摘要:

Techniques developed to study the kinetics of very fast luminescent systems are described. These techniques include lamps which generate subnanosecond light pulses and an instrument which measures their time characteristics. The lamps are of the gaseous discharge type. The conditions of gas pressure, capacitance, and gap width necessary to achieve fast light pulses have been established for several gases and mixtures of gases with oxygen. The experimental results indicate that high pressure (10 atm or larger) and minimum stray capacitance are required for lamps filled with pure gas. A lamp filled with hydrogen, and satisfying these requirements, yields light pulses with 0.35 nsec risetime and 0.5 nsec half‐width. The time characteristics of the fast light pulses are not affected by gap width in the range 0.1–0.6 mm. Lamps containing a mixture of a gas and oxygen produce similar light pulses at total pressures much less than 10 atm. The instrument used to study subnanosecond light pulses employs a modified image converter tube. The image converter tube converts a light pulse into a photoelectron beam which is subsequently sampled by sweeping over an aperture. A complete intensity vs time curve is achieved by varying the time at which the sample is taken. The time resolution of the instrument is dependent on the sweep rate and the transit time spread of electrons in the image converter. Experimental and theoretical results indicate that the time resolution is around 0.1 nsec. The sweep is produced by a special circuit, consisting of a series of avalanche transistors, which generates sweep voltages around 600 V/nsec and can be triggered, with time jitter less than 0.2 nsec, by an electrical pulse as short as 1 nsec and amplitude of 0.8 V. This circuit makes it possible to measure the time characteristics of any light source for which a small electrical pulse can be generated simultaneous with the light pulse. A special detecting system which measures the intensity of the sample taken from the electron beam makes it possible to measure, with high precision, very low intensity sources. Thus, the time characteristics of a light pulse which produces less than one photoelectron per pulse at the photocathode of the image converter can be measured down to one decade of its peak intensity.

ISSN:0034-6748    

DOI:10.1063/1.1719453

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Volume compression of isotropic solids at high pressure may be determined by measurement of the inductance of a coil wound tightly around the sample. For isotropic compression of a coil, inductance is exactly proportional to the cube root of coil volume. Cores of tungsten, strontium titanate, cadmium sulfide, and sodium chloride were compressed to 55 kbar to test coil performance. The reproducibility of compression values varied from ±5 to ±15%. The observed compressions agree closely with other published results on compression and elastic constants. For nonconductive samples, no corrections need be applied to the volumetric data.

ISSN:0034-6748    

DOI:10.1063/1.1719454

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A new method is described for making composite samples for the x‐ray diffraction, back reflection pole figure technique. Considerable savings, in material and machining costs, are realized by cutting strips, for lamination, at 45° to the rolling direction. The required reference surface is obtained, during lamination, by maintaining an angle of 54.7° between the strips and the surface developed by the cut edges. The advantages of the composite technique (better averaging, minimization of errors, and evaluation of random intensity from the pole figure data) are retained by this modification.

ISSN:0034-6748    

DOI:10.1063/1.1719455

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

An improved method is described for measuring small volume changes on mixing a polymer with a solvent. The change in volume, occurring in a special dilatometer, causes a shift of a mercury level inside a constant cross section capillary, whose external surface is silver coated. The capillary is thus acting as a cylindrical capacitor, any change in volume being converted into a capacitance change. To eliminate the influence of thermal fluctuations, the apparatus works as a differential set. The calibration is performed by producing a known thermal expansion of a given amount of solvent (contained in the dilatometer) whose expansion coefficient is known. The sensitivity achieved is better than 1 ppm.

ISSN:0034-6748    

DOI:10.1063/1.1719456

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A device for evaporating metals by electron beam bombardment within the electron microscope has been developed which operates without loss of image resolution or stability. This device is particularly applicable to dynamic studies of nucleation and growth of metallic films characterized by unusually high purity and/or high melting points. A hanging drop of molten material, formed by bombardment of the end of a vertical wire by a focused beam of 2–5 kV electrons, provides a controllable source of pure metal vapor.

ISSN:0034-6748    

DOI:10.1063/1.1719457

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A method has been developed for determining the peak irradiance of an optical pump and the total pump energy incident upon a laser crystal. Consideration is given to the variation of temperature within a copper cylindrical shell that is irradiated by an intense, short duration light pulse. A temperature distribution expression is derived which describes the variation of temperature with respect to time, at the innner wall of the shell. A copper, cylindrical shell was positioned within the helix of a xenon flash lamp and irradiated with light pulses of various intensities. The temperature rise of the inner surface was monitored with a fast response thermocouple and the temperature history displayed on an oscilloscope. The maximum temperature rise of the inner surface of the cylinder was used in conjunction with the derived temperature distribution expression and the peak irradiance and total incident energy determined.

ISSN:0034-6748    

DOI:10.1063/1.1719458

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

An electronic double flash unit has been constructed to measure photographically average linear velocity of blood flow in the bulbar conjunctival vessels of the human eye. Two exposures on the same photograph separated by a predetermined time delay (adjustable from 2 to 200 msec) permit computation of velocity from the displacement of red cells per delay time. The equipment is small and mobile, the procedure innocuous.

ISSN:0034-6748    

DOI:10.1063/1.1719459

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The critical role played by first stage gain in shaping the output pulse height distribution and detection efficiency of an electron multiplier used as an ion detector is studied theoretically and experimentally. In a well‐focused electron multiplier it is found that anode pulse height distributions observed for different ion species agree well with distributions calculated by using compound Poisson statistics. Models are developed to explain measurement bias in an electron multiplier which is used in either the dc or pulse counting modes and it is shown how these results can be applied to isotope ratio measurements. Design and operating characteristics are described for a 20 stage electron multiplier which was developed for high speed pulse counting and high detection efficiency. The surface of the first dynode is coated with a thin film of Al2O3to provide a stable first stage yield of 7–9 secondary electrons/incident ion for monatomic alkali ions with 20 kV impact energy. The polyatomic ion Na2BO2+yields about 16 secondary electrons/incident ion at 20 kV impact energy. Resolving time of the entire detector system is reduced to 10 nsec by using a specially designed solid state discriminator and pulse shaper. Also, a technique is described for the simultaneous detection and pulse counting of two ion beams.

ISSN:0034-6748    

DOI:10.1063/1.1719460

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

This work describes an electric discharge in air at atmospheric pressure between a thin wire and a cathode with an elliptical cross section. The short axis of the ellipse was so small that the cathode surface facing the thin anode wire could be approximated by a plane. The cathode was split in two parts with the split parallel to the wire. When this discharge was exposed to a wind blowing perpendicular to the wire and parallel to the plane, it was found that the average displacement of the positive ions was directly proportional to the free‐stream velocity. The actual displacement could be determined by moving the wire to an upstream position such that the two parts of the cathode carried the same current. The measurements were made in a wind tunnel with velocities from about 1 to 18 m/sec.

ISSN:0034-6748    

DOI:10.1063/1.1719461

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

An apparatus for the fluorination of hydroxyl‐ and oxygen‐contaminated fluoride compounds is described. This purification process yields oxide‐free fluorides. Optically clear lanthanum trifluoride single crystals were grown from material subjected to this treatment.

ISSN:0034-6748    

DOI:10.1063/1.1719462

出版商:AIP    

年代:1965

数据来源: AIP