US 3287581 A
Description (OCR text may contain errors)
Nov. 22, 1966 M. ROME ETAL 3,287,581
X-RAY VIDICON TUBE HAVING SCREEN HERMETICALLY SEALED TO ENVELOPE Filed April 50, 1962 INVENTORS MART/N ROME HAROLD OWJORDAN United States Patent 3,287,581 X-RAY VIDICON TUBE HAVING SCREEN HER- METICALLY SEALED T0 ENVELOPE Martin Rome and Harold 0. W. Jordan, Stamford, Conn.,
assignors to The Machlett Laboratories, Incorporated,
Springdale, Conn., a corporation of Connecticut Filed Apr. 30, 1962, Ser. No. 191,085 1 Claim. (Cl. 313-59) This invention relates to an X-ray vidicon and, more particularly, to a novel X-ray vidicon window assembly.
The application of television techniques to X-ray pick-up devices has necessitated utilizing a window minimum X-ray absorption in place of the conventional glass window as the vacuum-tight terminating element. Beryllium metal, noted by its low X-ray absorption characteristics, is an ideal wind-ow for use in X-ray sensitive pick-up tubes, particularly in applications involving low X-ray energy level incident radiation. The low X-ray absorption of beryllium metal, compared to glass, enhances the sensitivity of the camera tube, particularly at low energy levels, simply by permitting more radiation to become incident on the photoconductive surface.
However, beryllium surfaces cannot be conveniently prepared with the high degree of uniformity and polishing required for high resolution pick-up tubes. Both the microcrystalline structure and the protective oxide layer are detrimental influences on the selenium photoconductor substrate used with the beryllium window. That is, if the selenium photoconductor is vaporized directly onto the beryllium metal, there occurs a detrimental recrystallization of the selenium from the amorphous to a lower resistivity crystalline form due, at least in part, to the beryllium.
Accordingly, it is a primary object of our invention to provide structures in which the beryllium window may be sealed to a glass bulb forming the vacuum-tight envelope for the camera tube.
Another object of our invention is to provide a means for preventing a reaction or change in crystal structure by interposing a barrier layer between the beryllium and selenium.
Still another object of our invention is to provide a smooth polished uniform substrate for the selenium without a substantial increase in X-ray absorption.
Yet another object of our invention is to provide a thin smooth uniform metallic substrate for the selenium that is an exact replica of the original beryllium surface and which may be more'readily polished than the refractory beryllium.
A further object of our invention is to provide a thin, metallic, thermally conductive substrate which will also meet the requirements of low X-ray absorption and a smooth uniform surface.
A still further object of our invention is to provide a smooth, uniform, thermally conductive substrate for the selenium without a substantial increase in X-ray absorption.
The features of our invention, which we believe to be novel, are set forth with particularity in the appended claim. Our invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof, may be best understood by reference to the following description, taken in conjunction with the accompanying drawings in which:
FIG. 1 is a partial sectional view of our basic face-plate structure for an X-ray vidicon, and
FIG. 2 is a sectional view of a schematic representation of our novel beryllium window structure as used in a typical X-ray Vidicon.
Referring now to FIG. 1, there is shown the basic struc- Patented Nov. 22, 1966 ture utilizing a beryllium window in an X-ray Vidicon. In the basic structure, there is provided an envelope 16. A cylindrical ring 18, having the same configuration as envelope 16, is affixed to the end of the envelope by means of the Tf-shaped solder ring 20. Around the cross-bar portion of the T-shaped indium solder is a stainless steel ring 24. The whole assembly comprises Window assembly 13.
The window assembly is formed by joining beryllium window 14 to the kovar or monel ring 18. It has been found that monel is preferred since it is more easily brased than kovar and lends itself more readily to grinding and polishing. Grinding and polishing the mating surfaces is essential for the cold seal technique that is utilized in this invention. Having provided the seal between the beryllium and the monel ring the window assembly 14, 18 is sealed to the edge of envelope 16 by means of indium solder 20. The indium or indium alloy is first cast or joined to the inside surface of the stainless steel ring 24. The indium, which is soft and pliable, may be formed by machining or any other well-known means to the precise and desired configuration.
The indium stainless steel assembly 20, 24 is then interposed between the monel ring 18 and the envelope 16 and the window assembly is joined to the envelope by simultaneously applying a uniform pressure to both ring 18 and envelope 16.
Referring now to FIG. 2, it will be seen that when uniform pressure is applied to the mating surfaces of ring 18 and envelope 16, that portion of the solder lying therebetween is squeezed out into the inside of the envelope to form a shelf having upper and lower surfaces 10 and 12, respectively. It now becomes obvious that a photoconductive layer and a barrier layer (if necessary) may be applied to the under surface of beryllium layer 14 in accordance with the principles set forth in our c-opending application Serial No. 191,099 filed April 30, 1962 and entitled X-Ray Vidicon Assembly and Method.
FIG. 2 shows our invention incorporated in a typical X-ray Vidicon-type tube. The basic structure 13 is shown having ring 18 sealed to envelope 16, as previously described. The wall 16 and the structure 13 together comprise a vacuum-tight envelope having an electron gun 40 mounted in one end thereof. The components that make up gun 40 include the usual cathode 42, control electrode 44, and one or more accelerating electrodes 46, all of which are connected to lead-in means 48 in a well-known manner. An electron beam 50 emanating from gun 40 is directed onto the target 62 of photoconductive material at the other end of envelope 10, and means is provided for focusing beam 50 and scanning it over the photoconductor 62. Such means may include a focussing coil 52, a deflection yoke 54 and an alignment coil 56, all of which are arranged approximately as shown. Another electrode such as grid 58 having a suitable potential applied thereon is positioned adjacent the photoconductive material 62 and, in operation, functions cooperatively with focussing coil 52 to insure that electron beam 50, in its final approach to the surface 62, is normal thereto. A final accelerating electrode 60 is also provided and may take the form of a metallic cylinder or a conductive coating painted on the interior wall of the envelope between electrodes 46 and 58. The lead-in means 48, not shown in detail, are provided for the purpose of connecting electrode 60 as well as the gun electrodes 42, 44, and 46 to the appropriate source of electrical potential located externally of the tube.
While there has been described what is presently considered a preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the inventive concept contained therein, and it is, therefore, aimed in the appended claim to cover all such changes and modifications as fall within the true spirit and scope of the invention.
What is claimed is:
An X-ray vidicon tube comprising a glass envelope having one open end shaped to an annular configuration, and a window assembly mounted over said open end of the envelope comprising a metal ring and a beryllium disc sealed throughout its periphery within the ring, the ring having inner and outer surface configurations substantially the same as the annular open end of the envelope and superimposed thereon, brazing mate-rial sealing the ring to the open end of the envelope, metal means encircling the brazing material, an X-ray sensitive target on the in- 15 4- ner surface of the window assembly, and an electron beam-forming device in the envelope for scanning the target with electrons.
References Cited by the Examiner UNITED STATES PATENTS 2,394,984 2/1946 Claussen 31359 X 2,909,686 10/1959 Zunick 313-49 2,951,962 9/1960 Miller et al 313-65 10 3,061,664 10/1962 Kegg 31365X HERMAN KARL SAALBACH, Primary Examiner.
S. CHATMON, J R., Assistant Examiner.