摘要:

The complete electronic system of a frequency‐sweep 240 MHz NMR spectrometer working with a superconducting magnet is described. Full circuit and construction details are given for the rf sideband generator, pretuned coaxial cavity, af aperiodic synchronous detector, digital frequency synthesizer as well as a phase‐coherent, variable‐frequency, time‐sharing pulse generator. This system, with multichannel irradiation possibilities uses extensively standard integrated logic circuits and can be inexpensively built by any laboratory engaged in NMR research.

ISSN:0034-6748    

DOI:10.1063/1.1686043

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The development of a nozzle which gasdynamically accelerates neutral copper atoms at controlled energy levels, and flux rates suitable for the investigation of inelastic copper atom collision processes is reported. Preliminary test data demonstrate that vapor deposited rhenium nozzles do not degrade in the presence of copper vapor at high temperatures. Operation with high purity helium gas at nozzle stagnation temperatures in the range 2650–2700 K and total stagnation pressures from 1/4 to 2 atm with continuous copper atom flux rates of [inverted lazy s] 1018sec−1has been maintained, for a total time of 8 1/2 h to date.

ISSN:0034-6748    

DOI:10.1063/1.1686044

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Small tools can be made by etching one of a variety of crystallographically limited pits into a single crystal mandrel, filling the pit with tool material and removing the mandrel. Fabrication of arrays of chisels and pyramidal points using a silicon mandrel and process technology common in the semiconductor electronics industry is discussed.

ISSN:0034-6748    

DOI:10.1063/1.1686045

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Low temperature pumping is utilized to achieve pressures as low as 10−11Torr. In the first method, the entire sample chamber is immersed inside liquid helium. The second method, which is more economical than the first one, combines a large capacity titanium sublimation pump and a small cold trap immersed inside a liquid‐helium storage Dewar. The ultrahigh vacuum system described here is economically competitive with the best ion‐pumped vacuum system available today.

ISSN:0034-6748    

DOI:10.1063/1.1686046

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A simple method is described to reuse copper gaskets that seal the steel flanges of ultrahigh vacuum systems. A tapered‐leaf thickness gauge is employed to measure the air gap between the steel flanges. The same copper gasket can be used many times by successively reducing the distance between the sealing flanges.

ISSN:0034-6748    

DOI:10.1063/1.1686047

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

This paper describes a novel technique for monitoring the outside dimensions of clad or unclad optical fibers. An oscillating mirror is used to deflect a laser beam with constant velocity across a fiber in order to measure the time interval during which the fiber intercepts the beam and casts a shadow on a photodetector. For 110 &mgr; fibers, individual measurements made every 1/60 sec are repeatable within a spread of ± 1% from the 330 &mgr;sec mean time interval (rms deviation ≈ ± 0.6%). Results are displayed in digital form, but can be converted to an analog signal for use in a servo loop to control the pulling rate of fiber drawing machines. An additional feature of the technique is that fibers with noncircular cross sections can be monitored by making sequential diameter measurements along orthogonal axes of the fiber.

ISSN:0034-6748    

DOI:10.1063/1.1686048

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A new light scattering instrument is described for measuring, as a function of scattering angle, the elements of the matrix describing light scattered from small particle systems. The instrument uses a piezo‐optical birefringence modulator to modulate the polarization state of the incident light beam, and uses lock‐in amplifier detection of the scattered light. The first and second harmonics of the modulation frequency are used with various combinations of filters and orientations to give the separate matrix elements. A treatment of a simple scattering experiment by means of Mueller calculus is carried through to illustrate the interactions of the light with the scattering system and with the various components of the measuring instrument. Evaluation of the instrumental performance is shown through measurements on two systems of monodisperse polystyrene spheres of average radius 550 and 3940 Å, compared with Mie calculations. Further measurements on sulfur colloids are presented, and suggestions of the value of this type of instrument in future work are given.

ISSN:0034-6748    

DOI:10.1063/1.1686049

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

We have considered theoretically and experimentally a paramagnetic resonance spectrometer, whose cavity contains both the sample to be studied and a beam of ammonia molecules capable of stimulated emission. Different modes of operation are investigated: classical, ``Q‐multiplier'' and marginal oscillator spectrometer. In these two latter cases, the ultimate sensitivity is determined only by the thermal noise in the cavity. It is shown to be the theoretical sensitivity of a spectrometer using a perfect receiver. This sensitivity can be achieved if the stored energy does not exceed an upper limit, depending on properties of the active molecules‐typically 5 × 10−18J for NH3.

ISSN:0034-6748    

DOI:10.1063/1.1686050

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A filter‐wheel solar radiometer has been developed for monitoring the atmospheric optical depth at multiple narrow‐wavelength intervals in the visible and near ir regions of the spectrum. Measurements of the direct solar radiations are converted to a digital format and stored in punched tape for eventual analysis by a computer. During stable clear weather condition, the instrument is capable of providing monochromatic optical depths to an estimated rms accuracy of 0.005.

ISSN:0034-6748    

DOI:10.1063/1.1686051

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A simple cavity‐tuning arrangement, designed for use with a small sample area at variable temperatures, is described. It is easily and economically constructed.

ISSN:0034-6748    

DOI:10.1063/1.1686052

出版商:AIP    

年代:1973

数据来源: AIP