US3706543A

US3706543A - Method for producing tubular radioactive light sources

Info

Publication number: US3706543A
Application number: US832273A
Authority: US
Inventors: Oscar Thuler
Original assignee: Canrad Precision Industries Inc
Current assignee: Canrad Precision Industries Inc
Priority date: 1968-08-22
Filing date: 1969-06-11
Publication date: 1972-12-19
Anticipated expiration: 1989-12-19
Also published as: US3817733A; GB1230258A; CH495529A; CH495528A

Abstract

According to the invention, the process for making tube-shaped, radioactive light sources is characterized by the fact that a glass tube containing a Luminophor and a radioactive gas, is subdivided successively into glass tube sections intended for use as radioactive light sources, by means of a laser beam. This is accomplished with a closely localized lazer beam so that a sufficient quantity of glass is drawn from the sidewalls to form end walls, to devide the sealed tube and simultaneously seal the ends of the two tubes produced without loss of radioactive gas therein.

Description

Umted States Patent 1 1 3 Thuler 51 Dec. 19, 1972 [54] METHOD FOR PRODUCING TUBULAR 3.203.779 8/1965 Reber Hes/10s RADIOACTIVE LIGHT SOURCES 3,453,097 7/1969 Hafner HUGS/112 3.460.930 8/l969 Pityo ..65/l55 [72] Inventor: Oscar Thuler, Berne, Switzerland [73] Assignee: Canrad Precision Industries, Inc., 'f Exami7er S' Leon 1 New York NY Assistant ExammerRobert L. Lindsay, .lr.

Attorney-Blum, Moscovitz. Friedman & Kaplan [22] Filed: June 11,1969

[211 App]. No.: 832,273 [57] ABSTRACT According to the invention, the process for making tube-shaped, radioactive light sources is characterized [30] Foreign Apphcauon Priority Data by the fact that a glass tube containing a Luminophor Aug. 22, 1968 Switzerland ..l2639/68 and a radioactive gas, is subdivided successively into glass tube sections intended for use as radioactive light I52] [1.5. CI. ..65/l05.65/l l2, 65/I l3. sources, by means of a laser beam. This is accom- 65/l55 plished with a closely localized lazer beam so that a [Si I Int. Cl. ..C03b 21/06 sufficient quantity of glass is drawn from the sidewalls [58] Field of Search ..65/36, I05. H2, 113, 269, to form end walls, to devide the sealed tube and simul- 6S/l55.56, 57, 64 taneously seal the ends of the two tubes produced without loss of radioactive gas therein. [56] References Cited 6 Claims, 1 Drawing Figure UNITED STATES PATENTS 2,300,9l7 11/1942 Gaskill ..65/l05 PATENTEUW. w um METHOD FOR PRODUCING TUBULAR RADIOACTIVE LIGHT SOURCES BACKGROUND FOR THE INVENTION There are known radioactive light sources, consisting of hollow, fused glass bodies, which contains a Luminophor, for instance as an inside wall coating, or as filled-in particles, and a radioactive gas at a lower pressure than atmospheric pressure. In this, the glass body may have the external shape of a pane (disc), of a flattened-out or a cylindrical rod.

For producing such radioactive light sources, consisting of a glass tube, for instance a capillary tube, each glass tube filled with the Luminophor provided is connected to a vacuum source, evacuated, filled with the radioactive gas to the pressure necessary and then fused with a flame.

Inasmuch as this process is inconvenient and timeconsuming, especially for making very small light sources, that is, short capillary tubes, it has been a desire of the industry to provide procedures to subdivide a long glass tube containing the Luminophor and the radioactive gas by sectional fusion, i.e., by cutting the tube into sections with a flame into individual tube sections. In following this concept, however, various and somewhat serious disadvantages have developed in past procedures.

One problem involved has been the control of the flame, that is, it is difflcult to focus the flame sufficiently small, to turn the flame on and off in a simple manner in the shortest possible time, and to obtain a constant size of flame and flame temperature, especially immediately after turning it on. Furthermore, a considerable disadvantage has been found by virtue of the fact that a dead zone of several millimeters length has been formed at the hot, fused end of the capillary tube with respect to the illumination power of the radioactive light source. This dead zone is produced by the excessive and too prolonged heating of the glass body, as the heat generated by the flame is not sufficient to cause fusion with sufficient speed, so that the heating of the glass body is not localized only to the point which is to be melted. A further disadvantage consists in the fact that, as a result of the unavoidably intense heating of the glass body, the pressure of the radioactive gas rises greatly. Inasmuch as the pressure must remain below atmospheric pressure it is necessary to set a relatively low initial pressure before starting the fusion. This low gas pressure is again assumed, however, by the fused light source after cooling. As the light intensity of the radioactive light source rises with the gas pressure, the light source fused in the manner described exhibits a relatively low and by no means optimal brightness.

DESCRIPTION OF THE DISCLOSURE This invention as delineated in the abstract is further explained by reference to the drawing which illustrates in schematic form an example of construction and operation of an installation for carrying out the process according to the invention which delineates a novel and effective mechanism and procedure for effectuating the desired result.

DRAWING The FIGURE is a schematic front view of a device utilized in this invention.

Referring to the drawing, a cylindrical glass tube or capillary tube 1, both ends of which have been fused, contains a Luminophor inside, for instance zinc sulfide, which has been applied as an inside wall coating, or placed into the tube as a powdery substance, and as well as a radio-isotope which is gaseous at room temperature, for instance said radio-isotope may be Tritium or Krypton, which develops a pressure that is below ambient atmospheric pressure.

Glass tube 1 is provided with an outside diameter in the range of 0.5 to 10 mm. and an original length of, for instance, one meter. The glass tube 1 is held at both of its ends by

clamping devices

2 and 3. Clamping device 2 holds the glass tube during the whole process of subdividing by fusing, the glass tube being progressively movable in steps in the direction of arrow 4 by devices (not shown in detail). Clamping device 3 can be detached radially from the glass tube 1 in the direction of arrow 5, and clamp 2 may be fixed or displaceable as desired.

Laser 6 shown in block configuration, the output beam 7 of which is directed to glass tube 1, is disposed laterally and preferably normal to the glass tube 1. A focusing device 8, and/or a device for controling the output beam 7 such as a Kerr cell or crossed prisms shown in block configuration sets up a parallel Laser beam 9, which is directed toward the glass tube 1 at the point to be fused and said Laser beam 9 at that stage having about the same cross section as the glass tube. Laser beam 9 need not necessarily be parallelly directed but it can also have a convergent course. The diameter of the beam as it reaches the tube which is to be divided is preferably approximately as large as that of the tube. The purpose is to fuse enough glass to form the new sealed ends of the two tubes produced. The beam should be closely localized to the desired area to minimize waste of energy, and to avoid flow of heat to adjacent areas of the tube since this would deactivate the Luminophor in adjacent areas.

Alongside Laser beam 9, a metal plate 10 has been fitted, which can be oscillated (LP) swung in and out to and from the solid and dotted line position in the figure. In the position illustrated in solid line, metal plate 10 does not affect Laser beam 9, so that the latter can strike glass tube 1 unimpeded. In the position shown in a dotted line, metal plate 10 lies at an angle of about 45 in the Laser beam and deflects the latter by reflection by about from the normal parallel direction of Laser beam 9.

As shown in the drawing, opposite and spaced beam Laser 6 and from Laser 6 to glass tube 1, a metal reflector 11 is provided which reflects back passing rays of Laser beam 9, to the zone of the glass tube being fused and thereby makes possible a substantially complete utilization of the energy of the Laser beam 9 as well as a symmetrical effect of the Laser beam on the glass tube.

Laser 6 generates a beam whose wave length range lies in the optimum absorption range of the glass material of the glass tube, that is in the infrared spectral range. Laser 6 can for instance in C0, Laser unit develop and operate with a beam wave length of 10.6 and about Watt output.

Furthermore, devices (not shown) can be present for rotating glass tube 1 in the direction of arrow 12 during the fusion process. When the reflector 11 is provided, it may be unnecessary to turn the glass tube to assure uniform heating of the fusion point of the glass tube. It may also be expedient to provide further devices (not shown), which may for instance act on clamping device 3, for the purpose of pulling apart the formed glass tube parts from each other in the direction of the arrow 13 during the fusion process of the respective glass tube sections.

Finally, it is advantageous to provide corresponding associated control and operating devices, in order to carry out the process of automatically subdividing the glass tube into fused (melted-down) glass tube sections by means of a Laser beam. The operating sequence of this subdividing process is the following:

When Laser 6 is in continuous operation, that is when Laser beam 9 is continuously generated, metal plate 10 is at first in the swung-in position and deflects Laser beam 9 from glass tube 1. Glass tube 1 is grasped from both sides and is placed in such an axial position that, between the left-side end of the glass tube, which has already been fused, and the desired position of the Laser beam 9, and the desired length of glass tube section to be fused, i.e., to be cut off, is attained. Thereupon, if desired, while simultaneously turning glass tube 1, the metal plate is swung out, so that Laser beam 9 strikes the glass tube 1 unimpededly and instantaneously heats the tube at the desired zone and causes it to fuse at the point of impact. As soon as the successive ends of the fused glass tube section which have been separated, the remaining portions of glass tube 1 are successively fused, all of which takes but a few seconds. For this purpose, a pull can be applied on the untreated section of glass tube in the direction of arrow 13, and the metal plate 10 again swung into the Laser beam 9.

Thereupon glass tube 1 is advanced by the length of the section desired in the direction of arrow 4, and is grasped again adjacent the fused end by means of clamping device 3, whereupon the fusion process along the length of the remainder of the supported glass tube is repeated in the manner described.

During the process of subdividing the glass tube with the Laser beam, the glass material of the glass tube 1 becomes more fluid at the fusing point than by working therein with a flame. in this manner, a series of uniformly round, fused ends of subdivided sections of the glass tube is obtained, so that the work of finishing the ends with a flame, which is otherwise usually necessary under prior procedures, can be dispensed with.

By means of the Laser beam an instantaneous, intense and closely localized heating up of the glass tube is obtained, so that the remaining other parts of the length of glass tube to be separated into sections is heated up only slightly. Accordingly, the separated glass body sections do not exhibit at its ends undesirable dead zones with respect to illumination power.

Since there is produced only a slight heating effect on the glass tube sections being and to be separated, there is also only a very slight increase in pressure of the radioactive gas contained in the glass tube. This makes it possible to maintain the difference in pressure of the gas in the tube wjtg respect to atmospheric ressure a a low figure whic gives rise to an optimal y Intense brightness of the radioactive light source therein.

A further advantage of the process described lies in the fact that the Laser beam can be regulated and controlled with ease and precision, so that instantaneous heating of the glass tube, uniform in each melting process, can be obtained, while all the disadvantages of an open flame, which heats up the surroundings are eliminated.

The process described is, therefore, especially suitable for automatically and economically radioactive light sources, which constitute separated sealed fused sections by means of subdividing a long glass tube, incorporates the Luminophor and radioisotopes, said radioactive capillary light sources being for instance of 10 mm length, and which glow uniformly over their entire length.

What is claimed is:

l. A process of dividing a long, sealed glass tube containing a Luminophor and a radioactive gas at subatmospheric pressure into a shorter sealed tube suitable for use as a light source and a sealed remainder, comprising the step of heating said long, sealed glass tube to fusion with a closely localized Laser beam at the zone whereat said long, sealed, glass tube is to be divided so that a sufficient quantity of glass is drawn in from the side wall to form end walls, to divide said long sealed tube and to simultaneously seal the ends of the two tubes produced without the loss of radioactive gas by drawing inwardly glass fused by said beam, said inward movement of said fused glass resulting, at least in part, from said pressure within said glass tube being subatmospheric.

2. A process as defined in claim 1, and including the steps of rotating said glass tube during heating with said Laser beam and advancing said long, sealed glass tube axially past the Laser beam by an amount essentially equal to the length of the next of the shorter tubes to be divided from said remainder subsequent to dividing the previous shorter tube from said remainder.

3. A process as defined in claim 1, including the step of drawing apart said remainder and said shorter tube during the heating with said Laser beam.

4. A process in accordance with claim 1 including the step of deflecting the Laser beam by means of reflection from a metal plate after each fusion of a glass tube section of the glass tube.

5. A process in accordance with claim 1, including the step of reflecting back to the glass tube being fused those rays which pass beyond said tube.

6. A process in accordance with claim 1 wherein the Laser beam as it is focussed at the zone on the glass tube which is to be fused said Laser beam has approximately the same cross section as the glass tube.

# i I Q i

Claims

1. A process of dividing a long, sealed glaSs tube containing a Luminophor and a radioactive gas at subatmospheric pressure into a shorter sealed tube suitable for use as a light source and a sealed remainder, comprising the step of heating said long, sealed glass tube to fusion with a closely localized Laser beam at the zone whereat said long, sealed, glass tube is to be divided so that a sufficient quantity of glass is drawn in from the side wall to form end walls, to divide said long sealed tube and to simultaneously seal the ends of the two tubes produced without the loss of radioactive gas by drawing inwardly glass fused by said beam, said inward movement of said fused glass resulting, at least in part, from said pressure within said glass tube being subatmospheric.