X-ray source

Abstract

In an embodiment an X-ray source includes an electron source configured to emit electrons, an acceleration set-up configured to accelerate the emitted electrons and a transmission window downwards of the acceleration set-up, wherein the transmission window is configured to let through X-rays generated by the accelerated electrons, wherein the transmission window is located either in a straight extension of a line-of-flight of the accelerated electrons or off the line-of-flight and past the acceleration set-up, wherein the transmission window comprises a carbon carrier, and wherein the carbon carrier comprises sp2-hybridized carbon.

Claims

1. An X-ray source comprising: an electron source configured to emit electrons; an acceleration set-up configured to accelerate the emitted electrons; and a transmission window downwards of the acceleration set-up, wherein the transmission window is configured to let through X-rays generated by the accelerated electrons, wherein the transmission window is located in a straight extension of a line-of-flight of the accelerated electrons and past the acceleration set-up, wherein the transmission window comprises a carbon carrier, wherein the carbon carrier comprises sp2-hybridized carbon, and wherein the carbon carrier is an electron target and is configured to generate the X-rays of a characteristic carbon X-ray line based on being hit by the accelerated electrons.

2. The X-ray source of claim 1, wherein a mass proportion of carbon of the carbon carrier is at least 95%, wherein the carbon of the carbon carrier is predominantly sp2-hybridized so that in a deconvoluted Raman spectrum of the carbon carrier a 2D-peak, in a range between 2650 cm.sup.1 and 2750 cm.sup.1 measured with laser excitation at 532 nm, has by at least a factor of two a larger area content than a sp3-peak in a range between 1250 cm.sup.1 and 1350 cm.sup.1.

3. The X-ray source of claim 2, wherein the carbon carrier is of pyrolytic carbon.

4. The X-ray source of claim 1, wherein the transmission window further comprises a target layer carried by the carbon carrier, wherein the target layer is located on a side of the carbon carrier facing the electron source, and wherein the target layer is of at least on metal and is thinner than the carbon carrier.

5. The X-ray source of claim 4, wherein the target layer is configured to be hit by the accelerated electrons and a carbon layer is configured to be passed by the X-rays generated upon impact of the accelerated electrons on the target layer.

6. The X-ray source of claim 4, wherein the target layer is directly applied on the carbon carrier.

7. The X-ray source of claim 4, wherein the transmission window further comprises a bonding layer, and wherein the bonding layer is located between the target layer and the carbon carrier and is of at least one inorganic material.

8. The X-ray source of claim 4, further comprising a window frame, wherein the window frame carries the transmission window and is attached on the acceleration set-up.

9. The X-ray source of claim 1, wherein a diameter of the carbon carrier is between 4 mm and 4 cm, inclusive, and wherein the X-ray source is free of any auxiliary structures supporting a central part of the transmission window, seen in top view, where a focal spot of the accelerated electrons is located.

10. An X-ray source comprising: an electron source configured to emit electrons; an acceleration set-up configured to accelerate the emitted electrons; and a transmission window downwards of the acceleration set-up, wherein the transmission window is configured to let through X-rays generated by the accelerated electrons, wherein the transmission window is located off a line-of-flight of the accelerated electrons and past the acceleration set-up, wherein the transmission window comprises a carbon carrier, wherein the carbon carrier comprises sp2-hybridized carbon, wherein the carbon carrier is of pyrolytic carbon, wherein a thickness of a carbon layer is at most 10 m, wherein a mass proportion of carbon of the transmission window in an area configured to be passed by the X-rays is at least 90%, and wherein the acceleration set-up is configured for an acceleration voltage of at most 1.5 kV.

11. The X-ray source of claim 10, further comprising an electronics unit configured to provide the acceleration voltage, wherein a low-voltage side and a high-voltage side of the electronics unit are connected by a one-stage voltage changer.

12. The X-ray source of claim 10, wherein the carbon layer is configured to be electrically on ground.

13. The X-ray source of claim 10, wherein the transmission window is a side window, and wherein the accelerated electrons are divertible from the transmission window.

14. An X-ray source comprising: an electron source configured to emit electrons; an acceleration set-up configured to accelerate the emitted electrons; and a transmission window downwards of the acceleration set-up, wherein the transmission window is configured to let through X-rays generated by the accelerated electrons, wherein the transmission window comprises a carbon carrier, wherein the carbon carrier comprises sp2-hybridized carbon, wherein the acceleration set-up is configured for an acceleration voltage of at most 5 kV, wherein the transmission window is located off a line-of-flight and past the acceleration set-up so that the transmission window is a side window, wherein the accelerated electrons are divertible from the transmission window, wherein the carbon carrier is of pyrolytic carbon, wherein a thickness of a carbon layer is at most 10 m, wherein a mass proportion of carbon of the transmission window in an area configured to be passed by the X-rays is at least 90%, and wherein a low-voltage side and a high-voltage side of an electronics unit are connected by a one-stage voltage changer, the electronics unit is configured to provide the acceleration voltage.

15. An X-ray source comprising: an electron source configured to emit electrons; an acceleration set-up configured to accelerate the emitted electrons; and a transmission window downwards of the acceleration set-up, wherein the transmission window is configured to let through X-rays generated by the accelerated electrons, wherein the transmission window is located off a line-of-flight of the accelerated electrons and past the acceleration set-up, wherein the transmission window comprises a carbon carrier, wherein the carbon carrier comprises sp2-hybridized carbon, wherein the transmission window is a side window, wherein the accelerated electrons are divertible from the transmission window, wherein a thickness of a carbon layer is at most 25 m, and wherein a mass proportion of carbon of the transmission window in an area configured to be passed by the X-rays is at least 90%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1 and 2 show schematic sectional views of exemplary embodiments of X-ray sources described herein;

(2) FIGS. 3 and 4 are schematic sectional views of exemplary embodiments of transmission windows for X-ray sources described herein;

(3) FIG. 5 shows is a schematic representation of the G-peak and the D-peak of exemplary embodiments of transmission windows for X-ray sources described herein;

(4) FIG. 6 is a schematic sectional view of an exemplary embodiment of an X-ray source described herein;

(5) FIG. 7 is a schematic block diagram of an electronics unit for providing an acceleration voltage for exemplary embodiments of X-ray sources described herein;

(6) FIG. 8 is a schematic representation of X-ray emission spectra of exemplary embodiments of X-ray sources described; and

(7) FIG. 9 herein is a schematic block diagram of an exemplary embodiment of an operation method for X-ray sources described herein.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(8) FIG. 1 illustrates an exemplary embodiment of an X-ray source 1. The X-ray source 1 comprises a housing 5 with a base plate 53 through which a pin 55 is led. The pin 55 carries an electron source 2, which is, for example, a filament that may be heated. The base plate 53 can be housed in a socket 54 of the housing 5. Optionally, at the socket 54 there is an outer tube 52 of the housing 5. It is possible that the socket 54 and the first electrode 31 are of one single piece.

(9) The electron source 2 is configured to emit electrons 22. Downstream of the electron source 2, there is a first electrode 31 of an acceleration set-up 3. The first electrode 31 may be in one piece with the socket 54. Further, downstream of the first electrode 31 there is a second electrode 32 of the acceleration set-up 3. The acceleration set-up 3 is configured to accelerate the emitted electrons 22 along a direction away from the electron source 2, for example. Thus, the electrons 22 run through the second electrode 32 so that the latter can be a transmission anode.

(10) A relative position between the electrodes 31, 32 is defined by an inner tube 51 of the housing 5. Thus, the inner tube 51 may hold the second electrode 32.

(11) For example, within the inner tube 51 into which the first electrode 31 and the pin 55 carrying the electron source 2 protrude, there is an evacuated area 56 maintaining a pressure in the sub-mbar range. The outer tube 52 may reach beyond the first electrode 31, starting from the socket 54, but may not reach up to the second electrode 31 that also protrudes into the inner tube 51 but from an opposite direction. The second electrode 32 may cover end faces of the inner tube 51 remote from the base plate 53.

(12) Optionally, within an end portion of the second electrode 32 remote from the first electrode 31 there can be a window frame 6. The window frame 6 is configured to fix a transmission window 4 at an end of the inner tube 51. The window frame 6 may be a single piece, for example, like a half of a cylinder. Within the window frame 6, the transmission window 4 is arranged.

(13) For example, the transmission window 4 is glued, sintered, brazed, soldered or welded onto the window frame 6. As an option, hard-soldering, brazing, soft-soldering eutectic soldering or glass soldering may be used as well as laser welding, electron beam welding, friction welding, ultrasonic welding, electric resistance welding or the like. It is possible that at an edge part the window frame 6 and/or the transmission window 4 carries a ring-like connection layer, not shown, for providing adhesion between these two components. Further, there can be a geometric structuring, not shown, at least one of the transmission window 4 and the window frame 6 for mounting the transmission window 4.

(14) By means of the acceleration set-up 3, the electrons 22 are accelerated and optionally also focused onto the transmission window 4. Not shown, for focusing the electrons 22 there can be electron optics, realized, for example, by the shape of the electrodes 31, 32, like the shape of the second electrode 32. Upon impact of the electrons 22 onto the transmission window 4, X-rays X are generated that are emitted by the X-ray source 1 through the transmission window 4. Thus, the X-ray source 1 may also be referred to as an X-ray tube. The generated X-rays X are, for example, characteristic carbon X-rays.

(15) The transmission window 4 is not based on beryllium, but is based as its mechanically supporting component on sp2-hybridized carbon as explained in more detail below in connection with FIGS. 3 and 4.

(16) For example for X-ray fluorescence spectroscopy, the X-ray source 1 is configured for an operating power between 0.1 W and 15 W. Additionally, in ion mobility spectroscopy, operating powers down to 1 mW can be used. For example, an electron focal spot of the electrons 22 at the transmission window 4 has a diameter between 0.05 mm and 4 mm inclusive in case of serving for XRF, or may have a diameter between 5 mm and 20 mm inclusive in case of serving for IMS.

(17) In FIG. 1, the X-ray source 1 is of linear design, that is, for example, the electrons 22 and the generated X-rays X are led along a common straight axis. Otherwise, it is also possible that the X-ray source 1 is of angled design so that the electrons 22 and/or the X-rays X may be led along a kinked axis having, for example, a 90 angle, compare also FIG. 6 below. Accordingly, not only transmission anodes but also solid anodes with an additional separate transmission side window can be used. The same applies for all other examples of the X-ray source 1.

(18) In the example of the X-ray source 1 of FIG. 2, the window frame 6 comprises an outer part 61 and an inner part 62. The transmission window 4 is placed between these two parts 61, 62 so that the edge part of the transmission window 4 is fixed in the window frame 6 and can adhesively be connected to both parts 61, 62. As in all other examples, it is possible that the transmission window 4 is of plane-parallel fashion.

(19) Otherwise, the same as to FIG. 1 may also apply to FIG. 2, and vice versa.

(20) In FIGS. 3 and 4, examples of transmission windows 4 are illustrated. In each case, the transmission windows 4 comprise a carbon carrier 41 which is based on sp2-hybridized carbon and which mechanically carries the transmission windows 4. For example, a thickness of the carbon carrier 41 is between 0.02 mm and 0.1 mm inclusive. For example, a diameter of the carbon carrier 41 is between 5 mm and 9 mm inclusive. Optionally, the carbon carrier 41 is of pyrolytic carbon.

(21) The carbon carrier 41 itself can be used as a target material so that the generated X-rays are characteristic carbon radiation upon impact of the accelerated electrons 22. In this case, the transmission window 4 may consist of the carbon carrier 41, or of the carbon carrier 41 and of at least one protection layer, not shown.

(22) Optionally, if the carbon carrier 41 is not used as the target material, the carbon carrier 41 can carry a distinct target layer 42. Then, the target layer 42 is configured to generate the X-rays upon impact of the electrons 22. For example, the target layer 42 is of one of the following metals: W, Rh, Ag, Au, Mo, Pd. For example, a thickness of the target layer 42 is between 0.05 m and 10 m inclusive. The target layer 42 may be thinner than the carbon carrier 41 and may not be self-supporting so that the carbon carrier 41 is needed to mechanically support the target layer 42.

(23) As shown in FIG. 3, the optional target layer 42 is directly applied onto the carbon carrier 41, for example, by sputtering or evaporating. Contrary to that, according to FIG. 4 there is a bonding layer 43 between the carbon carrier 41 and the target layer 42. The bonding layer 43 can be thinner than the target layer 42. For example, the bonding layer 43 is of an oxide, a nitride or of Si.

(24) All the components 41, 42, 43 can be of single-layer fashion. However, as indicated in FIG. 4 by the dashed lines, one or a plurality of the carbon carrier 41, the target layer 42 and the optional bonding layer 43 can be of multi-layer fashion so that there is a plurality of sub-layers in the respective component. These sub-layers may differ from one another in material composition and/or in material configuration, like orientation or crystal lattice, and also in geometric properties, like thickness, lateral extend and/or shape. The same applies for all other examples.

(25) Moreover, based on FIG. 3, a sandwich structure of the transmission window 4 is also possible. That is, for example, the target layer 42 can be located between two of the carbon carriers 41 which may be of the same or of different thicknesses, wherein bonding layers 43 can be present between the layers 41, 42, 41 analogously to FIG. 4.

(26) As a further option, not shown in FIGS. 3 and 4, there can be at least one protection layer on at least one main side of the transmission window 4. By means of the at least one protection layer, the transmission window 4 can be protected from physical or chemical harsh conditions. For example, there is one protection layer at a side of the transmission window 4 facing away from the electron source 2. It is possible that the at least one protection layer is of an oxide or of a nitride, like a silicon oxide or an aluminum nitride. Further, the at least one protection layer may be of multi-layer fashion, for example, may be a combination of an aluminum oxide sub-layer and of a silicon dioxide layerFor example, an overall thickness of the at least one protection layer is at most 50 nm or is at most 10 nm or is at most 4 nm.

(27) Otherwise, the same as to FIGS. 1 and 2 may also apply to FIGS. 3 and 4, and vice versa.

(28) In FIG. 5, a Raman shift S vs. a Raman Intensity I of a Raman spectrum of the carbon carrier 41 is schematically illustrated in the region of the 2D-peak and of the defect-peak, that is around 2700 cm.sup.1 and around 1300 cm.sup.1, respectively. The peaks are fitted by Gaussian curves so that an area content A2D of the 2D-peak and an area content Adef of the defect-peak are revealed. These area contents A2D, Adef are a measure of the proportions of sp2-hybridized carbon and sp3-hybridized carbon. As can be seen from the example in FIG. 5, the area content A2D is about a factor of three larger than the area content Adef, for example. Thus, the carbon carrier 41 is predominantly of sp2-hybridized carbon. This applies, for example, for laser excitation of the carbon carrier at 532 nm.

(29) Concerning Raman spectroscopy of sp2-hybridized carbon, reference is also made to document Isaac Childres et al., Raman spectroscopy of graphene and related materials, New developments in photon and materials research, 1, from 2013, as well as to Joe Hodkiewicz, Characterizing Carbon Materials with Raman Spectroscopy, Thermo Fisher Scientific, Madison, WI, USA, Application Note: 51901. These two references are incorporated herein by reference in their entirety.

(30) In FIG. 6, another embodiment of the X-ray source 1 is shown. In this embodiment, the transmission window 4 is a side window. The target layer 42 is distant from the transmission window 4. Both the target layer 42 and the transmission window 4 can be located in the window frame 6 on top of the inner tube 51 of the housing 5. Thus, the target layer 42 can be comparably thick, and the electrons 22 hit the target layer 42 but not or only in a negligible extent the transmission window 4. The X-rays X produced by the electrons 22 at the target layer 42 are emitted through the transmission window 4. In an area the X-rays X pass through the transmission window 4, the latter may consist of the carbon carrier 41.

(31) As an option, the X-ray source 1 includes an electronics unit 7 configured to provide an acceleration voltage of at most 1.5 kV between the electron source 2 and the target layer 42, for example. It is possible that the target layer 42 and the transmission window 4 are on the same electric potential which may optionally be ground, for example, or any other voltage different from an anode voltage applied at the target layer 42.

(32) An example of the optional electronics unit 7 is schematically illustrated in FIG. 7. The electronics unit 7 can include or can be composed of a low-voltage side 71 and a high-voltage side 72.

(33) At the low-voltage side 71, there can be a resonant converter 73 and an electron source driver 76. On the one hand, the resonant converter 73 is connected to an electron source voltage output 75 by means of a high-voltage cascade 74 in order to provide a voltage for the electron source 2, for example, which could include a filament, like a heated filament. On the other hand, the electron source driver 76 is connected to an electron source current output 78 by means of high-voltage transformer 77.

(34) For example, the output voltage is 1.5 kV or less. The high-voltage cascade 74 may consist of only one stage, that is, may be or may include a rectifier. For example, the high-voltage cascade 74 includes a diode and a capacitor as well as a feedback resistor, not shown. The high-voltage transformer 77 may be configured for 1.5 kV as well and could be a standard device, for example. Hence, overall the electronics unit 7 can be composed of cost-efficient devices withstanding voltages of around 1.5 kV, and no components withstanding voltages of around 5 kV as often used in X-ray sources are required.

(35) Such an electronics unit 7 can also be present in all other examples of the X-ray source 1, especially it can also be present in the X-ray source 1 of FIG. 1.

(36) Otherwise, the same as to FIGS. 1 to 5 may also apply to FIGS. 6 and 7, and vice versa.

(37) Thus, concerning the X-ray source 1 of FIGS. 6 and 7, in contrast to a transmission anode as shown in context with FIG. 1, the transmission window 4 and the anode 42 could be at different potentials. However, to avoid interaction of high voltage with air, it may be desirable to operate the transmission window 4, that is, the carbon carrier 41, at ground potential. This means that for a construction with a transmission anode, see FIG. 1, the cathode at the electron source 2 is usually at negative high voltage. With a side window anode as in FIG. 6, the transmission window 4 could be operated at ground potential and the anode 42 at positive high voltage.

(38) This means that much less circuitry is required to control the electron source 2 and the electron beam can also be controlled by applying potentials to optional electron optics. However, a distance between the transmission window 4 and the anode 42 is inevitably greater, which can change the imaging properties and may require an adjustment of an electron focusing. In practice, the side window set-up of FIG. 6 may therefore also be operated with the cathode at negative high voltage and both target layer 42 and transmission window 4 at ground potential. However, since the X-rays x do not have to be transmitted through the target layer 42 in this case, a thicker target layer 42 and a better thermal connection of the target layer 42 can be realized.

(39) In addition, an X-ray source 1 with a low accelerating voltage of, for example, at most 1.5 kV can be realized, especially for ionization sources. Since components of the air are ionized in such an application and, for example, nitrogen is ionized first in atmospheric chemical gas phase ionization, much lower voltages or photon energies would be required for this purpose compared to conventional X-ray sources. However, since the photon yield increases with the energy of the electrons 22 and a transmission probability through the transmission window 4 also increases with the electron energy, X-ray sources 1 with 5 kV accelerating voltage and a thin beryllium window are currently used.

(40) The use of a thin graphite membrane with a thickness, for example, of at least 0.1 m and of at most 25 m allows a high transmission probability of photons with low energy and, thus, the necessary accelerating voltage could be reduced. For example, with a thickness of the carbon carrier 41 of 1 m and without any target material at the transmission window 4, one can observe a high intensity of the carbon K-line at 277 eV. FIG. 8 shows the X-ray spectra of a corresponding X-ray source 1 for different accelerating voltages normalized to the carbon peak. The lower energy of the photons could be compensated by a correspondingly larger emission current. This would allow the X-ray source 1 to be operated at acceleration voltages even below 1 kV and still achieve a sufficient ion density for ionization applications.

(41) Due to the lower photon energy of the generated X-rays X, a smaller penetration depth of the photons into the medium to be ionized is achieved. This enables more compact set-ups and, for example, an axial set-up in an ion mobility spectrometer in which there is no danger of ionization in a drift space. Likewise, a non-radioactive electron capture detector is conceivable with such an X-ray source 1. The carbon carrier 41 and the transmission window 4 used as a graphite anode described herein is non-toxic compared to a beryllium membrane and, thus, is in general less critical in application and production.

(42) Cost savings can also be achieved, since beryllium membranes are very expensive to manufacture. Due to the lower acceleration voltage, the circuitry can also be simplified, compare FIG. 7 which shows the simplified block diagram of parts of the drive electronics for the X-ray source 1. Due to the lower maximum voltage, either cascade stages could be saved or components with lower dielectric strength could be used compared to devices using acceleration voltages of at least 5 kV, for example. A feedback resistor (not shown) can also be used to measure the anode potential and the anode current. Said resistor would also have to withstand a lower voltage. Due to the lower number of components and simpler specifications especially in terms of voltage withstand capability, costs can be saved as well. For example, the electron source current output 78 is controlled via the high-voltage transformer 77, which then has to withstand the total acceleration voltage of around only 1 kV in this case. Furthermore, due to the lower maximum voltage either no potting is needed or smaller dimension of the device can be achieved.

(43) In FIG. 9, an operating method is schematically illustrated. In method step M1, the X-ray source 1 is provided. Then, in method step M2, the X-ray source 1 is operated with an acceleration voltage of, for example, at most 2 kV.

(44) Otherwise, the same as to FIGS. 1 to 8 may also apply to FIG. 9, and vice versa.

(45) The invention described here is not restricted by the description on the basis of the exemplary embodiments. Rather, the invention encompasses any new feature and also any combination of features, which includes in particular any combination of features in the patent claims, even if this feature or this combination itself is not explicitly specified in the patent claims or exemplary embodiments.