摘要:

The design and performance of an apparatus for measuring magnetic susceptibility using a superconducting magnetometer and superconducting magnet and shields are described. Measurements of static susceptibility and of nuclear magnetic resonance have been made with this system. Volume susceptibility changes of 10−10cgs can be measured with a 1 sec response time, a 100 Oe applied field, and a 1 cm3sample. Noise limitations and potential for improvement of sensitivity by several orders of magnitude are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1686418

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Frequency shifts of Zeeman lines have been observed in a Teflon‐coated storage bulb. The data suggests that the origin is a contamination dependent wall interaction. A simple model of unpaired electrons on the surface of the wall provides a possible explanation if the relaxation times for such wall spin sites is long enough.

ISSN:0034-6748    

DOI:10.1063/1.1686451

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A digital tracer scanner, which was constructed to measure the distribution of radio tracers along the surface of thin films in a nondestructive manner, is described. The radiation is measured through a stationary slit as the tracer source is scanned back and forth utilizing a stepping motor; simultaneously, the sweep of a multichannel analyzer operating in the multiscaling mode is synchronized to this motion, such that a given channel corresponds exactly to a given position on the film (to better than 3 &mgr; after many days of scanning). The tracer distribution can then be viewed on an oscilloscope or read out on a teletypewriter. An analysis is presented indicating the distortion of a profile when observed through a slit of finite width, and a method of unfolding the value of the diffusion coefficient,D, from the measured tracer distribution is given. During a typical measurement on a polycrystalline Au film, the value ofDwas determined to be 3.14±0.3 × 10−11cm2/sec at 500 °C and the ultimate resolution attainable for a 50 &mgr; slit and a 40 h anneal corresponds to ∼ 6 × 10−12cm2/sec.

ISSN:0034-6748    

DOI:10.1063/1.1686456

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Apparatus for epitaxial film thickness measurement by photoelectric detection of interference fringes is described. The apparatus features high speed, immunity to noise from ambient light and the ability to distinguish between films grown on opposite sides of a transparent substrate, and is implemented with a minimum of components.

ISSN:0034-6748    

DOI:10.1063/1.1686436

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A new velocity gauge that allows use of as many as 64 gauges per signal cable has been developed and tested. The gauge, designated ``make‐wire,'' uses moving wires contacting a printed circuit board to provide a digital signal consisting of a series of electrical offs and ons. The distance and the time between these discrete electrical changes are known; therefore, the velocity of the moving system can be determined. The gauge allows scaling up or down to obtain a sample exposure area as small as 0.6 cm2. The gauges have been used in an underground nuclear effects test. The minimum velocity measured with the present configuration was estimated to be 50 cm/sec.

ISSN:0034-6748    

DOI:10.1063/1.1686438

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Distortions of pressure measurements with a Bayard‐Alpert gauge in the range 10−4−10−3Torr were investigated, and changes in gauge sensitivity were found to be correlated with the observation of different electric charges on the glass envelope. A modified Bayard‐Alpert gauge was designed. The gauge incorporated a screen grid between the gauge elements and the glass envelope. The screen grid was connected to the gauge filament and was intended to reduce the impact energy of electrons on the glass surface and the interaction of electric charges on the envelope with charged particles in the gauge. Four modified gauges were built and tested, and the comparison of the gauges with a McLeod gauge showed that the ion‐collector current was a linear function of gas pressure over the range from 5 × 10−5to 7.2 × 10−4Torr. For further improvements, a beam type ionization gauge is proposed.

ISSN:0034-6748    

DOI:10.1063/1.1686439

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

An inexpensive GaAs laser diode pulse generator is presented. This generator has found application in the evaluation of optical pulse dispersion in glass fiber optical waveguide studies. It is capable of producing optical impulses as narrow as 110 psec at a wavelength of 0.9 &mgr; and a pulse repetition rate of 50 kHz. With a slight modification, it may be used to produce optical pulses of considerably longer duration at reduced repetition rates.

ISSN:0034-6748    

DOI:10.1063/1.1686440

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Phase comparison in an acoustic surface wave variable delay line is utilized to indicate precise micropositioning over distances of several centimeters. A special phase‐locked loop design provides thermal compensation to render a device capable of repeatable measurements with accuracies of better than 0.5 &mgr;.

ISSN:0034-6748    

DOI:10.1063/1.1686441

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

We study the apparatus response functiong(t) which must be known in order to deconvolute the fluorescence decay experiments obtained by the single photon counting method. Due to the flash and the PM characteristics,g(t) depends on the excitation and emission wavelengths. The PM contribution is analyzed qualitatively and found to be in agreement with the properties of the photoelectric effect. Therefore, the accurate determination of the ``true fluorescence decay'' cannot be obtained by the process commonly used, which consists in replacingg(t) by the apparatus response obtained with the PM receiving the light of the exciting pulse. The functiong(t) may be obtained in using a reference fluorescent solution with a known fluorescence decay‐time.

ISSN:0034-6748    

DOI:10.1063/1.1686442

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

An Eppley Laboratory pyrgeometer was tested in several different modes of operation to determine its ability to measure infrared irradiance from an aircraft platform. During the initial tests, the instrument output varied by 30–40 W m−2as the incident solar irradiance or air flow over the KRS‐5 dome changed. The long pass filter (the KRS‐5 dome) was found to be opaque to radiation of wavelengths shorter than 3.6 &mgr;. Hence, the fluctuations described above may be attributed to changes in the temperature of the filter. The pyrgeometer output was studied as a function of the incident infrared irradiance and the temperature difference between the sensor surface and the KRS‐5 dome. Laboratory tests verified this dependence and showed that by utilizing the thermopile cold junction and dome temperatures, infrared irradiances may be measured with a precision of ± 1.7 W m−2. Although not the original intent of this research, it is shown that the KRS‐5 shielded pyranometer may be used to measure infrared irradiance with a precision of ± 2 W m−2in a ground station installation. However, in order to realize the precision value mentioned above, two precautions must be taken. First, the temperature of the KRS‐5 dome must be monitored; and second, the entire instrument should have sufficient air flow over it to minimize temperature differences between the KRS‐5 dome and the thermopile cold junction. The pyrgeometer was also mounted in an upward‐looking configuration on an aircraft platform and measurements were made at constant pressure levels under clear sky conditions to approximate a constant irradiance. It was found that the intense flow over the instrument minimized the effect of the solar heating of the dome. Infrared irradiances measured on a day/night flight comparison differed by an average difference of 3.5 W m−2. rms deviations about the mean value at any level were less than ± 2.5 W m−2. Observed downward irradiance divergences differed from values calculated using a radiative transfer model by less than 0.3 W m−2mb−1. The ventilation, however, did not eliminate the sink‐dome temperature differences because the temperature response of the thermopile heat sink is an order of magnitude slower than that of the KRS‐5 dome; therefore, horizontal fluctuations of air temperature or abrupt changes of altitude result in erroneous output values. An attempt was made to determine an empirical correction for air temperature fluctuations from the aircraft air temperature data. No general correction factor relating temperature and output changes could be determined. However, individual applications of such an empirical relationship did reduce rms deviations of the output to less than 2 W m−2.

ISSN:0034-6748    

DOI:10.1063/1.1686443

出版商:AIP    

年代:1974

数据来源: AIP