Index of content:
Volume 22, Issue 6, June 1951
22(1951); http://dx.doi.org/10.1063/1.1745936View Description Hide Description
A new method for the assay of tritium is described. Radioactive water is reacted with methyl Grignard reagent to give radioactive methane which is then admitted into a proportional counting chamber to be counted. Advantages of the method are convenience, absence of memory effects, linearity, and a precision with a standard deviation less than 1 percent.
22(1951); http://dx.doi.org/10.1063/1.1745937View Description Hide Description
A low current integrator is described that successfully avoids the problem of current leakage by the use of electrometer tubes. In connection with the circuit an electronic master switch is described which permits the turning on and off of associated equipment with the beginning of the charging cycle of the integrator.
22(1951); http://dx.doi.org/10.1063/1.1745939View Description Hide Description
Using the simplest optical parts a monochromator with a nominal band width of about 15A was constructed, covering the range of 3600 to 9000A. This monochromator, in combination with suitable photocells and a direct reading, linear, negative feedback amplifier, permits the determination of extinctions with an error of about 1.5 percent.
The performance of the instrument was checked by measuring the absorption spectra of rare earth ions.
22(1951); http://dx.doi.org/10.1063/1.1745940View Description Hide Description
An electrostatic transformer of direct current which permits the continuous transfer of electrical charges from a primary circuit to a secondary circuit by means of a rotating dielectric is described. The primary circuit consists of a pair of metallic brushes connected to a source of high voltage, the moving dielectric being placed between them. A similar pair of brushes, placed at a convenient distance away, constitutes the secondary terminals. The continuous transfer of charges permits the passage of a steady current from the secondary brushes. In the one‐to‐one ratio electrostatic transformer the secondary voltage is slightly less than the primary voltage owing to losses, but since the primary circuit and secondary circuits are separated by insulating material, it is possible to place several disks on a shaft and to connect the primary brushes in parallel and the secondary brushes in series, obtaining in this way a step‐up transformer. The elementary theory is developed and experimental results are shown.
22(1951); http://dx.doi.org/10.1063/1.1745942View Description Hide Description
Of the several circuits for timing control of small spot welders which have recently appeared in the literature, the one which seems to the author to be most practical does not include circuit parameters or components. A certain amount of effort is required, therefore, in selecting parameters and components. It is the purpose of this article to provide this information.
22(1951); http://dx.doi.org/10.1063/1.1745943View Description Hide Description
Many instruments exist which will magnify small displacements to almost any degree desired but always at the expense of range. The micrometer screw is a notable exception, but does not given an electrical output nor will it measure distance directly and continuously without extra equipment. The present device combines a lever, a micrometer screw, a sensing element, and a servomotor to achieve this purpose.
Automatic Measurement Computation and Recording of Dielectric Constant and Loss Factor against Temperature22(1951); http://dx.doi.org/10.1063/1.1745944View Description Hide Description
An automatically computing and recording instrument for dielectric constant and dielectric loss as a function of temperature at any constant frequency from 50 cps to 600,000 cps is described. Sample curves are shown. Known magnification and zero shift are incorporated to cover the ranges of values encountered in most plastic materials. Automatic correction for and measurement of thermal expansion is incorporated.
22(1951); http://dx.doi.org/10.1063/1.1745945View Description Hide Description
The Yale linear accelerator has been designed to produce large currents of 10‐Mev electrons by the use of independent resonant cavities driven by 500‐kw triode power amplifiers. The design principles and construction methods used for this recently completed machine and data on its performance are presented.
22(1951); http://dx.doi.org/10.1063/1.1745946View Description Hide Description
A system is described whereby a gas may be circulated continuously between the cyclotron and the 14‐cm radius of curvature magnetic spectrometer. This apparatus does not modify the spectrometer itself but considerably increases its usefulness. Detailed descriptions are given of the chamber which is attached to the cyclotron for bombardment and of both beta‐ and gamma‐ray source holders in addition to an over‐all picture of the entire system.
22(1951); http://dx.doi.org/10.1063/1.1745947View Description Hide Description
An x‐ray microscope is described in which the mirrors are thin optical flats. These flats are mechanically bent to obtain the radius of curvature necessary to focus the image. The adjustable curvature increases the flexibility of the microscope and the ease of focusing the image. The difficulties of grinding and polishing concave cylindrical surfaces are avoided.
The degree of smoothness of reflecting surfaces was studied, and the anelastic properties of various mirrormaterials were investigated to find a material suitable for bending. Highly polished tungstencarbide was found to be an excellent mirrormaterial and does not require an evaporated surfacecoating of high density metal.
The x‐ray microscope promises to be a valuable research instrument.
22(1951); http://dx.doi.org/10.1063/1.1745948View Description Hide Description
A method is described for maintaining the separation of the component particles during the annealing of a metallic powder. The technique consists of mixing the metalpowder with a larger quantity of a second powder that is inactive chemically relative to the metal,annealing the mixed powders, and separating the metal by dissolving the inert powder after annealing. In this way gold,silver, and ironpowders have been annealed in sodium chloride without sintering.
22(1951); http://dx.doi.org/10.1063/1.1745949View Description Hide Description
A new coincidence device using crystal diodes has been developed. The new circuit does not necessitate equalizing and can be used for pulses with an amplitude spread of two orders of magnitude. The principle of the new circuit is to compare two measurements: one made in one of the channels, and the other made between the two channels. Resolving times down to 3×10−10 sec have been obtained, which represent an improvement of one order of magnitude over former circuits. The improvement in the sensitivity also turned out to be about one order of magnitude. The new circuit should be useful in nuclear experiments in determining decay times, disintegration rates, and for the reduction of noise in scintillation counters.
22(1951); http://dx.doi.org/10.1063/1.1745950View Description Hide Description
The EMI 5311 photomultiplier tube differs from the usual tube in that the electrodes are of the Venetianblind type rather than electron optical lenses. This type of tube has been used as a scintillation counter with trans‐stilbene crystals. The shape of the scintillation pulse is characterized by a rise time of 7.2×10−9 sec and a decay time of 1.8×10−8 sec. It is concluded that this type of multiplication structure results in an unusually large spread in the transit time of electrons moving through the structure.
22(1951); http://dx.doi.org/10.1063/1.1745951View Description Hide Description
The operation of a 6‐Mev linear electron accelerator is described. It is of the traveling‐wave type, 14 feet in length. A single magnetron is used as a power source, operating at a wavelength of 10.5 cm, with a peak power output of 0.9 megawatt. Electrons are injected at a velocity v=c/2. Approximately 1/20 of the injected electrons reach the target end of the accelerator, with energies falling in a 1‐Mev range near 6 Mev. The average current obtained is 0.05 μa. With an electron pulse length of 0.8 μsec and a pulse repetition rate of 60 per sec, this corresponds to a peak current of the order of 1 ma.
22(1951); http://dx.doi.org/10.1063/1.1745952View Description Hide Description
Principle and design of a new type of Stieltjes integrator are described. The general application of such an integrator is given. The advantages of the new design are: (a) the movement of either tracer does not cause a relative displacement of the other tracer from its curve; (b) only rectangular movements are employed; and (c) the mechanical parts are simple and very sturdy. The accuracy obtainable, as determined by sample ingrations, was found to be 0.1 percent if the curves are followed exactly.
22(1951); http://dx.doi.org/10.1063/1.1745953View Description Hide Description
A method is described for growing crystals of BaO from the vapor. Seeds of BaO crystals or ``pseudoseeds'' of MgO crystals are placed in an enclosure of BaO in a vacuum furnace and heated at 1400°C. Single BaO crystals as large as 1×10×10 mm have been grown by this method. Since BaO decomposes very rapidly in the ordinary atmosphere, special techniques for manipulating the crystals are described. These techniques are useful in experiments on the optical, electrical, and electronic properties of BaO.
22(1951); http://dx.doi.org/10.1063/1.1745954View Description Hide Description
Errors involved in the coincidence methods of measuring disintegration rates of radioactive sources are discussed and means to avoid or to evaluate them are given. The disintegration rate of Co60 gamma‐ray standard of the National Bureau of Standards is determined experimentally.
22(1951); http://dx.doi.org/10.1063/1.1745955View Description Hide Description
The usual procedure for making two‐dimensional fourier projections of crystal structures by means of the Huggins masks requires the expenditure of time in the photographic darkroom during which errors may be made. These errors can be corrected only by a repetition of the entire laborious procedure of successive exposures of the plate. An apparatus is described whereby 144 Huggins masks are projected simultaneously on a screen and the result photographed. The projection is accomplished without lenses and the cost of production is thereby reduced considerably. Grooves are provided for changing the signs of the fourier coefficients at will. Rheostats on the projection lamps are provided for controlling the lumination in proportion to the magnitude of the fourier coefficients.