Radiant energy – Inspection of solids or liquids by charged particles – Analyte supports
Reexamination Certificate
2001-06-28
2003-09-16
Lee, John R. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Analyte supports
C250S492210
Reexamination Certificate
active
06621085
ABSTRACT:
DESCRIPTION
The present invention relates to a device for the precision rotation of samples on a diffractometer, in particular for X-ray or synchrotron radiation diffraction experiments.
The diffraction of X-ray is a method which has been known for a long time and is used worldwide for investigating the structure of condensed materials. In this case, a sample to be examined is introduced into an X-ray beam previously defined with regard to its wavelength distribution, its dimensions, its coherence properties and the like, and the intensity distribution of the X-radiation diffracted by the sample is investigated with the aid of an X-ray detector. Thus, for example, the static crystal structure of a solid body can be explained by measuring the position and the intensity of the Bragg signals diffracted elastically by it at an orientation to be determined precisely in relation to the incident X-ray beam in emergence directions which likewise have to be determined precisely.
In order to carry out such diffraction experiments on X-ray apparatus or, preferably, on modern synchrotron radiation sources, which are able to supply particularly high-energy X-rays, the sample is generally held by a sample holder which is fixed to a diffractometer. Such a diffractometer generally comprises a number of linear displacement and sample rotation devices, which can be motor-driven and therefore permit the adjustment of the sample and rotation of the sample in the beam, for example when looking for Bragg signals, in a measuring cubicle which is generally not accessible to the experimenters for reasons of safety during measurement operations. In order to carry out the measurements, it is important that the sample is arranged in the beam as exactly centrally as possible in relation to the axis of rotation of the rotating shaft. This is because, otherwise, in the event of rotation of the rotating shaft, an additional displacement of the sample in the beam can occur. It is precisely in the case of biological samples, which frequently can be produced only with dimensions of the order of magnitude of
1
&mgr;m and for the examination of which X-ray or synchrotron radiation and beams with correspondingly small dimensions transverse to the propagation direction are used, that such centering is important, since the sample otherwise can even be rotated out of the beam during rotation of the rotating shaft.
For this reason, in the construction of diffractometers it is generally known to fix an additional displacement device, often referred to as an XY table, to the device for rotating the samples, said device comprising two linear displacement units which can be displaced orthogonally with respect to each other, generally by means of a motor. By means of the generally iterative adjustment of these two linear displacement units, the sample can be positioned substantially centrally in relation to the axis of rotation.
However, in the case of examining the aforementioned biological samples with typical dimensions of the order of magnitude of 1 &mgr;m, a device for rotating samples which is configured in this way exhibits disadvantages. For example, the motors which drive such linear displacement units are provided with cables which, during each rotation or displacement of the sample, exert a tensile stress on the end of the rotating shaft on the sample side. This can lead to the shaft being bent at the end on the sample side or the entire shaft, which has a certain amount of play, being displaced, so that the sample runs out of the axis of rotation and/or out of the beam. Furthermore, the motor cables that belong to the linear displacement units and corotate with the device for rotating samples hamper the free rotatability of the device for rotating samples and can even inadvertently be torn off if they wind around the device for rotating samples during the rotation of the sample. If, in order to avoid cables, the motor drive to the displacement units of the XY table is dispensed with and if said displacement units are adjusted manually instead, then the time required for the sample adjustment increases sharply, in particular in the case of synchrotron beam sites, because of the safety regulations when entering and leaving the measurement cubicle. In addition, in manually adjustable displacement units, the problem also occurs that their weight loads the rotating shaft, in particular in the case of horizontally mounted rotating shafts, which likewise can lead to the above-described bending or displacement of the rotating shaft.
It is therefore an object of the invention to propose a device for rotating samples on a diffractometer of this kind which permits the sample to be positioned in the beam simply, quickly and continuously during measurement operation.
According to the invention, this object is achieved by a device for the precision rotation of samples on a diffractometer, especially for X-ray or synchrotron radiation diffraction experiments, comprising:
a centering element which is held at one end of a motor-driven rotating shaft and can be displaced in a plane orthogonal to the axis of rotation of the rotating shaft,
a sample holder which is fixed to the centering element or integral with the latter for holding a sample substantially centrally with respect to the axis of rotation in an X-ray or synchrotron radiation beam,
at least one micrometer finger which is arranged in the region of the centering element and can be positioned orthogonally with respect to the axis of rotation of the rotating shaft by means of a micrometer finger drive device.
In order to position the sample substantially centrally with respect to the axis of rotation, the centering element, to which the sample holder holding the sample is fixed or with which it is integral, is attached to that end of the motor-driven rotating shaft which is provided for this purpose. In this case, the sample is generally not arranged centrally with respect to the axis of rotation of the rotating shaft. This can be detected from the fact that the sample or its center does not remain in a fixed position during rotation of the rotating shaft. Instead, the sample will run through a circular path during rotation of the rotating shaft through 360°. The center of this circular path identifies the axis of rotation of the rotating shaft. With the aid of the micrometer finger, the centering element can now be displaced with respect to the rotating shaft to such an extent that the sample is located at the center of the circular path previously observed, and therefore centrally with respect to the axis of rotation.
In practice, the procedure is, for example, as follows: after the centering element has been attached to the rotating shaft, the latter is rotated through 360° and the radius r of the circular path described by the sample in this case is measured. The rotating shaft is then rotated into a rotational position in which the orientation of the sample relative to the center of the circular path corresponds to the orientation of the micrometer finger relative to the centering element. If, for example, the micrometer finger in the laboratory system is arranged above the centering element, then the rotating shaft is rotated into a position in which the sample is arranged above the center of the circular path. The micrometer finger is then displaced, downward in the aforementioned example, until the sample is arranged centrally in relation to the center of the circle and therefore in relation to the axis of rotation. Following such positioning of the sample, the micrometer finger may possibly be withdrawn again by its drive device, in order not to hamper the free rotation of the rotating shaft. Since, as opposed to conventional diffractometers, in the case of the device for the precision rotation of samples according to the invention no heavy, generally motorized, displacement devices are attached to the rotating shaft, but instead only a centering element, which can substantially be designed as a disk and which can be displaced by the micrometer finger arrange
Castagna Jean Charles
Cipriani Florent
Europäisches Laboratorium für Molekularbiologie (EMBL)
Garzo Paul M.
Lee John R.
Rothwell Figg Ernst & Manbeck
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