摘要:

Two new methods are described to measure velocities and angles of incidence of charged cosmic dust particles with precisions of about 1% and 1°, respectively. Both methods employ four one−dimensional position−sensitive detectors in series. The first method utilizes a charge−dividing technique while the second utilizes a time−of−flight technique for determining the position of a particle inside the instrument. The velocity vectors are measured although mechanical interaction between the particle and the instrument is completely avoided. Applications to cosmic dust composition and collection experiments are discussed. The range of radii of measurable particles is from about 0.01 to 100 &mgr; at velocities from 1 to 80 km/sec.

ISSN:0034-6748    

DOI:10.1063/1.1134155

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A variable energy neutral beam source is presented which utilizes a class of large molecules having the property of forming long−lived temporary negative ions. Negative ions are produced, accelerated, and focused, after which autodetachment of the electrons occur, leaving a beam of neutral molecules. The source has been used in total cross section experiments, where SF6was the beam gas and various target gases were used in a scattering cell. Some results of the collision process SF6+ CO2are presented. At 1200 eV lab energy (27 eV c.m. energy) the total collision cross section for CO2is 54.2±15.9 A˚2. Advantages and disadvantages of this type of source are discussed, and extensions to other types of experiments are explored.

ISSN:0034-6748    

DOI:10.1063/1.1134156

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A capacitance manometer has been tested and compared to the method of volumetric pressure division using helium as a working gas in the range 2×10−4−5×10−6Torr. The results show that the unit tested was linear to the lowest pressures utilized, and the two methods were in agreement to about 0.6% plus 4×10−7Torr, in addition to the errors introduced by the least count of the capacitance manometer’s digital readout. Argon and air gave similar results.

ISSN:0034-6748    

DOI:10.1063/1.1134157

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The applicability of GM and proportional counters naturally extends into the vacuum ultraviolet (vuv) spectral region. A simple modification to this detector enables GM counters to be used to measure very small cross section variations or to be used as high efficiency detectors over a narrow spectral range with excellent second order discrimination.

ISSN:0034-6748    

DOI:10.1063/1.1134158

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A new instrument which electrically characterizes devices and materials at high voltages applied for short duration at low repetition rates is described. The instrument automatically measures and plotsI−VorJ−Esample and device characteristics up to very high voltage levels under pulsed dc conditions. In addition, the system measures and plots resistance, conductance, resistivity, and conductivity versus voltage, current, or electric field. Minor modifications in the analog computing circuit will extend the usefulness of the system to other types of pulsed data acquisition. The system was tested with resistive samples ranging from 60 &OHgr; to 125 k&OHgr;, using pulsed voltages from 0 to 8000 V, maintaining measurement error well below 1%. The system is particularly useful in characterizing semiconductor materials at high electric fields (warm and hot electron effects) and electronic devices under pulsed conditions (power transistors, IMPATTS, TRAPATTS, Gunn oscillators, PIN diodes, etc.). The design, operation, and performance of the instrument is described.

ISSN:0034-6748    

DOI:10.1063/1.1134159

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

This paper describes a new electronic circuit, the time domain difference amplifier, used to reduce strong drifts which bury weak repetitive signals. The principle is that the input, with signal and drift, is sampled at signal on and signal off states, and subtracted from each other. The random drift is reduced by integrating the subtracted values. Drift suppression is about 35 dB for 3.0 Hz ac drift and 100 repeatings for integration.

ISSN:0034-6748    

DOI:10.1063/1.1134160

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A large (50 mm long by 50 mm diam), clear, visually flawless, oriented single crystal of cerous zinc nitrate 24−hydrate (CZN) has been grown in a Teflon coated cylindrical Pyrex container at 30°C by evaporation of H2O from a saturated solution. The growth rate along theccrystal axis was 0.7 mm/day. The growth in theabplane was limited by the cylinder diameter. InitialpH of the solution was 0.8 (excess HNO3present). Two crystals similarly grown atpH 1.5 and 1.2 mm/day were translucent, while a crystal grown atpH 1.5, 0.5 mm/day and 0°C had small cracks as well as being translucent. It is suggested that the translucence is caused by light scattering from microscopic regions due to occluded water and/or hydrolysis products, which can be suppressed by a sufficient excess of H3O+. Crystals grown in a solution with excess acid, however, have a water deficiency. The translucent crystals have a Ce3+deficiency.

ISSN:0034-6748    

DOI:10.1063/1.1134161

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A minicomputer−based system for obtaining ’’absolute values’’ of tunnel conductance &sgr; to one part in 105and simultaneous measurement and ’’calibration’’ of its rate of changed&sgr;/dVis described. The analog, digital, and interface hardware along with the necessary software are discussed in detail and typical results are shown for the system used. The system is capable of presenting the calibrated results in only a few minutes after each sweep is completed, yet requires less than 8 k of core memory, provided a mass storage device such as magnetic tape is available.

ISSN:0034-6748    

DOI:10.1063/1.1134150

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A flow system for production of diatomic metal oxides and halides is described. Molecules are produced by reacting metal vapor in a flowing, inert gas with a suitable oxidizer. Product molecules are frequently formed in electronically excited states, making this system particularly useful for optical emission spectroscopic studies. Specific advantages are: (a) large number of reactant products; (b) little thermal excitation in the reaction region; (c) spectra uncluttered by emission from undesirable species; and (d) in many cases, formation of molecules in electronically excited states not produced or detected in other sources. Also discussed is a variation of the design which is used to produce small metallic particles. These particles are formed by homogeneous nucleation of the metal vapor and range in size from 5 to 500 nm.

ISSN:0034-6748    

DOI:10.1063/1.1134151

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Excess noise in total−power radiometers, its origin, and its effect on continuum radio astronomy measurements during data reduction are discussed. The theory of a new type of noise−adding radiometer is presented, and the resulting practical application of the theory in the form of a gain−stabilizing detector is described. It is shown that the performance of this type of noise−adding radiometer can be optimized, quite simply, to yield an effective system temperature which is less than that of an ideal Dicke system.

ISSN:0034-6748    

DOI:10.1063/1.1134152

出版商:AIP    

年代:1975

数据来源: AIP