Volume 20, Issue 12, December 1949
Index of content:
20(1949); http://dx.doi.org/10.1063/1.1741416View Description Hide Description
A rapidly responding calorimeter for continuous recording of biological heat exchange has been described. The method is based on the enclosure of the subject in a shell completely lined with a uniform heat flow metering layer (``gradient layer'') while ventilatory and respiratory heat losses are determined in heat exchange meters based on the same technic. The measurement comprises in one thermoelectric potential the sum of all components of heat loss (radiant, convective, conductive, and evaporative fractions). Partitioning measurements of respiratory and evaporative heat losses are readily obtained. Environmental conditions can be closely controlled, and widely varied.
The gradient calorimeter with its rapid response (time lag 42 seconds) is specifically designed for studies of reflex mechanisms involved in temperature control. It is, however, suggested that the characteristics described will, in general, encourage wider application of direct calorimetry in experimental and clinical studies.
20(1949); http://dx.doi.org/10.1063/1.1741417View Description Hide Description
The capabilities and limitations of several impulse generators and voltage dividers, and a micro‐oscillograph sweep circuit for dealing with kilovolt impulses in the millimicrosecond range, are described. The most successful combination produces and measures an impulse of a rise time equal to 4×10−10 sec.
20(1949); http://dx.doi.org/10.1063/1.1741418View Description Hide Description
A large double magnetic lens spectrometer has been constructed for the study of gamma‐ and beta‐ray spectra. The magnetic field is produced by two identical coaxial water‐cooled coils, each 10.2 cm wide, 31.7 cm I.D., 73.7 cm O.D., and spaced 95.6 cm apart. The source is placed on the axis at the center of one coil and the detector is placed on the axis at the center of the other. The instrument is characterized by a large transmission with moderate resolution. Scattering is virtually absent because of the nature of the trajectories which are used, and because the large dimensions have made possible the removal of scattering material to a considerable distance from the source. The design has lent itself easily to the application of accelerating voltages at the detector admitting the detection of beta‐rays down to 1 kilovolt. The maximum energy conveniently studied with the present arrangement is 2.8 Mev. Beryllium‐coated Zapon films of thickness 0.01 mg/cm2 have been used to mount sources. Charge does not accumulate on these sources. Observations with a Cs137 source 4 mm in diameter have shown a transmission of 1.4 percent with a resolution of 1 percent. The appearance of the internal conversion and Auger electron lines testifies to the absence of appreciable scattering.
20(1949); http://dx.doi.org/10.1063/1.1741419View Description Hide Description
A small scale differential analyzer is described which uses ball carriage integrators instead of the usual Kelvin disk integrators, and selsyn angle transmission instead of mechanical coupling of the rotating parts. The machine is inexpensive, easily constructed and is moderately accurate.
20(1949); http://dx.doi.org/10.1063/1.1741420View Description Hide Description
A slide rule has been developed to facilitate rapid calculations based on the Planck radiation formula. Quantities such as the radiant flux density in a given wave‐length region, the spectral radiant flux density at a given wave‐length, or the corresponding quantities expressed in photon units, can be obtained readily for a black body over a range λT=2×102 to λT=4×106 micron degrees with an accuracy of about 1 percent. Simple extension rules can be used for larger values of λT.
20(1949); http://dx.doi.org/10.1063/1.1741421View Description Hide Description
The oxygen consumption of fish and other aquatic animals can be determined in the gas phase of a closed system provided the water is thoroughly equilibrated with the gas phase. The present respirometer employs a simpler and more efficient equilibration system than the earlier described model [Scholander, Haugaard, and Irving, Rev. Sci. Inst. 14, 48 (1943).] and permits a continuous recording of the oxygen consumption over a considerable range. The apparatus is well suited to be set up in banks and has been used extensively in temperature studies on arctic and tropical fishes and crustaceans.
20(1949); http://dx.doi.org/10.1063/1.1741423View Description Hide Description
An x‐ray pulse generator capable of producing short bursts of x‐rays not greater than 3×10−7 seconds in duration has been constructed. These short bursts are obtained by supplying a negative 50 kv, 12.5 Joule trigger pulse to the cathode shield of a standard Westinghouse W.L. 389 flash x‐ray tube. This pulse generates a pre‐discharge plasma in the tube which blocks the main 100 kv, 290 Joule pulse until the cathode to anode gap impedance is lowered by ionization.
An arrangement is also described whereby 3 separate, successive radiographs of a single detonation may be taken at predetermined time intervals.
20(1949); http://dx.doi.org/10.1063/1.1741424View Description Hide Description
An ionization chamber is described which is nearly air‐equivalent from 0.5 to 2.5A, ``effective wave‐length.'' It has been made adaptable for use with the electrometer and charging system of the Victoreen Minometer. Its sensitivity is of the order of 0.15 roentgen per scale division. Suggestions are made for possible improvements.
20(1949); http://dx.doi.org/10.1063/1.1741425View Description Hide Description
An instrument is described for measuring x‐ray back reflection patterns for surface stress determinations. The chief feature of the apparatus is a curved slit in the optical system so that the beam of light which scans the diffraction ring is an arc having the same radius of curvature as the ring. This simple, inexpensive instrument has been found to be at least as precise as a microphotometer for these measurements and its use has resulted in a considerable saving of time. It is suggested that the instrument might appropriately be called a photomicrometer.
20(1949); http://dx.doi.org/10.1063/1.1741426View Description Hide Description
A simple device is described in which pairs of pulses are produced that are moved continuously with respect to each other (wobbled) by an a.c. voltage that also sweeps an oscilloscope spot horizontally. The pulses are applied to both inputs of a coincidence system. Vertical deflection of the c.r. scope spot is caused by the output pulses of the system. Thus various characteristics can be made visible and the resolution can be read from the scope screen at a glance. With the instrument resolving powers from 3.10−6−10−9 sec. approx. can be determined. The apparatus was calibrated by feeding the wobbling pulses into a radio receiver. The output of the receiver has a sharp minimum when the pulse distance (Δt) satisfies the condition Δt=(1+2n)/2ν where n is an integer, ν is the frequency to which the receiver is tuned.
20(1949); http://dx.doi.org/10.1063/1.1741427View Description Hide Description
The image shapes resulting from 180° focusing of charged particles in a homogeneous magnetic field have been computed. General curves are presented in terms of three variables for variable ρ‐spectrometers (as in the case of photographic detection) and in terms of four variables for constant ρ‐spectrometers (as in the case of detection with a fixed counter). The variables are source and exit‐slit height, source width, angular selection, and exit‐slit width.
The advantages of using sources and exit‐slits with a large dimension parallel to the magnetic field (i.e., height) are noted.
20(1949); http://dx.doi.org/10.1063/1.1741428View Description Hide Description
A compact, all‐metal, multi‐stage thermal diffusion apparatus for the separation of isotopes in quantity in non‐corrosive gases at any pressure up to 175 lb/in.2 is described. For a particular gas the proper pressure may be well‐enough calculated in advance as that giving maximum separation factor in the last column only. Operating with neon at 3 atmos. pressure, and using 12 meters of column consuming 4.9 kw for 260 hours, 7 liters of gas with a Ne22 content of 93.4 percent were produced.
20(1949); http://dx.doi.org/10.1063/1.1741429View Description Hide Description
The voltmeter described herein is capable of measuring the average amplitude of a single pulse with a random error of 0.2 percent of full‐scale deflection. The instrument consists of a gated cathode follower bridge in conjunction with a ballistic indicator. In its present form the circuit responds to the average pulse amplitude over an arbitrarily selected interval of two milliseconds; thus, it measures the actual amplitude in the special case of a flat pulse of sufficient duration. The required input is 0.8 volt for full‐scale deflection. The nonlinearity is less than 1 percent of any given deflection throughout the major part of the range of the instrument.
20(1949); http://dx.doi.org/10.1063/1.1741430View Description Hide Description
Measurements have been made of root‐mean‐square noise voltage in the frequency range 0.5 to 200 c.p.s. generated by contacts sliding at low speeds using four arrangements of contacting bodies and various materials. Mercury with amalgamated probes gave the lowest noise levels. Some solid contacts operating with low friction on clean metal surfaces yielded values of generated noise below 1 microvolt at a sliding speed of 35 cm/sec. when two contacts were in parallel.
The noise increases with speed and varies with normal force. The r.m.s. generated noise voltage of a large number of independently mounted contacts in parallel is inversely proportional to the square root of the number of contacts.
20(1949); http://dx.doi.org/10.1063/1.1741431View Description Hide Description
The dependence of gamma‐ray counting efficiency on energy has been determined in the range 0.17 Mev to 2.76 Mev for a G‐M counter with a lead cathode. The efficiency for six energy values was found by coincidence measurements utilizing the disintegration of In111, Au198, Co60, and Na24. The result indicates a smooth increase in counting efficiency for increasing energy over the range of energies investigated.
20(1949); http://dx.doi.org/10.1063/1.1741432View Description Hide Description
The requirements of high gain and low background current in an electron‐multiplier tube for the direct detection of high energy particles are considered. The design and construction of an experimental electron‐multiplier tube with a stable over‐all gain of at least 108 and a background at room temperature corresponding to three or four electrons per minute released at the input is described. An 0.0008‐inch thick nickel window is provided in the tube envelope to admit the high energy particles to the multiplier. The efficiency of this device is compared quantitatively with that of a Geiger tube as a detector of beta‐particles. It is found that the over‐all beta‐particle counting efficiency of the tube is of the order of 1.3 percent, and that the efficiency of the oxidizedsilvermagnesium target surface is 4.9 percent for a uranium source and 6.0 percent for a strontium source.
20(1949); http://dx.doi.org/10.1063/1.1741433View Description Hide Description
A high resolution scale of four has been developed to be used in conjunction with the nuclear particle detection devices in applications where the counting rate is unusually high. Specifically, it is intended to precede the commercially available medium‐resolution scaling circuits and so decrease the resolving time of the counting system. The circuit will function reliably on continuously recurring pulses separated by less than 0.1 μsec. It will resolve two pulses (occurring at a moderate repetition rate) which are spaced at 0.04 μsec. A five‐volt input signal is sufficient to actuate the device.
20(1949); http://dx.doi.org/10.1063/1.1741435View Description Hide Description
A vibrating wire system for measuring weak magnetic fields is described for use in very small spaces. Quartz crystals are used for drivers to get sufficient velocity with very small displacements. To adjust the driving voltage to correspond exactly to the natural crystal frequency, the crystal is also used to regulate the oscillator.