摘要:

A source of spin‐polarized electrons based on a laser‐pumped flowing helium afterglow is described. He(23S) atoms contained in the afterglow are optically pumped using circularly polarized 1.08‐&mgr;m (23S→23P) radiation provided by a NaF (F2+)*color‐center laser. Spin angular momentum conservation in subsequent chemi‐ionization reactions with CO2produces polarized electrons that are extracted from the afterglow. At low currents, ≲1 &mgr;A, polarizations of ∼70%–80% are achieved. At higher currents the polarization decreases, falling to ∼40% at 50 &mgr;A. The spin polarization can be simply reversed (P→−P) and the source is suitable for use in the majority of low‐energy spin‐dependent scattering experiments proposed to date.

ISSN:0034-6748    

DOI:10.1063/1.1137381

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A mathematical model of intensity dispersion at the detector plane in a molecular‐beam apparatus has been developed for the case of a ribbon‐shaped beam effusing from a narrow rectangular slit. The model is developed in terms of position probability distribution functions and Maxwellian velocity distribution functions. The relation derived for the axial flux density isnv¯(&Dgr;x′)(&Dgr;x′)/4&pgr;2L2in units of number of particles per unit area per unit time. A plot of flux densityversusoff‐axis position agrees with the reported distributions obtained experimentally.

ISSN:0034-6748    

DOI:10.1063/1.1137382

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A laboratory spectrometer for x‐ray absorption measurements is described which is adaptable to changing experimental requirements. The spectrometer is designed for the use of different types of curved crystals within large ranges of radii of curvature and of Bragg angles. Utilizing a 12‐kVA rotating anode x‐ray generator, Johansson‐type monochromator crystals, and a helium‐flow flexible beam line, photon fluxes between 105and 107photon/s are achieved in the photon energy range between 5 and 20 keV, where the energy resolution varies between 2 and 10 eV.

ISSN:0034-6748    

DOI:10.1063/1.1137383

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A flexible apparatus has been constructed to measure the spectra and time dependence of weak optically induced absorption changes in gas phase samples. The instrument uses a pulsed Nd:YAG‐pumped dye laser for excitation and a second, independent YAG/dye laser for probing in a coaxial counter‐propagating geometry. The excitation wavelength, probe wavelength, and time delay between the two pulses may be separately varied. An on‐line laboratory computer acquires induced absorbance data as a function of probe wavelength and delay, and helps to suppress ratiometric noise to the point that induced probe absorptions as low as 2×10−4absorbance units may be routinely detected in a path length of 75 cm. The sample cell forms part of a gas handling system that permits a wide range of sample and buffer gas mixtures to be prepared. The width of the instrumental time response is approximately 4 ns; it may be deconvoluted from kinetic data to provide an effective resolution of ∼1 ns. This combination of sensitivity and time resolution allows the study of collision‐free as well as collision‐induced effects in many molecular systems.

ISSN:0034-6748    

DOI:10.1063/1.1137384

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An automatic trigger for the discrete nebulization in a flame atomic spectrometry was improved to be compatible with any sample solutions irrespective of the electric conductivity and optical transparency. The sample solution in a Teflon tube can be detected by the specifically made photocoupler and electronics.

ISSN:0034-6748    

DOI:10.1063/1.1137385

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The construction details and performance characteristics for a fluorescence spectrophotometer are described. The system utilizes proton counting for signal detection and an Apple II microcomputer for data acquisition and analysis. Data‐acquisition techniques are given along with typical excitation, emission, and polarization spectra. Particular reference is made to application of the instrument to fluorescence studies of protein/polymer films.

ISSN:0034-6748    

DOI:10.1063/1.1137386

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

We report the development of a new technique manipulating the position of electrically neutral material using electronic signals. Dielectrophoresis, or the translational motion of neutral matter caused by polarization effects in nonuniform electric fields, is used in a geometry analogous to that of a charge‐coupled device. Water droplets and steel ball bearings are stepped between a series of electrodes at velocities on the order of 1 cm/s. We find that the average velocity is roughly proportional to the drive voltage divided by the droplet or bearing radius. A variety of applications are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1137387

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The scattered light approach to classification of cavitation nuclei provides speed and resolution advantages over holographic direct observation methods, but the conventional light‐scattering system has been unable to discriminate between bubbles and dirt particles. A two‐channel classification system has been developed to process information carried in bursts of light scattered along two different paths by candidate nuclei passing through an illuminated test volume. Processing is based upon an analysis of light‐scattering properties of spherical and nonspherical particles. The dual‐detector classifier has demonstrated its ability to accomplish the desired differentiation in initial water tunnel tests.

ISSN:0034-6748    

DOI:10.1063/1.1137388

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

In this paper we report the development of the single frequency dye laser as a plasma diagnostic for measuring ion velocity distributions with a resolution limited only by the natural linewidth of the laser excited resonance transition. For the 6S1/2–6P1/2transition in Ba+this corresponds to a velocity uncertainty of 103cm/s. Velocity selection is performed by the laser as it scans the Doppler broadened plasma absorption line, in contrast with the usual method of scanning an emission line with a high‐resolution spectrometer. Both sensitivity and resolution are improved by 2 orders of magnitude, allowing nonperturbing measurements to be made at densities below 107cm−3. In addition to a description of the technique, sample measurements of time‐resolved wave induced modifications of ion velocity distributions are shown.

ISSN:0034-6748    

DOI:10.1063/1.1137389

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The charge‐exchange system used on the Poloidal Divertor Experiment is comprised of four, ten‐channel, mass‐resolved, charge‐exchange analyzers. Each analyzer is constructed with parallel electric and magnetic fields and is calibrated over an energy range of 0.5–40 keV. The mass rejection between hydrogen and deuterium has been measured as better than 1000 to 1. For Ohmic heated discharges the system can provide single shot radial ion temperature profiles (four point) with 1‐ms time resolution. For neutral beam heated discharges, complete radial and temporal profiles can be obtained in two to four shots. The system is also equipped with a vertically aimed diagnostic neutral beam to allow local ion‐energy distribution measurements. This report describes the analyzer system and its calibration, and presents results from Ohmic and neutral beam heated discharges.

ISSN:0034-6748    

DOI:10.1063/1.1137366

出版商:AIP    

年代:1983

数据来源: AIP