摘要:

In pulse optically detected magnetic resonance (ODMR) spectroscopy, the precision in the spin relaxation data has been severely limited by instabilities in the timing of the sequence of pulses in the train. A digital pulse train generator is shown to be highly stable with resolution limited only by the response time of the circuit. In addition when the pulse train generator is controlled by a microprocessor, the programming capability allows an extremely wide variety of pulse sequences to be used in pulse ODMR. The use of this and an existing photon counter which is also under microprocessor control allows data manipulation to be made with ease and convenience. The microprocessor controlled pulse train generator is an inexpensive yet highly flexible apparatus useful in pulse ODMR, which can be adapted for application in pulse NMR.

ISSN:0034-6748    

DOI:10.1063/1.1136111

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The dual‐variable detection method is a device to provide a wider dynamic range to the light intensity measurement by a photomultiplier. A dynamic range as wide as seven orders of magnitude is attainable by controlling and analyzing both the dynode voltage and the anode current. The electronic circuit is illustrated and its application to the simultaneous measurement of the absorbance and the circular dichroism, which have used to require different light intensity range for the optimum operation, is described.

ISSN:0034-6748    

DOI:10.1063/1.1136112

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A laser beam manifold and particle photography system has been developed for use in fluid velocity measurements. The laser manifold is a device which transforms a single laser beam into several uniform parallel beams. By orienting two manifolds mutually perpendicular, an optical grid can be formed which acts as a reference for fluid velocity measurements. This optical grid is for all practical purposes totally nonperturbing to the flow. Tracer particles moving in the plane of the grid are then photographed to yield fluid velocities that can be measured relative to the optical grid. System construction and theory are presented.

ISSN:0034-6748    

DOI:10.1063/1.1136113

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A new simulation technique has been developed for the study of void swelling. Its salient characteristics include the use of fission‐fragment irradiation produced by doping with235U and irradiating in a thermal neutron flux; use of bulk specimens and the yield of continuous,insituswelling data. This technique has several unique advantages and, in conjunction with other conventional methods, it offers the possibility of detailed evaluation of void nucleation and growth theories. Preliminary results for low‐dose void swelling in Ni at 500°C are presented.

ISSN:0034-6748    

DOI:10.1063/1.1136114

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A rapid nondestructive (optical) technique, which can be used to monitor directly the chemical polishing/etching time required for removal of lapping (or sawing) damage in semiconductor wafers, is described. This technique utilizes dependence of the amplitude of surface photovoltage signal on the residual surface stress to determine the ’’end‐point’’ of chemical polishing/etching. It is shown that this technique is very sensitive and well suited for large scale polishing facilities.

ISSN:0034-6748    

DOI:10.1063/1.1136115

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Measurement of electrical resistance of pure metal samples at low temperatures poses special problems because the resistance is usually very small and must be measured very precisely to be useful. We present a tested design for a bridge which in several significant respects is superior to previous ones. At ultralow temperatures it permits the measurement of resistance to 0.1 ppm in resistors from ∼1 m&OHgr; to 0.1 &mgr;&OHgr;, or lower. Indeed, relatively high precision measurements can be made over the whole temperature range from ∼20 mK to near 7 K. Finally, a new technique is developed which eliminates most of the problems of making a comparison (or standard) resistor and at the same time eliminates the necessity of an extrapolation to zero temperature in order to obtain &rgr;0, as is conventionally done.

ISSN:0034-6748    

DOI:10.1063/1.1136116

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The extension of shock tube techniques to the study of ignition and burnout of pulverized coal is examined. Nonintrusive optical techniques for characterizing the particle size distribution and the particle temperature as a function of time during burnout are described. Comparison of surface oxidation rates of soot particles and several bituminous coals obtained in the shock tube are in excellent agreement with the higher temperature results found in other apparatus. Because of the wide but controllable ranges of total pressures, oxygen parital pressures, particle temperatures, and coal loadings obtainable, the shock tube offers an additional instrument for the study of solid particle ignition and reactivity under conditions comparable to those found in mine explosions and anticipated in high intensity combustors.

ISSN:0034-6748    

DOI:10.1063/1.1136117

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Crowbarring is achieved when a magnetically driven arc contacts an electrode in the crowbar circuit. No auxiliary timing circuitry is required and, at the time of crowbarring, the arc divides into two parts such that the load is isolated from the source. A discharge which peaks at 200 kA in 4 &mgr;s is crowbarred and displays a 50‐&mgr;s e‐folding time with a ripple current of less than 5%. Main switching and crowbarring are combined in a single 3‐electrode spark gap which is triggered by a pin between two of the electrodes. Crowbar timing is insensitive to gap dimensions and to current magnitude. Pin placement is critical but little energy is dissipated in the neighborhood of the trigger pin.

ISSN:0034-6748    

DOI:10.1063/1.1136118

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

This paper describes the theory and design of Rogowski‐wound coils used to measure nanosecond electrical curent pulses in the megampere range. The coils have risetimes of less than one nanosecond, microsecond decay times and typical sensitivities in the range of 10−3to 10−4V A−1. They operate in large radiation fields, under intense electron bombardment and at high rates of current rise.

ISSN:0034-6748    

DOI:10.1063/1.1136119

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The output voltage of spiral generators, which are used for high voltage pulse generation, is derived analytically from a coupled wave analysis that includes the switch impedance, loading of the output terminals, and the influence of the finite conductivity of the spiral‐wound conductors. It is demonstrated that the spiral generator behaves like a damped LC resonance element which is charged by a fraction of the switch current. Graphs of the output voltage as function of dimensionless parameters and scaling relationships for spiral generators are given.

ISSN:0034-6748    

DOI:10.1063/1.1136120

出版商:AIP    

年代:1980

数据来源: AIP