The present application is related generally to x-ray sources.
X-rays can be used in imaging, backscatter imaging, x-ray fluorescence analysis, and electrostatic dissipation. A large voltage between a cathode and an anode of the x-ray tube, and sometimes a heated filament, can cause electrons to emit from the cathode to the anode. The anode can include a target material. The target material can generate x-rays in response to impinging electrons from the cathode.
Definitions. The following definitions, including plurals of the same, apply throughout this patent application.
As used herein, the term “adjoin” means direct and immediate contact. As used herein, the term “adjacent” includes adjoin, but also includes near or next to with other solid material(s) between the adjacent items.
As used herein, the term “amorphous mixture” means a mixture that is completely amorphous or almost completely amorphous, such as for example a mixture resulting from simultaneous sputter deposition of multiple elements.
As used herein, the term “dispersed uniformly” means dispersed exactly uniformly, dispersed uniformly within normal manufacturing tolerances, or dispersed almost exactly uniformly, such that any deviation from dispersed exactly uniformly would have negligible effect for ordinary use of the device.
As used herein, the term “homogeneous” means exactly homogeneous, homogeneous within normal manufacturing tolerances, or almost exactly homogeneous, such that any deviation from exactly homogeneous would have negligible effect for ordinary use of the device.
As used herein, the term “Kα” means the K-alpha x-ray characteristic line resulting from an electron transition to the innermost “K” shell from a 2p orbital of the second or “L” shell. “Kα” includes both “Kα1” and “Kα2”. “Kα1” is higher in energy than “Kα2”.
As used herein, a mixture of two different chemical elements “mechanically bonded” to each other means that the mixture is primarily held together by mechanical bonding rather than primarily by metallic bonding. For example, simultaneous sputter deposition of multiple elements can form a layer of material with the different elements mechanically bonded to each other.
As used herein, the term “no sputter deposition” of a particular chemical element includes negligible sputter deposition of that chemical element.
As used herein, the term “parallel” means exactly parallel, or substantially parallel, such that planes or vectors associated with the devices in parallel would intersect with an angle of ≤30°. Intersection of such planes or vectors can be ≤5°, ≤10°, or ≤20° if explicitly so stated.
As used herein, the term “x-ray tube” is not limited to tubular/cylindrical shaped devices. The term “tube” is used because this is the standard term used for x-ray emitting devices.
Unless explicitly noted otherwise herein, all temperature-dependent values are such values at 25° C.
X-rays are used in backscatter imaging, in which hidden items can be identified by x-rays. For example, a gun or drugs behind a wall, or in a tire of an automobile, can be identified by emitting x-rays towards the wall, then imaging backscattered x-rays. High x-ray flux is useful for rapid analysis. A portable x-ray source is useful for taking the x-ray source to the sample. It would be beneficial to increase x-ray flux, with minimal or no increase in the size of the x-ray source, to maintain portability.
An x-ray tube can provide x-rays for backscatter imaging by impinging a target material with electrons. Each target material provides a unique range of x-ray energy with characteristic peaks of certain energies. It is desirable to provide characteristic peak energies that match materials in the item analyzed. If the x-ray energy is too high, then the x-rays will pass through and not provide the desired backscatter image. If the x-ray energy is too low, then the x-rays won't penetrate deeply enough or won't provide the desired backscatter image. Therefore, it would be helpful to provide an x-ray target that emits high and low energy x-rays.
X-rays are used in x-ray fluorescence analysis. A target material in the x-ray tube is selected with a peak near x-ray fluorescence energy of the sample to be analyzed. Sometimes there is a desire to analyze different materials, with a large range of x-ray fluorescence energies. Therefore, it would be helpful for the x-ray source to provide a large range of x-ray energies, from multiple, different chemical elements.
The x-ray tubes herein include a target 14 with materials that will emit x-rays 57 (see
As illustrated in
In all of these embodiments (
Multi-element targets 14, with multiple primary-layers PL, are illustrated in
The primary-layers PL can include a high-layer HL and a low-layer LL, as illustrated in
For simplicity of design and manufacture of the target 14, and efficiency of use of the x-ray tube, the high-layer HL can have a high percent of one element, called a high-element, the low-layer LL can have a high percent of one element, called a low-element, and the intermediate-layer IL can have a high percent of one element, called an intermediate-element.
For example, the weight percent of the high-element in the high-layer HL can be higher than any other element in the high-layer HL. The weight percent of the high-element in the high-layer HL can be ≥50%, ≥75%, ≥90%, or ≥98%. The weight percent of the low-element in the low-layer LL can be higher than any other element in the low-layer LL. The weight percent of the low-element in the low-layer LL can be ≥50%, ≥75%, ≥90%, or ≥98%. The weight percent of the intermediate-element in the intermediate-layer IL can be higher than any other element in the intermediate-layer IL. The weight percent of the intermediate-element in the intermediate-layer TL can be ≥50%, ≥75%, ≥90%, or ≥98%.
The high-element, the low-element, and the intermediate-element can all be different with respect to each other. If multiple chemical elements in a single layer have the same, highest weight percent, then the element, among these multiple chemical elements, with the highest atomic number is the high-element, the low-element, or the intermediate-element.
The primary-layers PL can be arranged according to material-characteristic(s), such as atomic number, density, x-ray fluorescent energy, absorption edge, or combinations thereof. The high-layer HL can have a highest value among the primary-layers PL of the selected material-characteristic(s). The low-layer LL can have a lowest value among the primary-layers PL of the selected material-characteristic(s). The intermediate-layer IL can have an intermediate value, between that of the high-layer HL and the low-layer LL, of the selected material-characteristic(s). If there is more than one intermediate-layer IL, then the multiple intermediate-layers IL can be ordered similarly, with increasing values of the selected material-characteristic(s) moving closer to the high-layer HL, and decreasing values of the selected material-characteristic(s) moving closer to the low-layer LL.
Following are example relative material-characteristics of the primary-layers PL: Z(H)>Z(L), Z(H)>Z(I), Z(I)>Z(L), Kα1(H)>Kα1(L), Kα1(H)>Kα1(I), Kα1(I)>Kα1(L), ρH>ρL, ρH>ρI, ρI>ρL. Z(H) is an atomic number of the high-element. Z(L) is an atomic number of the low-element. Z(I) is an atomic number of the intermediate-element. Kα1(H) is a higher energy K-alpha x-ray characteristic line of the high-element. Kα1(L) is a higher energy K-alpha x-ray characteristic line of the low-element. Kα1(I) is a higher energy K-alpha x-ray characteristic line of the intermediate-element. ρH is a density of the high-element. ρL is a density of the low-element. ρI is a density of the intermediate-element.
There can be a large enough difference between the atomic numbers and/or Kα1 of the primary-layers PL to provide a sufficiently broad range of characteristic peaks. For example, Z(H)−Z(L)≥5, Z(H)−Z(L)≥10, Z(H)−Z(L)≥20, Z(H)−Z(L)≥30, or Z(H)−Z(L)≥40; Z(H)−Z(L)≤50, Z(H)−Z(L)≤60, or Z(H)−Z(L)≤75; Kα1(H)−Kα1(L)≥5 keV, Kα1(H)−Kα1(L)≥15 keV, Kα1(H)−Kα1(L)≥25 keV, Kα1(H)−Kα1(L)≥50 keV, or Kα1(H)−Kα1(L)≥70 keV.
Listed in Table 1 are example elements, with properties, for the primary-layers PL. This table assumes five primary-layers PL, including three intermediate-layers IL1, IL2, and IL3, as illustrated in
For example, the target 14 can include the following primary-layers PL in the following order: the high-layer HL can be thorium with thickness ThHL=3.6 μm, the first-intermediate-layer IL1 can be rhenium with thickness ThIL=2.3 μm, the second-intermediate-layer IL2 can be gadolinium with thickness ThIL2=2.8 μm, the third-intermediate-layer IL3 can be molybdenum with thickness ThIL3=1.9 μm, and the low-layer LL can be copper with thickness ThLL=4.1 μm (see
As illustrated in
Adjoining primary-layers PL can develop thermal stress as the target 14 expands and contracts during temperature changes. Placement of the transition layer TL between the primary-layers PL can reduce this thermal stress.
An abrupt change from a chemical composition in one primary-layer PL to a different chemical composition in an adjoining primary-layer PL can result in a weak chemical bond between the primary-layers PL. Placement of the transition layer TL between the primary-layers PL can improve the chemical bond between the primary-layers PL.
Electrons and heat can build up at a junction between primary-layers PL, which can result in failure or reduced performance of the target 14. Placement of the transition layer TL between the primary-layers PL can improve electrical current and heat flow through the target 14.
As illustrated in
As illustrated in
The target 14 of
As illustrated in
As illustrated in
In
An example target 14 includes gold as the high-layer HL with thickness ThHL=5 μm, gadolinium as the intermediate-layer IL with thickness ThIL=4 μm, and silver as the low-layer LL with thickness ThLL=3 μm. A first-transition-layer TL1, with a thickness ThTL1=3 μm, is sandwiched between the high-layer HL and the intermediate-layer IL, with a smooth-transition ST of chemical composition from pure gold to pure gadolinium. A second-transition-layer TL2, with a thickness ThTL2=3 μm, is sandwiched between the intermediate-layer IL and the low-layer LL, with a smooth-transition ST of chemical composition from pure gadolinium to pure silver.
As illustrated in
The high-layer HL can be located at a high-side 14H of the target 14 and the low-layer LL can be located at a low-side 14H of the target 14. The high-side and the low-side 14H of the target 14 can be located for increased x-ray flux.
As illustrated in
As illustrated in
For x-ray tube 50 or 60, with the target 14 arranged as described above, high energy x-rays 57 generated in the high-layer HL can pass through the low-layer LL and any intermediate-layer(s) IL and out of the x-ray tube 50. Intermediate energy x-rays 57 generated in any intermediate-layer(s) IL can pass through the low-layer LL and out of the x-ray tube 50. Low energy x-rays 57 generated in the low-layer LL can pass out of the x-ray tube 50 without being attenuated by the high-layer HL or by the intermediate-layer(s) IL.
As illustrated in
The target 14 can be formed by sputter deposition to form a target of multiple layers of different materials and to facilitate formation of combinations of chemical elements. For example, some chemical combinations can be formed by sputter deposition that might not be possible to form by melting to create an alloy.
Sputter deposition can also result in a strong bond between adjacent layers, thus avoiding separation of layers that can result from welding foils of different materials together.
Sputter deposition can form a transition-layer TL between adjacent primary-layers PL, thus avoiding electron buildup at a boundary between the layers, and minimizing thermal stresses due to different coefficients of thermal expansion between the different primary-layers PL.
A method of making the target 14 can comprise some or all of the following steps, which can be performed in the following order or opposite order. Components of the target 14, and the target 14 itself, can have properties as described above. Any additional description of properties of the target 14 in the method below, not described above, are applicable to the above-described target 14.
As illustrated in
As illustrated in
As illustrated in
As illustrated in
As illustrated in
As illustrated in
As illustrated in
The target 14 in
The target 14 in
As illustrated in
As illustrated in
As illustrated in
In both
As illustrated in
The target 14 can include an amorphous mixture of two, three, or more different chemical elements. The target 14 can include a mixture of two, three, or more different chemical elements mechanically bonded to each other. The mixture (amorphous, mechanically bonded, or both) can be dispersed evenly throughout the target 14. There can be a substantial weight percent of each of the different chemical elements, such as for example ≥1%, ≥5%, ≥10%, or ≥25%, and a total weight percent of all chemical elements in the target material is 100%.
The target 14 can be made as described below in reference to
The amorphous mixture, the mechanical-bond, or both can extend throughout the entire target 14. The amorphous mixture, the mechanical-bond, or both can be uniform in material composition throughout the entire target 14. The multiple, different chemical elements can be dispersed uniformly throughout the target 14.
There can be a large enough difference between the atomic numbers, the Kα1, or both, of the two different chemical elements to provide a sufficiently broad range of characteristic peaks. For example, Z(1)−Z(2)≥5, Z(1)−Z(2)≥10, Z(1)−Z(2)≥20, Z(1)−Z(2)≥30, or Z(1)−Z(2)≥40; Z(1)−Z(2)≤50, Z(1)−Z(2)≤60, or Z(1)−Z(2)≤75; Kα1(1)−Kα1(2)≥5 keV, Kα1(1)−Kα1(2)≥15 keV, Kα1(1)−Kα1(2)≥25 keV, Kα1(1)−Kα1(2)≥50 keV, or Kα1(1)−Kα1(2)≥70 keV. Z(1) is an atomic number of an element of a highest atomic number in the mixture that has a weight percent of at least 10%. Z(2) is an atomic number of an element of lowest atomic number in the mixture that has a weight percent of at least 10%. Kα1(1) is a Kα1 value of an element of highest Kα1 value in the mixture that has a weight percent of at least 10%. Kα1(2) is a Kα1 value of an element of lowest Kα1 value in the mixture that has a weight percent of at least 10%. Table 1 above lists example elements for the mixture.
As illustrated in
Illustrated in
This application claims priority to U.S. Provisional Patent Application No. 63/080,336, filed on Sep. 18, 2020, which is incorporated herein by reference.
Number | Date | Country | |
---|---|---|---|
63080336 | Sep 2020 | US |