X-ray or gamma ray systems or devices – Electronic circuit – X-ray source power supply
Reexamination Certificate
1996-10-28
2001-03-20
Porta, David P. (Department: 2506)
X-ray or gamma ray systems or devices
Electronic circuit
X-ray source power supply
C378S102000, C378S114000
Reexamination Certificate
active
06205200
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to X-ray machines and, more particularly, to a battery operated X-ray machine having an improved circuit arrangement so as to generate intense relatively short pulsed of X-rays. This invention allows for the overall weight of the X-ray machine to be reduced with a corresponding reduction in its physical size so that it more advantageously serves as a portable device.
2. Description of the Prior Art is X-ray machines that generate X-rays from cold field emission of electrons from the cathode of an X-ray tube are commonly employed in pulsed shadowgraph radiographs. Pulsed or flash shadowgraph radiograph was developed in 1938 as a means for observing extremely rapid motion where the subject was obscured from observation with visible light or debris. To date, flash radiography remains the principal means of observing lensed implosions and ballistic impacts over microsecond and nanosecond time scales. The majority of these X-ray systems utilize the well known Marx generator which can be viewed as a distributed transmission-storage line, consisting of n-cascaded high-voltage barium titanate disc capacitors. To produce X-rays, the Marx generator is coupled to a field-emission X-ray tube either directly or by coaxial cables. Coaxial cables provide a low impedance energy store and can be rapidly discharged into the X-ray tube.
When high voltage (H.V.) pulses arrive at the anode of the X-ray tube they establish a large potential gradient in the anode-cathode gap. This gradient produces an intense electric field at the tips of the small metal whiskers which are present on the surface of the cathode mesh. The whiskers are heated by the passage of the field emission electron current and vaporize, creating a neutral plasma which acts as a virtual cathode capable of supporting a much larger current. Electrons emitted from the expanding virtual cathode are accelerated by the electric field in the anode-cathode gap and eventually collide with the anode creating X-rays by the usual Bremmstrahlung and line radiation processes. Electrons continue to cross the anode-cathode gap until the expanding cathode plasma reaches the anode at which time the X-ray tube impedance drops to a few ohms and effectively shorts the tube.
While Marx generator driven X-ray systems have worked well in the past, they have employed large transformer-rectifier high voltage power supplies for charging the Marx capacitors and generally use heavy coaxial cables to couple the Marx generator to the X-ray tube. The heavy coaxial cables act to sharpen the high voltage pulses produced by the Marx generator but, the physically large bundle of cables disadvantageously adds to the weight of the X-ray machine so as to hinder its portability. Further more, the heavy high voltage power supply also disadvantageously contributed to the weight of the X-ray machine while also hindering its maneuverability. It is desired that a means be provided that reduce the overall weight of the X-ray machine, while also eliminating the need for the heavy coaxial cables with both features contributing to an X-ray unit that is truly portable. More particularly, it is desired that a compact and portable design for X-ray machines be provided so that the X-ray machine may advantageously be used in remote locations, as in X-ray imaging devices for medical diagnostics and also for triage related to medical disasters.
OBJECTS OF THE INVENTION
Accordingly, it is a primary object of the present invention to provide an X-ray machine that is of a relatively light-weight, about 26 pounds,occupies less than one half of a cubic foot,and may serve as a compact and portable device for use in remote locations requiring ease of mobility.
It is the object of the present invention to provide a portable X-ray machine that develops an intense pulse of X-rays, but also has variable accelerating voltage so as to accommodate various X-ray applications.
Another object of the present invention is to provide a portable X-ray unit that generates a high dose X-ray pulse, which has a short time duration, 10-100 nanoseconds. This short X-ray pulse eliminates the need for long integration time, so that it advantageously may be used for high resolution digital detector arrays.
Detector arrays, such as charge coupled device(CCD) or a amorphous silicon devices both of which are used in digital processing cameras have high dark currents when integrating over long time exposures unless cooled to about 0° Fahrenheit; the dark current of these devices decreases their sensitivity.
Furthermore, it is an object of the present invention to provide an X-ray unit that may be used for dental X-ray imagery and controlled by a portable computer, such as a notebook computer, when used in remote or confined spaces or used for X-ray inspection, security detection, and medical applications requiring high quality X-ray images.
SUMMARY OF THE INVENTION
The present invention is directed to an X-ray unit which is relatively light-weight, thereby contributing to its portability, yet generating hard X-ray pulses without the need of any coaxial cables between its Marx generator and its X-ray tube. The X-ray unit comprises a high vacuum X-ray tube having a conical anode surrounded by a coaxial annulus of stainless steel mesh which serves as the cathode, control electronics, and a plurality of spark gap switches and ceramic disc capacitors which form the Marx generator
18
. The battery powered control electronics comprises: the H.V. power supply, Ultraviolet (U.V.) flash-gap assembly
57
, and power management circuit. The control electronics
20
can receive either a manual, an optical, or an electrical pulse and use that pulse to trigger the X-ray unit.
The control electronics also generates a sync pulse whenever the Marx generator is triggered and this pulse is brought to the front panel of the control electronics enclosure
20
so that it can be used to synchronize or command other devices to fire with the Marx generator.
The energy storage capacitors within the Marx column are surrounded with an insulating pressurized shell
12
and covered by a close fitting aluminum cylinder
32
which acts as the outer conductor of a lumped coaxial transmission line. The outer aluminum cylinder also functions as a very effective Faraday shield preventing the escape of potentially harmful electromagnetic radiation from the pulsed X-ray unit.
REFERENCES:
patent: 3878394 (1975-04-01), Golden
patent: 4924485 (1990-05-01), Hoeberling
patent: 5442677 (1995-08-01), Golden et al.
Boyer Craig N.
Holland Glenn E.
Seely John F.
Jameson George
McDonnell Thomas E.
Porta David P.
The United States of America as represented by the Secretary of
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