POLYMER LAYER ON X-RAY WINDOW

X-ray windows are designed to allow penetration of x-rays, even low energy x-rays. Desirable characteristics of x-ray windows include (1) minimal x-ray attenuation, (2) gas impenetrability, in order to maintain a vacuum on one side and perhaps ambient air on the other side, (3) corrosion resistance, (4) the ability to withstand high temperatures, and (5) high strength to withstand a pressure differential of at least one atmosphere.

Chemical vapor deposited poly(p-xylylene) polymers, known as parylene, has been used on top of a thin film of a beryllium x-ray window for corrosion protection. It would be beneficial to have an x-ray window that has improved corrosion resistance and improved ability to withstand higher temperatures than x-ray windows with a parylene coating on top of beryllium.

Boron hydride, known by Moxtek's trademark DuraCoat®, has been used on top of a thin film of a beryllium x-ray window for corrosion protection. It would be beneficial to have an x-ray window that has improved gas impenetrability and improved corrosion resistance than x-ray windows with a boron hydride coating on top of beryllium.

It has been recognized that it would be advantageous to provide an x-ray window x-ray that has improved gas impenetrability, improved corrosion resistance, and improved ability to withstand higher temperatures. The present invention is directed to an x-ray window comprising a plurality of layers stacked together, including a thin film layer and a polymer layer. The thin film layer can be diamond, graphene, diamond-like carbon, beryllium, and combinations thereof. The polymer layer can be a polyimide. A boron hydride layer may also be one of the plurality of layers. A polymer layer and a boron hydride layer can provide improved gas impenetrability and improved corrosion resistance to the thin film layer. Depending on the polymer selected, the x-ray window may be subjected to higher temperatures without breakdown.

• As used in this description and in the appended claims, the word “film” or “layer” means a continuous layer and does not mean a divided structural support such as a plurality of ribs.
• As used in this description and in the appended claims, the word “boron hydride layer” means a layer comprising boron hydride but may also include other materials.
• As used in this description and in the appended claims, the word “polymer layer” means a layer comprising a polymer but may also include other materials.
• As used in this description and in the appended claims, the word “polyimide layer” means a layer comprising polyimide but may also include other materials.
• As used in this description and in the appended claims, the word “beryllium layer” means a layer comprising beryllium but may also include other materials.

Reference will now be made to the exemplary embodiments illustrated in the drawings, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Alterations and further modifications of the inventive features illustrated herein, and additional applications of the principles of the inventions as illustrated herein, which would occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the invention.

As illustrated in FIG. 1, an x-ray window 10 is shown comprising a plurality of layers 11-13 stacked together, including a thin film layer, a boron hydride layer, and a polymer layer. The thin film layer can comprise a material selected from the group consisting of diamond, graphene, diamond-like carbon, beryllium, and combinations thereof. The x-ray window 10 or layers 11-13 can be substantially transmissive to x-rays having an energy in the range of 100-20,000 electronvolts. Thus, the layers may be sufficiently thin and the layers may be of a material that is substantially transmissive to x-rays. The layers may be disposed in any order such that boron hydride, the thin film layer, or the polymer layer may be disposed between the other two layers. In one aspect, the boron hydride layer can be between the thin film layer and the polymer layer. In another aspect, the thin film layer can be between the boron hydride layer and the polymer layer. In another aspect, the polymer layer can be between the thin film layer and the boron hydride layer.

Beryllium, diamond, graphene, and diamond-like carbon may be selected for x-ray window films due to low atomic numbers of these materials and due to their strength. Boron hydride may be selected for its corrosion resistance properties and its resistance to high temperatures. The use of boron hydride on x-ray windows is described in U.S. Pat. No. 5,226,067, which is incorporated herein by reference. A polymer layer may be added to an x-ray window comprising boron hydride on a thin film in order to improve the corrosion resistance and gas impenetrability of the window.

In one embodiment, the x-ray window or layers may be capable of withstanding a differential pressure of at least 1 atmosphere and capable of withstanding temperatures of greater than 350° C. Use of high temperature polymers, such as a polyimide for the polymer layer, can allow the x-ray window or layers to withstand high temperatures. Use of sufficiently thick layers of materials can allow the window or layers to withstand a differential pressure of at least 1 atmosphere.

In one embodiment, the thin film layer has a thickness of about 5 to 500 micrometers, the boron hydride layer has a thickness of about 20 to 2000 nanometers, and the polymer layer has a thickness of about 50 to 1200 nanometers. In another embodiment, the thin film layer has a thickness of about 5 to 12 micrometers, the boron hydride layer has a thickness of about 800 to 1600 nanometers, and the polymer layer has a thickness of about 20 to 300 nanometers. In another embodiment, the thin film layer has a thickness of about 50 to 1200 nanometers, the boron hydride layer has a thickness of about 20 to 2000 nanometers, and the polymer layer has a thickness of about 50 to 1200 nanometers. Thicknesses of the layers may be selected according to desired window strength, level of corrosion resistance desired, level of gas impenetrability desired, ease of manufacturing, and for minimal x-ray attenuation. The above thickness combinations are believed to provide the desired performance.

As shown in FIG. 2, an x-ray window 20 may be sealed to a mount 24. The mount can be a cylinder with a bore therethrough and an internal annular flange or lip to support the window or layers. A thin film layer 22 can be hermetically sealed to the mount 24, such as the annular flange or lip, at a perimeter of the thin film layer 22 defining a sealed joint 25. The thin film layer 22 may be sealed to the mount by an adhesive, brazing, diffusion bonding, or soldering. A boron hydride layer and a polymer layer, shown together as layer 21 in FIG. 2, can extend beyond the perimeter of the thin film layer 22, and over the sealed joint and onto the mount, thus providing corrosion protection to the sealed joint 25. The boron hydride layer may be disposed between the thin film layer 22 and the polymer layer, or the polymer layer may be disposed between the thin film layer 22 and the boron hydride layer. The boron hydride layer and polymer layer, shown together as layer 21 in FIG. 2, may be called a first boron hydride layer and a first polymer layer.

Also shown in FIG. 2, a second boron hydride layer 23 can be disposed on an opposite side of the thin film layer 22 from the first boron hydride layer and first polymer layer 21. The second boron hydride layer 23 can extend beyond the perimeter of the thin film layer 22 and onto the mount or annular flange or lip to cover the sealed joint 25, and the second boron hydride layer can provide corrosion protection to the sealed joint.

The second boron hydride layer 23 may further comprise a second polymer layer. The second polymer layer can be disposed on an opposite side of the thin film layer 22 from the first polymer layer. The second polymer layer can extend beyond the perimeter of the thin film layer to cover the sealed joint 25. The second polymer layer can provide corrosion protection to the sealed joint. The second boron hydride layer may be disposed between the thin film layer 22 and the second polymer layer, or the second polymer layer may be disposed between the thin film layer 22 and the second boron hydride layer.

As shown in FIG. 3, various embodiments, shown generally at 30, of the x-ray window 31 described herein may be mounted on an x-ray tube 32, thus forming a hermetically tight enclosure. The x-ray tube can be a cylinder closed at both ends to form a vacuum, and with a cathode element and cathode 33 at one end, and with an anode 34 and the window 31 at the opposite end.

As shown in FIG. 4, various embodiments, shown generally at 40, of the x-ray window 31 described herein may be attached to a mount 24 and an x-ray detector 42. The x-ray window (or layers) can allow x-rays, represented by 41, to impinge upon the detector 42.

As shown in FIG. 5, an x-ray window 50 can comprise a beryllium layer 52 and a polyimide layer 51 disposed over the beryllium layer. The beryllium layer can be hermetically sealed to a mount 24 or the annular flange or lip at a perimeter of the beryllium layer defining a sealed joint 25. The polyimide layer 51 can extend beyond the perimeter of the beryllium layer 52 and onto the mount, and the polyimide layer 51 can provide corrosion protection to the sealed joint 25. The beryllium and polyimide layers can be substantially transmissive to x-rays having an energy in the range of 100-20,000 electronvolts, and can be capable of withstanding a differential pressure of at least 1 atmosphere and capable of withstanding temperatures of greater than 350° C. A second layer 53 can be disposed on an opposing side of the beryllium layer 52 from the polyimide layer 51. The second layer may be a polymer layer, a polyimide layer, a boron hydride layer or combinations thereof. The second layer 53 can extend beyond the perimeter of the beryllium layer 52 and onto the mount, and can provide corrosion protection to the sealed joint 25.

In one embodiment, the beryllium layer 52 has a thickness of about 5 to 500 micrometers and the polyimide layer 51 has a thickness of about 50 to 1200 nanometers. In another embodiment, the beryllium layer 52 has a thickness of about 5 to 12 micrometers and the polyimide 51 layer has a thickness of about 20 to 300 nanometers. In another embodiment, the beryllium layer 52 has a thickness of about 50 to 1200 nanometers and the polyimide layer has a thickness of about 50 to 1200 nanometers.

Layers may be made by chemical vapor deposition, spin-on, or spray on.

It is to be understood that the above-referenced arrangements are only illustrative of the application for the principles of the present invention. Numerous modifications and alternative arrangements can be devised without departing from the spirit and scope of the present invention. While the present invention has been shown in the drawings and fully described above with particularity and detail in connection with what is presently deemed to be the most practical and preferred embodiment(s) of the invention, it will be apparent to those of ordinary skill in the art that numerous modifications can be made without departing from the principles and concepts of the invention as set forth herein.