摘要:

Modifications to a commercial miniature x‐ray probe are described which allow elemental analysis to be made on diffusion samples with an effective aperture of 15 &mgr;. Elemental concentrations as a function of depth are shown for Al, Nb, and Ta.

ISSN:0034-6748    

DOI:10.1063/1.1684345

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The problems encountered in the electrical excitation of pulsed CO2lasers operating at atmospheric pressure are briefly reviewed, with some solutions developed at the Defence Research Establishment Valcartier, and their limitations. A new approach, based on a double transverse discharge technique, has permitted the design of a 3.8 m long laser which delivered up to 9 J/pulse with a peak power of 12 MW. An output energy density of 5.5 mJ/cm3of excited gas has been achieved.

ISSN:0034-6748    

DOI:10.1063/1.1684346

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The problem of observing low level transient optical signals, with better than 1 nsec resolution, is discussed. A practical system is described which is limited by shot noise in the photocathode current and by the quantum efficiency. Novel circuitry was developed which automatically reduces the gain of the photomultiplier to avoid damage from excessive average anode current.

ISSN:0034-6748    

DOI:10.1063/1.1684347

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The design and operational characteristics of a scanning double beam‐dual photometer for simultaneous comparison of two spectrographic density images are described. With a three decadic log ratio device, the photometer‐log ratio converter functions as a densitometer unit providing differential density measurements of spectrographic records. The method of analysis has several limitations but the utilitarian value of the dual photometer‐log ratio converter unit in extracting molecular absorption bands of metastable molecules as recorded spectrographically in flash photolysis studies is illustrated with results from experiments on flash photochemical production of phenoxyl radical fromp‐t‐butylphenol in hydroxylic media.

ISSN:0034-6748    

DOI:10.1063/1.1684348

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

An apparatus is described for the measurement of internal friction under conditions of hydrostatic pressure transmitted by a liquid. The material to be tested is in the form of a helical spring. The motion of this spring under the influence of an axial sinusoidal force is compared to the motion of a reference spring made of a material exhibiting negligibly small losses under the influence of the same force. The phase angle between stress and strain and thus the internal friction in the specimen can be determined by this procedure. External damping due to viscous interaction between the specimen surfaces and the pressure transmitting fluid is kept inappreciably small by employing very low frequencies of vibration (in the order of 1 cycle/min and less). There is no theoretical limit to the lowest frequency that can be used. Strain amplitudes of 10−7−10−5have so far been realized; values beyond these limits are possible. A simple theoretical analysis of the behavior of the test arrangement is discussed. Some experimental results are presented.

ISSN:0034-6748    

DOI:10.1063/1.1684349

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A versatile optical cell using light pipe optics with a self‐contained detector operating at 1 K for ir studies of solids and liquids that are gases at room temperature is described. The sample length is continuously variable up to 10 cm and the sample temperature can be varied from 1 to ∼200 K.

ISSN:0034-6748    

DOI:10.1063/1.1684350

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A technique is described for the automatic measurement of ultrasonic velocity changes of one part in 105in continuous wave experiments. An oscillator is frequency modulated by an analog circuit which terminates frequency change when a mechanical resonance is achieved in an ultrasonic interferometer. Velocity changes appear as changes in terminal frequencies of the oscillator and are easily recorded. A typical result is presented. The possibilities of using the technique to measure temperature changes of 10−3°C and displacements as small as 10−6cm are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1684351

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The combination of amplitude modulation of the nuclear rf power at a frequencyf1and 180° modulation of the phase of the resonance microwave signal with respect to the reference microwave signal at a frequencyf2, wheref1≫f2, with successive amplification and phase sensitive detection at the two frequencies, has proved useful in electron‐nuclear double resonance (ENDOR) of unordered solids. The alternative of amplitude modulation alone often results in poor baseline stability, and the alternative of amplitude modulation plus magnetic field modulation results in the complication of summing in an uncontrolled manner ENDOR contributions from crystallites resonating at different fields and with different orientations with respect to the applied dc magnetic field.

ISSN:0034-6748    

DOI:10.1063/1.1684352

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

In this paper we describe a circuit for reducing the transmitter ringdown time and thereby improving the recovery time in pulse NMR experiments. The circuit uses only solid state devices and requires no external switching. For transmitter voltages less than 0.5 V peak to peak the effective resistance in parallel with the transmitter coil in a crossed coil spectrometer is only 6 &OHgr;, whereas for larger voltages the shunting resistance is of the order of 1–2 k&OHgr;. This circuit thus has the effect of significantly squaring the envelope of an rf pulse. It has the extra advantage of suppressing noise generated by the transmitter during the time interval between pulses.

ISSN:0034-6748    

DOI:10.1063/1.1684353

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The construction and performance of mechanical transducers suitable for generating and detecting second sound in pure4He, and also in dilute3He&sngbnd;4He mixtures at millidegree temperatures, are described. It is shown that when the normal fluid density is small, the behavior of the transducers can be explained by a simple acoustical model which enables their sensitivity, frequency response, and reflection coefficient to be calculated in terms of easily measured parameters.

ISSN:0034-6748    

DOI:10.1063/1.1684354

出版商:AIP    

年代:1970

数据来源: AIP