X-ray Tube

Abstract

An X-ray tube whose vacuum vessel contains a target made of electrical insulation material, a source of charged particles and an electrode for accelerating charged particles emitted from said source wherein the target is impacted by a beam of charged particles thus accelerated so as to produce soft X-rays of particularly great intensity.

Description

BACKGROUND OF THE INVENTION

This invention relates to an X-ray tube capable of generating strong X-rays and more specifically to an X-ray tube capable of easily producing soft X-rays of particularly great intensity.

Generally, an X-ray tube is formed by receiving in a vacuum vessel an electronic gun, an electrode for accelerating emitted electrons and a target impacted by a beam of accelerated electrons. With the conventional X-ray tube, the target consists in all cases of metals, for example, tungsten, chromium and aluminum. The X-rays thus obtained generally have a low intensity, and moreover there are encountered difficulties in generating soft X-rays. It is, therefore, difficult for the conventional X-ray tube to meet requirements for special applications, for example, analytical work. Particularly where there is to be analyzed the content of light elements by the fluorescent X-ray analytical method, it is necessary to apply soft X-rays. Further where a sample of analysis is of minute quantity, it is required to employ soft X-rays of particularly great intensity in order to elevate the analytical sensitivity.

Heretofore, however, there has not been developed any X-ray tube adapted for generation of soft X-rays, particularly of great intensity.

SUMMARY OF THE INVENTION

It is accordingly the object of this invention to provide an X-ray tube capable of generating soft X-rays of particularly great intensity.

According to this invention, there is provided an X-ray tube whose vacuum vessel contains a source of charged particles; an electrode for accelerating charged particles emitted from said source; and a target of electrical insulation material adapted upon impingement of charged particles thus accelerated so as to generate soft X-rays of prominent intensity, said soft X-rays being drawn out from a proper outlet port provided in the vacuum vessel.

The source of charged particles may consist of an ordinary electronic gun or a source of positive or negative ions. The acceleration electrode is impressed with voltage having a proper polarity for acceleration of emitted charged particles. The electrical insulation material constituting a target is, for example, alumina (A1.sub.2 O.sub.3). This target produces characteristic K-X ray having an energy of 1.49 KeV of aluminum and characteristic K-X ray having an energy of 0.52 KeV of oxygen. Other target materials used in this invention include, for example, quartz, tungsten calcium oxide (CaWO.sub.4 mica (KAL.sub.2 (ALSi.sub.3 O.sub.10)(OH).sub.2), and lithium niobate (LiNbO.sub.3). Where there is used an electronic gun as a source of charged particles, the vacuum vessel in which said gun is received may be permanently sealed. And where there is used an ion generator as a source of charged particles, the vacuum vessel is not completely sealed, but may receive means for adjusting gas pressure prevailing therein. It is generally preferred that an outlet port through which to draw out soft X-rays be formed of, for example, a thin film of aluminum or beryllium which least tends to absorb said X-rays. However, where the X-ray tube of this invention is used particularly with a fluorescent X-ray analyzer requiring soft X-rays, the outlet port member may be connected to the vacuum area of said analyzer without using an X-ray permeable film. Even in this case it is also possible to constract said outlet port of a particularly thin film least liable to absorb soft X-rays.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an X-ray tube according to an embodiment of this invention;

FIG. 2 is a sectional view of an X-ray tube according to another embodiment of the invention;

FIG. 3 is a sectional view of an X-ray tube according to still another embodiment of the invention; and

FIG. 4 compares the intensity of characteristic X-rays of aluminum obtained with the X-ray tube of FIG. 1 with that of the prior art X-ray tube using a target made of aluminum.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, numeral 1 represents a glass vacuum vessel. At one end of said vessel 1 is disposed an ion generator 2 (generally referred to as an "ion gun"), and at the other end is sealed in airtightness an acceleration electrode at a seal point 4. In the embodiment of FIG. 1, the ion generator 2 is of Penning ionization gauge (PIG) type, which generates positive ions, for example, protons. The acceleration electrode 3 is in a blind cylindrical form. To the inner wall of the bottom of said cylinder is fixed a target 5 made of electrical insulation material, for example, alumina (A1.sub.2 0.sub.3). The ion generator 2 comprises a negative electrode 6, positive electrode 7, and a magnet device 8 for generating a magnetic field acting in the axial direction of the X-ray tube, both electrodes 6 and 7 being impressed with proper voltage through lead lines 9. Voltage across said electrodes 6 and 7 and the magnetic field deionize gas present in the ion generator 2 and a beam of the resultant charged particles 10, for example, protons is drawn out from the aperture 11 of the negative electrode 6. The acceleration electrode 3 is impressed with sufficient negative voltage to accelerate the beam 10 of protons to the energy of, for example, scores from tens to hundreds of KeV. Said voltage allows the proton beam 10 to proceed straight through a beam hole 12 and impinge on the target 5, thereby generating characteristic X-rays 13 of the material of said target 5. In that portion of the acceleration electrode 3 which faces the X-ray-generating surface of the target 5 is formed an X-ray outlet port 14, which is sealed with an X-ray permeable film 15 least liable to absorb X-rays produced and fully withstanding the magnitude of vacuum applied. The characteristic X-rays 13 are drawn outside through said film 15.

The acceleration electrode 3 is fitted with a device 16 for adjusting gas pressure prevailing in the ion generator 2. Said gas pressure adjustment device 16 may consist of, for example, an ion pump. The X-ray tube can be so designed, when operated to generate X-rays, as to introduce gas thereinto and, when out of operation, to cause the gas therein to be absorbed to an adsorbent placed in the ion pump 16.

FIG. 4 presents a comparison between the relative intensity of X-rays obtained with the X-ray tube according to the embodiment of FIG. 1 and that of the prior art X-ray tube. Referring to FIG. 4, the abscissa represents the energy of protons expressed in KeV. The left ordinate or the curve 17 shows the relative count rate of characteristic K-X rays of aluminum obtained with the X-ray tube of this invention and the right ordinate or the curve 18 indicates the relative count rate of similar X-rays obtained with the conventional X-ray tube using a target of aluminum. The fact that the graduation numerals on the left ordinate have a value equal to 10.sup.3 times those on the right ordinate proves that the characteristic X-rays of the material of a target included in the X-ray tube of this invention are of prominent intensity. Where the target consisted of other electrical insulation materials than alumina (A1.sub.2 0.sub.3), there was obtained a comparative diagram closely resembling that of FIG. 4. The energy of soft X-rays characteristic of aluminum represented by the curve 17 is of the order of 1.49 KeV as previously described.

This invention also includes the case where there is used an electronic gun as a source of charged particles. When electrons emitted by known means (not shown) are accelerated to a prescribed magnitude of energy by the voltage impressed on the acceleration electrode 3, and a beam of accelerated electrons is made to impinge on a target, then there is also obtained a desired type of X-rays. In this case, the gas pressure adjustment device may be omitted, thus enabling the entire X-ray tube to be permanently sealed.

FIG. 2 denotes an X-ray tube wherein the X-ray outlet port is not provided with an X-ray permeable film for preservation of vacuum in order effectively to utilize soft X-rays having a particularly low degree of energy. Such X-ray permeable film has a nature of absorbing more or less amounts of X-rays, however thin it may be formed. Consequently the X-ray outlet port member 14 of FIG. 2 may be formed without any additional X-ray permeable member and directly connected to the vacuum area of an apparatus subjected to X-ray impingement. In the case of FIG. 2 the gas pressure adjustment device 16 may be made to communicate directly with the ion generator 2.

FIG. 3 is a sectional view of an X-ray tube according to still another embodiment of this invention wherein the X-ray permeable film 15 fitted to the outlet port assembly 14 of X-rays can be allowed to be extremely thin. Said outlet port assembly 14 consists of a flanged cylindrical member 19; a first vacuum valve 20 which, when opened, permits the passage of X-rays 13; a thin X-ray permeable film 15; a gas pressure adjustment space 21 provided between the first vacuum valve 20 and X-ray permeable film 15; and a second vacuum valve for causing said gas pressure adjustment space 21 to communicate with or be shut off from the space in the acceleration electrode 3. A flange formed at the outer end of the flanged cylindrical member 19 is connected in airtightness to an apparatus 24 subjected to X-ray impingement, for example, a fluorescent X-ray analyzer, the interior of which is evacuated through an exhaust port 23.

When the X-ray tube of FIG. 3 is not in operation, the first valve 20 is left closed and the second valve 22 is kept open. Under such arrangement, there is applied an equal pressure on the opposite surfaces of the X-ray permeable film 15, enabling said film to be made extremely thin. When the X-ray tube is put into operation, the X-ray-receiving apparatus 24 is evacuated until gas pressure therein is made equal to that of the X-ray tube. Thereafter the first and second valves 20 and 22 are opened in turn. The embodiment of FIG. 3 enables not only soft X-rays of great intensity to impinge on an X-ray-receiving apparatus with the absorption of X-ray energy in the X-ray permeable film 15 prominently minimized, but also backward gas diffusion into the X-ray tube to be prevented during the evacuation of the X-ray-receiving apparatus 24.

Claims

What is claimed is:

1. An X-ray tube comprising a vacuum vessel; a source of charged particles received in said vacuum vessel; an acceleration electrode disposed opposite to said source of charged particles so as to accelerate charged particles emitted therefrom; a target made of alumina to generate characteristic X-rays of said material upon impingement of said accelerated charged particles; and an outlet port through which to draw out said X-rays.

2. The X-ray tube according to claim 1 wherein the source of charged particles is an ion generator including means for adjusting gas pressure prevailing therein.

3. The X-ray tube according to claim 1 wherein there is provided an X-ray outlet port for directly projecting the characteristic X-rays of the material of a target on an X-ray-receiving apparatus without using an X-ray permeable film.

4. The X-ray tube according to claim 1 wherein there is provided means for equalizing gas pressure acting on the opposite surfaces of an X-ray permeable film through which to draw out said characteristic X-rays and there is also provided an X-ray outlet port assembly for projecting said characteristic X-rays through said film on an X-ray receiving apparatus.

5. The X-ray tube according to claim 2 wherein there is provided means for equalizing gas pressure acting on the opposite surfaces of an X-ray permeable film through which to draw out said characteristic X-rays and there is also provided an X-ray outlet port assembly for protecting said characteristic X-rays through said film on an X-ray receiving apparatus.