X-ray or gamma ray systems or devices – Specific application – Diffraction – reflection – or scattering analysis
Reexamination Certificate
1999-11-15
2001-05-08
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Diffraction, reflection, or scattering analysis
C378S145000
Reexamination Certificate
active
06229874
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an X-ray monochromator with simultaneous tuning of an asymmetric angle-and-radius of curvature, and more particularly relates to a single crystal X-ray monochromator which has a high focusing capability and a wide wavelength range from 1 Å to 2 Å.
2. Related Art Statement
In these days, X-ray monochromators which are capable of selecting an arbitrary wavelength have become important due to the development of radiation light, and many developments for X-ray monochromators have been proposed. Recently a two-crystal monochromator and an asymmetric cut triangle monochromator (curved asymmetric triangle crystal spectroscopes) have been practically used. The two-crystal monochromator is remarkably convenient for use, because an exit X-ray direction is invariant for whichever wavelength. However, it has a disadvantage that the focusing capability is too low to exhibit the high intensity. Therefore, the asymmetric cut triangle bent monochromators have been used for many beamlines for protein crystallography which utilizes beamline BL6A from a bending electromagnet BL6A installed in the Photon Factory in Tsukuba, Ibaraki, Japan.
The asymmetric cut triangle bent monochromator has an advantage in realizing high intensity, with placed expectation for its application to various X-ray analyses. However, in this type of monochromators, the demagnification rate of a beam passing through the asymmetric cut crystal monochromator depends on the angle between the beam and the crystal surface with the asymmetry factor, which is then related to the wavelength. Therefore, the demagnification rate depends on the wavelength, and thus a usable wavelength range is narrow. For this reason, about ten kinds of different asymmetric cut crystals are required in order to generate X-rays of wavelengths ranging from 1 Å to 2 Å. In order to perform the beam demagnification and focusing over a wide range of wavelengths, several different asymmetric cut spectral crystals have to be prepared, and any desired one of them has to be used for respective wavelengths. Therefore, when a measurement using various wavelengths, e.g. a measurement using the abnormal dispersion effectively, is to be conducted, a very long time is required for replacing spectral crystals, and such a long time could not be practically accepted.
Further, the use of a strong X-ray source such as emitted light makes it difficult to cool the conventional asymmetric cut triangle monochromator, which unexpectedly provides a problem related to heat load. In particular, it is pointed out that the intensity of the emitted X-rays varies due to the heat load with the lapse of time, although the crystal does not melt due to the heat.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an X-ray monochromator, which is capable of effectively generating monochromatic X-rays having high intensity and covering a wide range of wavelengths by using only one monochromator crystal.
In order to attain such an object, according to the present invention, a monochromator comprises:
a base member having an asymmetric cut curved-surface obtained by cutting a cylindrical body at a maximum asymmetric angle &agr;
0
with respect to a plane orthogonal to a center axial line of the cylindrical body to obtain an ellipsoidal asymmetric cut surface, and then curving the thus obtained ellipsoidal asymmetric cut surface; and
a monochromator crystal bonded to said asymmetric cut curved-surface of the base member;
wherein said asymmetric cut curved-surface of the base member is shaped along a peripheral surface of an imaginary cylindrical body having a radius R
0
, and an asymmetric angle and a radius of curvature for a desired wavelength are simultaneously tuned by rotating said base member around a center axial line thereof.
In the monochromator according to the present invention, both the asymmetric angle and radius of curvature can be simultaneously tuned over a wide wavelength range only by rotating the base member around the center axial line (&phgr;-axis) thereof.
In a preferable embodiment of the monochromator according to the invention, the base member serving as a pedestal is provided with cooling means for preventing an undesired excessive temperature rise of the monochromator. Therefore, a variation in a beam intensity can be suppressed during the measurement.
Preferably, the center axial line of the imaginary cylindrical body intersects with the center axial line of the base member, and makes an angle of 90°-&bgr; with respect to a major axis of the ellipsoidal asymmetric cut surface where &bgr; is an offset angle ranging from 0 to 90° viewed from the above in a direction of the center axial line of the base member.
Further preferably, the angle &bgr; is approximately 20.9°.
Also preferably, the maximum asymmetric angle &agr;
0
is approximately 19.7°.
More preferably, the micrometer-service crystal is made of a silicon after cut at the maximum asymmetric angle &agr;
0
from a plane (
111
).
According to the present invention, a method of manufacturing a monochromator having an asymmetric cut curved-surface as a reflecting surface, comprises the steps of:
cutting a cylindrical body having a center axial line at a maximum asymmetric angle &agr;
0
with respect to a plane orthogonal to the center axial line to obtain an ellipsoidal asymmetric cut surface;
shaping the thus obtained ellipsoidal asymmetric cut surface along a peripheral surface of an imaginary cylindrical body having a radius R
0
to obtain an asymmetric cut curved-surface; and
bonding a monochromator crystal to the asymmetric cut curved-surface;
wherein said step of determining the asymmetric angle &agr;
0
includes the following steps of:
determining an asymmetric factor b defined by an equation of b=L/F, where L is a distance between an X-ray source and the monochromator crystal, and F is a distance between the monochromator crystal and a focusing point;
determining a wavelength range to be used;
determining a monochromator crystal and a reflecting surface thereof;
determining a maximum angle of diffraction &thgr;
max
of the monochromator crystal corresponding to a longest wavelength &lgr;
max
within the wavelength range, according to the Bragg equation; and
determining an asymmetric angle &agr;
max
corresponding to the maximum angle of diffraction &thgr;
max
by a following equation:
b=sin(&thgr;+&agr;)/sin(&thgr;−&agr;)=L/F
where &thgr; is an angle of diffraction of the monochromator crystal, and &agr; is an asymmetric angle, and then determining the maximum angle of diffraction &thgr;
max
based on the thus determined maximum angle of diffraction &agr;
max
.
In a preferable embodiment of the method according to the invention, the step of shaping the ellipsoidal asymmetric cut surface along the peripheral surface of the imaginary cylindrical body having the radius R
0
, comprises the steps of:
determining a minimum radius R
min
of the imaginary cylindrical body corresponding to the longest wavelength &lgr;
max
by a following equation:
2/R=[sin(&thgr;+&agr;)]/L+[sin(&thgr;−&agr;)]/F
where R is a radius of the imaginary cylindrical body, and then determining a radius R
0
of the imaginary cylindrical body based on the thus determined minimum radius R
min
;
obtaining an offset angle &bgr; according to a difference between an azimuth angle &phgr;
a
corresponding to an ideal asymmetric angle &agr;, and an azimuth angle &thgr;
R
corresponding to a radius R of an ideal imaginary cylindrical body, and
curving the ellipsoidal asymmetric cut surface using the radius R
0
of the imaginary cylindrical body and the offset angle &bgr;.
REFERENCES:
patent: 5004319 (1991-04-01), Smither
patent: 5923720 (1999-07-01), Barton et al.
Sakabe Noriyoshi
Watanabe Nobuhisa
Kim Robert H.
Le Phuong
Stevens Davis Miller & Mosher LLP
The University of Tsukuka
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