Index of content:
Volume 18, Issue 8, August 1947
Filters for Spectral Corrections of Multiplier Photo‐Tubes Used from Scotopic to Photopic Brightness Levels18(1947); http://dx.doi.org/10.1063/1.1740997View Description Hide Description
The difficulties encountered in photometry at low levels of brightness are in a wide measure due to changes in the spectralcharacteristics of the eye as it becomes light‐ or dark‐adapted. A study has been made of filter glasses suitable for correcting two types of multiplier photo‐tubes used in photometric work where there is a wide variation in field brightnesses. Results of this study are described, and filter glass numbers as well as thickness specifications are given for filters used to correct RCA 1P21 and 1P22 tubes over brightness levels corresponding to the Purkinje range.
18(1947); http://dx.doi.org/10.1063/1.1740998View Description Hide Description
A simplified and portable design of the 180° deflection‐type mass spectroscope was developed for quantitative analyses in the mass range from 4 to 65. The principal features include an oscillating accelerating voltage, permanent magnetic field, the use of a.c. amplifiers, and an oscilloscope. Successful application has been made to fixed gas, liquid and solid samples, and continuously flowing gases with changing component concentration. Accuracy from isotope ratio determinations is of the order of 2–5 percent.
18(1947); http://dx.doi.org/10.1063/1.1740999View Description Hide Description
A furnace is described for use with the electron diffractioncamera for the study of chemical and physical reactions occurring on surfaces up to 1000°C. The specimens are mounted in the body of a 25 Cr‐12 Ni alloy block which is surrounded by a series of radiation shields. The metal block is heated internally by a tungsten‐wire heating element mounted on a BeO core and operates in a hydrogen atmosphere. The several motions necessary for manipulation of the specimens are accomplished through a Wilson seal. Temperatures of 1000°C are achieved with a heat input of the order of 450 to 500 watts in forty minutes. The use of the furnace is illustrated.
18(1947); http://dx.doi.org/10.1063/1.1741000View Description Hide Description
A method is described for detecting coincidence between the discharges of Geiger counters. The basic circuit uses diodes as coincidence tubes. The output from a diode circuit is the same polarity pulse as the inputs, hence the output from one coincidence circuit can be used to generate more complex coincidences. An example is given of a typical counter‐tube experiment utilizing the diode scheme. A formula is developed for the ratio of output for total and partial coincidence in terms of the pulse width and circuit parameters; in a practical case with a pulse width of 1μ second a fourfold to threefold output ratio of 40 is obtained. Mention is also made of a combination diode‐pentode coincidence circuit.
18(1947); http://dx.doi.org/10.1063/1.1741001View Description Hide Description
The use of NaBO2 as a target material for the preparation of radioactive Na24 through the deuteron bombardment reactionis discussed. The general advantages of NaBO2 as a target material, compared to metallic sodium or other sodium containing compounds, are given, as well as the procedure for target preparation and the details of the chemical treatment used for the purification of the Na24.
The general use of metaborate targets is discussed briefly for other deuteron bombardment reactions in which an elementary target material is less practical to use.
18(1947); http://dx.doi.org/10.1063/1.1741002View Description Hide Description
An electrostatic analyzer has been built for use with the high pressureelectrostatic generator at the University of Wisconsin. The proton beam from the generator is deflected through a 90° arc of 40″ radius by means of a radial electric field between curved metal plates spaced apart. Suitably disposed slits select a beam which has a very small energy spread. The apparatus has been operated with energy resolutions up to 5000, and preliminary tests have been made, using the 985‐ and 1020‐kv γ‐ray resonances in the reaction Al27+H1→Si28+hν.
18(1947); http://dx.doi.org/10.1063/1.1741003View Description Hide Description
The prototype of the computers in question is a Wheatstone bridge, with the resistances in two opposite legs proportional to two magnitudes, x 1 and x 2, respectively, and the resistance in a third leg proportional to x 3. The fourth leg is adjusted to balance the bridge, either manually or by a servo mechanism. The resistance of the fourth leg is then proportional to x 1 x 2/x 3. This bridge can be generalized by replacing the resistors in each leg by a series connection of resistors, each of which is proportional to a variable. Such a bridge solves quadratic equations, but only if the equation is of rank 4 and signature zero. By connecting several resistances in parallel into each leg of the bridge, one can solve higher order equations. A bridge used for the solution of a quartic equation will be shown. The equation was the equation of a straight line in bipolar coordinates and was used to guide an airplane on a straight line when the distances of the plane from two fixed ground stations were known by Shoran.
18(1947); http://dx.doi.org/10.1063/1.1741004View Description Hide Description
The general features of electron collection in a parallel‐plate ionization chamber are discussed with reference to the detection of single particles. If the particles come from the surface of one of the electrodes and end their paths within the chamber, the pulses obtained by electron collection can give information regarding the energy of the particles, their range, the angle between the tracks and the field of the chamber, and their ``range‐energy'' function. Electronic and photographic measurements are described which confirm the expected form of the pulses and indicate the quantitative possibilities of this method of detection.
18(1947); http://dx.doi.org/10.1063/1.1741005View Description Hide Description
An apparatus is described for heating an x‐ray specimen to 1200°C in vacuum while its diffraction pattern is being recorded continuously on a Geiger counter spectrometer. The heater consists of a length of 0.030‐inch tungsten wire embedded in beryllium oxide, the whole enclosed in a polished tantalum case. Either a flat metal sheet, or powder packed in platinum gauze mounted on sheet metal is suitable as a specimen. An area about one centimeter square in the center of the specimen is irradiated by the x‐ray beam in the focusing type of spectrometer. The temperature is uniform over this area to ±5 degrees centigrade. Two concentric radiation shields reduce heat loss. The outer shield also acts as the vacuum‐tight body of the oven and has beryllium windows to pass the x‐rays. Results indicate that rapid structure changes may be observed as they occur with this apparatus.
18(1947); http://dx.doi.org/10.1063/1.1741006View Description Hide Description
A method based on kinetic theory principles has been developed whereby the slope of the vapor‐pressure temperature curve of a liquid can be obtained at 25°C when the vapor pressure is of the order of 10−7 mm Hg at this temperature. A simple apparatus consisting of a boiler, slit system, and target is used to determine a dew point of the material under high vacuum. From the temperature of this dew point the slope can be calculated directly. If in addition a single value is known by other methods for the vapor pressure in the region of 10−3 mm then the value at 25°C is easily found. The results are believed to be accurate to 30 percent, as contrasted with other methods which give errors of several hundred percent in this region.
18(1947); http://dx.doi.org/10.1063/1.1741007View Description Hide Description
- LABORATORY AND SHOP NOTES