Abstract:
The invention includes an XRF analyzer with reduced x-ray attenuation between sample and target and between sample and detector. Attenuation can be reduced by removing atmospheric-air paths through which the x-rays must travel. Reduced x-ray attenuation can allow for easier detection of low-atomic-number elements. Cost saving can be achieved by reducing the number of x-ray windows.

Description:
CLAIM OF PRIORITY 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 62/183,082, filed on Jun. 22, 2015, which is hereby incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present application is related generally to x-ray fluorescence (XRF) analyzers. 
       BACKGROUND 
       [0003]    X-ray fluorescence (XRF) analyzers can include an x-ray source and an x-ray detector. The source can include an electron emitter that is sealed inside of an x-ray tube. The x-ray detector can be sealed inside of an evacuated housing. 
         [0004]    The electron emitter can emit electrons towards a target that is also within the x-ray tube. The target can then emit x-rays out through a window in the x-ray tube towards a sample. The sample can absorb the x-rays from the source, then fluoresce elemental-specific, characteristic x-rays. The characteristic x-rays can pass through a window in the housing and impinge on the x-ray detector. The x-ray detector can then analyze sample chemistry. 
         [0005]    It can be difficult to detect low-atomic-number elements (e.g. Z≦20 and especially Z≦17) because of x-ray attenuation by air. This air attenuation occurs between the sample and the window of the x-ray detector and within the detector housing if internal components emitted gasses (out-gassed) after the device has been evacuated and sealed. 
         [0006]    Out-gassing can also cause reduced detector cooling (cooling is needed for improved sample analysis resolution). Out-gassing within the x-ray tube can result in gas ion formation due to the electron beam. These gas ions can cause electron spot instability and/or deterioration and early failure of the x-ray tube. 
         [0007]    XRF analyzers can be costly due to the high cost of manufacturing two, separate, hermetically-sealed devices—the x-ray tube and the x-ray detector. 
       SUMMARY 
       [0008]    It has been recognized that it would be advantageous to improve detection of low-atomic-number elements, reduce detrimental effects of out-gassing, and reduce manufacturing cost. The present invention is directed to various embodiments of XRF analyzers that satisfy these needs. Each embodiment may satisfy one, some, or all of these needs. 
         [0009]    The XRF analyzer can comprise a source and a detector located within an enclosure. The source can include an electron emitter and a target. The electron emitter can emit electrons towards the target and the target can emit x-rays in response to impinging electrons. 
         [0010]    In one embodiment, the XRF analyzer can also include an interior of the enclosure that is capable of having a single vacuum therein and a window, for transmission of x-rays, hermetically sealed to the enclosure. The source and the detector can be located within the interior of the enclosure. The target can emit the x-rays towards the window and the detector can face the window and receive and detect x-rays emitted through the window. 
         [0011]    In another embodiment, the XRF analyzer can also include a first solid-material-free straight-line path from the detector to the window and a second solid-material-free straight-line path from the target to the window. 
         [0012]    In another embodiment, the XRF analyzer can also include a removable or openable cover across an aperture in the enclosure. The detector can face the aperture and can receive and detect x-rays emitted from or through the aperture. A first hermetically-sealed-window-free straight-line path can extend from the detector to the aperture. A second hermetically-sealed-window-free straight-line path can extend from the target to the aperture. The cover can be closeable to protect the source and detector when the XRF analyzer is not in use. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic cross-sectional side view of an XRF analyzer  10 , showing solid-material-free straight-line paths  18  &amp;  19  from the detector  13  and the target  16  to the window  12 , respectively, in accordance with an embodiment of the present invention. 
           [0014]      FIG. 2  is a schematic cross-sectional side view of a portion of an XRF analyzer  20 , showing an expanded view of the window  12 , in accordance with an embodiment of the present invention. 
           [0015]      FIG. 3  is a schematic cross-sectional side view of an XRF analyzer  30 , showing a removable target  16  and removable filters  36 , in accordance with an embodiment of the present invention. 
           [0016]      FIG. 4  is a side view of the XRF analyzer  30  of  FIG. 3 , showing openings  16   o  and  13   o  in a wall of the enclosure  11  for replacement of target  16  and filter  36 , plus doors  16   d  and  13   d  for hermetically sealing the enclosure  11 , in accordance with an embodiment of the present invention. 
           [0017]      FIG. 5  is a schematic cross-sectional side view of an XRF analyzer  50 , with a removable or openable cover  52  across an aperture  54  in the enclosure  11 , in accordance with an embodiment of the present invention. 
       
    
    
     DEFINITIONS 
       [0018]    As used herein, the term “detector” means an electronic component for detecting x-rays. Examples of detectors include lithium drifted silicon detector (Si(Li)), silicon drift detector (SDD), and PIN diode. There is no window in front of or attached to the detector except as specified herein. 
         [0019]    As used herein, the term “vacuum” means a substantial vacuum, such as is typically found within functional x-ray tubes. 
         [0020]    As used herein, the term “single vacuum” in reference to an interior of the enclosure means that there is no hermetically-sealed barrier separating the interior into separate, hermetically-sealed sections. Thus, a single vacuum pump attached to a single port on the enclosure could draw a vacuum throughout the interior of the enclosure. 
       DETAILED DESCRIPTION 
       [0021]    As illustrated in  FIGS. 1-5 , XRF analyzers  10 ,  20 ,  30 , and  50  are shown comprising a source  14  and a detector  13  located within an enclosure  11 . The XRF analyzers  10 ,  20 ,  30 , and  50  can be bench-top XRF analyzers. The source can be attached to the enclosure  11 . The source  14  can include an electron emitter  15  and a target  16 . The electron emitter  15  can emit electrons  33  towards the target  16  and the target  16  can emit x-rays  34  in response to impinging electrons  33 . The x-rays  34  can hit and be absorbed by a sample  39 . The sample  39  can absorb the x-rays  34  from the source  14 , then fluoresce elemental-specific, characteristic x-rays  38 , The characteristic x-rays  38  can impinge on the detector  13 . 
         [0022]    An analyzer  41  can be electrically-coupled to the detector  13 . The detector  13 , based on the x-rays  38 , can send a signal to the analyzer  41 . The signal can be sent through wires  21 , which can be electrically insulated, or the wires can pass through an electrically-insulative plug in a side of the enclosure  11 . The analyzer can receive the signal from the detector  13 , and can analyze the signal to determine a material composition of the sample. The analyzer  41  can be located outside of the enclosure  11 , as shown, or can be located inside. 
         [0023]    The source  14  and the detector  13  can be angled towards where the sample  39  would be located, for more efficient emission and reception of x-rays  34  and  38 . There can be a support  22  in or near the center of the enclosure  11  to support the source  14  and the detector  13  and to incline them to face towards the sample  39 . The support  22  can be triangle-shaped as shown in the figures. The source  14  and or the detector  13  can attach to and be supported by the support  22  on one side and attach to and be supported by the enclosure  11  on an opposite side. 
         [0024]    The electron emitter  15  can attach to the enclosure  11  and support  22  by an electrically-insulative material  24  (e.g. ceramic). Wires of the electron emitter  15  can extend through the enclosure through an electrically-insulative plug  27  in a wall of the enclosure  11  or electrical insulation can be wrapped around each wire. Wires of the electron emitter  15  can be attached to a power supply that can provide appropriate electrical power for the electron emitter  15 . 
         [0025]    A barrier  26  can be located between the detector  13  and the source  14  and can be positioned to block x-rays  34 , emitted from the source  14 , from hitting the detector  13 . The barrier  26  can attach to and extend from the support  22 . The barrier  26  can be metallic. The barrier  26  can comprise tungsten. The barrier can include a high percent of tungsten, such as for example at least 80% tungsten in one aspect, at least 90% tungsten in another aspect, or at least 97% tungsten in another aspect. Tungsten can be a useful barrier  22  material because tungsten has a high atomic number and thus is effective at blocking x-rays and because tungsten is less likely to evaporate and deposit on other XRF analyzer components than some other metals. 
         [0026]    The XRF analyzer  10  can be hermetically sealed by a window  12  and can include an interior  31  of the enclosure  11  that is capable of having a single vacuum therein. The source  14  and the detector  13  can be located within the interior  31 . The source  14  and the detector  13  can both be windowless, such that there is no individual window for each. The window  12  in the XRF analyzer  10  can be a single window  12 . In other words, the window  12  can be the only x-ray window used on the XRF analyzer  10 . XRF analyzer  10  can have reduced manufacturing cost because only one hermetically-sealed window  12  is needed (instead of at least two—one on a housing of the detector and one on the x-ray tube). 
         [0027]    The electrically-insulative structure  23  and the electrically-insulative material  24  can both have holes or openings along their edges to allow air flow when evacuating or pumping down the interior  31 . Thus, there can be an air-flow path, within the interior  31 , from the detector  13  to the electron emitter  15 , allowing both the detector  13  to the electron emitter  15  to be located in a single vacuum which can be created by a single device. 
         [0028]    The XRF analyzer  10  (or other XRF analyzers described herein) can also include a vacuum pump  28  attached to a pump-port  35  in the enclosure  11 . The vacuum pump  28  can draw a vacuum within the interior  31  of the enclosure  11 . The vacuum pump  28  can operate continuously during XRF analysis. The XRF analyzer  10  can be continually pumped down during use, thus reducing gas molecules with in the interior  31 . Thus, there can be reduced gas ions in the interior  31  that can degrade components or cause electron spot movement. There can be fewer gas molecules to attenuate x-rays  34  and  36 . A lower vacuum in the interior  31  can also improve detector cooling, and thus improve sample  39  analysis resolution. 
         [0029]    Alternatively, the vacuum pump can draw a vacuum throughout the interior  31 , then the pump port  35  can be pinched shut. An electrically fired getter  29  can help maintain the vacuum by continual adsorption of gas molecules. A decision of whether to continuously pump or whether to seal off the XRF analyzer  10  can be based on factors such as cost and the benefit of improved vacuum. 
         [0030]    The sample  39  can be placed outside of the enclosure  11  and adjacent to the window  12 . Thus, x-rays  34  from the target  16  need not pass through air between the x-ray tube  14  and sample as is typical of other XRF analyzers. 
         [0031]    Consequently, lower source  14  power is needed due to decreased x-ray  34  attenuation. Also, characteristic x-rays  38  from the sample need only pass through a single window  12 , then through a vacuum to the detector  13 . Thus, there can be less attenuation of the characteristic x-rays  38  and lower atomic number elements can be more readily detected. 
         [0032]    For reduced x-ray  34  &amp;  38  attenuation, there can be an absence of solid material between the detector  13  and the window  12  and between the target  16  and the window  12 . In other words, the XRF analyzer  10  can include a first solid-material-free straight-line path  18  from the detector  13  to the window  12  and a second solid-material-free straight-line path  19  from the target  16  to the window  12 . XRF analyzer  10  can also include a cup  25  for holding the sample  39 . The cup  25  can be especially useful for liquid and powder samples  39 . An annular ring  5  can be sealed to an exterior of the XRF analyzer  10  with the window  12  located at a base of the annular ring  5 , thus forming the cup  25 . Other XRF analyzers described herein can also include the cup  25 . 
         [0033]    The cup  25  can be configured to hold a chemical sample  39  for analysis. For example, annular ring  5  and window  12  materials can be suitable (e.g. chemically resistant) for the type of chemical. Also, the cup  25  can be sealed to prevent leakage out of the cup  25 . 
         [0034]    As an example of a corrosion resistant window  12 , the window can include a stack of thin film layers. As shown in  FIG. 2 , the thin film layers can include an outer-layer  12   o , located farthest from the interior  31 , an inner-layer  12   i , located closest or adjacent to the interior  31 , and a middle-layer  12   m , located between the outer-layer  12   o  and the inner-layer  12   i . 
         [0035]    In one aspect, the outer-layer  12   o  can be a corrosion-barrier layer and can be made of or can include amorphous carbon and/or hexamethyldisilazane. The corrosion-barrier layer can be resistant to chemical corrosion from the sample  39 . The middle-layer  12   m  and/or the inner-layer  12 , can be an aluminum layer (i.e. made mostly of aluminum). The aluminum layer can provide improved gas impermeability to the window  12 . 
         [0036]    The middle-layer  12   m  and/or the inner-layer  12   i  can be a polymer layer (i.e. made mostly of a polymer). If the polymer layer includes mostly polyimide, then it is called a polyimide layer. The polymer layer can provide structural strength to the window  12 . The above described stack of thin film layers is described in more detail in US patent publication number 2014/0140487 and is incorporated herein by reference in its entirety. 
         [0037]    It can be important for the window  12  to be sufficiently strong to avoid breakage or excess deflection, to have a high transmissivity of x-rays  34  and  38 , to block visible light transmission and/or to block infrared light transmission. For example, the window  12  can have a deflection distance of less than 400 micrometers, a transmissivity of greater than 50% for x-rays  34  and  38  having an energy of 1.74 keV, a transmissivity of less than 10% for visible light at a wavelength of 550 nanometers, and/or a transmissivity of less than 10% for infrared light at a wavelength of 800 nanometers. These window characteristics are described in more detail in U.S. patent application Ser. No. 14/597,955, filed on Jan. 15, 2015, which is incorporated herein by reference in its entirety. Each XRF analysis can have its own optimal, input x-ray  34  energy spectrum. Thus, it can be important to have the ability to select among different targets  16  for each different XRF analysis. As shown in  FIGS. 3 and 4 , the target can slide between and be supported by, but not attached to, support members  17 . There can be a target-opening  16   o  in the enclosure  11  that is adjacent or close to the target  16 . The target-opening  16   o  can be sized and located to allow removal and insertion of the target  16 , thus allowing the user to select a target  16  that is better suited for each XRF analysis. A target-door  16   d  can be be openable (i.e. capable of being opened, such as a hinged door for example) or removable for insertion or removal of the target  16  through the target-opening  16   o . The target-door  16   d  can allow sealing the XRF analyzer. Thus, the target-door  16   d  can have a size and material to allow a hermetic seal of the target-door  16   d  to the enclosure  11  at the target-opening  16   o . 
         [0038]    It can be difficult in an XRF analysis to determine elements in low concentrations. It can also be difficult to distinguish between elements that emit similar energy spectra. Filtration of x-rays  34  emitted from the source  14  or x-rays  38  from the sample  39  can improve analysis in these situations. Filtration of x-rays can provide a narrow energy band specific to a target element, allowing easier detection of that element. A user of an XRF analyzer typically would use the analyzer for detection of multiple, different elements. Thus, the user may desire different filters for different applications. 
         [0039]    As shown in  FIGS. 3 and 4 , the XRF analyzer  30  can include removable filters  36  that are placed between the target  16  and the window  12  and/or between the detector  13  and the window  12 . The filters  36  can slide between and be supported by, but not attached to, support members  17 , to allow easy removal and insertion. 
         [0040]    A source-filter-opening  36   o  in the enclosure  11  can be sized and located to allow removal and insertion of a filter  36  between the target  16  and the window  12 . A source-filter-door  36   d  can have a size and material for a hermetic seal to the enclosure  11  at the source-filter-opening  36   o . The source-filter-door  36   d  can be openable or removable for insertion or removal of the filter  36  through the source-filter-opening  36   o . The source-filter-opening  36   o  can be the same opening as, or separate from, the target-opening  16 . The source-filter-door  36   d  can be the same door as, or separate from, the target-door  16   d . 
         [0041]    A detector-filter-opening  13   o  in the enclosure  11  can be sized and located to allow removal and insertion of a filter  36  between the detector  13  and the window  12 . A detector-filter-door  13   d  can have a size and material for a hermetic seal to the enclosure  11  at the detector-filter-opening  13   o . The detector-filter-door  13   d  can be openable or removable for insertion or removal of the filter  36  through the detector-filter-opening  13   o . The detector-filter-opening  13   o  can be the same as, or separate from, the source-filter-opening  16 , and/or the target-opening  16   o . Thus, there can be one opening for all target and filter insertion and removal or there cal be multiple. The detector-filter-door  13   d  can be the same as, or separate from, source-filter-door  16   d  and/or the target-door  16   d . 
         [0042]    The removable filters  36  and/or removable target  16  shown in  FIGS. 3-4  can be used in other XRF analyzer designs  10 ,  20 , and  50  described herein. 
         [0043]    As shown in  FIG. 5 , the XRF analyzer  50  can include a removable or openable cover  53  across an aperture  54  in the enclosure  11 . The XRF analyzer  50  can, with its cover  53  open or removed, be placed in a container and can face a sample  39 . The container can then be evacuated for the XRF analysis. 
         [0044]    The target can face the aperture  54 , typically at an angle A. The target can emit x-rays  34  towards the aperture  54 . These x-rays  34  can hit a sample  38 . The detector  13  can face the aperture  54 , typically at an angle. The detector  13  can receive and detect x-rays  38  emitted from the sample  39 . XRF analyzer  50  can be a windowless device, with no x-ray windows. 
         [0045]    A first hermetically-sealed-window-free straight-line path  58  can extend from the detector  13  to the aperture  58 . A second hermetically-sealed-window-free straight-line path  59  can extend from the target  16  to the aperture  54 . The cover  53  can be closeable to protect the source  14  and detector  13  when the XRF analyzer  50  is not in use. The hermetically-sealed-window-free straight-line paths  58  and  59  can be solid-material-free straight-line paths (like paths  18  &amp;  19  in  FIG. 1 ) or can include filters  36 , as shown in  FIG. 3 . XRF analyzer  50  can include removable filters  36  and/or removable target  16  as described above in reference to XRF analyzer  30 . 
         [0046]    In comparison of XRF analyzer  50  with XRF analyzer  10 , XRF analyzer  50  can be advantageous because the XRF analysis can be performed with no window  12  attenuation of x-rays  34  and  38 . A disadvantage of XRF analyzer  50  can be a need for an additional container for holding a vacuum during analysis. XRF analyzer  10  might also be more convenient for analysis of liquids. 
         [0047]    As shown in  FIGS. 1 and 5 , acute angle A of target  16  orientation with respect to the window  12  or the aperture  54  can be important for irradiation of the sample  39  and overall size of the XRF analyzer. This orientation is described as follows. A plane aligned with a face of the window  12  defines a window-plane  32  (or aligned with a face of the aperture  54  defines an aperture-plane  52 ). A plane aligned with a face of the target  16  defines a target-plane  37 . An angle A of intersection between the window-plane  32  and the target-plane  37  can be less than 45 degrees in one aspect, less than 30 degrees in another aspect, or less than 20 degrees in another aspect. An angle A of intersection between the aperture-plane  52  and the target-plane  37  can be less than 45 degrees in one aspect, less than 30 degrees in another aspect, or less than 20 degrees in another aspect. Smaller angles allow for smaller overall XRF analyzer size. Cost and separation of voltages are additional factors that may impact selection of angle A for a particular design. 
         [0048]    The target  16  can be physically separated from the window  12  (or aperture  54 ). There can be a solid-material-free gap  9  between the target  16  and the window  12  (or aperture  54 ). The electron emitter  15 , the target  16 , and the window  12  (or aperture  54 ) can be located along a single, straight-line path, with the target  16  between the electron emitter  15  and the window  12  along this straight-line path.