C. C. Lauritsen

A magnetic analyzer for charged-particles from nuclear reactions.

A double‐focusing magnetic spectrometer for detecting and analyzing charged particles from nuclear reactions is described. The magnetic field, varying as r^(−½) near an average radius of 10.5 in., extends over a semicircle yielding object and anastigmatic image positions some distance outside of the region of strong field. The acceptance solid angle is Ω=0.0061 sterad. and the momentum resolution with an 8‐mm slit at the detector is R=128. The ultimate resolution determined by spherical aberration and some residual astigmatism is about 1000. Applications to the study of the energy and yield of nuclear reaction products are discussed.

A Simple Quartz Fiber Electrometer

The quartz fiber electrometer to be described in the following note has proved to be an extremely useful instrument in the study of weak radioactive sources. Because of its low capacity, simplicity of construction and general ruggedness, it has found many applications.

A High Potential Porcelain X‐Ray Tube

An x‐ray tube which operates successfully up to 650,000 volts has been constructed from a conical porcelain transformer bushing, rated at 750,000 volts external flashover. Although the bushing had previously been filled with transformer oil, no difficulties were encountered in outgassing the inner surface. With a pumping system of about 300 liters per second capacity, a vacuum of 10−5 mm can be maintained, and this does not change appreciably during operation. Cold emission from the anode, rather than gas current or breakdown of the porcelain, limits the voltage which can be applied. Filament emission currents up to 4 milliamperes can be employed without undue heating of the target. For a given voltage, a porcelain tube of this type is much more compact than a glass tube, the strength of its walls against puncture makes elaborate internal shielding unnecessary, and there is no more difficulty in maintaining a good vacuum than in a glass tube of comparable volume. The source of high potential is the 1,000,...

Electrostatic Analyzer for 1.5‐Mev Protons

A system for analyzing the ion beam of an electrostatic generator is described. A weak magnetic field separates protons from heavier components and a 90° electrostatic deflection gives the required energy resolution. With the analyzer controlling the generator voltage, a proton beam of one microampere with an energy spread of the order of 300 volts in one million is obtained.

A Combined Tesla Coil and Vacuum Tube

An oil emersed high frequency resonance coil has been constructed and combined with a vacuum tube in such a way that none of the high voltage parts are exposed to the air. This makes a very compact apparatus, and it is not subject to corona losses. Potentials up to 750,000 volts have been produced on the inner electrode, by exciting the primary circuit with a condenser discharge. An improvement in the design is proposed, which makes use of a system of concentric shields around the inner electrode, for the purpose of distributing the potential drop in a more advantageous manner, and making it possible to go to higher voltages before cold emission occurs. Excitation of the apparatus by means of a continuous wave oscillator, and its use as a high voltage x‐ray outfit for practical purposes is discussed.

The Biological Effect of High Voltage X Rays

For many years radiologists have debated the question whether equal doses of X rays of different wave-lengths produce the same or different quantitative biological effects, a problem of practical importance in therapy. The chief obstacles in deciding the matter were the lack of a standard unit of X-ray intensity, the lack of adequate measuring apparatus, and the highly variable character of the biological materials which were used in making the tests. The adoption of a standard unit, the Roentgen, now permits an accurate definition of dosage, where previously none was possible. The question now is this: When a definite number of r units, measured by an air ionisation chamber, is delivered to a suitable material, will the amount of effect which is produced vary with the wave-length of the beam, that is, with the voltage. An almost ideal biological material consists of the eggs of the wild fruit fly, Drosophila. These eggs when freshly laid are comparatively sensitive, and are remarkably uniform in response...

A Short Ion Path High Voltage Tube

A vacuum tube for the acceleration of charged particles is described. The total acceleration of the ions takes place in a distance of 18 inches although the total height of the tube is about 14 feet. It has been used at one million volts peak a.c. with target currents of 5 ma of electrons and 0.2 ma of positive ions.

The Development of High Voltage X-ray Tubes at the California Institute of Technology1

THE difficulties encountered in constructing x-ray tubes for operation at voltages above two or three hundred kilovolts are well known. Stray charges may accumulate on the envelope in such a manner that a dangerously high potential is applied through the wall, with the result that it is punctured. Punctures may also result from tiny pieces of metal torn out of the electrodes by the intense electric fields. Gas may be liberated by stray bombardment caused by the field and resulting in destructive discharges. These difficulties may be at least partly eliminated by several means. We have attempted to decrease the stray discharges by using electrodes with large curvature and large spacing, so as to decrease as far as possible the field strength at the surfaces. In addition, the glass or other envelope is protected against stray discharges and excessive potentials by proper subdivision and shielding, and any gas which may be liberated during operation is quickly removed by fast pumping. The first tube to be us...

Spectrum of the Radiation from a High Potential X-ray Tube

A spectrograph of the Seemann type has been constructed for the purpose of investigating the radiation from the high potential x-ray tube at the California Institute. A typical spectrogram obtained with 600 kilovolts on the tube is presented. The photometer record shows a continuous spectrum with its maximum intensity at about 200 kilovolts and a short wave-length limit in the neighborhood of 600 kilovolts. The range covered is roughly from 100 to 20 x-units. It is proposed to use the apparatus for determining absorption coefficients by photographing the spectrum of radiation which has passed through an absorbing screen. No anomalies of any kind have been observed so far.