摘要:

A Michelson interferometer is described for the measurement of low‐frequency vibrational amplitudes in the sub‐angstrom range (down to 10−3Å) as a function of temperature. For this purpose a temperature stabilizing circuit has been developed. The use of a condensor microphone as an electromechanical feedback transducer opens up the possibility to relate the amplitude measurements to the wavelength of light. By these means the accuracy, reliability, and versatility of the interferometer are considerably improved and the draw‐backs of existing set ups are effectively eliminated.

ISSN:0034-6748    

DOI:10.1063/1.1686444

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A low noise FET amplifier has been constructed and applied to noise thermometry. The amplifier noise is less than 1 nV/(Hz)1/2above 5 kHz. Temperatures between 300 and 4 K have been measured to better than 1% with a time constant of 5 sec. A description of the complete noise thermometer system is given.

ISSN:0034-6748    

DOI:10.1063/1.1686445

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

We have measured using optical means the absolute density of the saturated vapor pressure of cesium by absorption of resonance radiation corresponding to the 62P3/2→62S1/2transition. Experimental results are compared with those obtained with a surface‐ionization gauge and with the Taylor‐Langmuir equations. Density was measured between 12.5°C and 39.2°C; in this temperature range the experimental error is about 10%. For higher temperatures, the absorption increases with the temperature but is not in a simple fashion related to the atom density in the absorption cell. A different method is proposed which permits density to be measured up to temperatures above 100°C, but this requires calibration using the Taylor‐Langmuir formulae.

ISSN:0034-6748    

DOI:10.1063/1.1686446

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The irradiation of thin films of solid material by a moderate energy (0.5 J/pulse) Q‐switched ruby laser beam has been used to produce intense pulses of neutral atoms and molecules in the 1 to 10 eV energy range. For a given total laser beam energy, both the flux and energy range of atoms within the pulse can be varied within limits by adjusting the energy density of the laser light at the target surface. As observed at a distance of 60 cm from a thin BiF3compound target, the flux of 5 eV fluorine atoms from a typical burst was estimated to be about 1.3×107atoms/cm2/sec. For the same burst, the flux integrated over the 1 to 10 eV range yields a value of ∼2×1013atom/cm2. Similar results were obtained with aluminum and uranium thin films.

ISSN:0034-6748    

DOI:10.1063/1.1686447

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A ``plasmascope'' device which permits visual display of the floating potentials from a 7 × 7 matrix of Langmuir probes immersed in a low‐density plasma is described. The probe potential, which is proportional to the plasma space potential, is sampled through a high impedance FET circuit. These potentials are displayed by a matrix of light emitter diodes such that the light intensity at a point on the matrix is proportional to the corresponding probe floating potential. This device is useful to determine the qualitative location of the plasma, its configuration, and slow motion.

ISSN:0034-6748    

DOI:10.1063/1.1686448

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A simple arrangement based upon sun glint, the brilliant image of the sun behind a convex reflecting surface, is used to produce a nearly stationary image of the sun. Using a telescope mirror, this image is directed into a spectrometer and is spectrally analyzed for the purpose of remote sensing of trace species in our atmosphere. Typical data using a reflecting sphere are reported and discussed qualitatively in relation to the atmospheric absorbers between the sun and detector. The over‐all uses of the system are described, and some cautions concerning its limitations are discussed. Alternate geometries and possible variations of the system are described.

ISSN:0034-6748    

DOI:10.1063/1.1686449

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The magnetoresistance of 1/2 W, grade 1002, Speer carbon resistors with nominal room temperature resistances of 100, 200, and 470 &OHgr; and of 1/8 W, 10 &OHgr;, Allen‐Bradley resistors was measured at various temperatures between 0.5 K and 4.2 K in static magnetic fields up to 140 kG. In this temperature range the maximum magnetic field induced temperature error of these thermometers amounts to 14%. The Allen‐Bradley unit is to be preferred over the Speer resistors for use as a thermometer in a magnetic field for the following reasons: it has a more reproducible and regular magnetic field dependence, greater temperature sensitivity, and its much smaller physical size facilitates its incorporation in experimental apparatus where dimensions are restricted. One drawback of the 10 &OHgr; Allen‐Bradley resistor is its relatively high impedance at the lowest temperatures. In addition, the effects of magnetic fields up to 150 kG on the characteristics of Chromel P/Au+0.07 at.% Fe and Chromel P/constantan (type E) thermocouples were determined in the temperature range 4.2–45 K. A description is given of the measuring apparatus along with a discussion of possible measurement errors and the necessary precautions which must be observed. The magnetic field induced temperature errors for the Chromel P/Au+0.07 at.% Fe thermocouples are relatively large at temperatures below 20 K, and are nonreproducible between sections of gold‐iron wire taken from the same lot. We do not recommend the use of these thermocouples below 20 K at fields greater than 50 kG. In contrast, Chromel P/constantan thermocouples have small, reproducible temperature errors up to 150 kG for 4.2≤T≤45 K. The data indicate that even in strong magnetic fields, at temperatures above 20 K, it is practical to correct for magnetic field induced temperature errors when using thermocouples. The reproducibility of the field induced errors in wires from different sources is still an open question and is worthy of further investigation.

ISSN:0034-6748    

DOI:10.1063/1.1686450

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The laser Doppler spectrometer consists of a laser source, a scattering cell, a photomultiplier, a spectrum analyzer, and electrodes for applying an electric field. In a suitably applied field, bioparticles or macromolecules in the scattering cell will be forced to move along the electric field lines with a velocity given by the product of the electrophoretic mobility and the field amplitude. This induced motion causes a Doppler shift of the scattered laser light which is detected and measured by the spectrometer. Both the electrophoretic mobility and the diffusion constant can be measured simultaneously by measuring the scattered light spectrum in this way. Several procedures are used to obtain high resolution Doppler spectra. Convective instabilities due to Joule heating are minimized by use of rectangular electrodes with a very narrow gap (200 &mgr; to 1 mm). Gas bubbling is minimized by a platinization of the Pt electrodes and by use of a square wave electric field. Examples of high resolution Doppler spectra from suspensions of polystyrene spheres are given and the various resolution limiting factors are described.

ISSN:0034-6748    

DOI:10.1063/1.1686452

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

An ultrasonic nebulizer system capable of converting solution into an aerosol of various controlled droplet sizes with conversion rates in excess of 1 ml/min is described. This design allows generation of various sizes of droplets through overtone operation and simplified transducer substitution. The described irradiation cell is constructed from glass and fluorocarbon materials providing a high degree of chemical inertness.

ISSN:0034-6748    

DOI:10.1063/1.1686453

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A continuous flow system for use with an unmodified Varian A‐69A NMR spectrometer is described. Normal sample spinning is preserved, and high resolution is maintained. The transfer time of the sample stream between a reaction cell placed in a variable external magnet and the spectrometer may be made as short as 1 sec. The apparatus has been used to obtain chemically induced dynamic nuclear polarization (CIDNP) spectra during the photolysis ofdi‐t‐butyl ketone in low magnetic fields.

ISSN:0034-6748    

DOI:10.1063/1.1686454

出版商:AIP    

年代:1974

数据来源: AIP