The present invention pertains to an X-Ray generator with a cold cathode, in particularly, to a process of heating a tungsten filament and vacuuming a glass ball-tube container simultaneously in an X-Ray generator encapsulated process.
An x-ray generation device with a cold cathode generating field emission electrons is known according to a quantum theory of field electron emission. The basic principle of the field emission electrons is that the electrons of a conductor must have sufficient energy to get a chance to cross the potential energy barrier to the vacuum side when no electric field is applied. When an electric field is applied the energy band is bent, as a result, electrons cross the potential energy barrier to the vacuum side without huge amount of energy. When the applied electric field is increasing, the potential energy barrier by electrons is decreasing and the strength of the derived current is increasing. According to electromagnetic theory, if a charged object has a sharp point, the electric field strength around that point will be much higher than elsewhere. Air near the electrode can become ionized (partially conductive), while regions more distant do not. Therefore, for a field emission cathode, more upper-ward carbon fibers are desired so that the electric field will be generated even the applied voltage on the cathode is low.
At present time, an x-ray generation device usually serves as an electron source within a microwave element, sensor, panel display, or the like. The efficiency of electron emission mostly depends on the element structure, material, and shape of a field emission cathode (i.e. an x-ray generation device). A field emission cathode is made of metal, such as silicon, diamond, and carbon nano-tube. Among these materials, carbon nano-tube is particularly important because its openings are extremely thin and stable, it has low conducted field and high emitting current density, and it is highly stable. With these characteristics, carbon nano-tube is extremely suitable for a field emission cathode. Therefore, it is highly possible that carbon nano-tube will replace other materials and becomes the material of field emission in the next generation.
Field emission cathode can serve as a cathode of an x-ray generation device, such as an x-ray tube. An x-ray generation device encapsulates a cathode, electromagnetic-lens aperture, and an anode target within a glass container. The conventional thermionic cathode neon tube can be replaced by the carbon nano-tube. When using a thermionic cathode neon tube in an x-ray generation device, around 99% of electricity is transformed to heat. Thus, the thermionic cathode neon tube must be cool down by cooling water. On the contrary, carbon nano-tube can emit electron beams under smaller electric field intensity, so the efficiency of transferring electricity to electronic beams is higher than that of thermionic cathode nano-tube. In addition, cooling process is not required when using carbon nano-tube in an x-ray generation device.
The U.S. Pat. No. 6,553,096 presented by Zhou et al. discloses an x-ray generation device adopting carbon nano-tubes. Zhou et al. use materials with nanometer structures as an emitting source of a cathode field emission. Furthermore, Zhou et al. claimed that generating a current density of about 30 mA/cm2 can be achieved by an x-ray generator using carbon nano-tubes. The x-ray generator has a threshold electric field of about 3.5 V/μm.
Since the threshold is still too high to use for a hand-held x-ray device, the inventors of the present invention discloses a novel x-ray generator having a threshold electric field as low as 0.3 V/μm. Please refer to U.S. Pat. No. 8,559,599. Referring to
An object of the present invention is to provide an encapsulated structure of the X-ray generator with a cold cathode having a vacuum level keeping as the initial even after the X-ray generator used for a long time so as to keep the X-ray photo quality well.
The other object of the present invention is to provide a method to reduce vacuuming time cost before an opening of the X-ray glass ball-tube is melting to seal, during an encapsulating process.
Another object of the present invention is to provide an X-ray glass ball-tube structure includes an insulating gel having extremely high breakdown voltage resist avoiding corona discharge at the electrode pins.
The present invention discloses an encapsulated structure of an X ray generator with a cold cathode and method of vacuuming the same. The X ray generator has a glass ball-tube having a base, a tungsten filament, a cold cathode, a focus cap, and an anode target inside, associated with a first electrode pin, a second electrode pin, a single-used pin, and anode pin extended out. The tungsten filament located at the periphery of the base has a first wire end connected with the second electrode pin and a second wire end connected with the single-used pin. While vacuuming the glass ball-tube before melting an end to seal, a voltage is exerting on the single use pin to heat the tungsten, and a high voltage is exerting on the anode target to accelerate the hot electrons emitting from the filament to bombard the inside wall of the glass ball-tube and the anode target so as to shorten the vacuuming time and increase the vacuum level.
The present invention discloses an X ray generator has a glass ball-tube100 having a base 100, a cold cathode 110C, a focus cap 125, a tungsten filament 115, and an anode target 140 having a incline plane facing to the cold cathode 110C in a way that the generated X-rays due to the cold electrons hitting the incline plane 140 are capable of through an X ray window 130 out. The X ray generator may have three electrode pins 1101, 1102, 1153, and an anode pin 1404 extended out of the glass ball-tube, as shown in
The distinct point between the
Referring to
The function of the tungsten filament 115 is used in the vacuuming process to the glass ball-tube only, and nothing with the operation of the X-ray generator. Thus the position of the tungsten filament 115 is located at the periphery of the base, so that it will not hinder the cold electrons emitted from the cold cathode. Before the glass ball-tube is sealed, the glass ball-tube 100 is vacuuming, a voltage of about 2V˜10V is exerted on the third electrode pins 1153 and the second electrode pin is grounded to generate a current of about 1˜5 A to heat the tungsten filament 115 so as to generate hot electrons. And a high voltage as high as several thousand volts to several tens of thousands e.g. 70 kV is preferred to further applied on the anode pin 1404 so as to accelerate the hot electrons bombard any organic material, moisture, contamination out of the inner glass ball-tube 100, and the anode target 140. The hot electrons have very lightly mass so that the accelerated hot electrons can bombard the contamination out without cause the glass ball-tube damage. The dissociate contaminations are then vacuuming out.
During the vacuuming process, heating turn on and heating off process to the tungsten filament 115, are preferred to be alternative in turn to prevent glass ball-tube from overheating. The rest time i.e., heating off may be 1-5 minutes. After several ON and OFF alternative processes, any contaminations attached on the inner wall of the glass ball-tube 100 and anode target 140 will be throughout removed and cleaned. For a glass ball-tube 100 with a diameter of about 30-45 mm in section, or 40-60 mm3 in volume, the vacuuming time cost including any heating turn off time is of about 1 hour. Thereafter, the end opening of the glass ball-tube is sealed by melting out.
It is found that a glass ball-tube with a tungsten filament 115 to assist the vacuuming process not only shorten the vacuuming time cost but also prompt the X-ray photo quality while comparing with the glass ball-tube without a tungsten filament.
An X-ray generator with a single use tungsten filament 115 can keep the X-ray photo quality as the initial even after 10,000 shot. By contrast, the X-ray photo quality is found to be deteriorated for an X-ray generator without a single use tungsten filament 115 due to deteriorated vacuum level in the glass ball-tube.
After sealing the end opening by melting, the glass ball-tube 100 has four electrode pins 1101, 1102, 1153, 1404 extended out of the glass ball-tube.
In an X-ray generator with two electrode pins, the cold cathode 110C is constituted by a plurality of metal rods 110C1 formed each with a carbon layer 110C2 thereon, which are fixed on a base 100 with a planar surface by a silver gel or solder. The metal rods 110C1 may be formed of nickel or platinum.
In an X-ray generator with three electrode pins, the foresaid metal rods 110C1 are fixed by insulating material such as ceramic. The metal bars 110C1 are connected with the first electrode pin 1101.
In another preferred embodiment, the cold cathode 110C is a carbon film formed on a curve surface such as a convex surface, as shown in
To take X-ray photo of the human body, the voltage drop between the anode pin 1404 and the first electrode pin 111 is demanded to be as high as 50 kV-{grave over ( )}75 kV. Such a high voltage easily cause air breakdown in the vicinity of the anode pin 1404 and the first electrode pin 1101 to produce spark.
Referring to
The packaged structure with two thin foils, a first lead foils 101 inside and a second foil 102 outside thereof, is found better than just with singe but one thicker lead foil 102 outside. It can make the hand-held X-ray device by 10% weight reduce.
A preferred hand-held X ray device 200 may have a structure like a pistol, as shown in
According to the present invention, the X-ray generator in use provide a current as low as 100 μA-200 μA, which is just one tenth of that of a current used in a well-known X-ray hand-held device, Normad pro 2, made by ARIBEX company. The Normad pro 2 is a conventional X-ray device used a tungsten filament as a cathode to generate hot electrons. The current for this type X-ray generator is at least of about 1 mA and is demanded to be rest by at least 1 minute for 1 second shot so as to cool the X-ray generator.
The benefits of the present invention are:
(1). the hand-held X-ray generator can be shot continuously and with very good penetration under a voltage of about 65 kV. In comparison with the conventional hand-held X-ray device, the latter needs at least 1 minute rest for each shot by one second.
(2) The vacuum level in the glass ball-tube can be kept well so that the X-ray photo quality is the same as the initial even after several thousand shots. The X-ray photo quality is found becomes worse after 100 shots if the hand-held X-ray generator without a tungsten filament inside to assist vacuuming the glass ball-tube.
(3) The dosage of the X-ray is very low comparing with the Normad pro 2. Although the current is low, the X-ray photo quality is still very good. The X-ray generator used for human chest, dental care, and skeletal gives least damage and is thus better than the conventional, which has high dosage.
As is understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrated of the present invention rather than limiting of the present invention. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structures.
Number | Date | Country | Kind |
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103140325 A | Nov 2014 | TW | national |
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Number | Date | Country | |
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20160148777 A1 | May 2016 | US |