摘要:

The distortion of the sample flux by a superconducting material produces a change of magnetometer output known as an image effect. Image effects for three Nb–Ti magnets were examined using a small current‐carrying coil as a source of a field‐independent and adjustable, controlled moment of a vibrating sample magnetometer. This allowed determination of the initial image effect (in zero field) and the field‐dependent image effect from zero to maximum magnetic field. The initial image effect (not detected by conventional calibration) can be large, and the field‐dependent part was 0.25–0.35 of initial image effect. The variation of the field‐dependent image effect on field sweep rate and magnet temperature, and the change of the spatial distribution of the detection coil sensitivity were also observed. The image effect is independent of sample moment and decreases rapidly with decreasing detection coil radius. The method of images was employed to calculate the image effect for perfect shielding as the function of detection coil dimensions relative to the magnet bore. For a small superconducting volume fraction &lgr;, the initial image effect for multifilamentary wire magnets is smaller than calculated by an approximate factor &lgr;/(1−&lgr;) in agreement with observations for the three Nb–Ti magnets. Some influences of the multifilamentary structure of the superconducting wire on the image effect are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1137359

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

InSb evaporated films for magnetic sensors are prepared by controlling the evaporation rate and the substrate temperature gradient in order to obtain elements of high sensitivity. There are In needles in the films which are precipitated parallel to one another during the evaporation process. The In needles have diameters of 0.5∼2 &mgr;m and lengths of 50∼200 &mgr;m. The films have thicknesses of 1.0∼3.5 &mgr;m. The results of the sensing characteristics and crystalline structure of InSb films are presented. The latter was analyzed by an electron microscope. A magnetoresistance value (&Dgr;R/R0) of 1400% is obtained at a length‐to‐width ratio (l/W) of 0.1 and an applied magnetic flux density (B) of 1 Wb/m2(=T), at room temperature.

ISSN:0034-6748    

DOI:10.1063/1.1137360

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Metastable fractions of singly charged ion beams extracted from different ion sources have been determined by measurement of secondary electron spectra which result from slow ion‐induced potential emission from a well‐defined solid surface. Data are presented for Ar+, Kr+, Xe+beams produced by a NIER‐type electron impact source, a ‘‘COLUTRON’’‐type low‐pressure arc plasma source, and a ‘‘DUOPLASMATRON’’‐type magnetically compressed arc plasma source, respectively. The measured metastable fractions are accurate within 25%, and their dependence on various ion source parameters can be well explained with a simple model of metastable ion production and loss kinetics.

ISSN:0034-6748    

DOI:10.1063/1.1137361

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The cataphoretic deposition method for preparing lanthanum hexaboride coatings has been modified to permit the preparation of several different types of surfaces. Some of these surfaces had good adhesion to the substrate, overcoming a major drawback to earlier methods. The surfaces ranged from smooth and dense, which were excellent electron emitters but poor halide ion producers, to porous, which were excellent halide ion producers.

ISSN:0034-6748    

DOI:10.1063/1.1137362

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Semitransparent S1 photocathodes have been developed on a low‐resistivity SnO2layer for streak camera image converter tubes. The 50‐&OHgr;/&laplac; resistivity combined with good photocathode sensitivity prevents parasitic effects and provides an efficient diagnosis tool for 1.06‐&mgr;m laser–plasma interaction experiments. Furthermore, the lifetime in the 1‐&mgr;m range has been greatly increased by a rebaking process which may reestablish the 1.06‐&mgr;m sensitivity.

ISSN:0034-6748    

DOI:10.1063/1.1137363

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A simple optical detector of position versus time providing submillimeter spatial and nanosecond time resolution is described. The spatial beam profile of a nanosecond‐pulse‐width nitrogen laser is sampled simultaneously when the UV light strikes multiple turns of a spiral fiber‐optic delay line. Fluorescent light coupled into the fiber converts the profile samples into serial bursts of light. These bursts are detected by avalanche photodiodes; electrical pulses are recorded on fast oscilloscopes. An interposed absorbing or refracting material casts a ‘‘shadow’’ which is measured by comparison with a reference recording. Applications are suggested, and two long‐time‐base recording methods are described.

ISSN:0034-6748    

DOI:10.1063/1.1137364

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

We report dependence of the extreme ultraviolet quantum efficiency (QE) of a microchannel plate (MCP) detector upon the electric field strength above its input face. Using an uncoated plate, we measured increases up to 80% as the field was raised from 0V/&mgr; to between 0.01 and 0.1V/&mgr;. Further increases in electric field resulted in a monotonic decrease in QE. Detector spatial resolution was found to degrade for these small field values but could be recovered, while maintaining most of the QE increase, by operating with fields in excess of 0.3V/&mgr;. Other detector parameters such as modal gain and output charge pulse‐height distribution were not significantly affected by the applied electric field. We explain the QE and resolution variations in terms of photoelectrons ejected from the interchannel web and subsequently returned to the input face of the MCP by the applied electric field. We present a model and a computer simulation which quantitatively reproduce our experimental results. Applying our model to MCPs coated with photocathode materials, we conclude that the maximum QE is obtained by optimizing the combined contributions from the web area and open area of the MCP, rather than by maximizing the open area alone. In this case, most of the QE can arise from the interchannel web rather than from the directly illuminated channels.

ISSN:0034-6748    

DOI:10.1063/1.1137365

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A low‐pressure, high‐flow, recirculating gas system has been designed and constructed for use on a large volume (250 ft3) ionization sampling drift chamber (CRISIS), which operates at an absolute pressure of less than 1 in. of water relative to atmospheric pressure. The system was also designed to control and monitor the detector gas mixture and to reduce the oxygen level in the detector below 4 ppm. In operation the system demonstrated very stable long and short term stability and also demonstrated the gas cost savings inherent in recirculating systems.

ISSN:0034-6748    

DOI:10.1063/1.1137323

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A computer‐based interactive system has been developed and successfully used for scanning proton‐recoil tracks in nuclear research emulsions. To our knowledge, this system is the first truly interactive system developed and used for emulsion scanning. Interfaces have been developed between the three fundamental interacting entities, namely man, microscope, and computer. Computer codes can be developed for different applications, thereby providing wide flexibility and versatility. Use of this system for neutron metrology is described. Differential neutron spectrometry as well as integral neutron dosimetry have been carried out in both 4&pgr; and unidirectional neutron fields. Results are presented which quantify the accuracy attained with this system for each of these different neutron measurement emulsion techniques. This system provides a substantial advance in the state‐of‐the‐art of emulsion scanning in terms of both accuracy and cost effectiveness. The ability to store, in computer memory, all relevant emulsion and track parameters enables off‐line data analyses which were heretofore not practical. The uncertainty in track length measurements with this system is approximately 0.52&mgr; (1&sgr;). While emulsion scanning rates vary for the different modes of system operation, scanning rates of 30 to 40 tracks/h have been typically obtained.

ISSN:0034-6748    

DOI:10.1063/1.1137324

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An in‐lab x‐ray spectrometer is described which is capable of rapid acquisition of x‐ray absorption fine structure data for either extended x‐ray absorption fine structure measurements (EXAFS), or x‐ray absorption near edge structure studies (XANES). Intensities in excess of 107photons/s in an ∼10 eV bandpass near 9 keV have been obtained using only a conventional sealed, fixed anode x‐ray tube operating at 1.5 kW. The spectrometer utilizes a focusing Johansson cut and bent single crystal as the monochromator and scans continuously from 8≲2&thgr;≲160 degrees with only a single stepping motor driven movement. For 3dmetal absorption edges, resolutions of ∼10eV are obtained in first order with a Ge(111) crystal and ∼1 eV in third order allowing in‐lab acquisition of both EXAFS and XANES data of synchrotron‐like quality.

ISSN:0034-6748    

DOI:10.1063/1.1137344

出版商:AIP    

年代:1983

数据来源: AIP