US2075146A - Metallic roentgen tube with revolving anticathode - Google Patents

Description

ROENTGEN TUBE WITH REVOLVING ANTICATHODE March 30, 1937. s. SERGEEFF METALLIC Filed 'Dec.

Patented Mar. 30, 1937 METALLIC ROENTGEN TUBE WITH REVOLV- ING ANTICATHODE Sergei Sergeefi, Moscow, Union of Socialist Soviet Republics Application December 6, 1934, Serial No. 756,313. In Union of Socialist Soviet Republics June 25,

5 Claims.

There are known powerful (up to 200 ma.) metallic Roentgen tubes for microstructural analysis which work in connection with a four-stage diffusion pump and permit a rapid change of the anticathode (as, for example, the tube by Mr. G. N. Selmayr with a four-stage diffusion pump by Gaede, see the Scientific Journal of Physics, 1924, page 598).

A further increasing of the tube capacity is limited by the degree of heating of the anticathode, said heating being too high in spite of an intensive cooling.

It has been also proposed to overcome this difficulty by employing a revolving anticathode, in the first time in X-ray tubes for surgical diagnosis. No prolonged exposure being required in such cases, these tubes had a revolving anticathode which was cooled owing to the thermal conductivity of the metal without the use of cooling water.

A thoroughly designed construction of a tube with revolving anticathode has been proposed by Bowers, who determined the necessary number of revolutions of the anticathode, the latter being rotated by a magnetic field produced externally of the tube.

This tube is adapted to operate at 650-500 ma. at 40-50 kv. during 0.05 second and at 500-400 ma. during 0.2 second.

But such a short duration of exposure is not sufiicient for microstructural analysis.

If the exposure lasts several minutes, a continuous water cooling is needed even in the case of a revolving anticathode.

The rotation of a water cooled anticathode in X-ray tubes of this kind requires the use of various stufiing boxes which makes very difficult the obtaining of the necessary vacuum within the tube.

In a contrary way the present invention permits the arrangement within a high vacuum X-ray tube of a revolving water cooled anticathode without the use of any packing means or any rotary tight sleeves in the high vacuum zone.

The invention consists therein that the rod of the anticathode passes through the four-stage dilfusion pump which constitutes an integral part with the Roentgen tube.

The rod passes through the pump in such a manner that the space between these parts constitutes a diffusion diaphragm through which the air is exhausted by mercury vapours or the like flowing with great velocity out of an annular nozzle as in usual diffusion pumps.

As the rod passes through the second, third and fourth stages of the pump, the interstices between the rod and the washers separating the stages are overlapped by mercury stoppers.

Such a manner of obtaining tightness is possible owing to the small pressure difference existing between consecutive pump stages and because beginning with the second stage the pres sure in the stages is smaller than the mercury vapour pressure at ordinary temperatures.

Thus the tightening by means of stuffing boxes is removed to the zone of preliminary vacuum (low vacuum), where in the four-stage pump the vacuum need not be higher than 15-20 mm. of

. the mercury column.

The accompanying drawing illustrates, by way of example, two forms of embodiment of the arrangement according to the invention; in both cases the four-stage diffusion pump is of Gaedes system.

The shell I of the Roentgen tube is a hollow cylindrical body with passages 2 for the cooling water. A window 3 made of aluminium foil is provided in the shell and serves for letting out the X-rays. On the upper part of the shell I is mounted a glass tube 4 which is welded to chromium steel sockets BI. The glass tube 4 serves for insulating the cathode 5.

To provide for a prolonged operation of the tube at a large load the water cooling of thecathode can be effected. through the nipples 8 and 9. The incandescent cathode is formed as a tungsten coil. For still greater loads the cathode may be of the indirect heating type.

The detachable junction between the shell I and the difiusion pump underneath it is effected by a gas-tight glass sleeve I0, hermetically drawn upon a metallic cone which is connected to the shell I by means of elastic member II. The so formed glass receptacle I2 is filled with liquid air for freezing out the mercury vapours.

The revolving anticathode comprises the flat piece I3 firmly fastened to the through tubular rod I4.

In the inner cavity of the anticathode is fixed the funnel-shaped end of a stationary tube I6, through the lower end II of which is introduced the cooling water. This water flows out through the annular space between the tube I6 and the inner wall of the tubular rod I4.

The rod I4 of the revolving anticathode I3 is rotated from without by means of the toothed gearing I8.

It revolves in two bearings: the upper bearing I9 operating without lubrication is situated in the high vacuum zone, and the lower bearing 20 ing outthrough the annular nozzle surrounding;

the part'22.

The four stages of the' 'mercury pump 2l are 7' separated from one another by the discs 23pmvided with mercury stoppers- 1 Such a packing is possible in this case onlybea' cause of the fact that the pressure differences. between each two consecutive stages of the pumpare very small and because beginning with the second stage the pressure in each stage is smaller than the pressure of mercury vapours at ordinary temperature. V

V .Thevacuumpumpis connected to the connecting'tube 25. v r V Themercury vapours ascend from the boiling vessel 26 and pass" through the nozzles 21-which are arranged in parallel, and through the annu larnozzle on the part 22. The condensed mercury flows down through the mercury stoppers 24 and the tube 28, returning back to the boiling I 30 vessel 26. Thus the stufling box is located in Such avacuum..makes surethe operation of' the four-stage difiusion pump.

If a water vjet pump is to be used for producing '45 a pressure drop where the anode rod passes from the preliminary vacuum zone into the atmosphere, the arrangement is such that the water flowing out. of the anode rod, as indicated by-arrows in Fig; 1,'draws the air from the preliminary 5 0 .vacuum 'throughthe air space between the anode tube and the tubular casing. The anode rod is V mounted in the preliminary vacuum zone in a ball bearing similarly to the arrangement in the high vacuum zone. Since in the case of a considerable pressure drop for a water jet pump, the velocity of pumping out is much too small, there is provided in the present constructional form a pipe-20 which is connected toa vacuum-pump. @What I claim is: r Q

1'. In combination, .a Roentgen'tube including a rotary water cooled anticathode and a carrying rod for said anticathode, amulti-stage diffusion pumpqconnected with said tube and having high and low vacuum zones, said rod extending a through said pump and externally thereof 7 through the low vacuum zone, a bearing for'said rod in thehighvacuumzone of the pump, a. second bearing for said rod in the low vacuum zone and a stufling box at the point where said rod passes from the low vacuum zone into the atmosphere.

-2. In combination, a Roentgen tube including a rotary water cooled anticathodeand a carrying rod forisaid anticathode, a multi-stage .diflusion pump connected with said tube and having high 7 and low vacuum zones, said rod extending through said pump and externally, thereof through the low vacuum zone, a bearingitor said rod in the high vacuum zone of the pump, a bearing for said rod in the low vacuum zone and a water jet pump at a point where the rod extends through the multi-stage diflusion' "pump for creating a vacuum for the operation :01 the multi-stagedifiusion pumpand corresponding to .15-20 mmnof the mercurycolumn.

3. 'An arrangement as claimed in claim 1, char- .acterized in thatIsaidimulti-stage diffusion pump includes a'diflusion diaphragm surrounding said carrying rod. 7 1 V 4. An. arrangement as claimed in claim .1,

characterized in that said multi-stage diflusion pump includes a diffusion diaphragm surrounding said carrying rod'in' the high vacuum zone oi v said diffusion pump. V

5. An {arrangement as claimed .in claim-1,

characterized in that #said multi-stage diffusion SERGEI SERGEEFF.

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