This report describes in detail with photographs and cross‐sectional views an x‐ray tube with a gyrating water‐cooled target which the authors have operated continuously for periods of hours at 287,000 volts and 105 milliamperes. The theoretical predictions of DuMond, Watson and Hicks as to the ratio of safe load in moving and fixed targets seems to be roughly fulfilled by these results. The computed power output in the form of x‐rays alone is some 3/4 kilowatt. The report further describes in detail the power supply equipment consisting of a synchronous motor driven 40 kw motor generator set giving 150 cycle current both half‐waves of which, after transformation to high voltage, are rectified by two thermionic valves (filament emission 2 amperes maximum) of our own design and construction here fully described. The powerful electrical filter system to reduce the ripple to a low value and some technical problems arising from the large power rating of the equipment as well as the facilities now almost completed for stabilizing and measuring precisely the high voltage supplied to the x‐ray tube are discussed. At the outset a brief indication of the program of research work projected for this set is given.
REFERENCES
1.
J. W. M.
DuMond
, Rev. Mod. Phys.
5
, 1
(1933
). This article is a summary giving references to an extensive literature in the field.2.
3.
In this letter Birge points out that the discrepancy may be ascribed either (1) to the inappropriateness of the perfect crystal assumption in computing e by the x‐ray crystal grating method or (2) that the theoretical formula for the Rydberg constant may be seriously in error (by a factor of order ). DuMond and Bollman have since shown by a crystal powder method which avoids the first pitfall above mentioned that this pitfall cannot vitiate the values of e obtained with macroscopic crystals by a sufficient amount to explain the discrepancy,
Birge
, Phys. Rev.
50
, 524
(1936
).4.
Bouwers’s tube is designed for use in snapshot radiography advantage being taken of the heat capacity of a massive anode to store the energy of each exposure which is subsequently dissipated slowly by a radiative means. Such a tube does not permit of high continuous power input but is perfectly adapted for its special purpose.
Clay
, Proc. Phys. Soc.
46
, 703
(1934
) has designed a five‐kilowatt rotating anode tube that is water cooled. See also reference 7.5.
Alex
Müller
, 125
, 507
(1929
);Alex
Müller
, 132
, 646
(1931
).6.
7.
Fournier, Gondet and Mathieu, Communication at Paris meeting of the French Physical Society, Dec. 18 (1936)
see
J. de Phys.
8
, 171S
(1937
).8.
A few cc of distilled mercury are warmed gently in a test tube under a ventilating hood with a sufficient quantity of pure gold (sheet or filings) to furnish the desired size and thickness of coating. When the gold has dissolved completely the pasty mass of amalgam is squeezed in a chamois bag to express all the free mercury, leaving a lump resembling butter in consistency. The copper target surface to be gilded is thoroughly cleaned mechanically in the lathe with clean grease‐free emery cloth. (Attempts to clean it chemically and to preamalgamate the surface, frequently recommended in books, have proven less successful in practice, we find.) The amalgam is buttered onto the copper surface immediately after cleaning with a clean springy steel spatula. It will probably not adhere at first at all. The target is now to be gently warmed (under the ventilating hood) by conduction of heat from a flame which does not play on the surface to be coated. As the target temperature rises the amalgam must be continually buttered and spread about with the knife and soon with continued heating adherence will take place. Some skill is required when this point is reached to spread the analgam uniformly before it stiffens from vaporization of the mercury too much to spread. Finally when an adherent uniform coating is obtained the target is warmed vigorously until every trace of mercury is expelled and the surface has a matte golden color. If the target is hollow (for water cooling) we now cast it full of molten lead or type metal alloy so that when cool the gilded face can be hammered without deformation. This hammering is indispensable, for the gilded coat produced as we describe is very spongy. Hammering however consolidates it into a uniform homogeneous mass which is very rugged indeed against both mechanical and thermal abuse. Finally the lead or type metal is melted out of the interior.
9.
10.
11.
12.
We owe this technique to C. C. Lauritsen and R. Crane. The beginning end of the gum tape is first thinned by stretching. It is then wrapped straight around the pipes a little more than one whole turn so that it laps about equally over both sides of the fissure. From here on it is wrapped so that it overlaps on itself about half its width for a distance of about an inch along the pipe first to right (say) then all the way back over the wrapping to a point one inch to the left of the fissure then back to the middle where it is cut off and the end pressed tightly against the underlying layers to give good adherence. If this has been carefully done there are in the joint now only two critical places the “cross overs” one at either end of the wrapping where the direction of spiraling was reversed so that the tape crossed back over itself. At these points where the tape climbs up over its own thickness on the turn below a small duct spiraling in along the edge of the tape may lead all the way to the fissure to be bandaged. These cross over points should be thoroughly squeezed with the thumb nail to close up the duct and should be thoroughly shellacked and carefully observed in case the shellac may “suck in” before it has dried. Needless to say it is wise to make the cross over points at a convenient location for observation and painting.
13.
14.
In a recent paper
DuMond
and Bollman
(Phys. Rev.
51
, 400
(1937
)) have outlined practical methods they have used successfully for calibrating such resistance ratios in the case of a pair of 14 megohm stacks.
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© 1937 American Institute of Physics.
1937
American Institute of Physics
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