Thermionic emission device, focus head, X-ray tube and X-ray emitter

Abstract

A thermionic emission device includes an indirectly heatable main emitter with a main emission surface and a connectible heat emitter with a heat emission surface. The heat emission surface is disposed at a predefinable distance from the main emission surface. In the operating state, the main emitter is at a constant main potential and the heat emitter can be switched between at least two heating potentials which differ from one another and which differ from the main potential. Through the use of the thermionic emission device, the radiation load for a patient is reduced in the case of dose-modulated x-ray recordings.

Claims

1. A thermionic emission device, comprising: an indirectly heatable main emitter having a side with a main emission surface and having an opposite side with a further emission surface; and a connectible heat emitter having a heat emission surface; said heat emission surface being disposed at a predefinable distance from said main emission surface; said main emitter configured to be at a constant main potential; said heat emitter configured to be switchable between at least a first heating potential being more negative than the main potential during normal operation and a second heating potential being more positive than the main potential during dose modulation operation.

2. The thermionic emission device according to claim 1, wherein said main emitter is a flat emitter and said main emission surface is formed with slots or has a meander-shaped conductor path.

3. The thermionic emission device according to claim 1, wherein said main emitter is a flat emitter and said main emission surface does not have slots or recesses.

4. The thermionic emission device according to claim 1, wherein said heat emitter is a flat emitter and said heat emission surface is formed with slots or has a meander-shaped conductor path.

5. The thermionic emission device according to claim 1, wherein said heat emitter is a flat emitter and said heat emission surface does not have slots or recesses.

6. The thermionic emission device according to claim 1, wherein said main emitter is a coil emitter.

7. The thermionic emission device according to claim 1, wherein said heat emitter is a coil emitter.

8. The thermionic emission device according to claim 1, wherein said heat emitter is an anode.

9. A focus head, comprising a thermionic emission device according to claim 1.

10. An x-ray tube, comprising: an anode; and a thermionic emission device according to claim 1.

11. An x-ray tube, comprising: an anode; and a focus head including a thermionic emission device according to claim 1.

12. The x-ray tube according to claim 10, wherein said thermionic emission device includes an anode.

13. The x-ray tube according to claim 11, wherein said focus head includes an anode.

14. The x-ray tube according to claim 10, wherein said anode is a rotary anode.

15. The x-ray tube according to claim 10, wherein said anode is part of a rotary piston tube.

16. The x-ray tube according to claim 10, wherein said anode is a stationary anode.

17. An x-ray emitter, comprising: an emitter housing; and an x-ray tube disposed in said emitter housing, said x-ray tube including an anode and a thermionic emission device according to claim 1.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a diagrammatic, vertical-sectional view of a first embodiment of a thermionic emission device during normal operation;

(2) FIG. 2 is a vertical-sectional view showing the thermionic emission device according to FIG. 1 during dose modulation operation; and

(3) FIG. 3 is a vertical-sectional view showing a second embodiment of a thermionic emission device during dose modulation operation.

DETAILED DESCRIPTION OF THE INVENTION

(4) Referring now in detail to the figures of the drawings and first, particularly, to FIGS. 1 and 2 thereof, there is seen a thermionic emission device in accordance with the invention which includes an indirectly heatable main emitter 1 with a main emission surface 11 and a connectible heat emitter 2 with a heat emission surface 21.

(5) The main emitter 1 and the heat emitter 2 are disposed together in a focus head 3. The main emitter 1 is held mechanically in the focus head 3 and is connected in an electrically conducting manner thereto.

(6) In contrast, the heat emitter 2 is held mechanically in the focus head 3, but is electrically insulated from the focus head 3. The heat emitter 2 can thus be switched independently of the main emitter 1.

(7) Furthermore, the main emitter 1 and the heat emitter 2 are distanced from one another in such a way that the heat emission surface 21 and the main emission surface 11 run at a predefinable distance 4 and substantially in parallel with one another.

(8) In the operating state, the main emitter 1 is at a constant main potential U.sub.1 and the heat emitter 2 can be switched between at least two heating potentials U.sub.21 and U.sub.22 which differ from one another and which differ from the main potential U.sub.1. In the exemplary embodiment shown, the heat emitter 2 can be switched between precisely two different heating potentials U.sub.21 and U.sub.22, namely between a first heating potential U.sub.21 and a second heating potential U.sub.22.

(9) In the exemplary embodiment shown, the main emitter 1 is at a main potential U.sub.1=70 kV, whereas the heat emitter 2 can be switched between the first heating potential U.sub.21=71 kV (FIG. 1) and a second heating potential U.sub.22=69 kV (FIG. 2).

(10) During normal operation (FIG. 1), the first heating potential U.sub.21 is thus more negative than the main potential U.sub.1 (U.sub.21<U.sub.1). During normal operation electrons which are focused on an electron beam 5 by the focus head 3 are thus emitted by the heat emitter 2. The electron beam 5 strikes the main emitter 1 and heats up the main emitter 1. The main emitter 1 emits electrons from the main emission surface 11. Those electrons are focused on an electron beam 6 and are accelerated in the direction of an anode 8. When the electron beam 6 strikes, x-ray radiation is generated in a known manner in the material of the anode 8.

(11) With a dose modulation (FIG. 2), the second heating potential U.sub.22 is more positive than the main potential U.sub.1 and the main potential U.sub.1 is in turn more positive than the first heating potential U.sub.21 (U.sub.22>U.sub.1>U.sub.21). During dose modulation operation, no more electrons are emitted from the heat emission surface 21 of the heat emitter 2 due to a potential assignment which is modified compared with normal operation. Instead, electrons which are focused on an electron beam 7 are additionally emitted from the main emitter 1 in the direction of the heat emitter 2 and strike the heat emission surface 21 there. The main emitter 1 thus emits significantly fewer electrons across its main emission surface 11, so that the electron beam 6 is accordingly weaker and the anode 8 is thus not reached. No x-ray radiation is therefore generated in the material of the anode 8. The potential assignment during dose modulation operation thus reliably counteracts a post heating of the main emitter 1 by the heat emitter 2.

(12) The inventive measure can also be transferred to conventional emitter technologies (FIG. 3). To this end, in addition to the main emitter 1 provision is only to be made for a connectible anode 9, which is at an anode potential of U.sub.9=69 kV for instance which corresponds to the second heating potential U.sub.22 (FIG. 2). During dose modulation operation, the main emitter 1 is thus cooled in the manner described with regard to FIG. 2.

(13) This takes place in such a way that the electrons which are focused on the electron beam 7 are additionally emitted from the main emitter 1, in the direction of the connectible anode 9 and strike there. The main emitter 1 thus emits significantly fewer electrons across its main emission surface 11, so that the electron beam 6 is accordingly weaker and the anode 8 is thus not reached. No x-ray radiation is therefore generated in the material of the anode 8. The potential assignment during dose modulation operation thus reliably shortens the cooling phase of the main emitter 1 with a conventional thermionic emission device.

(14) Although the invention has been illustrated and described in detail on the basis of the preferred exemplary embodiment, the invention is not limited by the disclosed examples and other variants can be derived in this case therefrom by the person skilled in the art without departing from the scope of protection of the invention.