X-ray or gamma ray systems or devices – Specific application – Diffraction – reflection – or scattering analysis
Reexamination Certificate
1999-03-16
2001-06-19
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Diffraction, reflection, or scattering analysis
C378S084000
Reexamination Certificate
active
06249566
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an apparatus for X-ray analysis which uses a composite monochromator having combined two elliptic monochromators, the composite monochromator being arranged between an X-ray source and a sample.
In the field of X-ray analysis, there has always been required to make the X-ray intensity as high as possible. A stationary-anode X-ray tube (e.g., 0.4 mm×12 mm in focal spot size and 2.2 kW in maximum power) has a limit for increasing the X-ray intensity. To overcome this limitation, a rotating-anode X-ray tube which provides a higher X-ray intensity has been developed and used. There has also been used synchrotron radiation which provides a much higher X-ray intensity. The X-ray generator having such a higher X-ray intensity, however, is big and complicated in handling, and further spends much energy. Under the circumstances, there is more and more of a need to develop an apparatus for X-ray analysis which can increase the X-ray intensity on a sample even though it can be handled easily in laboratories.
Assuming that a sample is set at a distance of several hundred millimeters apart from an X-ray source and an X-ray beam is incident on the sample directly from the X-ray source, the sample receives only a very small percentage of the X-rays which are emitted in all directions from the focal spot on the target of the X-ray source. Accordingly, it is known that optical elements such as mirrors or monochromators are used to focus X-rays on the sample. Persons in the art have sought for an improved focusing efficiency of such an X-ray optical system to save energy further.
Elliptic or parabolic focusing elements with a synthetic multilayered thin film have recently been developed and given attention by persons in the field of X-ray analysis, the elements having high focusing efficiencies and high reflectivity for X-rays of a predetermined wavelength of interest. The focusing elements of this type are disclosed, for example, in U.S. Pat. Nos. 5,799,056; 5,757,882; 5,646,976; and 4,525,853; and M. Schuster and H. Gobel, “Parallel-Beam Coupling into Channel-Cut Monochromators Using Curved Graded Multilayers”, J. Phys. D: Appl. Phys. 28(1995)A270-A275, Printed in the UK; G. Gutman and B. Verman, “Comment, Calculation of Improvement to HRXRD System Through-Put Using Curved Graded Multilayers”, J. Phys. D: Appl. Phys. 29(1996)1675-1676, Printed in the UK; and M. Schuster and H. Gobel, “Reply to Comment, Calculation of Improvement to HRXRD System Through-Put Using Curved Graded Multilayers”, J. Phys. D: Appl. Phys. 29(1996)1677-1679, Printed in the UK. There are further disclosed structures of the synthetic multilayered thin film for X-ray reflection and methods for producing them, for example, in Japanese Patent Post-Exam Publication No. 94/46240 and U.S. Patent No. 4,693,933.
The synthetic multilayered thin film acts as a focusing monochromator for X-rays. It is certain that a combination of an ordinary X-ray source and the above focusing-type synthetic multilayered thin film may greatly increase the X-ray intensity on a sample.
There will now be described with reference to
FIGS. 5
to
12
the shape, structure and function of the prior-art elliptic monochromator having the synthetic multilayered thin film. First, the meaning of the terms “elliptic monochromator”, “elliptic-arc surface” and “focal axis” will be described. Referring to
FIG. 5
, a three-dimensional rectangular coordinate axis XYZ is set in space and an ellipse
10
is drawn in an XY-plane. Imagining a curve
12
which is a portion of the ellipse
10
, the curve
12
is referred to hereinafter as “elliptic-arc”. The elliptic-arc
12
is translated in the Z-direction (i.e., the direction perpendicular to the plane including the elliptic-arc
12
) to make a trace which becomes a curved surface
14
. The curved surface
14
is referred to hereinafter as “elliptic-arc surface”. The two foci F
1
and F
2
of the elliptic-arc surface
12
are translated in the Z-direction to make two traces
20
and
22
each of which is referred to hereinafter as “focal axis”. The focal axes
20
and
22
of the elliptic-arc surface
14
become parallel to the Z-axis. A normal line drawn at any point on the elliptic-arc surface
14
becomes always parallel to the XY-plane. Under the above positional relationship, the elliptic-arc surface
14
can be represented by “elliptic-arc surface with focal axes parallel to the Z-axis”. It should be noted that the monochromator whose reflecting surface consists of an elliptic-arc surface is referred to simply as “elliptic monochromator”.
Next, the function of the elliptic monochromator will be described. Referring to
FIG. 6
, imagine an elliptic monochromator
24
with focal axes parallel to the X-axis. The drawing sheet of
FIG. 6
is parallel to the YZ-plane. The reflecting surface
26
of the elliptic monochromator
24
appears as an elliptic-arc on the drawing sheet of FIG.
6
. In view of geometrical optics, a light ray emitted from a light source, which is positioned at one focal point F
1
of the elliptic-arc, is reflected at the reflecting surface
26
and reach the other focal point F
2
.
In view of X-ray optics, an X-ray emitted from an X-ray source, which is positioned at one focal point F
1
, may be reflected at the reflecting surface
26
only when an X-ray incidence angle &thgr; on the reflecting surface
26
, an X-ray wavelength &lgr; and the lattice spacing d of crystal of the reflecting surface
26
satisfy the Bragg equation for diffraction. The reflected X-ray will reach the other focal point F
2
. It should be noted that the lattice surfaces of crystal contributing to the diffraction are parallel to the reflecting surface
26
.
Incidentally, the X-ray incidence angle &thgr; on the reflecting surface
26
depends upon the position, on which an X-ray is incident, of the reflecting surface
26
of the elliptic monochromator
24
. Therefore, to satisfy the Bragg equation at any point of the reflecting surface
26
, the lattice spacing must be graded along the elliptic-arc (i.e., must vary with the incidence angle &thgr;). The elliptic monochromator for X-rays has accordingly a synthetic multilayered thin film in which the d-spacing of the multilayers varies continuously. The d-spacing varying continuously is referred to hereinafter as graded d-spacing.
FIG. 7
shows the functional principle of the elliptic monochromator having graded d-spacing. X-rays emitted from the X-ray source
32
are incident on a point A, having d-spacing d
1
, of the reflecting surface
26
of the elliptic monochromator
24
with an incidence angle &thgr;
1
and on a point B having d-spacing d
2
with an incidence angle &thgr;
2.
The Bragg equation at the point A is
2
d
1
sin&thgr;
1
=&lgr; (1)
where &lgr; is the wavelength of the X-rays. The Bragg equation at the point B is
2
d
2
sin&thgr;
2
=&lgr;. (2)
If the positional relationship between the X-ray source
32
and the elliptic monochromator
24
is predetermined, the incidence angle &thgr; could be calculated at any point of the reflecting surface
26
of the elliptic monochromator
24
, and accordingly the d-spacing for every incidence angle &thgr; could also be calculated so as to satisfy the Bragg equation.
With the use of such an elliptic monochromator having the graded d-spacing, X-rays of a particular wavelength of interest always satisfy the Bragg equation even if the X-rays are incident on any point of the reflecting surface, so that the reflected X-rays of the particular wavelength can be focused at the other focal point F
2
. The elliptic monochromator having such a synthetic multilayered thin film per se is known as mentioned above.
Referring to
FIG. 6
, X-rays, emitted from the focal point F
1
and traveling in the direction within a divergence angle &agr;, are reflected by the reflecting surface
26
of the elliptic monochromator
26
and focused on the other focal point F
2
with a convergence angle &bgr;. With such a focusing effect, X-rays with th
Harada Jimpei
Hayashi Sei-ichi
Omote Kazuhiko
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Ho Allen C
Kim Robert H.
Rigaku Corporation
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