US 2063329 A
Description (OCR text may contain errors)
M. MORRISON Dec. 8, 1936.
X-RAY TUBE SHIELD Filed Feb. l, 1933 r fluff fr' Patented Dec. 8, 1936 UNITED STATES X-RAY TUBE SHIELD Montford .Morrison, Montclair, N. J., assignor to Westinghouse X-Ray Company, Inc., a cori poration of Delaware Application February 1, 1933, VSerial No. 654,653
My invention relates to `X-ray tube shields and particularly to such shields having high dielectric strength and heat resisting characteristics. These devices are usually employed with 5 X-ray tubes for radiographic and uoroscopic purposes and closely surround the tube during operation to protect the latter from breakage as well as to prevent stray radiation striking the operator or patient. Shields of this general character are necessarily subjected to high temperature due to their proximity to the tube during operation and contain as an essential ingredient a material of high atomic weight capable of absorbing X-rays thus prohibiting passage of X-rays through the shield except at a designated part of the shield where a window pervious to X-rays is provided. As the shield is in most cases directly in contact with the tube at some points it must have a higher dielectric strength than air to preventsparkover between the terminals of the X-ray tube during operation as the air-gap between the terminals is lessened by the shield. Moreover, it is highly desirable that the dielectric strength of the shield and its X-ray opaqueness should remain unaiected despite the extremely high rise in temperature of the shield attendant operation of the X-ray tube.
` Such devices are well known to the art but heretofore the useful life thereof has been of considerably short duration. The most common form of X-ray tube shield has consisted mainly of glass having incorporated therewith a considerable quantity of ray opaque material, such as'lead, for absorbing stray radiation. Although the dielectric strength of this type of shield remains substantially constant its useful life is generally very limited due to its fragility. `This latter characteristic being inherent the possibility of destruction by accidentally striking the shield is always present and requires considerable care on the part of the operator. Moreover, the considerable rises in temperature to which the shield is subjected during operation of the tube too frequently causes destruction thereof and results not only in annoyance to the operator but may also be attendant with danger to a patient.
A further type of X-ray tube shield which is well known to the art consists mainly of a phenolc condensation product having incorporated therewith a ray opaque material for preventing the passage therethrough of X-rays. While the' fragility of this latter type of shield is considerably less than the aforementioned lead glass (Cl. Z-34) shield it nevertheless has an objectionable feature in that its useful life is limited. The rise in' temperature of the shield during operation of the tube will, in a comparatively short time, cause the shield to become softened thus losing its con- '5i figuration and ray opaqueness or it will carbonize allowing spark-over across the carbonized path,` formed on the surface of the shield, between thek electrodes of the X-ray tube as Well as lose its opaqueness due to carbonization. r i
It is accordingly an object of my present invention to provide an X-ray tube shield having high dielectric strength and heat resisting characteristics and a long useful life. i
Another object of my invention is to provide 152 a substantially non-fragile X-ray tube shield having high dielectric strength and heat resisting characteristics in which the dielectric strength remains constant throughout the entire life thereof.V 20
Another object of my invention is to provide a simplifiedA method of producing a substantially non-fragile X-ray tube shield having high dielectric strength and heat resisting characteristics. i
Still further objects of my invention will become obvious to those skilled in the art by reference to the accompanying drawing illustrating one form of my invention may take and in which, 30
Figure 1 is a longitudinal View in cross-section of one embodiment of my X-ray tube shield; f Figure 2 is a transverse sectional view of one end of my tube shield taken on the line II-II `of Figure 1 35 Figure 3 is still another transverse sectional View of my shield taken on the line III-III of Figure 1 looking in the direction indicated by the arrows;
Figure 4 Vis a still further transverse sectional 40 view of my shield taken at substantially the center thereof on the line IV-IV of Figure 1, and Figure 5 is an interior plan view of the lower section of my tube shield. n
Referring now to the drawing in detail I have 45 shown an X-ray tube shield consisting of an upper section 5 and a similar complementary lower section 6. The upper section 5 is provided with a longitudinal groove 1 disposed around its outer edge while the lower section 6 is providedwith a i5p similar groove 8, but disposed around the inner edge. These respective grooves extending longitudinally at each side of the sections accordingly form a ridge 9 in the upper section 5 and a corresponding ridge I'I in the lower section 6. 1155i The grooves of'each section being opposed to each other enable the ridge 9 of the upper sec- `tion to engage the groove 8 of the` lower section and/similarly the ridge N of the lower section to. engage the groove 'I of the upper Section thus forming ra dovetail joint between the sections to prevent lateral movement and emission of light orX-rays.from the interior. of the shield when thesections'are joined together.
The upper section is provided with a pair of .laterally extending portions I2 and I3 and the lower section is likewise provided with similar portions I4 and I5 which align with the portions ofthe upper section when the sections are placed in engagement with each other. Theselaterally extending portions are provided with openings I6 and suitable fastening means, such as a bolt I1 passing through these openings and held in place byna nutv I8, is provided for rigidly holding the sections together to form a composite shield conformin'gsubstantiallyto the contour of the X-ray fThe bolts I1 areflrigidly secured to the lower section ofthe shield by means of a shoulder I9 whichfits into a'recess 2i provided in the latterally extendin'gportions I4 and I5 to allow the disengagement of the sections by removal of the nuts AI8.y ywithout removal of the bolts.
This shoulder maybe ra threadedwash'ervrun down upon vthe bolt in whichlatter event the bolts with the shoulder I9 are: inserted in the openings It andf'a-n'ut screwed thereon and rigidly held in place by Vmeans1of Ya pin. 22 to form a head for The lower. section 6 is provided at its extremitiesA with vlongitudinally extending slots 23 and 24 and shortfloolts 25` and 2,6, .provided with col- -lars 2.1 and2l8 rigidly secured thereto by means,
such .asset screws 29, flt into these slots.
Springv clips 30 and 3l are carried by these bolts. 25. and 26 which are positioned interiorly .of 'thel lower section G of the shield and one of thesebolts' 25 is provided with an opening 32 Vextending therethrough for a purposeto be hereinaftermorefully described. Y f' An jX-ray'tubel 33l isr secured-atits respective ends vtofthexspring Vclips 3l]r and 3I in spaced re- 'lationwith the shield toallow `a slight circulation of air therebetween to assist in cooling the X-ray tube during operation of the latter. TheX-ray tube is provided with apin 34. extending in a lateral'direction .from one of its ends which ts intotheopening 32 provided in the bolt 25 for the purpose of .preventing longitudinal or rotary lin;
" I'I readily becomes disengaged from the upper section. `f
' My shield is formed of ceramicv material hav- -ing high: dielectric strength and heat resisting [characteristics and is of a substantially nonv fragile composition.
"refractory oxides are particularly adaptable for this: purpose, such for-example as the oxides of I'have found. that certain silic'on aluminum, zirconium, boron, calcium,
sodium and magnesium in composition. AlthoughI have found that the oxides vof these elements' are very satisfactory it is equally true that/other compounds, such for example as the ,the ring process.
carbonates of these elements, operate just as efciently.
In its broadest aspect my invention contemplates selecting a ceramic material having a composition the characteristics of which are that it has high dielectric strength and heat resisting qualities. To this ceramic composition I add a high atomic weight material that is opaque to X-rays and which composition when fired in a furnace may be formed into any desired configuration. However, the ceramic material selected as well as the particular high atomic weight material incorporated therewith must be such that in the ring of the admixture fusion of the ray opaque material will readily take place and the same flux with the ceremic material and be equally distributed throughout the product. It must be appreciated that, as the product, when fired in a mold, is subjected to comparatively high temperature this latter is a controlling factor in the selection of both the particular ceramic composition and the ray opaque material. Accordingly the high atomic weight material itself must be such that fusion thereof will not occur too readily during the ring process, which would cause a concentration at some portion of the product, or a fluxing material may be utilized to increase the fusion temperature to prevent this latter occurrence.
In the actual embodiment of the shield constructed by me I combined the oxides of some of the above noted elements to form a desired ceramic material and incorporated therewith a high atomic weight material, such as the oxide of lead. The following proportions by weight of these oxides I found met all necessary requirements:
SO2 30.9 A1203 13.8 ZIOz 14.6 PbO 39.3 N220 0.4 B203 0.8
Any one of several methods may be employed to form my shield from the composition of the above proportions. I may first mix all of the above mentioned oxides in the form of a plasticl admixture then pour this plastic mass into a mold vof the required configuration and re in a suitable furnace until a ceramic shield is formed after which it is allowed to cool and removed from the mold.
Two further methods which produce an equally eflicient shield are in both instances to omit the lead oxide from the plastic mixture until after Then the high atomic weight material may be impregnated in the ceramic shield in one instance or, the ceramic shield may' lbe coated with the ray opaque material and rered to produce a glazed surface thereon.
I found that in the absence of the oxide of zirconium, when the mold was red with the ray opaque material either in the admixture or incorporated therewith by the other above noted methods, there was a tendency for the shield to become distorted and the ray opaque material to have too low a fusion point. This caused the latter material to become concentrated at portions of the shield rather than evenly distributed throughout the latter.
By adding this other oxide of zirconium, which incidentally has an atomic weight approximately half that of lead but a melting point a little greater than seven times the latter, the fusion point of the lead oxide was materially increased. This resulted in the ray opaque material remaining evenly distributed throughout the admixture after completion of the firing process and a shield, which Was opaque to X-rays having high dielectric strength and heat resisting characteristics. Moreover, my ceramic shield is substantially non-fragile in character being of relatively strong composition and capable of withstanding considerably high degrees of temperature Without cracking.
Although I have described one embodiment of my invention and several methods by which the same may be constructed I do not desire to be limited thereto as various other modications thereof may be made Without departing from the spirit and scope of the appended claims.
What is claimed:
1. An X-ray tube protective shield having high i dielectric strength and heat resisting characteristics comprising paired members joined together and formed of a plurality of refractory oxides including those of silicon, aluminum and zirconium with the proportion by Weight of the silicon oxide being slightly greater than the sum of the proportions by weight of the oxides of aluminum and zirconium, and an X-ray opaque material combined num and zirconium, and an X-ray opaque material combined with said aforementioned oxides comprising the oxide of lead, the proportion by weight thereof being greater than the proportion of the oxide of silicon, but less than the sum of the oxides of silicon and aluminum.
3. An X-ray tube protective shield having high dielectric strength and heat resisting characteristics comprising paired members joined together and formed of a plurality of refractory oxides including those of silicon, aluminum, and zirconium, with the proportion by Weight of the oxide of silicon being slightly greater than the sum of the proportons by weight of the oxides of aluminum and zirconium, an X-ray opaque material combined with said aforementioned oxides comprisingthe oxiderof lead, the proportion byweight thereof being greater than the proportion of the oxide o-f silicon, but less than the sum of the oxides of silicon and aluminum, said oxide of zir' conium being incorporated in said shield to cause the oxide of lead to remain uniformly distributed throughout said shield during the molding and ring thereof.
4. An X-ray tube protective shield having high dielectric strength and heat resisting characteristics comprising paired members joined together and formed of a plurality of refractory oxides including the following in proportions by weight SiOz 30.9