X-ray or gamma ray systems or devices – Specific application – Diffraction – reflection – or scattering analysis
Patent
1996-02-15
1998-09-01
Porta, David P.
X-ray or gamma ray systems or devices
Specific application
Diffraction, reflection, or scattering analysis
378149, 2503631, 25037009, G21K 102
Patent
active
058021370
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates generally in one aspect to x-ray optics and in particular to x-ray optics configurations and to a method of x-ray imaging or radiography. In another aspect, the invention also relates to a corresponding neutron beam analysis configuration.
BACKGROUND ART
Conventional x-ray radiography uses very simple optics usually consisting of a small source and possibly some geometrical defining slits and collimators.
One of the principal limitations on the obtaining of high resolution, high contrast images in conventional radiography is the problem of sample and air scatter, leading to additional background and blurring of images. This scatter is alleviated in some cases by adopting the technique of contact radiography, in which the imaging medium is placed in direct contact with the sample. The technique, however, achieves no direct magnification and is only effective for thin samples. In other cases some form of (so called "focusing") collimator may be placed between the sample and the detecting medium, as for example in some methods for recording chest x-ray radiographs.
Another limitation of conventional radiography is the problem of polychromaticity and the effect of beam hardening in a sample leading to difficulties in quantitative interpretation of radiographs.
On the other hand, a wide variety of very high-resolution x-ray optical devices have been developed for x-ray scientific applications such as the imaging of defects in semiconductor crystals, the measurement of small-angle scattering, and certain types of x-ray tomography. See for example Hashizume & Matsushita (1983) in Handbook on Synchrotron Radiation, Vol. 1, Chap. 4, pp 303-307, ed E. E. Koch, North Holland.
These techniques enable very precise definition of wavelength and collimation of both the incident radiation on the sample and also the radiation passed by the analyser. Typically in these cases the key x-ray optical elements such as the monochromator and analyser crystal are separate devices and require very high-precision independent goniometers to control the angular setting. It would be useful if reliance on such high precision components could be reduced.
Two Russian groups have recently proposed (for example, Soviet patent potentially revolutionary new x-ray analytic method called refractometry or phase contrast imaging. This method is especially suitable for imaging weak absorption contrast features such as capillaries and arteries in vivo without the need for injecting a contrast medium (i.e. it is non-invasive). The technique entails irradiation of the sample by an x-ray beam which has been monochromated and collimated by Bragg diffraction from a first single crystal. The transmitted signal is then received after passing through the sample, by a second single crystal.
The arrangement disclosed in SU 1402871 by Mitrofanov et al involves two perfect crystals set at the exact matching Bragg condition with the angular collimation of the beam from the first crystal less than the range of angles of refraction from the sample, while the angular acceptance of the second crystal is also less than the angular range of refraction from the sample. The method essentially corresponds to "bright field" refractometry or phase contrast imaging. The proposal described in WO92/21016 by Belyaevskaya et al (English language counterpart U.S. Pat. No. 5,319,694) involves production of a pseudoplane wave by a first crystal before the sample such that the divergence in the plane of diffraction of the beam from the first crystal is less than half that of the acceptance range of a second crystal after the sample, and allows for fine tuning of the second crystal in order to enhance the contrast of selected features.
This new technique, in theory, can detect very fine angular path deviations, or equivalently x-ray phase shifts, but in many cases would be difficult to practicably implement with current monochromator/analysis configurations. In simple terms, x-ray refractometry i.e. imaging is the x-ray analogue of op
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Fillard, et al., "Computer Simulation Of Super-Resolution Point Source Image Detection," Optical Engineering, Nov. 1993, vol. 32, No. 11, pp. 2936-2944.
Bonse, et al., "High Resolution Tomography With Chemical Specificity," Nuclear Instruments and Methods in Physics Research A246 (1986), pp. 644-648.
Bruce David Vernon
Commonwealth Scientific and Industrial Research
Porta David P.
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