape of a secondary target member 12 is a polygon. Secondary
target members 12a through 12f are formed in polygonal shapes
having different side lengths, and disposed such that respective
center positions of the target members coincide with the central
axis C.
[0072] In the third to seventh examples of the target member,
divided secondary target members are assembled. In the third
example shown in FIG. 9(a), secondary target members 13 formed into
sector shapes by dividing a circumference at predetermined angels
are assembled, and in the fourth and fifth examples respectively
shown in FIG. 9(b) and FIG. 9(c), secondary target members 14 and
15 formed into rectangular shapes are assembled radially from the
central axis, respectively.
[0073] Also, FIGS. 9(d) and 9(e) show conditions of secondary
target members 16 and 17, respectively, seen from the X-ray source
side in the sixth and seventh examples. In the sixth example, the
secondary target members 16 having sections in circular shapes are
arranged around the central axis, and in the seventh example, the
secondary target members 17 having sections in rectangular shapes
are arranged around the central axis.
[0074] In the eighth and ninth examples of the target member,
secondary target members 18 and 19 shown in FIGS. 10(a) and 10(b)
are respectively divided in lateral and vertical directions, and
divided in a lateral direction (or vertical direction).
[0075] As in the first example, in the respective divided target
members shown in the third through seventh examples and the
respective divided target members shown in the eighth and ninth
examples, the length in the central axis direction and disposition
intervals in the diametral direction between the adjacent target
members are formed to satisfy the first condition, in which an
effective solid angle of observing the target surface from the
primary X-ray source coincides with an effective solid angle of
observing a space between the target member and an adjacent target
member at the side of the target surface from the primary X-ray
source side, and a second condition, in which an effective solid
angle of observing the target surface from the sample irradiation
position coincides with an effective solid angle of observing the
space between the target member and the adjacent target member from
the sample irradiation position.
[0076] As described above, according to the target device of the
invention, the X-ray irradiating condition can be maintained
constant in case of switching the irradiated X-rays, and at the
same time, enough secondary X-rays can be irradiated to the sample.
Also, the secondary X-rays can be irradiated to a minute portion of
the sample.
[0077] Also, according to the fluorescent X-ray analyzing apparatus
of the invention, the X-ray irradiating condition can be maintained
constant in case of switching the irradiated X-rays, and at the
same time, enough secondary X-rays to be irradiated to the sample
can be obtained to thereby improve the detection sensitivity.
Further, an analyzing sensitivity with respect to the minute
portion of the sample can be increased.
[0078] While the invention has been explained with reference to the
specific embodiments of the invention, the explanation is
illustrative and the invention is limited only by the appended
claims.
* * * * *