U.S. patent application number 13/540652 was filed with the patent office on 2012-10-25 for wavelength-classifying type x-ray diffraction device.
This patent application is currently assigned to Rigaku Corporation. Invention is credited to Kimiko Hasegawa, Masataka Maeyama, Kazuyuki MATSUSHITA, Takuto Sakumura, Yuji Tsuji.
Application Number | 20120269322 13/540652 |
Document ID | / |
Family ID | 44485268 |
Filed Date | 2012-10-25 |
United States Patent
Application |
20120269322 |
Kind Code |
A1 |
MATSUSHITA; Kazuyuki ; et
al. |
October 25, 2012 |
WAVELENGTH-CLASSIFYING TYPE X-RAY DIFFRACTION DEVICE
Abstract
A wavelength-classifying type X-ray diffraction device bombards
a sample with characteristic X-rays generated from an X-ray
generation source, and detects characteristic X-rays diffracted by
the sample using an X-ray detector. The X-ray generation source is
composed of several metals of different atomic number, respective
metals generating several characteristic X-rays of different
wavelengths. An X-ray detector is composed of several pixels for
receiving X-rays and outputting pulse signals corresponding to
X-ray wavelengths. Pixels are respectively furnished with
classification circuits. The classification circuits classify and
output pixel output signals based on each of characteristic X-ray
wavelengths. X-ray intensity is detected on a per-wavelength basis
in individual pixels 12. Measurement data based on different
wavelength X-rays are acquired simultaneously in just one
measurement. Data of diffracted X-rays of different wavelengths are
acquired using the entire region of the receiving surface of a
two-dimensional detector.
Inventors: |
MATSUSHITA; Kazuyuki;
(Ome-shi, JP) ; Sakumura; Takuto; (Hachioji-shi,
JP) ; Tsuji; Yuji; (Hamura-shi, JP) ; Maeyama;
Masataka; (Ome-shi, JP) ; Hasegawa; Kimiko;
(Hamura-shi, JP) |
Assignee: |
Rigaku Corporation
Akishima-shi
JP
|
Family ID: |
44485268 |
Appl. No.: |
13/540652 |
Filed: |
July 3, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13170708 |
Jun 28, 2011 |
|
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13540652 |
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Current U.S.
Class: |
378/71 |
Current CPC
Class: |
H01J 2235/086 20130101;
H01J 35/10 20130101; G01N 23/207 20130101; H01J 2235/081
20130101 |
Class at
Publication: |
378/71 |
International
Class: |
G01N 23/207 20060101
G01N023/207 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 29, 2010 |
JP |
2010-148384 |
Claims
1. A wavelength-classifying type X-ray diffraction device for
bombarding a sample with characteristic X-rays generated by X-ray
generating means, and detecting using X-ray detecting means the
characteristic X-rays that have been diffracted by said sample,
wherein: said X-ray generating means is made of a plurality of
metals having different atomic numbers, and generates from said
respective metals a plurality of characteristic X-rays of mutually
different wavelengths; said X-ray detecting means is a pulse
counting type pixel array detector, which is made of a plurality of
pixels that receive characteristic X-rays of a plurality of
wavelengths diffracted by said sample and that output signals
corresponding to the wavelengths of said respective characteristic
X-rays; and said pixels are respectively furnished with classifying
means, said pixels outputting signals in different states for every
wavelength of X-rays, said classifying means being adapted to
classify output signals of said pixels into each of the wavelengths
of the characteristic X-rays, and output the signals.
2. The wavelength-classifying type X-ray diffraction device
according to claim 1, further comprising counters for counting the
number of signals that have been classified by said classifying
means for every wavelength.
3. The wavelength-classifying type X-ray diffraction device
according to claim 1, comprising computing means for computing
relational values of diffracted X-ray wavelength, diffraction
angle, and intensity, on the basis of a position of diffracted
X-rays detected by said X-ray detecting means, and the counted
value of every wavelength of diffracted X-rays detected by said
classifying means.
4. The wavelength-classifying type X-ray diffraction device
according to claim 1, wherein said X-ray generating means has a
rotor target made of a plurality of different metals disposed in
alternating fashion along an electron scanning direction; has a
rotor target made of a plurality of different metals disposed in
respectively continuous fashion along the electron scanning
direction, the metals being disposed adjacently to one another in a
direction perpendicular to the electron scanning direction; or has
a first X-ray generating section for generating X-rays of a first
wavelength, and a second X-ray generating section for generating
X-rays of a second wavelength different from the first wavelength,
the first X-ray generating section and the second X-ray generating
section arranged at mutually different positions and respectively
arranged at positions such that a given sample can be bombarded
with X-rays.
5. The wavelength-classifying type X-ray diffraction device
according to claim 1, wherein said X-ray detecting means is a
two-dimensional pixel array detector made of a plurality of pixels
lined up two-dimensionally, and having a reception surface area
capable of detecting a plurality of types of diffracted X-rays of
different wavelengths, or a one-dimensional pixel array detector
made of a plurality of pixels lined up one-dimensionally, and
having a reception length enabling a plurality of diffracted X-rays
of different wavelengths to be detected.
6. The wavelength-classifying type X-ray diffraction device
according to claim 1, wherein said sample is a powder sample or a
single crystal sample; said X-rays of different wavelengths are Cu
rays and Mo rays; the lattice constant is determined based on a
diffraction profile obtained using Cu rays; and refining of the
crystal structure is carried out on the basis of a diffraction
profile obtained using Mo rays.
7. The wavelength-classifying type X-ray diffraction device
according to claim 3, further comprising a display device for
displaying the results of measurements made according to
instructions from said computing means, said display device being
able to display diffraction image in which a plurality of
diffraction images obtained by X-rays having mutually different
wavelengths are distributed in combination, and said display device
also being able to display another diffraction image in which one
of the plurality of diffraction images obtained by X-ray having
selected single wavelength is selectively displayed.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an X-ray diffraction device
of a wavelength-classifying type, having a function whereby X-rays
that include a plurality of X-rays of different wavelengths may be
classified into X-rays of each of the wavelengths, and X-ray
measurements may be carried out using X-rays of the individual
wavelengths.
[0003] 2. Description of the Related Art
[0004] In the field of X-ray diffraction devices, there are
instances in which it is desired to use a plurality of
characteristic X-rays of different wavelengths when measuring a
single substance to be measured. For example, for analysis in
situations where the wave vector of the X-rays necessitates large
radial range (for example, as in radial distribution analysis), or
in the case of the multi-wavelength anomalous dispersion (MAD)
method used in analyzing the structures of native proteins, there
are instances in which a plurality of X-rays of different
wavelengths are desired.
[0005] Hitherto, one procedure employed in instances where a
plurality of X-rays of different wavelengths are used in an X-ray
diffraction device involves swapping out the X-ray tube. The
operation to swap out the X-ray tube is typically a manual
operation performed by the operator. Because of this, problems have
been encountered in regard to the considerable time needed for the
swap out, and the difficultly of adjusting the emission optical
path of the X-rays subsequent to swap out.
[0006] In particular, in the case of a demountable X-ray tube,
which is a tube that uses a rotating anti-cathode, namely, a rotor
target, as the anti-cathode, namely, as the target, swapping out
the demountable X-ray tube requires first releasing the vacuum in
the vacuum chamber in which the demountable X-ray tube is disposed,
before swapping the tube out; and subsequently carrying out an
operation to reestablish a vacuum state. In such instances, an
extremely long period of time is needed before the vacuum chamber
interior can be restored to a degree of vacuum enabling generation
of X-rays.
[0007] Also, because demountable X-ray tubes are quite heavy, a
risk is presented in regard to the demountable X-ray tube being
dropped during the replacement operation, or of the demountable
X-ray tube coming into contact with the device chassis. Another
risk is that coolant introduced into the interior of the X-ray tube
will drip down into the vacuum chamber interior during the swap-out
operation of the X-ray tube.
[0008] Furthermore, in many instances, once the X-ray tube is
replaced, the position of the X-ray generation source will be very
slightly shifted out of position for reasons relating to the
accuracy of mechanical attachment, and it has therefore been
necessary to make readjustments to the optical system for
measurement, which is supported by a goniometer inside the X-ray
diffraction device.
[0009] Because operations to replace X-ray tubes are extremely
laborious and time-consuming as discussed above, the operational
efficiency of replacing a plurality of X-ray sources in a single
X-ray generation device is extremely poor.
[0010] On the other hand, in instances of using a plurality X-rays
of different wavelengths in an X-ray diffraction device, one method
involves preparing an X-ray generation device for each of a
plurality of X-ray sources of different wavelengths. However, a
single X-ray generation device is quite expensive, making it
extremely difficult to provide a plurality of these devices.
[0011] Furthermore, in instances where a substance being measured
is a substance unable to maintain crystal structure for an extended
period, the crystal structure may change during replacement of the
X-ray tube or in the course of conducting measurements multiple
times, so that sometimes accurate measurement data cannot be
obtained.
[0012] To address the aforementioned problems, there have been
proposed a multitude of X-ray generation devices adapted to
generate a plurality of types of X-rays simultaneously, or to
periodically switch among generating a plurality of types of
X-rays. For example, one known device of this kind is an X-ray
generation device that uses a so-called stripe target. With an
ordinary rotating anti-cathode (namely, a rotor target), a metal of
the same given type is deposited uniformly on a round tubular metal
face which constitutes the X-ray generating section. With a stripe
target, on the other hand, two or more different types of metal are
deposited to predetermined width in cyclically alternating fashion
(namely, in a stripe pattern) along the direction in which thermal
electrons scan the surface of the target.
[0013] When this stripe target is rotated at high speed, X-rays of
different wavelengths that correspond to the different types of
metal can be elicited in a constant cycle. X-rays having
wavelengths used for measurement can then be sorted using an
analyzing crystal (namely, a monochromator). In an instance of
changing the wavelength, the analyzing crystal is rotated about its
own centerline to change the angle with respect to the impinging
X-rays, or the analyzing crystal is exchanged for one of a
different type.
[0014] In a known method according to Japanese Patent Laid Open
Publication No. H7-073831, in place of a wavelength classification
method that uses an analyzing crystal, diffracted X-ray data are
acquired only at times of X-rays from the same given metal, in
synchronization with rotation of a stripe target. Another method
according to Japanese Patent Laid Open Publication No. H5-152091
teaches classification of X-ray wavelengths by opening and closing
of a rotating shutter in synchronization with rotation of a stripe
target.
[0015] Yet another method according to Japanese Patent Laid Open
Publication No. H11-339703 teaches disposing ring shapes, namely,
annular shapes, of two or more different metals along a direction
perpendicular to the direction in which the thermal electrons scan
the surface of the target, and classifying X-ray wavelengths by
changing the electron emission angle of the electron gun. Still
another method according to Japanese Patent Laid Open Publication
No. 2007-323964 teaches disposing ring shapes of two or more
different metals along a direction perpendicular to the direction
in which the thermal electrons scan the surface of the target, and
classifying X-ray wavelengths through parallel travel of the
electron gun.
[0016] Another method according to Japanese Patent Laid Open
Publication No. H5-089809 teaches disposing ring shapes of two or
more different metals along a direction perpendicular to the
direction in which the thermal electrons scan the surface of the
target, and classifying X-ray wavelengths through travel of the
target relative to the electron gun. Yet another method according
to Japanese Patent Laid Open Publication No. H5-135722 teaches
disposing ring shapes of two or more different metals along a
direction perpendicular to the direction in which the thermal
electrons scan the surface of the target, and classifying X-ray
wavelengths by changing the direction of advance of the electron
beam to change the metal being struck by the electrons.
[0017] In a device according to Japanese Patent Laid Open
Publication No. H6-215710, ring shapes of two or more different
metals are disposed, electron guns are disposed facing the
individual different metals, and X-rays of different wavelengths
are generated simultaneously while a plurality of types of
measurement are carried out simultaneously using the X-rays. Also,
in a known target for generating X-rays of different wavelengths
according to Japanese Patent Laid Open Publication No. H5-325851,
the target is formed of an alloy which is a combination of
different metals.
[0018] In a known X-ray generation device according to Japanese
Patent Laid Open Publication No. H8-094547, a plurality of X-ray
tubes are provided for generating X-rays of different wavelengths,
and control means are provided for controlling operation of these
X-ray tubes under individually appropriate conditions. In a known
X-ray diffraction device according to Japanese Patent Laid Open
Publication No. 2002-039970, a plurality of X-ray tubes are
provided for generating X-rays of different wavelengths, X-rays are
caused to impinge on a sample from different directions, and a
plurality of types of diffracted X-rays arising from X-rays of
different wavelengths are received by a two-dimensional X-ray
detector as they are emitted from the sample.
[0019] Further, in a known X-ray diffraction device according to
Japanese Patent No. 4074874, X-rays of mutually different
wavelengths are elicited respectively from an upper half region and
a lower half region of a rotating target, and these bombard a
single sample, whereupon diffracted X-rays emitted from an upper
half region and diffracted X-rays emitted from a lower half region
of the sample are detected simultaneously by a two-dimensional CCD
detector. According to this device, measurement data based on
X-rays of different wavelengths can be obtained simultaneously
through just one measurement.
SUMMARY OF THE INVENTION
[0020] As described above, X-ray diffraction devices known in the
prior art generate X-rays of a plurality of wavelengths either
simultaneously or individually, while diffracted X-ray data are
measured on the basis of the respective X-rays. However, because
the detectors for detecting the diffracted X-rays lack the ability
to distinguish between wavelengths, diffracted X-rays cannot be
detected simultaneously while distinguishing among them in terms of
their wavelengths (namely, in terms of their energies); rather,
detection of diffracted X-rays has been carried out through sorting
of the source of one specified X-ray wavelength only, and
individually measuring each single X-ray wavelength.
[0021] With this method, X-rays of wavelengths that make no
contribution to measurement are consumed needlessly. For this
reason, problems such as waste of energy and accelerated wear of
the target are encountered. Also, measurements made with X-rays of
different wavelengths unavoidably have to be carried out in
individual time slots, resulting in the problem of extended
measuring times.
[0022] With a conventional X-ray diffraction devices, the extended
measuring times meant that substances unable to maintain crystal
structure for an extended period have been impossible to
measure.
[0023] Japanese Patent No. 4074874 discloses an invention involving
a time delay integration (TDI) operation in which a semiconductor
detector of charge integration design, such as a two-dimensional
charge coupled device (CCD) detector, is divided into an upper half
region and a lower half region for use, thereby making possible
simultaneous measurement of diffracted X-rays of different
wavelengths. However, in this invention, there are encountered a
number of problems, such as that the detection regions of the upper
and lower halves are close to one another with each region having
constricted surface area; measuring time is limited by the readout
speed of intensity data; and a limited effective dynamic range
results in susceptibility to becoming saturated easily.
[0024] With the foregoing in view, it is an object of the present
invention to enable measurement data based on X-rays of different
wavelengths in an X-ray diffraction device to be acquired
simultaneously through just one measurement, and thereby to prevent
waste of energy and wear of the target within a short time, as well
as to enable measurement data based on X-rays of different
wavelengths to be acquired in a short time.
[0025] Yet another object of the present invention is to make
possible acquisition of diffracted X-ray data of different
wavelengths using the entire region of the light-receiving face of
a one-dimensional X-ray detector or a two-dimensional X-ray
detector, so that highly reliable diffracted X-ray data may be
obtained.
[0026] The wavelength-classifying type X-ray diffraction device
according to the present invention is a wavelength-classifying
X-ray diffraction device for bombarding a sample with
characteristic X-rays generated by X-ray generating means, and
detecting using X-ray detecting means the characteristic X-rays
that are diffracted by the sample. The X-ray generating means is
made of several different, namely, a plurality of, metals having
different atomic numbers, and generates from the respective metals
a plurality of characteristic X-rays of mutually different
wavelengths. The X-ray detecting means is made of a plurality of
pixels that receive the characteristic X-rays of a plurality of
wavelengths diffracted by the sample and that output signals, for
example, pulse signals, corresponding to the wavelengths of the
respective characteristic X-rays. The pixels are respectively
furnished with classifying means, the classifying means being
adapted to classify output signals, for example, output pulse
signals, of the pixels into each of the wavelengths of the
characteristic X-rays, and output the signals.
[0027] In a known semiconductor X-ray detector according to
Japanese Patent Laid Open Publication No. 2010-038722, which is
adapted to output an electrical signal upon receiving an X-ray, the
semiconductor X-ray detector has a function of outputting an
electrical signal depending on the energy of the received X-ray
(namely, the wavelength of the X-ray) (herein also referred to as
energy resolution). This detector also has a function of
discriminating, namely, sorting, the X-rays on the basis of the
amount of energy from an upper limit value and a lower limit value
of the value of pulse height, and through this discrimination
function is able to eliminate the background component in a
diffracted X-ray profile.
[0028] However, Japanese Patent Laid Open Publication No.
2010-038722 does not disclose bombarding a sample with X-rays of
different wavelengths. Also, whereas Japanese Patent Laid Open
Publication No. 2010-038722 discloses a silicon strip detector
having a function of eliminating wavelength components that
correspond to the background, the publication does not disclose the
pixel array detector according to the present invention, namely, a
detector composed of a plurality of pixels which are individually
endowed with a function of classifying a plurality of X-rays that
bombard a sample, the X-rays having mutually different
wavelengths.
[0029] Japanese Patent Laid Open Publication No. 8-299318 discloses
a technique for bone densitometry using X-rays, wherein a living
body, namely, an organism, is bombarded with a plurality of types
of characteristic X-rays of different wavelengths; the X-rays that
pass through the living body are detected by a semiconductor
detector; output signals of the semiconductor detector are
discriminated on a per-wavelength basis by a plurality of types of
pulse height discriminating circuits; and computations of bone
density are carried out in relation to X-rays of the individual
discriminated wavelengths.
[0030] However, the technique disclosed in this publication relates
to the field of measuring bone density, and thus the technical
field to which the publication relates is completely different from
the field of measuring X-ray diffraction as in the present
invention. That is, Japanese Patent Laid Open Publication No.
8-299318 contains no disclosure that could be considered to
anticipate classification of a plurality of diffracted X-rays of
different wavelengths that are emitted from a sample. Moreover, the
publication does not touch upon a unique characteristic of the
pixel array used in the present invention, namely, that of
furnishing a pulse height discriminating circuit to every pixel of
a one-dimensional or two-dimensional semiconductor detector.
[0031] In the wavelength-classifying type X-ray diffraction device
according to the present invention, a diffracted X-ray beam
containing diffracted X-rays of different wavelengths is detected
by a pixel array detector in which every pixel is given a
wavelength classifying function, and therefore despite the presence
of a combination of diffracted X-rays of different wavelengths in
the diffracted X-ray beam, diffracted X-rays may be detected and
classified according every wavelength. Because of this, measurement
data based on X-rays of different wavelengths can be acquired
simultaneously and classified through just one measurement. In so
doing, waste of energy can be prevented, wear of the target within
a short time can be prevented, and measurement data based on X-rays
of different wavelengths can be acquired in a short time. Because
measurements are completed within a short time, measurements can be
carried out without problems, even on substances which are unable
to maintain crystal structure for extended periods.
[0032] Moreover, in the wavelength-classifying type X-ray
diffraction device according to the present invention, rather than
dividing the two-dimensional receiving surface of the X-ray
detector and receiving diffracted X-rays of different wavelengths
in each of these divided regions, diffracted X-rays of different
wavelengths are instead respectively received over the entire
region of the receiving surface of the X-ray detector, and
therefore data of a plurality of diffracted X-rays of different
wavelengths can be respectively acquired over a wider range, and
highly reliable diffracted X-ray data can be obtained as a
result.
[0033] By adopting a configuration whereby measurement data for
every classified wavelength is saved on a per-wavelength basis to
memory, and then image information is generated on the basis of the
per-wavelength basis measurement data and supplied to image display
means, for example, a flat panel display, the measurement results
can be displayed on a per-wavelength basis on the image display
means, or a combination of measured results for different
wavelengths may be displayed on the image display means.
[0034] Optionally, the wavelength-classifying type X-ray
diffraction device according to the present invention comprises
counters for counting the number of signals, for example, pulse
signals, that have been classified by the classifying means for
every wavelength. Through these counters, the intensity of
diffracted X-rays in relation to X-rays of the individual
wavelengths can be represented by the magnitude of counter
values.
[0035] Optionally, the wavelength-classifying type X-ray
diffraction device according to the present invention comprises
computing means for computing relational values of diffracted X-ray
wavelength, diffraction angle, and intensity, on the basis of
positions of diffracted X-rays detected by the X-ray detecting
means, and the counted value of every wavelength of diffracted
X-rays detected by the classifying means. In so doing, a diffracted
X-ray diagram, namely, a diffracted X-ray profile, that represents
a relationship between diffraction angle and diffraction intensity
of diffracted X-rays can be represented on a per-wavelength
basis.
[0036] Optionally, in the wavelength-classifying type X-ray
diffraction device according to the present invention, the X-ray
generating means can be constructed using a rotor target made of a
plurality of different metals disposed in alternating fashion along
an electron scanning direction. Because this rotor target is
provided with a striped pattern of different metals on the target
surface, it is called a stripe target. This target is also called a
zebra target.
[0037] Alternatively, the X-ray generating means is constructed
using a rotor target made of a plurality of different metals
disposed in respectively continuous fashion along the electron
scanning direction, the metals being disposed adjacently to one
another in a direction perpendicular to the electron scanning
direction.
[0038] Optionally, the X-ray generating means is constructed of a
first X-ray generating section for generating X-rays of a first
wavelength, and a second X-ray generating section for generating
X-rays of a second wavelength different from the first wavelength.
The first X-ray generating section and the second X-ray generating
section are arranged at mutually different positions, and are
respectively arranged at positions such that a given sample can be
bombarded with X-rays.
[0039] Further, the electron receiving surface (namely, the X-ray
generating surface) of the rotor target can be formed by an alloy
which is a mixture of different metals.
[0040] In the wavelength-classifying type X-ray diffraction device
according to the present invention, optionally, the X-ray detecting
means is a two-dimensional pixel array detector made of a plurality
of pixels lined up two-dimensionally and having a reception surface
area capable of detecting a plurality of types of diffracted X-rays
of different wavelengths. Alternatively, the X-ray detector is a
one-dimensional pixel array detector made of a plurality of pixels
lined up one-dimensionally and having reception length enabling a
plurality of diffracted X-rays of different wavelengths to be
detected.
[0041] A two-dimensional pixel array detector can acquire
diffracted X-ray information at each of positions in a
perpendicular direction to the equatorial plane. A one-dimensional
pixel array detector integrates, namely, combines, diffracted X-ray
information of a perpendicular direction to the equatorial
plane.
[0042] The wavelength-classifying type X-ray diffraction device
according to the present invention is favorably used for structure
analysis of samples having small molecular mass and including a
heavy atom. Examples of heavy atoms are Fe, Co, Mo, and W. Small
molecular mass refers to substances of low molecular weight, and
these are typically substances with lattice length of 20 .ANG. or
smaller. In the case of structure analysis, the X-rays of different
wavelengths may be CuK.alpha. rays (wavelength 1.542 .ANG.) and
MoK.alpha. rays (wavelength 0.711 .ANG.). Specifically, the initial
structure can be determined using CuK.alpha. rays, while using
MoK.alpha. rays for refining of the structure.
[0043] The wavelength-classifying type X-ray diffraction device
according to the present invention is favorably used for
determining absolute structure of a molecule having optical
activity. In this case, the X-rays of different wavelengths may be
CuK.alpha. rays (wavelength 1.542 .ANG.) and MoK.alpha. rays
(wavelength 0.711 .ANG.), with the Flack parameter being derived
using CuK.alpha. rays, and refining of the structure being carried
out using MoK.alpha. rays.
[0044] The wavelength-classifying type X-ray diffraction device
according to the present invention is favorably used for structure
analysis of proteins. In this case, the X-rays of different
wavelengths may be CuK.alpha. rays (wavelength 1.542 .ANG.),
CoK.alpha. rays (wavelength 1.7892 .ANG.), and CrK.alpha. rays
(wavelength 2.290 .ANG.), and the phase of the crystal structure
factor can be derived based on a known MAD method.
[0045] Alternatively, the X-rays of different wavelengths using
CrK.alpha. rays and CuK.alpha. rays, the phase of the crystal
structure factor can be determined based on the known
single-wavelength anomalous dispersion (SAD) method using
CrK.alpha. rays, and measurements of diffracted X-ray intensity may
be refined using CuK.alpha. rays, which are characteristic
X-rays.
[0046] The wavelength-classifying type X-ray diffraction device
according to the present invention is favorably used for structure
analysis of powder samples. In this case, the X-rays of different
wavelengths can be CuK.alpha. rays and MoK.alpha. rays, the lattice
constant can be determined based on a diffraction profile obtained
using CuK.alpha. rays, and refining of the crystal structure can be
carried out on the basis of a diffraction profile obtained using
MoK.alpha. rays.
BRIEF DESCRIPTION OF THE DRAWINGS
[0047] FIG. 1 is a perspective view showing an embodiment of the
wavelength-classifying type X-ray diffraction device according to
the present invention.
[0048] FIG. 2A is a perspective view showing an embodiment (point
focus) of an X-ray generating section constituting a principal
section of the device of FIG. 1.
[0049] FIG. 2B is a perspective view showing another embodiment
(point focus) of the X-ray generating section.
[0050] FIG. 3A is a perspective view showing yet another embodiment
(line focus) of an X-ray generating section constituting a
principal section of the device of FIG. 1.
[0051] FIG. 3B is a perspective view showing yet another embodiment
(line focus) of the X-ray generating section.
[0052] FIG. 4 is a block diagram showing an embodiment of a control
system constituting another principal section of the device of FIG.
1.
[0053] FIG. 5 is a block diagram showing an embodiment of internal
circuitry of the principal section of the block diagram of FIG.
4.
[0054] FIG. 6 is a diagram showing an example of a diffracted X-ray
image obtained as a measurement result.
[0055] FIG. 7 is a diagram showing a diffracted X-ray image
obtained from the measurement data of FIG. 6 by compiling and
discrimination with Cu only.
[0056] FIG. 8 is a diagram showing a diffracted X-ray image
obtained from the measurement data of FIG. 6 by other compiling and
discrimination with Mo only.
[0057] FIG. 9 is a perspective view showing another embodiment of
the wavelength-classifying type X-ray diffraction device according
to the present invention.
[0058] FIG. 10A and FIG. 10B are respectively diagrams illustrating
yet another embodiment of the wavelength-classifying type X-ray
diffraction device according to the present invention.
[0059] FIG. 11 is a diagram illustrating yet another embodiment of
the wavelength-classifying type X-ray diffraction device according
to the present invention.
[0060] FIG. 12A and FIG. 12B are respectively diagrams illustrating
yet another embodiment of the wavelength-classifying type X-ray
diffraction device according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
[0061] The embodiments of the wavelength-classifying type X-ray
diffraction device according to the present invention are described
below. It should be noted that the present invention is not limited
to the following embodiment. While the following description makes
reference to the drawings, in some instances, constituent elements
may be depicted in the drawings at proportions different from the
actual ones in order to aid understanding of characteristic
portions.
[0062] FIG. 1 shows an embodiment of the wavelength-classifying
type X-ray diffraction device according to the present invention.
This wavelength-classifying type X-ray diffraction device 1 has an
X-ray focal spot 2 provided as X-ray generating means for
generating X-rays, a sample support device 4 supporting a sample 3,
and an X-ray detector 6 for detecting diffracted X-rays emitted
from the sample 3.
[0063] As shown in FIG. 2A for example, the X-ray focal spot 2 is
formed as a region where an electron flux emitted from a filament 7
constituting a cathode collides with the outside peripheral face of
a rotor target 8 constituting the anti-cathode. In order to prevent
damage from occurring in the region of the X-ray focal spot 2, the
rotor target 8 is driven by a drive device, not shown, and rotates
about its own center line X0 as shown by arrow A. Because of this,
the direction in which electrons scan the surface of the rotor
target 8 is the opposite direction from the rotation direction of
the rotor target 8, as shown by arrow B.
[0064] When electrons collide with the X-ray focal spot 2, X-rays
are emitted from the X-ray focal spot 2. An X-ray R1 is then
emanated to the outside from an X-ray window 11 which is provided
in a dividing wall (not shown) enclosing the rotor target 8. This
X-ray R1 bombards the sample 3 (see FIG. 1). In the present
embodiment, of the X-rays emitted from the X-ray focal spot 2, the
X-ray R1 is the X-ray that emanates from a short side of the X-ray
focal spot 2 to form an X-ray beam with a cross sectional shape
that is circular or a rectangular dot, known as point focus.
[0065] On the outside peripheral face of the rotor target 8 there
are provided a plurality of different metals (in the present
embodiment, two) having mutually different atomic numbers, namely,
a first metal 9a and a second metal 9b. The first metal 9a is Cu
(copper) for example, and the second metal 9b is Mo (molybdenum)
for example. The metals 9a and 9b are respectively continuous along
the direction in which the electrons from the filament 7 scan the
outside peripheral face of the target 8 (the direction indicated by
arrow B), namely, they are provided as ring shapes or annular
shapes. Furthermore, the metals 9a and 9b are provided adjacent to
one another in a direction perpendicular to the direction in which
the electrons scan the outside peripheral face of the target 8
(namely, a direction parallel to the center line X0 in FIG.
2A).
[0066] When electrons collide with the first metal 9a, X-rays
containing CuK.alpha. rays (wavelength 1.542 .ANG.) which are
characteristic X-rays is emitted. On the other hand, when electrons
collide with the second metal 9b, X-rays containing MoK.alpha. rays
(wavelength 0.711 .ANG.) which are characteristic X-rays, is
radiated. That is, in the present embodiment, the X-ray R1 radiated
from the rotor target 8 contains a combination of CuK.alpha. rays
and MoK.alpha. rays, which are characteristic X-rays of the
mutually different target materials.
[0067] Depending on the type of sample being measured and the
parameters of X-ray measurement, in some cases, instead of a point
focus X-ray beam emanating, a line focus X-ray beam like that shown
in FIG. 3A will emanate. A line focus X-ray beam refers to an X-ray
beam which, of the X-rays radiated from the X-ray focal spot 2,
contains X-rays that emanate from a long side of the X-ray focal
spot 2, and which has a cross sectional shape of oblong shape
elongated in one direction.
[0068] Returning to FIG. 1, the sample support device 4 is composed
of a simple support stage lacking a moveable member, a three circle
goniometer, a four circle goniometer, or the like. A three circle
goniometer is a goniometer (namely, an angle measuring instrument)
that includes rotation systems rotatable respectively about three
rotation axes. A four circle goniometer is an angle measuring
instrument that includes rotation systems rotatable respectively
about four rotation axes. The decision as to which sample support
device structure to use is made depending on the characteristics of
the sample 3 and the type of measurement.
[0069] The sample 3 is any substance whose molecular structure one
wishes to analyze, for example, a single crystal substance, a
protein substance, a medicine to be created, or the like. The way
in which the sample 3 is supported may be selected appropriately
depending on the characteristics of the sample 3. For example, the
case of a solid sample such as a single crystal substance, the
sample may be affixed to the distal end of a support rod; in the
case of a fluid sample, the sample may be placed in a capillary
tube; or in the case of a powder sample, the sample may be packed
into a recess or through hole of a sample holder. In the case of a
protein sample, the sample may be placed in a prescribed storage
receptacle. In FIG. 1, the sample 3 is depicted as having spherical
shape, but in actual practice, samples of any appropriate shape,
depending on the type of sample, may be subjected to
measurement.
[0070] In the present embodiment, a so-called pulse counting type
pixel array two-dimensional detector is used as the X-ray detector
6. This X-ray detector 6 has a planar X-ray detection section 13
constituting the X-ray detecting means, and a signal processing
circuit board 14 of about the same surface area as the X-ray
detection section 13. The planar type X-ray detection section 13 is
formed by arraying two-dimensionally a plurality of X-ray reception
pixels 12. In FIG. 1, the individual pixels 12 are depicted larger
than actual size in order to aid understanding. The mode of
alignment of the plurality of pixels 12 may be selected freely,
provided it is a regular alignment.
[0071] The signal processing circuit board 14 is provided in
contact with or in close proximity to the X-ray detection section
13, at the back face of the X-ray detection section 13 (namely, the
opposite face from the receiving surface). As shown in FIG. 4,
classification circuits 15 which are individually connected to the
plurality of X-ray reception pixels 12, counter sections 16 which
are individually connected to the classification circuits 15, a
counter readout circuit 17 connected to each of the counter
sections 16, and an input/output interface 18 are provided on the
signal processing circuit board 14. In FIG. 4, the plurality of
pixels 12 are depicted as having a one-dimensional line pattern,
but in actual practice, the classification circuits 15 and the
counter sections 16 are connected individually to the plurality of
pixels 12 disposed in the matrix pattern shown in FIG. 1.
[0072] The classification circuits 15 are circuits for classifying
the pulse signals of the pixels 12 according to each X-ray
wavelength, and outputting the signals. The counter sections 16 are
circuits adapted to count the respective numbers of signals that
have been classified into every wavelength by the classification
circuits 15. The counter sections 16, for example, house counter
circuits equal in number to the number of pulse signals classified
by the classification circuits 15.
[0073] Via the interface 18, the output signal of the counter
readout circuit 17 is transmitted through a communication line to
an external computer 19, for example, a desktop PC. Alternatively,
the output signal of the counter readout circuit 17 may be read out
through yet another interface circuit 20, with data processing such
as sorting, correction, and the like being carried out by this
interface circuit 20. The computer 19 is composed of processing
means of known type, for example, a central processing unit (CPU)
as operation control means; memory as storage means; system
software stored in a prescribed area in memory; application program
software stored in another prescribed area in memory, and the
like.
[0074] A display 21 such as a liquid crystal display device, and a
printer 22 such as an electrostatic transfer printing apparatus,
are connected to output ports of the computer 19. If needed, the
display 21 and the printer 22 can display, on screen or on paper
respectively, the results of measurements made according to
instructions from the computer 19.
[0075] Each of the plurality of pixels 12 is formed by a
semiconductor which is predominantly silicon or the like, and upon
receiving X-rays, outputs a pulse signal in which a charge
generated depending on the wavelength (namely, the energy) of
X-rays is represented in terms of integration of the number of
X-ray photons. For example, when X ray photons of CuK.alpha. rays
are received, a peak waveform of wave height V1 is output, whereas
when X-ray photons of MoK.alpha. rays are received, a peak waveform
of wave height V2 is output. Because CuK.alpha.<MoK.alpha. is
satisfied with regard to the energy of the X-ray photons, V1<V2
is satisfied.
[0076] The classification circuits 15 are circuits adapted to
classify the output signals of the pixels 12 in terms of every
wavelength, which signals are output in different states (in the
present embodiment, as different peak height values) for every
wavelength (namely, for every energy level); and to then output the
signals. As shown for example in FIG. 5, the classification circuit
15 has a signal amplification amp 23, a waveform shaping circuit 24
for shaping the peak waveform to a peak waveform appropriate for a
counter, and two comparators 26a, 26b. Voltages Va and Vb are
respectively applied to the standard reference voltage terminal of
each of the comparators 26a, 26b.
[0077] V1<Va<V2, and Vb<V1. Consequently, the comparator
26a outputs an output signal of wave height V2 (corresponding to
MoK.alpha. rays) which is greater than Va. On the other hand, the
comparator 26b outputs both the wave heights V1 (corresponding to
CuK.alpha. rays) and V2 (corresponding to MoK.alpha. rays), which
are greater than Vb.
[0078] As shown in FIG. 5, the counter section 16 of FIG. 4 has
counters 27a and 27b which are connected to individual output
terminals of the comparators 26a, 26b. Each time that a signal is
output to an output terminal of the comparators 26a, 26b, the
counters 27a, 27b count the output signal, and output the count
number observed within a prescribed time interval as an output
signal. The counter 27a outputs the count number of the wave height
V2, while the counter 27b outputs a count number obtained by
addition of the count number of the wave height V1 and the count
number of the wave height V2.
[0079] The counter readout circuit 17 determines the count number
of the wave height V2 from the count number of the counter 27a, and
calculates the count number of the wave height V1 from a value
obtained by subtraction of the count number of the counter 27a
(namely, the count number of the wave height V2) from the count
number of the counter 27b (namely, the count number of the wave
height V1+the count number of the wave height V2). The counter
readout circuit 17 then outputs how many pulses of wave height V1
(corresponding to CuK.alpha. rays) were counted and how many pulses
of wave height V2 (corresponding to MoK.alpha. rays) were counted,
in a pixels 12 at a row/column address (i,j). In FIG. 4, this
output signal is transmitted to the computer 19.
[0080] On the basis of in-plane positions of diffracted X-rays
which have been detected by the planar X-ray detection section 13
shown in FIG. 1, and of intensity count values for every wavelength
of diffracted X-rays which have been calculated by the counter
readout circuit 17, the computer 19 computes relationships among
diffracted X-ray wavelengths, diffraction angles of diffracted
X-rays, and intensity of diffracted X-rays. Namely, for X-rays of
specific wavelength, the computer 19 computes the diffraction angle
of diffracted X-rays and the intensity count of diffracted X-rays.
By doing this, diffractograms representing relationships of
diffraction angle and diffraction intensity, namely, diffraction
profiles, of diffracted X-rays can be acquired on a per-wavelength
basis, and can also be displayed on a screen or the like.
[0081] Because the wavelength-classifying type X-ray diffraction
device 1 according to the present embodiment is configured as
above, in FIG. 1, a point focus X-ray R1 (see FIG. 2A) containing
CuK.alpha. rays and MoK.alpha. rays from the X-ray focal spot 2
which is the X-ray source, or in some cases a line focus X-ray R1
(see FIG. 3A) if needed, is radiated, and the X-ray impinges on the
sample 3. If the sample 3 has a crystal lattice plane matching
CuK.alpha. rays, a diffracted X-ray R2 of CuK.alpha. rays is output
from the sample, or if the sample 3 has a crystal lattice plane
matching MoK.alpha. rays, a diffracted X-ray R3 of MoK.alpha. rays
is output from the sample.
[0082] The diffracted X-ray R2 of CuK.alpha. rays and the
diffracted X-ray R3 of MoK.alpha. rays are received simultaneously
(namely, when the sample 3 is bombarded with X-rays one time)
within the entire region of the receiving surface of the
two-dimensional X-ray detection section 13. At this time, an image
of the diffracted X-ray R2 and an image of the diffracted X-ray R3
are classified individually in the plurality of pixels 12 by the
classification circuits 15 of FIG. 4, and the images so classified
are counted in terms of every wavelength and in terms of every one
of the individual pixels, by the counter sections 16.
[0083] The intensity of diffracted X-rays of every wavelength are
derived as count numbers by the counter readout circuit 17, and the
results are transmitted in the form of an electrical signal to the
computer 19. According to control by program software installed
therein, the computer 19 determines diffracted X-ray intensities of
every wavelength in association with addresses (i, j) of the pixels
12, and saves the resultant data to a prescribed area in memory in
the computer 19.
[0084] If the data of diffraction images of both the image of the
diffracted X-ray R2 (namely, Cu image) and the image of the
diffracted X-ray R3 (namely, Mo image) which have been saved to
memory is displayed by the display 21 or the printer 22 according
to a prescribed image display program, there will be displayed a
two-dimensional diffraction image in which both the diffracted
X-ray R2 (Cu image) and the diffraction image of the diffracted
X-ray R3 (Mo image) are widely distributed in combination, as
shown, for example, in FIG. 6.
[0085] Meanwhile, if according to a prescribed wavelength selection
program, the image of the diffracted X-ray R2 (Cu image) is
selected from the diffraction image data of both the image of the
diffracted X-ray R2 (Cu image) and the image of the diffracted
X-ray R3 (Mo image) which have been saved to memory, and this
selected data is displayed on the display 21 or the like, only the
image of the diffracted X-ray R2 (Cu image) is selectively
displayed and can be observed, as shown in FIG. 7.
[0086] On the other hand, if according to a prescribed wavelength
selection program, the image of the diffracted X-ray R3 (Mo image)
is selected from the diffraction image data of both the image of
the diffracted X-ray R2 (Cu image) and the image of the diffracted
X-ray R3 (Mo image) which have been saved to memory, and this
selected data is displayed on the display 21 or the like, only the
image of the diffracted X-ray R3 (Mo image) is selectively
displayed and can be observed, as shown in FIG. 8.
[0087] In the above manner, according to the wavelength-classifying
type X-ray diffraction device 1 of the present embodiment, a
diffracted X-ray beam containing diffracted X-rays of different
wavelengths (e.g., CuK.alpha. rays and MoK.alpha. rays) is detected
by the pixel array detector 6 in which every pixel 12 is given
wavelength classifying functionality, and therefore diffracted
X-rays of every wavelength can be detected. Because of this,
measurement data based on X-rays of different wavelengths can be
acquired simultaneously by measurement just one time. In so doing,
waste of energy in the X-ray generation section shown in FIG. 2A
can be prevented, wear of the target 8 within a short time can be
prevented, and measurement data based respectively on X-rays of
different wavelengths can be acquired in a short period of time.
Because measurements are completed within a short period of time,
measurements can be carried out without problems even on a sample 3
(FIG. 1) which is unable to maintain crystal structure for extended
periods.
[0088] In certain conventional X-ray diffraction devices, the
planar X-ray detection section that makes up the X-ray detector is
not formed by a pulse counting type pixel array detector, but
rather by a charge integrating type CCD detector, and the receiving
surface of the X-ray detection section is divided into upper and
lower halves or the like, with diffracted X-rays of different
wavelengths being received by the respective divided regions. With
this structure, the detection region for each wavelength is
constricted, and there is a risk of diminished reliability of data.
With the X-ray diffraction device of the present embodiment, by
contrast, diffracted X-rays of different wavelengths are
respectively received over the entire region of the receiving
surface of the X-ray detection section 13 of the X-ray detector 6,
and therefore data of a plurality of diffracted X-rays of different
wavelengths can be respectively acquired over a wider range, and
highly reliable diffracted X-ray data can be obtained as a
result.
Second Embodiment
[0089] The present embodiment is similar to the first embodiment,
but with a modification made to the X-ray generation section.
[0090] As shown in FIG. 2A and FIG. 3A, in the first embodiment
described above, the first metal 9a and the second metal 9b are
respectively continuous along the direction in which electrons from
the filament 7 scan the outside peripheral face of the target 8
(the direction indicated by arrow B), namely, they are provided as
ring shapes or annular shapes. Furthermore, the first metal 9a and
the second metal 9b are provided adjacent to one another along a
direction perpendicular to the direction in which electrons scan
the outside peripheral face of the target 8 (a direction parallel
to the center line X0 in FIG. 2A).
[0091] By contrast, in the present embodiment, the first metal 9a
and the second metal 9b are provided in alternating prescribed
widths along the direction in which electrons from the filament 7
scan the outside peripheral face of a target 28 (the direction
indicated by arrow B) as shown in FIG. 2B and FIG. 3B. In this
structure, the metal 9a and the metal 9b are provided in a striped
pattern, namely, in a stripe pattern, and it is therefore sometimes
referred to as a stripe type target. The structure is also called a
zebra type target. FIG. 2B is a structure for the purpose of
emanating a point focus X-ray beam, and FIG. 3B is a structure for
the purpose of emanating a line focus X-ray beam.
[0092] According to the present embodiment as well, by emission of
electrons from the filament 7 and rotation of the target 28 about
its center axis X0, the X-ray R1 emitted from the X-ray focal spot
2 can contain X-rays of different wavelengths. That is, according
to the present embodiment, the X-ray R1 emitted from the rotor
target 28 contains a combination of characteristic X-rays of the
mutually different target materials, i.e., CuK.alpha. rays and
MoK.alpha. rays.
Modified Examples
[0093] The first metal 9a shown in FIGS. 2A, 2B, 3A, and 3B is not
limited to Cu. Likewise, the second metal 9b is not limited to Mo.
The X-rays of R1, R2, and R3 shown in FIG. 1 are not limited to Cu
rays and Mo rays. In FIG. 5, the two comparators 26a, 26b, the
counters 27a, 27b, and the counter readout circuit 17 utilize
subtraction to classify two wavelengths, i.e., the wavelength
indicated by the pulse height V1 and the wavelength indicated by
the pulse height V2. However, by instead establishing three or more
standard reference voltages, namely, threshold values, the
wavelength indicated by the pulse height V1 and the wavelength
indicated by the pulse height V2 may be classified directly,
without performing a subtraction operation.
[0094] Further, whereas in the embodiment described above, the
targets 8, 28 in FIGS. 2A, 2B, 3A, and 3B are provided with two
metals 9a, 9b, optionally, the target surfaces may instead be
provided with three or more metals, and X-rays of three or more
wavelengths generated. In this case, the numbers of the comparators
26a, 26b and the counters 27a, 27b of FIG. 5 will increase as
needed.
Third Embodiment
[0095] FIG. 9 shows another embodiment of the
wavelength-classifying type X-ray diffraction device according to
the present invention. The present embodiment is likewise similar
to the first embodiment, but with a modification to the X-ray
generation section. In the first embodiment described previously,
an X-ray R1 containing a plurality of characteristic X-rays of
different wavelengths emitted from a single X-ray source, namely,
the X-ray focal spot 2, as shown in FIG. 1.
[0096] By contrast, according to the present embodiment shown in
FIG. 9, an X-ray R1a radiated from a first X-ray source 2a
constituting a first X-ray generation section and an X-ray R1b
radiated from a second X-ray source 2b constituting a second X-ray
generation section simultaneously bombard the sample 3. The X-ray
R1a and the X-ray R1b are both X-rays of a single wavelength. In
this embodiment, the incident angles of the X-ray R1a and the X-ray
R1b onto the sample 3 differ. The structure is otherwise the same
as the X-ray diffraction device 1 shown in FIG. 1. Here, the X-rays
of R1a, R1b, and R3 are not limited to Cu rays and Mo rays.
Fourth Embodiment
[0097] Following is a description of an embodiment in a case where
the present invention is implemented in structure analysis of a
sample having small molecular mass, containing a heavy atom. The
overall structure of the wavelength-classifying type X-ray
diffraction device of the present embodiment can be the structure
shown in FIG. 1 or FIG. 9. In the case of FIG. 1, characteristic
X-rays arising from the mutually different target materials,
namely, CuK.alpha. rays and MoK.alpha. rays, are emitted
simultaneously from the X-ray focal spot 2 and are supplied to the
sample 3. The X-rays supplied to the sample are point focus (see
FIGS. 2A, 2B), for example.
[0098] The heavy atoms mentioned above are Fe, Co, Mo, and W for
example. Light atoms, on the other hand, are C, H, N, O, and S, for
example. Typically, CuK.alpha. rays (wavelength 1.542 .ANG.) is
readily absorbed by heavy atoms, whereas MoK.alpha. rays
(wavelength 0.711 .ANG.) is absorbed with difficulty by heavy
atoms. Consequently, in most instances, MoK.alpha. rays is used in
structure analysis of samples having small molecular mass.
[0099] However, because CuK.alpha. rays has higher X-ray
efficiency, there is the advantage that a high intensity X-ray can
be supplied to a small crystal. Also, because samples of long
lattice length have narrow spacing between diffraction images of
point form, it is difficult to carry out observation of diffraction
images. Meanwhile, because CuK.alpha. rays have a long wavelength,
there is wide spacing between diffraction images, and a resultant
advantage is that it is easy to carry out observation of
diffraction images. Owing to the advantages mentioned above, in
cases of small crystal size or long lattice length, it is desirable
to use Cu rays, even if heavy atoms are contained.
[0100] Consequently, for samples of long lattice length containing
heavy atoms and having small crystal size, there is sometimes a
need to determine the initial structure using Cu rays, and to carry
out refining of the structure using Mo rays. The
wavelength-classifying type X-ray diffraction device of the present
embodiment is adapted to meet this need. According to the
wavelength-classifying type X-ray diffraction device of the present
embodiment, data by Cu rays and data by Mo rays can be acquired
simultaneously in a single process (namely, X-ray bombardment of a
sample just one time).
[0101] The planar size of the two-dimensional pixel array detector
is from 60 mm.times.80 mm to 120 mm.times.160 mm, for example.
There are no specific limitations as to the size and number of
individual pixels forming the pixel array detector. However, pixel
size is preferably a size such that resolution of at least
0.1.degree. can be attained. Once the planar size of the detector
and the pixel size have been determined, the number of pixels is
determined automatically.
Fifth Embodiment
[0102] In the field of analyzing crystal structure, optical
isomers, namely, chirality, are known. The wavelength-classifying
type X-ray diffraction device of the present embodiment may be used
for structure analysis of substances having optical activity. The
overall structure of the wavelength-classifying type X-ray
diffraction device of the present embodiment can be the structure
shown in FIG. 1 or FIG. 9. In the case of FIG. 1, characteristic
X-rays arising from the mutually different target materials,
namely, Cu rays and Mo rays, are emitted simultaneously from the
X-ray focal spot 2 and are supplied to the sample 3. The X-rays
supplied to the sample are point focus (see FIGS. 2A, 2B), for
example.
[0103] As depicted generically in FIGS. 10A and 10B, optical
isomers are substances that, despite having the same chemical
structural formula, exhibit different behavior stemming from
differences in steric structure. For example, the R-configuration
of FIG. 10A is useful as a drug, whereas the S-configuration of
FIG. 10B exhibits toxicity. Ordinarily, diffracted X-rays of two
optical isomers are substantially equivalent, but slight
differences arise in relation to a portion of anomalous scattering,
namely, a portion of abnormal dispersion; and slight discrepancies
between the two in terms of diffracted X-ray intensity are
observed.
[0104] When deriving which structure is present by detecting such
slight discrepancies, namely, when deriving absolute structure, the
Flack parameter provides an indicator.
[0105] However, in the case of organic compounds composed
exclusively of light atoms such as C (carbon), H (hydrogen), N
(nitrogen), and O (oxygen), these slight differences cannot be
detected unless X-rays of particularly long wavelength are used,
and structural determination using the Flack parameter is
difficult. Consequently, in structure analysis of optical isomers,
there is sometimes a need to derive the Flack parameter using
CuK.alpha. rays, and to then carry out refining of structure using
MoK.alpha. rays. The wavelength-classifying type X-ray diffraction
device of the present embodiment is adapted to meet this need.
[0106] According to the wavelength-classifying type X-ray
diffraction device of the present embodiment, data by Cu rays and
data by Mo rays can be acquired simultaneously in a single process
(namely, X-ray bombardment of a sample just one time).
Sixth Embodiment
[0107] Following is a description of an embodiment in a case of
implementation of the invention in structure analysis of protein
crystals. The overall structure of the wavelength-classifying type
X-ray diffraction device of the present embodiment can be the
structure shown in FIG. 1 or FIG. 9. In the case of FIG. 1, a
plurality of characteristic X-rays based on mutually different
target materials are emitted simultaneously from the X-ray focal
spot 2 and are supplied to the sample 3. The X-rays supplied to the
sample are point focus (see FIGS. 2A, 2B), for example.
[0108] As is well known, proteins are amino acid substances formed
of light atoms, such as C (carbon), N (nitrogen), etc. Analysis of
crystal structure using X-rays is a favorable method for
determining steric structure of proteins on an atomic level.
Specifically, the positions of atoms can be determined through
calculations from the intensity distribution of scattered rays
leaving the protein crystal. More specifically, structure analysis
using X-rays involves subjecting a structure factor F (hkl) to
Fourier transformation to derive electron density .rho. (xyz).
[0109] As shown in FIG. 11, the structure factor F (hkl) is a
complex quantity, and the complex quantity F (hkl) cannot be
specified unless |F (hkl)| (absolute value) and phase angle .alpha.
are known. The absolute value |F (hkl)| of the structure factor is
obtained by measuring diffracted X-ray intensity I
(=|F(hkl)|.sup.2). The phase angle .alpha. cannot be derived
empirically. There are any of a number of known conventional
methods which may be used as the method for determining phase angle
.alpha.. One known method among these is the multi-wavelength
anomalous dispersion (MAD) method. In recent years, the
single-wavelength anomalous dispersion (SAD) method has come to be
used as well.
[0110] MAD method is a method of utilizing the effect of anomalous
scattering in the vicinity of the absorption edge of a specific
atom contained in a protein, in order to determine phase.
Specifically, diffracted X-ray intensity is measured using X-rays
of at least three different wavelengths which bracket the
absorption edge of a specific atom. SAD method is a method of
determining phase exclusively from the intensity of X-rays
scattered anomalously, as measured with an X-ray of a single given
wavelength.
[0111] In the present embodiment, where the phase angle .alpha. of
the structure factor F (hkl) is to be derived by the MAD method,
using three kinds of X-rays selected from CuK.alpha. rays
(wavelength 1.542 .ANG.), CoK.alpha. rays (wavelength 1.789 .ANG.),
CrK.alpha. rays (wavelength 2.290 .ANG.) and MoK.alpha. (wavelength
0.711 .ANG.), the diffraction angle and diffracted X-ray intensity
are measured on the basis of each X-ray. In this case, the electron
receiving surface (namely, the X-ray emitting surface) is formed by
providing the metals Cu, Co, Cr and Mo to the surface of the rotor
target that makes up the X-ray generation device.
[0112] In the present embodiment, where SAD method is implemented,
phase angle is determined using either CrK.alpha. rays or
CoK.alpha. rays, and then refining of measurement of diffracted
X-ray intensity is carried out using CuK.alpha. rays. Because both
CrK.alpha. rays and CoK.alpha. rays experience high absorption by
the sample, it is suitable for determining phase angle. Because
CuK.alpha. rays experiences low absorption by the sample and
diffracted X-ray intensity of CuK.alpha. rays is strong, good
diffraction data can be obtained, and refined analysis can be
carried out.
[0113] Proteins are substances of long lattice length.
Specifically, lattice length ranges from 100 to 500 .ANG.. If
lattice length is long, the diffraction images of point form
obtained therefrom will be represented by a narrow scale (namely, a
narrow scale of diffracted angle), making observation difficult. In
this case, by using Cu rays, which has longer wavelength than Mo
rays, the scale for representing diffracted images is wider, and it
is possible for observation of the diffraction profile to be
carried out easily.
[0114] According to the present embodiment, both in the case of the
MAD method and in the case of the SAD method, X-rays of a plurality
of wavelengths bombard a single protein sample, and diffracted
X-rays corresponding to those wavelengths are received
simultaneously by a two-dimensional pixel array detector. The
two-dimensional pixel array detector then detects the diffraction
angles and the diffracted X-ray intensities in relation to the
received diffracted X-rays, on a per-wavelength (i.e. a per-energy
level) basis.
[0115] The planar size of the two-dimensional pixel array detector
is from 80 mm.times.120 mm to 240 mm.times.240 mm, for example.
There are no specific limitations as to the size and number of
individual pixels forming the pixel array detector. However, the
pixels are preferably of such size that resolution of at least
0.1.degree.can be attained. Once the planar size of the detector
and the pixel size have been determined, the number of pixels is
determined automatically.
Seventh Embodiment
[0116] Following is a description of an embodiment in a case of
implementation of the invention in structure analysis of powder
samples. The overall structure of the wavelength-classifying type
X-ray diffraction device of the present embodiment can be the
structure shown in FIG. 1 or FIG. 9. In the case of FIG. 1, a
plurality of characteristic X-rays based on mutually different
target materials are emitted simultaneously from the X-ray focal
spot 2 and bombard the sample 3. The X-rays bombarding the sample
are line focus (see FIGS. 3A, 3B), for example.
[0117] As shown in FIG. 12A, in analysis of a powder sample, in
typical practice two-dimensional diffraction images I.sub.1,
I.sub.2, I.sub.3 . . . are derived through measurements, the
diffraction images are individually integrated, and diffracted
X-ray intensities at individual angles of diffraction angle
2.theta. are identified. The diffraction images are then displayed
as a diffraction profile on the diffractogram of FIG. 12B, whose
horizontal axis is an axis corresponding to the equatorial line
E.
[0118] Because the diffraction angle becomes progressively smaller
at shorter wavelengths of the X-rays used for measurements, the
scale for representing diffraction images (the so-called diffracted
X-rays) on the axis of the diffractogram is a narrow
representation. On the other hand, because the diffraction angle
becomes progressively larger at longer wavelengths of the X-rays
used for measurements, the scale for representing diffraction
images (so-called diffracted X-rays) on the axis of the
diffractogram is a wide representation.
[0119] Thus, when X-rays used for measurement have a long
wavelength, the diffraction profile thereof is easily observed once
analysis has been implemented in relation to the diffraction
profile of diffraction images (so-called diffracted X-rays).
Consequently, in normal powder measurement, apart from special
circumstances there are few instances in which short-wavelength
.lamda.-rays are used. For example, CuK.alpha. rays, which has a
wavelength of 1.5418 .ANG., has a longer wavelength than MoK.alpha.
rays, which has a wavelength of 0.7107 .ANG., and is the X-ray most
widely used for powder measurement.
[0120] However, for substances that belong to the class of metals,
CuK.alpha. rays typically experiences an especially high proportion
of absorption as compared with MoK.alpha. rays, and for this reason
there arises the problem of lack of distinctness of two-dimensional
diffraction images derived using CuK.alpha. rays, owing to the
effects of scattered X-rays caused by this absorption; and
specifically, a problem of insufficient characteristics of
distinctly representing diffraction images (so-called diffracted
X-rays) on two-dimensional images. Also, in measurements in which
X-rays transmit (namely, pass through) a sample, in cases where the
sample contains heavy atoms, there is the problem that, with
CuK.alpha. rays, transmission is difficult due to high absorption.
Because MoK.alpha. rays has a short wavelength, the scale for
representation in the diffraction angle direction (typically the
horizontal axis direction) of diffraction images (so-called
diffracted X-rays) obtained on a diffractogram represented by
coordinates narrows; and in the case, for example, of a sample of
large crystal structure, such as a mineral or polymer, adjacent
diffraction images (so-called diffracted X-rays) may overlap,
making it difficult to determine the index of lattice plane (hkl)
representing the diffraction images (so-called diffracted
X-rays).
[0121] In view of the above problem, in the present embodiment, the
surface of the rotor target that makes up the X-ray generation
device is provided with metals Cu and Mo which are metals of
mutually different atomic numbers, in order to form the electron
receiving surface (namely, the X-ray emitting surface). Two types
of X-rays, CuK.alpha. rays and MoK.alpha. rays, are emitted
simultaneously from the X-ray focal spot within the electron
receiving surface, namely, the X-ray source, and simultaneously
bombard the powder sample.
[0122] Then, based on a diffraction profile obtained with
CuK.alpha. rays, the crystal system and the lattice constant are
determined from the index of lattice plane (hkl). Simultaneously,
refining of crystal structure is carried out on the basis of
diffraction images obtained with MoK.alpha. rays. Specifically, the
number of atoms per unit lattice and the positions of the atoms are
clearly identified.
[0123] In the case of the powder sample described above, because
two-dimensional data is converted to one-dimensional data on the
equatorial line, the detector may be considered as fundamentally
one-dimensional (namely, linear) rather than two-dimensional
(namely, planar). While certainly this may be said to be the case,
an advantage of using a two-dimensional pixel array detector is
that in cases where there is a preferred orientation of the powder
sample, the effect of non-uniformity of diffraction intensity
arising from this orientation can be better ameliorated, as
compared with the case of the one-dimensional pixel array
detector.
[0124] The planar size of the two-dimensional pixel array detector
is 30 mm.times.80 mm, for example. There are no specific
limitations as to the size and number of individual pixels forming
the pixel array detector. However, pixels are preferably of such
size that resolution of 0.01.degree. on a diffraction profile of
diffraction images (so-called diffracted X-rays) can be attained.
Once the planar size of the detector and the pixel size have been
determined, the pixel count is determined automatically. In the
case measurement data of a wide 2.theta. angle range is desired,
the planar size of the detector can be made larger; or a method of
scanning with a detector of small planar size can be adopted.
Another Embodiment
[0125] While the present invention was shown hereinabove in terms
of certain preferred embodiments, the invention is not limited to
these embodiments; various modifications are possible within the
scope of the invention recited in the claims.
[0126] For example, in the embodiment shown in FIG. 1, the signal
processing circuit board 14 is provided in contact with or in close
proximity to the back face of the X-ray detection section 13 which
is composed of a plurality of pixels 12 aligned two-dimensionally,
namely, in planar fashion. However, the X-ray detection section 13
and the signal processing circuit board 14 could instead be
positionally separated, and connected to the individual pixels 12
and the processing circuits by appropriate connection lines.
[0127] In the preceding embodiments, different metals are provided
through a method such as adhesion to different positions on the
surface of the target, but instead, a structure whereby the target
surface is formed of an alloy that is a combination of different
metals can be adopted.
[0128] In the preceding embodiments, as shown in FIG. 5, the
threshold values Va and Vb are set such that
Vb<V1<Va<V2
where V1 is a potential corresponding to CuK.alpha. rays and V2 is
a potential corresponding to MoK.alpha. rays. That is, the Mo
wavelength and the Cu wavelength are classified by Va and Vb.
However, a classification method such as the following can be
adopted instead.
[0129] In a case where, for example, MoK.alpha. rays and CuK.alpha.
rays are used for the purpose of measurement, Mo and Cu are used as
the different metals forming the target. In this case, Mo and Cu
also generate characteristic X-rays besides K.alpha. rays, for
example, K.beta. rays, L.alpha. rays, L.beta. rays, and the like.
These characteristic X-rays besides K.alpha. act as noise for the
purposes of measurement. Where highly accurate measurements are
desired, it is preferable to elicit only energy corresponding to
K.alpha. rays, while eliminating other noise components. Through
finer setting of threshold values in place of the threshold values
Va and Vb described above so as to be able to shave the upper and
lower regions of a desired wavelength, excess noise components in
X-rays can be excluded, and measurements can be carried out with
high accuracy.
[0130] In the preceding embodiments, the anti-cathode which is a
constituent element of the X-ray source is a rotor target, namely,
a rotating anti-cathode; however, it could instead be a fixed
target, namely, a non-rotating anti-cathode. As techniques for
simultaneously obtaining different characteristic X-rays from a
fixed target, there may be contemplated, for example, a technique
in which the fixed target is formed of an alloy; or in which very
small areas of different metals combine, for example, combine in a
dappled manner, on the surface of the fixed target, and so on.
* * * * *