Volume 27, Issue 9, September 1956
Index of content:
27(1956); http://dx.doi.org/10.1063/1.1715670View Description Hide Description
A 256‐channel pulse‐height analyzer using a magnetic core memory is now in use at the Argonne National Laboratory. This analyzer uses a form of the Wilkinson method of generating numbers in response to input pulses. These numbers are proportional to the amplitudes of the input pulses, and correspond to the channel numbers into which the individual counts are to be recorded. The digital data processing circuits comprise a simple computer, with an internal memory which can store 256 sixteen digit binary numbers. A cathode‐ray tube display of the data in the form of a plot of counts versus channel number is available during and after operation. Permanent readout is in the form of a similar curve traced by a recording potentiometer. Printed decimal readout is also available. The normal average analyzer dead time is 80 μsec, and pulse rates in excess of 5 million per minute at the input circuit can be tolerated without appreciable data distortion.
27(1956); http://dx.doi.org/10.1063/1.1715671View Description Hide Description
A 1024‐channel time‐of‐flight analyzer for recording data obtained in neutron time‐of‐flight experiments has been placed in operation at the Argonne National Laboratory. Channel widths are adjustable from ½ μsec to essentially any higher value. The analyzer dead time is 16 μsec following each recorded count. The storage circuits may be divided into two sections for recording events detected by two separate counters. The analyzer may also be divided into four groups of 256 channels each. These groups may be independently located in any time region up to 4096×T, where T is the channel width in use. Readout is by means of simultaneous teletype punched tape and analog pen recording. There is a linear cathode ray tube display of counts vs channel number. The device uses a magnetic core memory system similar to that used in the 256 channel pulse height analyzer described in the preceding article.
27(1956); http://dx.doi.org/10.1063/1.1715672View Description Hide Description
A little trick is described, which facilitates the carrying out of anatomical or physiological preparations that are extremely delicate to handle with free hands. It consists mainly in a support and a screwdriver acting as a lever to reduce the movements of the hands.
For very fine micromanipulations, where even touching the operating table must be avoided, an air‐driven micromanipulator has been built, in which a small air‐driven turbine rotates the adjusting screws of the manipulator. Movement in various directions can be performed by pressing keys which open air pressure valves. All the movements can be programmed in advance by means of prepunched holes in a paper strip of the type used in teletype systems.
27(1956); http://dx.doi.org/10.1063/1.1715673View Description Hide Description
The apparatus described here permits the study of phase diagrams either by heating or cooling. One temperature control circuit permits a preset temperature gradient, either positive or negative, to be maintained between the sample and bath with the temperature of the bath being controlled by that of the sample. The appearance or disappearance of solids in the sample is followed by measurement of the light transmission of the sample. A second control circuit provides constant bath temperatures. A step‐wise approach to the liquidus point, with the light transmission used to indicate the establishment of equilibrium between solid and liquid at each step, offers a means of determining this point under equilibrium conditions.
27(1956); http://dx.doi.org/10.1063/1.1715674View Description Hide Description
Two Faraday‐cup electron collectors have been developed which are capable of measuring the absolute integrated beam current of the Stanford linear accelerators to better than 0.5% at electron energies ranging from 4 to 300 Mev. A description of these instruments is given and complete design criteria are offered which allow the extension of the range to Bev energies.
27(1956); http://dx.doi.org/10.1063/1.1715675View Description Hide Description
27(1956); http://dx.doi.org/10.1063/1.1715676View Description Hide Description
Expressions are derived relating counting rate measured with quantum detectors to the dosage rate in roentgens. The number of quanta/cm2 per roentgen is strongly energy dependent. In the x‐ray region 5 to 50 kv, however, the variation of the quantum counting efficiency with wavelength of some counters (e.g., argon Geiger counter) matches fairly closely the energy dependence factor, and hence such detectors can be used as r‐meters.
27(1956); http://dx.doi.org/10.1063/1.1715677View Description Hide Description
The square‐wave principle for electromagnetic flow recording offers several theoretical advantages over the dc or ac systems, particularly for blood flow recording from intact vessels. The degree to which these advantages may be obtained in practice depends upon the extent to which the equipment meets the specific requirements of the principle. This paper considers the objectives that should be considered in design and construction of a practical equipment.
27(1956); http://dx.doi.org/10.1063/1.1715678View Description Hide Description
The importance of Compton backscattering in gas proportional spectrometry in the energy range 10 to 100 kev is pointed out. If the backscatteredphotons are unresolved from the main peak, a large error may be introduced under certain conditions in absolute and relative intensity measurements based on theoretical quantum efficiency (geometry×absorption); if the backscattered peak is resolved, failure to recognize its origin may result in the ``discovery'' of a new gamma ray. The effect is especially pronounced when a collimator is used to establish geometry; for example, the intensity of backscatteredphotons can amount to as much as half the intensity of the main peak at 46.5 kev with a ¼‐in. diameter collimator.
27(1956); http://dx.doi.org/10.1063/1.1715679View Description Hide Description
An apparatus is described which provides a simple means of obtaining stirring or pumping action in a pressurized system. Since no packing glands are employed, the device is leak‐proof. The required mechanical action is provided by reciprocating motion of a soft‐iron armature enclosed in the system and driven by a pair of electromagnetic coils. Input to the coils is provided by a thyratron‐controlled circuit. The circuit and constructional details are given.
27(1956); http://dx.doi.org/10.1063/1.1715680View Description Hide Description
An iterative numerical integration procedure has been developed to correct both beta spectra and differential beta‐gamma directional correlations for the effects of finite instrument energy resolution including the effect of backscattering from a scintillation detector.
The method has been tested and found to reproduce the true spectral shape in the cases of Re186, Au198, Tl204, and to allow separation of composite beta spectra as in the case of W187. Application of the method is limited to maximum beta energies exceeding 200 kev.
27(1956); http://dx.doi.org/10.1063/1.1715681View Description Hide Description
The operation of an omegatron is discussed with polyphase electric excitation. Use is then made of this analysis to investigate the ionic trajectories in an omegatron in which the natural frequency of the ion is a function of the orbital radius. This circumstance comes about from either the influence of space charge or from the use of a magnetic field which decreases with increasing radius.
The nonuniform magnetic field and the radial electric field can enhance the resolving power. It also influences the peak shape, causing the sides to be nearly vertical.
Trapping of the ions is essential for satisfactory operation of the omegatron. Two experimentally proven means of accomplishing trapping are presented.
27(1956); http://dx.doi.org/10.1063/1.1715682View Description Hide Description
The solution calorimeter described previously [Rev. Sci. Instr. 26, 477 (1955)] has been modified by using an electrically heated shield for the adiabatic control. In this way the response time has been decreased by a factor of ten which greatly facilitates operation of the control. Under steady conditions the fluctuation in temperature between the calorimeter and its surroundings has been reduced from ±0.002 to ±0.001°C max. The calorimeter has a working range of 10° to 50°C.
27(1956); http://dx.doi.org/10.1063/1.1715683View Description Hide Description
An apparatus originally conceived for directly preparing capillaries of powders of reactive alloys for x‐ray study inspired the present device. The unit is simply a hermetically sealed chamber which is provided with a drive mechanism at the top, specimen and sight ports at the sides, and a funnel at the bottom. The drive mechanism is used to rapidly rotate a rotary cutter. Particles of any desired size are produced by a suitable choice of cutter and screen. The unit is extremely effective in its original role but has been used to prepare small quantities of powders of reactive alloys for other purposes, and is a versatile research tool.
27(1956); http://dx.doi.org/10.1063/1.1715684View Description Hide Description
A means for measuring the density or the volume of the whole body is essential to reliable estimates of fat in humans. Although Archimedes' principle has often been employed to determine density directly, a method that is less demanding on the subject has been developed for measuring body volume. The apparatus is a closed‐circuit system consisting of two chambers and utilizing a gas‐dilution principle. With the subject in one chamber and helium in the other, the gases in the system are mixed. The helium concentration, measured by thermal conductivity, is related to the tissue volume displacement of the subject. The standard deviation in volume determination is estimated as ±0.12 liter.
27(1956); http://dx.doi.org/10.1063/1.1715685View Description Hide Description
An atomic clock utilizing the Stark effect has been designed and constructed. In this clock, the error caused by the reflections in the microwave circuits has been successfully reduced to within the error by random noises, and the authors are sure of its possibility of long time operation. The accuracy has been estimated to be about 5×10−9 from observation of the received frequency of the standard station JJY, and comparison with the frequency of a quartz chronometer. The various components of this clock are described in detail, and the theoretical limits of the accuracy are also discussed.
27(1956); http://dx.doi.org/10.1063/1.1715686View Description Hide Description
The power sensitivity and the line voltage variation effects of a phase‐shifting thermoregulator making use of a thermal element in a Wheatstone bridge and a grid‐controlled thyratron are expressed in terms of the circuit parameters. The conditions for line voltage variation compensation are derived and the calculated results are found to be in good agreement with the experimental value.
27(1956); http://dx.doi.org/10.1063/1.1715687View Description Hide Description
For direct measurements of electron intensities in the image plane of the RCA electron microscope a scanning electrometer device has been designed. It consists of a probe and preamplifier, a mechanical drive, an amplifier, and a recording unit. A linear resolution of 0.06 to 0.92 μ is achieved. Sensitivity range is 10−12−10−11 amp.
27(1956); http://dx.doi.org/10.1063/1.1715688View Description Hide Description
An electromechanical device is described for computing the two‐dimensional structure factor formulas,.fr, ur, vr are fractional and may be fed in to the third decimal place; h and k may vary from −20 to +20. Each term in the series is computed individually to an accuracy of approximately ½% and is automatically added to the existing sum whilst the next term is being computed. The speed of computation is generally equal to the speed with which the variables of each term are fed into the computer. The machine makes use of ``magslip'' resolvers for computation of the trigonometrical functions.
27(1956); http://dx.doi.org/10.1063/1.1715689View Description Hide Description
An improved four‐window demountable rotating anode x‐ray tube fitted with rapidly interchangeable targets has been constructed. Compactness equal to that of a standard sealed‐off tube has been achieved by the use of an improved re‐entrant vacuum seal and bearing assembly. By employing peripherally directed water cooling in the anode behind the focal spot and a full wave rectified high tension supply, it has been possible to obtain greatly improved performance. With a copper target five inches in diameter rotating at 1000 rpm and with a focal spot 8×0.5 mm, the continuous load at 50 kv was 120 ma without any signs of target erosion.