摘要:

Many liquids, which are normally isotropic, become double refracting when subjected to shearing stresses produced by a velocity gradient established within them. A detailed description is given of a concentric cylinder apparatus in which velocity gradients of the order of 4000&pgr; sec−1have so far been produced. Higher values are possible. The annular gap between the cylinders varies from about 0.3 mm to 0.8 mm and has an average radius of about 25 mm. The outer cylinder can rotate at speeds up to 2500 rpm or more: these are accurately determined by an electronic tachometer. The inner cylinder can be rigidly clamped or allowed to move subject to restriction by a beryllium copper torsion wire. In the latter case the viscous drag due to the moving liquid can be measured, as in a Couette viscometer, and hence values for the viscosity coefficient found simultaneously with measurements of double refraction. A cooling system, controlled by thermostats, is provided to maintain the liquid at a constant temperature; this is recorded by a thermocouple embedded in the inner cylinder. The optical system is described with brief details of the methods for the determination of the extinction directions in the liquid and the magnitude of the double refraction. The latter is measured by a sensitive quarter‐wave plate compensator with a half‐shadow device. The accuracy of the instrument is fully discussed.

ISSN:0034-6748    

DOI:10.1063/1.1715177

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

A fast neutron spectrometer, using the time of flight method, which may also be used to study reactions involving the simultaneous emission of neutrons and gamma rays, is described. One stilbene scintillation counter is placed close to the source, the other a suitable distance away. The two are connected to a new type of coincidence time sorter which converts delay time between associated events into a pulse amplitude distribution which may be analyzed by a kicksorter, so enabling the whole range of delay times or energies to be displayed and recorded at one time. The delay time may result from neutron flight time following scattering in the first counter, from the time of flight of a neutron from the target associated with a gamma ray entering the first counter, or from a charged particle associated with a gamma ray. Using D(d,n)He3neutrons and a flight path of 50 cm, it has been possible to measure the energy with an accuracy of 10%. Angular correlations arising from (−,n&ggr;) reactions may be studied with energy discrimination of the neutrons; typical results are presented for the case Be9(d,n&ggr;)B10.

ISSN:0034-6748    

DOI:10.1063/1.1715178

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

High sensitivity and wide‐band frequency characteristic for a microwave spectrograph are required for the detection of weak absorption lines and for researches on the hyperfine structures of the spectral lines of free molecules in the millimeter wave range. In order to improve the important components of spectrograph, the author has designed a low‐loss K‐band Stark cell, a frequency multiplier of wide‐band frequency character, a Wheatstone bridge‐type triode lock‐in detector and a compact square wave generator. The overall sensitivity of the spectrograph using these elements was about 5×10−8cm−1in the 6 mm wave range. Thus, the author has succeeded in detecting new spectral lines [J. Phys. Soc. Japan9, 135 (1954)] of CH2O and in observing their new magnetic hyperfine structures (to be published).

ISSN:0034-6748    

DOI:10.1063/1.1715179

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

A 180° point‐focusing magnetic spectrometer was constructed for high resolution analysis of the momentum distribution of protons up to 2 Mev in energy. Mechanical adjustments of the poles enabled the field shape to be empirically adjusted for minimum radial aberration in the focal plane. The aperture is 0.0025 steradian, and the momentum resolution is better than 2000.

ISSN:0034-6748    

DOI:10.1063/1.1715180

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The operation of proportional counters at temperatures up to 900°C has been investigated and it is shown that the factors determining the maximum working temperature are thermal emission of electrons from the cathode, and the conductivity of heated insulating materials. Several types of proportional tubes are discussed and the advantages of counters with external cathodes are pointed out. Pulse spectra from quartz and glass counters containingK‐capture A37sources indicate satisfactory operation at temperatures of 810°C in the case of quartz and 450°C in the case of glass.

ISSN:0034-6748    

DOI:10.1063/1.1715181

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The neutron transformation of helium‐3 has been applied to neutron spectroscopy in the medium energy range in order to overcome the disadvantages of previous methods which have usually been based on neutron scattering. By observing the pulse‐height distribution when a proportional counter filled with helium‐3, krypton, and carbon dioxide is irradiated with neutrons, the spectrum can be obtained. Details of the counter construction and vacuum equipment for filling the counter are described. In the range of energy from thermal to 1 Mev the spread (relative standard deviation of a peak) is about 3% and the wall effect agrees with theoretical predictions. The pulse height varies linearly with energy and some evidence suggesting that the mean energy required to produce an ion pair in krypton for helium‐3 nuclei is about 6% greater than that for protons is presented. Since the neutron reaction cross section of helium‐3, as a function of energy, is required to evaluate neutron spectra from observed distributions, it has been remeasured in the range 120 kev to 1 Mev with greater accuracy than previous measurements made by J. H. Coon [Phys. Rev.80, 448 (1950)].

ISSN:0034-6748    

DOI:10.1063/1.1715182

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

A point focusing x‐ray monochromator which uses Bragg reflection from a single lamina of quartz bent in such a way that its atomic planes are given two principal radii of curvature has been constructed for use in low‐angle diffraction studies. It was found that the crystal reflects 2.78% of the incident Cu K&agr;1radiation into a converging beam one meter long, with a resolution of better than half a millimeter except for a very faint halo. The instrument has been used to obtain diffraction patterns from normal and sickle‐cell human hemoglobin and also from southern bean mosaic virus. The speed of the present instrument is roughly two hundred times that of an equivalent pinhole collimating system. A similar but still faster instrument is being constructed.

ISSN:0034-6748    

DOI:10.1063/1.1715183

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Controls are described for maintaining a constant level of liquid nitrogen in a still‐head can. A small electric solenoid valve is employed directly in the liquid nitrogen line, operating under the control of a sensitive level switch. The method and associated instruments are described, including a rapid means for changing supply cans.

ISSN:0034-6748    

DOI:10.1063/1.1715184

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The high‐pressure diffusion cloud‐chamber system in use at the University of Chicago is described. The chamber is characterized by (1) 30 atmospheres of hydrogen operating pressure, (2) a sensitive volume 16 inches in diameter and 2½ to 3 inches deep, (3) a quite uniform and accurately known magnetic field of 12 600 gauss, and (4) unit assembly in which the magnet pole is an integral part of the chamber. Pictures are analyzed by a three‐dimensional reprojection system designed to eliminate optical distortion. Devices for rapid and accurate measurement of several different types of events are described.

ISSN:0034-6748    

DOI:10.1063/1.1715185

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

A relative method has been developed whereby two conventional flow calorimeters, connected in a series combination, serve to determine the ratio of theCpof a fluid in one state to that in another, this ratio being measured as a function of resistance ratios. Measurements of flow rate and of power input are not required, while simplifications in other respects are also to be found.Although its determinations are not ``absolute,'' the gains in speed and simplicity, without loss of accuracy, are considered sufficient to warrant its use in exploratory work or in researches requiring the extension of known values over new temperatures and pressures, as is often the case with tables. The method is offered, therefore, as a worthwhile research tool. A brief description is given.

ISSN:0034-6748    

DOI:10.1063/1.1715186

出版商:AIP    

年代:1955

数据来源: AIP