摘要:

An adiabatic twin calorimeter is described in which sample and dummy are heated by bombarding them with 5 keV electrons. The electron beam coming from outside the adiabatic jacket is directed alternatingly to sample and dummy. The heating power generated in the sample is varied by changing the hold‐up time of the beam at the sample with respect to that at the dummy. The required measurement of the ratio of heating powers in sample and dummy is replaced by a time measurement. The calorimeter is capable of measuring the ratio of the heat capacities of sample and dummy with a resolution better than 10−3. By measuring the specific heat of nickel and comparing the result with literature data the systematic error of the calorimeter was found to be less than 1%.

ISSN:0034-6748    

DOI:10.1063/1.1686333

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

High accuracy determinations of 2e/husing the ac Josephson effect require correspondingly accurate measurements of small dc voltages. In the preliminary stages of a determination of 2e/hwith substantially improved accuracy, two different potentiometric instruments based on two independent principles of operation were designed and built. Both instruments were used in an extended series of 2e/hmeasurements at the University of Pennsylvania and subsequently at the National Bureau of Standards where they have been used to realize the U. S. legal volt as recently redefined via the ac Josephson effect. One of these instruments is based on a modified series‐parallel technique and is described in detail in this paper. After treating the general theory of the low resistance case, the design and construction of a portable self‐checking instrument based on the double series‐parallel exchange method is described. This series‐parallel comparator (SPC), built to compare a Josephson device (10 mV) and a standard cell (1 V), was evaluated and tested in the course of determinations of 2e/hwith one standard deviation (1 &sgr;) uncertainties of about 0.1 ppm. The sources of systematic uncertainty are discussed. The uncertainty attributable to the comparator alone is about 3 parts in 108(1 &sgr;).

ISSN:0034-6748    

DOI:10.1063/1.1686334

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The integral value of the refractive index of a plasma in a toroidal device is measured by a stabilized Michelson interferometer with a HeNe gas laser (&lgr; = 0.63 &mgr;) as light source. A calibrated phase modulator enhances the accuracy with which small phase shifts are measured, and automatically indicates phase shifts exceeding &pgr;/2.

ISSN:0034-6748    

DOI:10.1063/1.1686335

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The Berg‐Barrett technique has been used extensively for the observation of imperfections in crystals. A further developement of the Berg‐Barrett camera has been achieved which has two significant advantages over previous designs. First, this design provides a totally enclosed camera which completely prevents the operator's exposure to X‐ray radiation without decreasing the diffracting area of the crystal. In certain cases a large area of the crystal surface gives no Bragg reflection due to large tilt angles in the substructure or because an off‐zero layer reflection is being used. A scanning attachment has been built which helps overcome these difficulties.

ISSN:0034-6748    

DOI:10.1063/1.1686336

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Use of an integrated circuit differential amplifier and passive RC integration provides magnetic probe signals of large bandwidth untroubled by electric pickup.

ISSN:0034-6748    

DOI:10.1063/1.1686337

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

An apparatus for the study of relative ion concentrations in the positive column of noble gas capillary discharges is described. The technique employs ion sampling through a small orifice in the wall of the discharge tube. Consideration is given to identification and removal of possible systematic errors. The performance of the instrument is studied for discharges in helium and neon for pressures varying from 0.10 to 30 Torr and for discharge currents between 10 and 40 mA.

ISSN:0034-6748    

DOI:10.1063/1.1686338

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A resonator and a pulse method for relative ultrasonic absorption measurements in liquids from about 0.5 to 100 MHz are described and discussed. Due to the small sample volumes needed (around 1 ml) both techniques are suitable for relaxational studies on fast biochemical reactions. Cells are described, which have been operated with aqueous and organic media in a temperature range from − 10 to 80 °C.

ISSN:0034-6748    

DOI:10.1063/1.1686339

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A peak height measurement system (PHMS) is described which detects and measures the peak height of several simultaneous pulses with peaks as narrow as 1 nsec. Jitter in the input pulses produces no error in the measured heights. A detailed description of the peak detector circuit is given, and an experimental setup is presented for determining two‐photon absorption cross‐sections with PHMS. It is expected that this system will see application to numerous experiments which use pulsed lasers.

ISSN:0034-6748    

DOI:10.1063/1.1686340

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A direct coupled linear amplifier is described which has been used as an interface between time mode operated multichannel analyzers or instrument computers and electromagnet control amplifiers or voltage controlled oscillators for magnetic resonance signal averaging. The amplifier accepts the analog memory channel address voltage from the analyzer or instrument computer and attenuates, biases, amplifies, and inverts the signal as required. Operating techniques and circuit stability are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1686341

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

We have measured the coefficient of thermal expansion of potassium acid phthalate crystals in the direction perpendicular to the cleavage planes. This is the direction applicable to x‐ray diffraction with interplanar spacings of 13.3 Å. The measured value is 40.5 × 10−6°C−1with an estimated uncertainty of about ± 5%.

ISSN:0034-6748    

DOI:10.1063/1.1686342

出版商:AIP    

年代:1973

数据来源: AIP