摘要:

A parallel detection system has been added to the Wien Filter electron spectrometer on the dedicated scanning transmission electron microscope at IBM. The system uses an intensified diode array that is optically coupled to a single‐crystal YAG screen by a vacuum window and anf/1.4–22 camera lens. The YAG screen shares the spectrometer image plane with energy selecting slits used for bright field STEM images and for single‐channel energy loss analysis. Energy calibration to ±0.05 eV for scans over arbitrary energy ranges is accomplished by combining many parallel spectra having different energy centers. This process can remove channel gain variations, background variations, and nonlinear energy scale effects.

ISSN:0034-6748    

DOI:10.1063/1.1139739

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

In charged particle beam experiments, the electromagnetic signal produced at the beam injection point (conducting foil or aperture) by a fast‐rise beam will reflect off conducting boundaries (pipe walls) to produce constructive and destructive interference.B‐dot loop diagnostics can, in that case, give rather complicated signal histories that are difficult to interpret. An idealized, cylindrical model of a sudden rise beam on axis is solved analytically and shows, in the relativistic limit, how the interference is manifested. Results of the model corroborate and provide interpretation of corresponding PIC simulation results.B‐dot loop diagnostics of fast‐rise charged particle beams are most easily interpreted when the loops are close to the beam axis, or far downstream from the injection plane, and when frequency filtering of the signal is performed.

ISSN:0034-6748    

DOI:10.1063/1.1139740

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Experiments are described which document the utility of gas electron diffraction (GED) as a means of detecting analytes emerging from the column of a gas chromatograph (GC). In these experiments electron diffraction patterns from GC effluents are made visible on a phosphor screen, and the intensities of each GC peak are recorded on line by a 1024‐channel linear photodiode array detector. The technique not only indicates the presence of elutants but also provides auxiliary information on their molecular structures under favorable conditions. Minimum sample sizes of about 1 &mgr;l per component are currently required for GC‐GED, but indications are that further detector enhancements will allow the recording of electron intensities from smaller samples.

ISSN:0034-6748    

DOI:10.1063/1.1139741

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A silicon single‐photon avalanche diode (SPAD) detector and a proximity‐focus‐type microchannel‐plate photomultiplier tube (MCP‐PMT) are compared with respect to their performance in time‐correlated single‐photon counting (TCSPC) applications. A solution of pinacyanol (1,1’‐diethyl–2,2’‐carbocyanine) in ethanol, which is used as a test substance with short‐lived fluorescence, is excited at 620 nm with a synchronously pumped, cavity‐dumped rhodamine 6G dye laser. Deconvolution analysis of the fluorescence decay with a biexponential decay model gives excellent fits to the experimental data recorded with any one of the detectors. The fluorescence lifetimes for the dominating decay component are 13±2 and 11±2 ps as measured at 635 nm with the SPAD detector and the MCP‐PMT, respectively. The excellent agreement of these values and the quality of the fits show that the SPAD detector as well as the MCP‐PMT can resolve fluorescence decay time constants of the order of 10 ps. This is significantly better than what had been expected on the basis of the instrumental response widths of 70 ps (FWHM) with the SPAD detector and 50 ps (FWHM) with the MCP‐PMT.

ISSN:0034-6748    

DOI:10.1063/1.1140258

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A method for the determination of the refractive index of liquids using a He–Ne laser is presented. The experimental setup is simple and utilizes equipment which is normally available in most optics laboratories. Measurements carried out on water and several organic liquids are reported. The values of the refractive indices obtained by this method are in good agreement with those given in literature. The accuracy of results is of the order of ±5×10−3and can be improved by the use of a scale of higher precision.

ISSN:0034-6748    

DOI:10.1063/1.1139742

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

This article is devoted to the theory and experiment of the forced Rayleigh scattering method for measurement of thermal diffusivity of liquids which can be employed in the form of an instrument operated optically in a contact‐free manner. The theoretical considerations included are: (1) effect of cell wall, (2) effect of dye, (3) effect of Gaussian beam intensity distribution, (4) effect of heating duration time, and (5) effect of coupled dye and wall for a heavily absorbing sample. The errors caused by inadequate setting of optical conditions are also analyzed: (1) effects of grating thickness and (2) effects of initial temperature amplitude. Experimental verifications of the theory have been carried out through the measurements on toluene and water as standard reference substances. As a result of these experiments and theory, the criteria for optimum measuring conditions became available. To demonstrate the applicability of the present theory and the apparatus, the thermal diffusivities of toluene and methanol have been measured near room temperature under atmospheric pressure. The accuracy of the present measurement is estimated to be ±3%.

ISSN:0034-6748    

DOI:10.1063/1.1139743

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A novel, inexpensive calorimetry system is described for the analysis of the specific heat anomalies of shape memory effect (SME) alloys cycled through the martensitic transformation. By loading the sample on heating through the martensitic to austenitic transformation and unloading on cooling through the reverse transformation, a typical SME heat engine cycle is simulated. Analysis of the specific‐heat anomalies from these simulations gives a direct measure of the thermal efficiencies of the SME alloy. The requirements of externally stressing the sample as well as a changing sample shape produced heat losses which were difficult to estimate. An algorithm is described which estimates the combined heat losses by thermal base‐line subtraction. Measurements of the specific heats and enthalpies of transformation for heating and cooling through the transformations are presented, from which the thermal efficiencies were calculated.

ISSN:0034-6748    

DOI:10.1063/1.1139744

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

An extension of the square‐wave excitation method for measuring heat capacity is reported. In particular, attention is focused on the limit where the period of the heat pulse excitation is much smaller than the thermal relaxation time of the calorimeter‐sample system. In this limit, one finds that the thermal ripple induced by the heat pulse is inversely proportional to the heat capacity. This technique allows one to do real‐time heat‐capacity measurements as in the conventional ac technique with the same instrumentation as the square‐wave method. The ripple method is demonstrated with a measurement of the heat capacity of strained Al near its superconducting phase transition.

ISSN:0034-6748    

DOI:10.1063/1.1139745

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The construction of a probe suitable for pulsed NMR for the investigation of fluids and solids at hydrostatic pressures up to 3 kbar is reported. The probe fits in a cryostat constructed inside the room‐temperature bore of a superconducting magnet. The temperature can be controlled in the range from 80 to 380 K. The apparatus has been used successfully in a NMR study of self‐diffusion in gaseous and liquid xenon, using129Xe and131Xe spin echoes at 75 and 22 MHz, respectively.

ISSN:0034-6748    

DOI:10.1063/1.1139746

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Temperature distribution in a cylindrical furnace used in a high‐pressure apparatus has been calculated by the difference method. The calculated values are in good agreement with the experimental observations obtained by an x‐ray diffraction method. A steep temperature gradient exists in a simple cylindrical furnace. In order to obtain a homogeneous temperature distribution, a furnace composed of a graphite tube and two graphite disks has been designed. It has been demonstrated that a homogeneous temperature distribution can be obtained by selecting proper resistivities for the tube and the disks. The design requires a large power input, which could result in a shorter lifetime of the anvils.

ISSN:0034-6748    

DOI:10.1063/1.1139747

出版商:AIP    

年代:1988

数据来源: AIP