Index of content:
Volume 25, Issue 3, March 1954
25(1954); http://dx.doi.org/10.1063/1.1771023View Description Hide Description
A flowmeter system is described which gives continuous readings of flow velocity, with a fast rate of response. The ``upstream‐downstream'' method is used in which velocity of a fluid is determined by measuring the phase difference between an upstream and downstream ultrasonic wave of, say, 100 000 cycles. The functions of the transmitting and receiving transducers are interchanged at a fast rate, say 100 cycles per second, allowing the use of a synchronous rectifier. In this way, no long time stability of the phasemeter is required so that very small flow rates can be measured.Velocities as low as 0.1 cm/sec were successfully measured. A special commutator switch with very low transfer capacitance and, as an alternative, an electronic switch are described. The transducers used are barium titanate crystals mounted in a manner so that their contact with the fluid is avoided.
25(1954); http://dx.doi.org/10.1063/1.1771024View Description Hide Description
An instrument is described which makes possible universal evaluation of time‐displacement records with regard to velocity and kinetic energy, acceleration and accelerating force, time, and displacement. It consists of a measuring device for reading distances, angles, and second derivatives, and a slide rule for direct conversion of the measured values into the desired values. The instrument can be attached to a standard drafting machine of a drawing board. It has many advantages over the present methods of evaluation; no lines need to be drawn on the record, and the instrument permits much more rapid evaluation with fewer errors and can be used by less highly trained personnel.
25(1954); http://dx.doi.org/10.1063/1.1771025View Description Hide Description
The process of generating millimeter microwave energy from a crystal multiplier driven by a reflex klystron is discussed. Quantitative data are given on the intensity of the various harmonics down to a wavelength of 1.9 mm. A harmonic generator of novel construction which has proven superior to the previously used types is described, and the details of our version of a built‐in crystal detector are given.
25(1954); http://dx.doi.org/10.1063/1.1771026View Description Hide Description
A new technique for the calibration of static, differential pressure sensing devices is described. The system of calibration is explained and the necessary equations are developed in detail. The basis of this technique for producing known values of very small static pressure differences is that of the air centrifuge. This method has been employed for developing pressure differences as small as 10−6 psi.
25(1954); http://dx.doi.org/10.1063/1.1771027View Description Hide Description
The primary considerations which were employed in the design of a cloud chamber for a recent experiment were to incorporate into its characteristics as high a magnetic field strength and as short a cycle time as practical, and a sequencing control circuit which would be both simple to adjust and reliable over long periods of data‐taking time. A description is given of the important constructional details of the cloud chamber as well as a discussion of the more important auxiliary circuits. These are: the control circuits for the diesel‐driven generator which supplies the current for the cloud‐chamber field coils, the pulsed light system for photographic illumination, and the temperature regulating circuit for the cloud chamber.
25(1954); http://dx.doi.org/10.1063/1.1771028View Description Hide Description
The method and apparatus are described for determining velocities of detonation over one to five adjacent segments of an explosive charge. Time intervals are determined to the nearest 0.1 microsecond, which permits an accuracy of the order of 1 percent where distances of 10 centimeters are employed in 7000 m/sec explosives. Representative data are included to show the accuracy of the method as well as application techniques.
25(1954); http://dx.doi.org/10.1063/1.1771029View Description Hide Description
A parallel‐plate chamber with electrode separation variable from 2 mm to 2 cm has been used to measure recombination, attachment, and energy resolution for beta‐ray ionization in liquid argon. A collecting voltage up to 30 kv was used without introducing spurious pulses. Amplifier noise sets the lower limit to beta‐ray detection at about 150 kev and limits the energy resolution to about 100 kev (full width at half maximum at any energy).
25(1954); http://dx.doi.org/10.1063/1.1771030View Description Hide Description
A description is given of apparatus used to measure the heat capacity of metal wires by pulsed heating. The electrical energy supplied to the wire is determined with respect to a platinum standard while the temperature rise is determined from the change in resistance and the measuredtemperature coefficient of resistance. A maximum error of 5 percent in the specific heat might be expected with the apparatus as built, but the results agree with most published data to within a few percent in the range 0°C to 650°C.
25(1954); http://dx.doi.org/10.1063/1.1771031View Description Hide Description
The transit time of an electron between the cylinder and the central wire of a self‐quenching Geiger counter has been measured as a function of several counter parameters. The partial pressure, total pressure, and nature of the filling mixture were varied. The measured times are presented in graphic form.
A Semi‐Automatic Electrical Manometer Designed to Calibrate a Mach‐Zehnder Interferometer System for the Recording of Transient Pressure Changes25(1954); http://dx.doi.org/10.1063/1.1771032View Description Hide Description
A pressure‐sensitive element is described which provides an electrical output proportional to the pressure difference existing on the two sides of the element. By means of an electrically conducting lead in each arm of a U‐tube manometer the liquid (mercury) represents the contact point of a potentiometer; under the influence of an applied pressure this contact point is moved electrically. In the application described, the variation of light intensity at a point in the fringe system of an optical interferometer is calibrated as a function of density or pressure changes occurring in one of the interfering light beams.
25(1954); http://dx.doi.org/10.1063/1.1771033View Description Hide Description
An apparatus has been developed for the determination of the melting temperatures of alloys up to 2200°C, which attains blackbody conditions for the temperature measurements and precludes the possibility of contamination from a refractory container. Its operation has been checked by melting gold,nickel,iron,titanium,platinum,zirconium, and rhodium with an average reproducibility of ±5° and an average deviation from the recognized melting points of 5°C. The melting point of pure vanadium has been determined as 1919±2°C.
25(1954); http://dx.doi.org/10.1063/1.1771034View Description Hide Description
An instrument for the accurate measurement of resistance in the range 109 to 1013 ohms is described. A constant current flows through the resistor under test, and the resulting potential drop is measured with an electrometer. The constant current is the displacement current flowing through a standard condenser when the potential difference across the condenser changes linearly with time. The potential drop across the resistor is measured by a recording dynamic‐condenser electrometer. Provision is made for measuringresistance with potential drops from 3 mv to 10 volts across the resistor. The accuracy of the resistancemeasurement is dependent only upon wire‐wound potential dividers, the dimensions of a parallel plate condenser, and the power‐line frequency. The accuracy of the present instrument is about 0.5 percent. For this accuracy, the time of measurement is about 6R×10−11+10 seconds.
25(1954); http://dx.doi.org/10.1063/1.1771035View Description Hide Description
Angular distributions of elastically‐scattered protons, and of deuterons, tritons, and alpha particles from (p,d), (p,t), and (p,α) reactions are being measured with the internal 22‐Mev proton beam of the Oak Ridge National Laboratory 86‐in. cyclotron. The particles are detected by observing the activities induced by them—Cu(p,n)→38 min for protons,Pb(d,p)→3.3 hr for detuerons, Co(t,p)→1.6 hr for tritons, and P(α,n)→34 min for alphas. Energy discrimination is obtained by absorbers. The energy and energy distribution of the incident beam are found by measuring the excitation function for Cu(p,n) and comparing with published data. The angle of incidence and its inhomogeneity are determined by beam‐locating experiments, and checked by the Rutherford law for elastic scattering from heavy elements at small angles. The current is monitored by neutron counters, and measured by counting the activity in the target after bombardment. This is calibrated in a separate run against the published Cu(p,n) cross section. The background is reduced (to <5 percent at most angles) by various types of carbon shielding. Several projects based on these methods have been carried out using the ORNL 86‐Inch Cyclotron, and extensions to other types of measurements are in progress.
25(1954); http://dx.doi.org/10.1063/1.1771036View Description Hide Description
A camera lens system, applicable to a schlieren optical system, is described, that yields an image in which the magnification perpendicular to the airflow is much greater than the magnification parallel to the airflow. Examination of boundary layer development along an airfoil surface is thereby facilitated. Optical design formulas are given and illustrated by an example in which a 24‐to‐1 ratio of magnifications is obtained without loss of schlieren sensitivity and without noticeable aberrations.
25(1954); http://dx.doi.org/10.1063/1.1771038View Description Hide Description
The properties of the focusing systems using alternating convergent and divergent electrostatic lenses which were proposed by Courant et al. and Blewett are studied in detail, applied to Alvarez type of linear accelerators. It is found that the introduction and the removal of the focusing force of the system can be made approximately adiabatic by using half‐length injection and extraction lenses. The appropriate choice of the parameters of the lenses in practical cases and the behavior of the ion beam going through such a system are discussed. The results can easily be reinterpreted to apply to magnetic lens systems.
25(1954); http://dx.doi.org/10.1063/1.1771039View Description Hide Description
A system is described for obtaining quantitative amplitude distribution data for events which can be displayed as proportional voltage pulses for visual observation on a cathode‐ray oscilloscope. The use of a circuit which intensifies the top of each flattened pulse during display permits photographing the events as dots on a moving 35‐mm film at rates of 20 000 per sec or greater. An automatic electromechanical ``reader'' is described which will scan the resulting film and produce a printed record of the number of events in each of 100 discrete ``channels'' with an accuracy comparable to the best available from other ``kicksorting'' schemes. A spectrum of over 500 000 events can be recorded on 100 feet of film.
25(1954); http://dx.doi.org/10.1063/1.1771040View Description Hide Description
An electronic voltage integrator has been used in the magnetic measurements program of the Berkeley Radiation Laboratory since 1948. The device can explore magnetic fields in the range from 500 to 15 000 gauss to an accuracy of better than one percent. The heart of the integrator consists of a direct coupled high gain amplifier that is connected in a ``feedback time constant'' circuit. The amplifier uses the cascode connection, the filament drift compensation circuit of Miller, and an internal positive feedback adjustment for ``infinite'' gain. Some other features of the integrator amplifier include low grid current operation, large linear output range, and provision for adjustment of the input and the output voltages to zero potential when no signal is present.
25(1954); http://dx.doi.org/10.1063/1.1771041View Description Hide Description
An electron‐beam tube capable of accurate, high‐speed, analog multiplication has been built and tested under both static and dynamic conditions. The maximum errors in multiplication under static conditions were approximately two percent of the maximum product; the output voltage corresponding to the maximum product was approximately three volts. Dynamic measurements show that with sinusoidal input voltages the performance is independent of frequency up to at least 100 kilocycles per second at the output, except for the effects of parasitic capacitance shunting the output circuit. The capacitance effects can be made negligible by appropriate choice of impedance levels.
25(1954); http://dx.doi.org/10.1063/1.1771043View Description Hide Description
The beam of a linear accelerator has desirable properties regarding its geometry but frequently contains secondaries produced in the machine and has an unsuitable energy spectrum.
Two systems have been designed which translate the accelerator beam without energy dispersion. In the one system, now in operation, the emergent beam has an ``energy focus,'' i.e., a point at which the initial beam geometry is reproduced independent of energy. The second system is designed to produce a beam translated but otherwise unmodified in geometry, independent of beam energy to the first order.
Both systems permit easy control of energy width and produce a beam free from secondaries.