摘要:

The construction and signal processing methods of several experimental gas‐filled, position‐sensitive proportional counters (PSPCs) using resistance–capacitance (RC) position encoding are described, and guidelines for the design and operation of these counters are given. Using these guidelines, we were able to improve the spatial resolution and shorten the signal processing time; for example, the intrinsic spatial uncertainty in the position measurement was reduced to 28 &mgr; FWHM for alpha particles and 100 &mgr; FWHM for low‐energy x rays (2–6 keV). Also, the signal processing time was reduced to 0.6 &mgr;sec without seriously degrading the spatial resolution. These results have widened the field of application of theRCposition encoding method for position measurements of low‐energy photons, neutrons, and charged particles in a wide variety of nuclear physics experiments, in nuclear medicine imaging, and in low‐dose, medium‐resolution radiography.

ISSN:0034-6748    

DOI:10.1063/1.1134379

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A computer‐assisted measurement system is described which has been optimized for the precise measurements of the amplitudes, phases, and frequencies of the de Haas–van Alphen oscillations. System software, architecture, and control concepts are described which have general utility in computer‐controlled and automated measurements. The system is made flexible for a broad class of experiments by partitioning control functions, by providing efficient control parameter handling and editing, and by utilizing program chaining. The experimeter’s role is enhanced with an interface control board which allows the manual control and flexibility essential in a research laboratory.

ISSN:0034-6748    

DOI:10.1063/1.1134380

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A diamond‐anvil type optical cell of improved design has produced static pressures in gasketed samples up to 500 kilobar as measured by the ruby fluorescence technique. The ruby R1line pressure shift is linear to 291 kilobar, and the maximum measured shift is extrapolated to 500 kilobar assuming continued linearity of the pressure dependence. The ultimate pressure capability of this diamond cell has not been established. Transition pressures in the semiconductors Si, ZnSe, ZnS, and GaP measured by the ruby method indicate that the revised 1970 fixed point scale and the ruby (NaCl) scale diverge above 135 kilobar and disagreement may be by as much as a factor of 2 in the 500 kilobar range with the ruby scale defining the lower pressure.

ISSN:0034-6748    

DOI:10.1063/1.1134381

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A special stabilization system has been constructed to control the overall gain of photomultiplier tubes in a liquid scintillation counter. The system uses GaAsP light emitting diodes in the measurement chamber to produce separate reference light pulses for each photomultiplier tube. The system has provided a significant improvement in both short and long term stability and in operational reliability.

ISSN:0034-6748    

DOI:10.1063/1.1134382

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

An airlock door modification for the JEM 100B electron microscope is described. This modification permits prefrozen specimens to be introduced into the microscope without frost forming on the specimen or the specimen warming excessively. The imaging of hydrated biological material using frozen specimens is demonstrated with crystalline catalase as a test specimen.

ISSN:0034-6748    

DOI:10.1063/1.1134383

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Several new techniques for processing signals from dual‐wavelength/split‐beam spectrophotometers are discussed and contrasted with earlier methods. Based on these techniques, a signal‐processing instrument has been built which achieves significant improvements in speed, range, accuracy, and noise reduction. Since this instrument does not use dynode feedback, any light detector (photodiode or photomultiplier) can be used. Additionally, the instrument can be interfaced to virtually all spectrophotometers by simply connecting it to the detector output and a signal of the same frequency as the light chopper. Older spectrophotometers can, therefore, be upgraded easily. At the heart of this instrument is a new type of phase sensitive detector (PSD) which can demodulate the detector output (which has been modulated by the light chopper) in such a way as to provide two simultaneous signal outputs: one corresponds to the ’’reference’’ beam or sample, while the other is the ’’measure’’ beam/sample. Any function of these two signals (e.g., difference, ratio, or log ratio) can easily be computed directly. Because the PSD is gated in such a way as to ignore switching transients from the light chopper, these transients do not appear as an error in the demodulated output. The full theoretical signal bandwidth of one‐half the chopper frequency is available at the output since sample and hold amplifiers are used instead of low pass filters. Not only is speed improved, but chopper ripple in the output is reduced considerably.

ISSN:0034-6748    

DOI:10.1063/1.1134384

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

After having used an analytical expression in the form of a power series expansion to calculate the interelectrode electrostatic field in the general case of a toroidal electrostatic analyzer, we derive approximate analytical expressions for the most interesting response functions (geometrical factor, angular aperture, energy resolution, etc.). Results of a study of the dependence of these quantities with respect to the geometrical parameters of the analyzers are given in the form of grids of curves. By using such grids one is able to determine the optimal parameters to obtain any particular solution. Examples of such a choise are given in the case of measurements of low energy particles in space (10 eV to 50 keV).

ISSN:0034-6748    

DOI:10.1063/1.1134412

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A high‐vacuum Raman cell using the backscattering geometry for use in studies of microcrystals, surface effects, and physical and chemical adsorption is described. The circuit and description for a temperature controller are also included.

ISSN:0034-6748    

DOI:10.1063/1.1134396

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

For the measurement of the ionic composition of the atmosphere a reprogrammable control unit for a quadrupole mass filter has been constructed. The heart of this unit consists of two programmable read only memories which allows the choice of 16 different measuring jobs by six telecontrol channels. The underlying principles as well as the performance of the unit are described.

ISSN:0034-6748    

DOI:10.1063/1.1134397

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A pressure gauge is described which accurately measures high static pressures. It features continuous digital readout, simple construction, and freedom from aging and hysteresis effects. While this device is thoroughly tested over the pressure range 170–1000 bar, its characteristics can be reliably extrapolated to 7000 bar. As tested, the maximum pressure uncertainty is typically 0.1%, and substantial improvement is anticipated with minor design modification. This gauge is shown to be a practical alternative to the commonly used manganin cell at pressures less than 7000 bar. It uses the well‐established principle of the acoustic dilatometer: A compressible fluid (n‐hexane) is contained in a closed volume by a piston of mercury, and the height of the free mercury surface is accurately monitored using a sound‐ranging (ultrasonic echo time) technique. Pressure changes cause the compressible fluid to expand or contract. This in turn changes the height of the mercury surface and hence also the ultrasonic echo time. Thus, a measurement of ultrasonic echo time provides an indication of the pressure on the system.

ISSN:0034-6748    

DOI:10.1063/1.1134398

出版商:AIP    

年代:1975

数据来源: AIP