Patent Publication Number: US-7711092-B2

Title: X-ray lens assembly and X-ray device incorporating said assembly

Description:
FIELD OF THE INVENTION 
   The present invention relates to an X-ray lens assembly and a method of manufacturing the assembly. The invention further relates to an X-ray device such as an X-ray spectrometer or an X-ray diffractometer comprising an X-ray lens assembly. 
   BACKGROUND OF THE INVENTION 
   The advent of so-called X-ray lenses (also called “Kumakhov lenses”) over two decades ago has prepared the ground for lightweight, portable X-ray devices with a broad spectrum of applications in areas as different as metallurgy, geology, chemistry, forensic laboratories and customs inspection. In a similar way as conventional optical lenses redirect visible or near-visible photons, X-ray lenses redirect electromagnetic radiation in the X-ray radiation band and may thus be used to collimate or focus a beam of X-rays. 
   An X-ray lens is conventionally formed from a plurality of capillaries. Each capillary guides the X-rays captured at a front end thereof to the opposite end by way of total external reflection. This rule applies so long as the angle of incidence at the front end does not exceed a critical angle. If the critical angle is exceeded, X-rays can no longer be captured within the capillary. In such a case, the capillary becomes transparent to the X-rays. 
   Originally, an X-ray lens was a bulky device with dimensions in the region of up to several meters. These large dimensions were mainly the result of separate support structures that were required to keep the individual capillaries in place. Commercial use of X-ray lenses became feasible when it was recognized that the support structures can be omitted if the X-ray lens is produced out of one or more glass capillary bundles using glass drawing techniques. By fusing the capillary mantles together, separate support structures became obsolete. 
   Today, the commercial application of X-ray lenses includes portable X-ray spectrometers, lightweight X-ray diffractometers and many other small-sized devices. Such devices typically comprise an X-ray source (such as an X-ray tube), an X-ray lens and a detector. X-rays emitted from the X-ray source are focused by the X-ray lens onto a tiny spot on a sample. The detector detects the X-rays emitted back from the sample and generates an output signal that can for example be spectrally analysed to determine the chemical elements included in the sample. 
   In X-ray devices the X-ray lenses have to be reliably mounted to ensure a proper operation of the X-ray devices. Often, the X-ray lenses have to be mounted such that the distance of the lens to either one or both of the X-ray source and the sample is adjustable. Due to the fragileness of capillary X-ray lenses the transport, mounting and adjustment of X-ray lenses often poses a challenge. The mounting of X-ray lenses is further complicated by the fact that X-ray lenses may have varying individual dimensions. 
   Accordingly, there is a need for an X-ray lens assembly that facilitates at least one of transport, mounting and adjustment of a capillary X-ray lens. Also, there is a need for an X-ray device including such an X-ray lens assembly and a method for manufacturing the X-ray lens assembly. 
   SUMMARY OF THE INVENTION 
   According to a first aspect of the invention, an X-ray lens assembly comprising a tube member including an inlet opening for X-rays and an outlet opening for X-rays as well as a capillary X-ray lens mounted inside the tube member is provided. 
   The tube member may have internal and external cross-sections of arbitrary shapes. The cross-sections may for example have a circular, oval or polygonal shape. The X-ray lens may comprise one or more capillaries. The capillaries may be grouped into one or several capillary bundles. 
   In one variation, the X-ray lens is mounted inside the tube member by a stabilizing agent. Preferably, the stabilizing agent (e.g. a glue) possesses at least one of hardening and interconnecting properties. 
   In a region between the inlet opening and the outlet opening of the tube member at least one chamber may be defined between the X-ray lens and the tube member. The at least one chamber may serve for various purposes. In one embodiment, the at least one chamber is filled with the stabilizing agent. 
   Between the inlet opening and the outlet opening of the tube member one or more further openings may be provided. Preferably, the one or more further openings are communicating with the at least one chamber. The further openings may be used to fill the stabilizing agent into the chamber. Additionally or in the alternative, the one or more openings may serve as air outlets (e.g. during the insertion of the X-ray lens into the tube member and/or during the filling of the chamber with the stabilizing agent). 
   In addition to the stabilizing agent, or in the alternative, one or more mounting structures may be provided for mounting the X-ray lens inside the tube member. Two axially spaced mounting structures may be provided for limiting the at least one chamber in an axial direction of the tube member. 
   One or more of the mounting structures may have a substantially circular opening in which the X-ray lens is received. The one or more mounting structures may comprises at least one elastic member such as an elastic ring (e.g. an O-ring). 
   The at least one mounting structure may allow for an axial displacement of the X-ray lens within the tube member. An axial adjustment may become necessary when adjusting the position of the X-ray lens in relation to the tube member. Moreover, an axial adjustment may be required in context with positioning the X-ray lens in relation to at least one of an X-ray source and a sample to be irradiated with X-rays. 
   The tube member is preferably made from a material substantially intransparent to X-rays such as steel. In one embodiment, the axial length of the tube member is equal to or larger than the axial length of the X-ray lens. 
   According to a further aspect of the invention, an X-ray device is provided. The X-ray device comprises an X-ray source and an X-ray lens assembly including a tube member having an inlet opening for X-rays and an outlet opening for X-rays as well as a capillary X-ray lens mounted inside the tube member. 
   According to a still further aspect of the invention, a method of manufacturing an X-ray lens assembly is provided. The method comprises the steps of providing a tube member having an inlet opening for X-rays and an outlet opening for X-rays, providing a capillary X-ray lens, and mounting the X-ray lens inside the tube member. 
   The step of mounting the X-ray lens inside the tube member may include the sub-step of arranging the at least two lens mounting structures at an axial distance between the tube member and the X-ray lens. Additionally or in the alternative, the mounting step may include the sub-steps of defining at least one chamber between the tube member and the X-ray lens, and filling a stabilizing agent into the at least one chamber. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further aspects, advantages and variations of the invention will become apparent from the following description of a preferred embodiment and from the drawings. 
       FIG. 1  shows a cross sectional view of an X-ray spectrometer embodiment of the present invention; 
       FIG. 2  shows a cross sectional view of a mounting and positioning apparatus for a lens assembly included in the X-ray spectrometer of  FIG. 1 ; 
       FIG. 3  shows a perspective view of the downstream end of the apparatus of  FIG. 2 ; 
       FIG. 4  shows a perspective view of the upstream end of the apparatus of  FIG. 2 ; and 
       FIG. 5  shows a cross sectional view of an embodiment of the lens mounting assembly. 
   

   DESCRIPTION OF A PREFERRED EMBODIMENT 
   In the following, the invention will exemplarily be described with reference to a preferred embodiment in the form of an X-ray spectrometer comprising an X-ray lens assembly comprising two axially spaced mounting structures that define a chamber filled with a stabilizing agent. It should be noted that the invention can also be practiced in other X-ray devices such as diffractometers and using different mechanisms for mounting the X-ray lens inside the tube member. For example, the stabilizing agent may be omitted if the mounting structures allow for a sufficiently reliable connection between the X-ray lens and the tube member. Alternatively, the mounting structures may be completely omitted (or subsequently removed) if the stabilizing agent allows for a secure and durable mounting of the X-ray lens in the tube member. Also, the number and types of mounting structures may be varied. 
     FIG. 1  shows a cross sectional view of an X-ray spectrometer  10  according to an embodiment of the present invention. The spectrometer  10  includes an X-ray source  12  constituted by an X-ray tube. The spectrometer  10  further comprises a shutter  14 , a positioning/shielding module  16 , a sample housing  18  with a sample  20  arranged on a sample positioning platform  22 , and a detector  24 . 
   An X-ray beam generated within the X-ray source  12  and indicated by reference numeral  26  passes along an optical axis  30  through the shutter  14 . A capillary X-ray (or Kumakhov) lens  28  mounted inside a tube member  50  focuses the X-ray beam onto a tiny spot on the sample  20  (note that the size of the sample  20  is exaggerated in the schematic drawing of  FIG. 1 ). The detector  24  collects the X-rays emitted back from the sample  20  and outputs a spectrum signal indicative of the chemical elements included in the sample  20 . In the view of  FIG. 1 , the X-ray source  12  and the shutter  14  have been rotated by 90° about the optical axis  30  of the spectrometer  10  to better illustrate their structure. 
   The spectrometer  10  shown in  FIG. 1  has a compact tabletop design and is transportable for in-situ analysis. The samples may be provided in a wide range of physical forms, including solids, powders, pressed pellets, liquids, granules, films and coatings. The typical element detection capabilities of the spectrometer  10  under atmospheric conditions range from aluminum (Al) to uranium (U). The spectrometer  10  allows for a qualitative and quantitative elemental analysis down to very low elemental concentrations and sample sizes of 20 μm. 
   Like conventional X-ray tubes, the X-ray source  12  includes a cathode  32  to emit electrons and an anode  34  to collect the electrons emitted by the cathode  32 . Thus, a flow of electrical current is established as the result of a high voltage connected across the cathode  32  and the anode  34 . The electron flow within the X-ray source  12  is focussed onto a very small spot (the “hot spot”)  36  on the anode  34 . The anode  34  is precisely angled at typically 5 to 15 degrees off perpendicular to the electron current so as to allow the escape of some of the X-rays generated at the “hot spot”  36  upon annihilation of the kinetic energy of the electrons colliding with the anode  34 . The X-ray beam  26  thus generated is emitted from the “hot spot”  36  essentially perpendicular to the direction of the electron current and essentially along the optical axis  30  at diverging angles. 
   The X-rays emitted from the X-ray source  12  first pass the shutter  14  attached to a housing  38  of the X-ray source  12 . The shutter  14  selectively blocks the X-ray beam  26  generated within the X-ray source  12  and thus provides a control mechanism for selectively switching the irradiation of the sample  20  “on” or “off”. 
   The positioning/shielding module  16  is arranged downstream (in relation to X-ray source  12 ) of the shutter  14  and is rigidly attached to the shutter  14  by means of an interface member (not shown in  FIG. 1 ). The positioning/shielding module  16  includes an X-ray shielding component  40 , a positioning component  42  for the X-ray lens  28 , and a lens assembly mounting component  44  for rigidly coupling the tube member  50  with the X-ray lens  28  to the positioning component  42 . The individual components  40 ,  42 ,  44 , which are shown only schematically in  FIG. 1 , are illustrated in more detail in the various views of  FIGS. 2 to 4 . 
   As becomes apparent from  FIGS. 3 and 4 , the X-ray shielding component  40  has an outer flange  46  with two screw holes  48  for rigidly attaching the entire positioning apparatus  16  to the shutter  14  (and thus to the X-ray source  12 ). The outer flange  46  therefore serves as an interface member of the positioning/shielding module  16  in relation to the shutter  14 /the X-ray source  12 . The X-ray shielding component  40  further comprises structural elements for limiting the X-ray beam essentially to an inlet opening  90  of the tube member  50 . 
   As will be explained in more detail below, the X-ray lens  28  is rigidly mounted inside the tube member  50 . The tube member  50  in turn is rigidly coupled to the mounting component  44 . The mounting component  44  comprises a base member  52  attached to the positioning component  42 . The base member  52  has a central opening for receiving the tube member  50 . A plurality of tongues  54  with outer threaded portions  56  extend from the opening of the base member  52  and in the axial direction of the tube member  50 . 
   The lens mounting component  44  further comprises a collar member  58  with a central opening through which the tube member  50  extends. The collar member  58  can be screwed onto the tongues  54  and cooperates with their outer threaded portions  56 . Be means of an additional screw (not shown) extending in perpendicular to the tube member  50  and through the collar member  58 , the free end of at least one of the tongues  54  can be moved towards the tubular member  50  as the screw is screwed into the collar member  58 . Accordingly, a clamping connection between the tubular member  50  on the one hand and the lens mounting component  44  on the other hand is established. 
   The positioning component  42  is arranged upstream of the lens mounting component  44  and includes two translation stages  60 ,  62  as well as two goniometer stages  64 ,  66 . As can be seen from  FIG. 2 , the base member  52  of the lens mounting means  44  is attached to the bottom of the first translation stage  60 . 
   The individual positioning stages  60 ,  62 ,  64 ,  66  are arranged one behind the other. Starting with a first translation stage  60  as the most downstream positioning stage, a second translation stage  62 , a first goniometer stage  64  and a second goniometer stage  66  as the most upstream positioning stage follow. Each of the positioning stages  60 ,  62 ,  64 ,  68  has a central X-ray passage  68 ,  70 ,  72 ,  74 , respectively, through which the tubular member  50  extends. 
   In combination, the first translation stage  60  and the second translation stage  62  form an xy translation stage. Accordingly, the first translation stage  60  has a first axis of translation, namely the x axis, which in  FIG. 2  runs perpendicular to the axis of the tubular member  50  and in parallel to the drawing plane. The second translation stage  62  has a second axis of translation, namely the y axis which runs perpendicular to the x axis and perpendicular to the axis of the tubular member  50 . By means of respective knobs, the first and second translation stage  60 ,  62  can be actuated independently from each other. In an alternative embodiment not shown in the drawings, a third translation stage having a third axis of translation (z axis) that runs perpendicular to both the first and second axis of translation may be provided. 
   The two goniometer stages  64 ,  66  are arranged upstream of the two translation stages  60 ,  62 . In their combination, the first goniometer stage  64  and the second goniometer stage  66  form a theta-phi goniometer that provides for two independent rotations about a common centre of rotation. This common centre of rotation is substantially constituted by the “hot spot”  36  shown in  FIG. 1 , i.e. by the X-ray emitting portion of the X-ray source  12 . 
   An actuation of the first goniometer stage  64  tilts the tube member  50  (with the X-ray lens) about a first tilting axis that runs through the “hot spot”  36  shown in  FIG. 1  and in the drawing plane of  FIG. 1  perpendicular to the optical axis  30 . An actuation of the second goniometer stage  66  tilts the tube member  50  about a second tilting axis that also runs through the “hot spot”  36  and that is perpendicular to both the first tilting axis and the drawing plane of  FIG. 1 . 
   The X-ray shielding component  40  (only schematically shown in  FIG. 1  and not completely shown in  FIG. 4 ) is attached to the upstream end of the second translation stage  66  via screws extending through openings  92  in the flange portion  46  ( FIG. 4 ). The shielding component  40  is configured to block all X-rays outside the circular X-ray passage defined by the upstream (inlet) opening  90  of the tubular member  50  and thus efficiently shields the positioning component  42  from X-rays. Accordingly, the individual components of the positioning component  42  (such as the translation stages  60 ,  62  and the goniometer stages  64 ,  66 ) can without any X-ray safety problem be manufactured from conventional materials (such as aluminium) which generally are transparent or nearly transparent to X-rays. 
     FIG. 5  shows a cross sectional view of the X-ray lens assembly including the tube member  50  and the capillary X-ray lens  28  mounted inside the tube member  50 . In addition to the inlet opening  90  for X-rays already explained with reference to  FIGS. 2 and 4 , the tube member  50  further includes an outlet opening  94  for X-rays. In the embodiment shown in  FIG. 5 , the tube member  50  has a length that is larger than the length of the X-ray lens  28 . In an alternative embodiment, the length of the tube member  50  could be chosen to be equal or smaller than the length of the X-ray lens  28 . 
   The X-ray lens assembly shown in  FIG. 5  includes two mounting structures  96 A,  96 B in the form elastic O-rings. The first mounting structure  26 A is arranged close to the outlet opening  94  of the tube member  50 , and the second mounting structure  96  is arranged close to the inlet opening  90 . The two mounting structures  96 A,  96 B limit a chamber  98  that is located between an inner surface of the tube member  50  and an outer surface of the X-ray lens  28 . The chamber  98  is filled with hardened glue reliably stabilizing the position of the X-ray lens  28  within the tube member  50 . The glue has been filed into the chamber  98  through openings  100  provided in a wall of the tube member  50  in a region between the two mounting structures  96 A,  96 B. 
   The X-ray lens assembly shown in  FIG. 5  can be manufactured as follows. First, the two mounting structures (i.e. the O-rings)  96 A,  96 B are put over the body of the X-ray lens  28  and pre-positioned. Thereafter, the X-ray lens  28  is introduced together with the mounting structures  96 A,  96 B into the tube member  50 . In a next step, the X-ray lens  28  is brought into the correct axial position with respect to the tube member  50 . In the embodiment shown in  FIG. 5 , the correct axial position is obtained by arranging an inlet opening  102  of the X-ray lens  28  in the same plane as the inlet opening  90  of the tube member  50 . This plane intersects the axes of the tube member  50  and the X-ray lens  28  at a right angle. 
   Once the X-ray lens has been brought into the correct axial position inside the tube member  50 , the mounting structures  96 A,  96 B are pushed uniformly into the tube member  50 . Due to the barrel-shape of the X-ray lens  28  (which is thicker in the centre than at its ends), the elastic mounting structures  96 A,  96 B get expanded when pushed (from opposite sides) into the tube member  50 . By means of this expansion, the X-ray lens  28  is clamped into the tube member  50 . Moreover, the mounting structures  96 A,  96 B provide a fluid-tight termination of the lateral ends of the chamber  98 . When pushing the mounting structures  96 A,  96 B into the tube member  50 , the X-ray lens  28  automatically gets centred. More specifically, the longitudinal axis of the X-ray lens  28  is aligned in relation to the longitudinal axis of the tube member  50 . 
   In a next step the axial position of the X-ray lens  28  in relation to the tube member  50  is checked again and, if required, corrected. In a last step a viscous glue is introduced into the chamber  98  through one or more of the openings  100  in the wall of the tube member  50 . By choosing a glue (such as a silicon glue) having a comparatively high viscosity, the number and dimensions of openings  100  can be reduced. Preferably, the number of openings  100  is reduced to four or less, and in may cases two openings  100  will be sufficient. 
   In the assembled state, the tube member  50  functions as a mechanical protection for the capillary X-ray lens  28  during transport and/or mounting in the mounting component  44  and/or adjustment by means of the positioning component  42 . The tube member  50  can accommodate X-ray lenses  28  of different dimensions, so that the mounting component  44  can be pre-adapted to the outer diameter of the tube member  50 . Additionally, the reference for the adjustment of the X-ray lens  28  can be chosen to be the plane defined by the inlet opening  90  or the outlet opening  94  of the tube member  50 . Accordingly, any necessary variations of the axial position of the X-ray lens  28  (e.g. due to different inlet focus distances of the X-ray lens  28 ) can be covered by choosing an appropriate axial position of the X-ray lens  28  within the tube member  50 . Accordingly, there will be no need for additional customized flanges or adapters to adjust different types of X-ray lenses  28 . Any remaining tolerance of the axial position of the X-ray  28  inside the tubular member  50  (of typically ±2.5 mm or less) can be compensated by the positioning unit  42  shown in  FIGS. 1 to 4 . 
   While the current invention has been described with respect to a particular embodiment, those skilled in the art will recognize that the current invention is not limited to the specific embodiment described and illustrated herein. Therefore, it is to be understood that the present disclosure is only illustrative. It is intended that the invention be limited only by scope of the claims appended hereto.