摘要:

An adiabatic calorimeter with automatic shield control is described which has been used for the measurement of heat capacities and transition heats in the range 15 to 600°K. The apparatus was designed specifically for the study of bulk polymers. Over most of the temperature range a precision of better than ±0.2% may be attained.

ISSN:0034-6748    

DOI:10.1063/1.1720152

出版商:AIP    

年代:1966

数据来源: AIP

摘要:

A triangle and square wave generator designed to excite Mo¨ssbauer velocity drives is described. The version shown runs from 1 to 25 cps, and has frequency and amplitude stability and linearity substantially better than 0.1%.

ISSN:0034-6748    

DOI:10.1063/1.1720153

出版商:AIP    

年代:1966

数据来源: AIP

摘要:

Until MacKenzie recently emphasized the dominating role of space charge beam blowup at small radii in synchrocyclotrons, the importance of this factor was not appreciated. Much largely futile effort had been expended on attempts to increase average beam currents by improving other factors. Lawson's extension of MacKenzie's treatment for ordinary cyclotrons is considered in more detail, with numerical examples and a detailed discussion of the extension of the theory to synchrocyclotrons. In addition, a simpler semi‐empirical formula is obtained which gives a good match to existing currents in all present synchrocyclotrons. Current gains up to a factor ∼100 should be feasible, and a discussion is given as to how such an improvement might be gained by modifications of existing synchrocyclotrons.

ISSN:0034-6748    

DOI:10.1063/1.1720154

出版商:AIP    

年代:1966

数据来源: AIP

摘要:

A detailed comparative analysis of several possible input circuits for observing NMR free precession signals is given. Special attention is paid to the case of signals having short decay time constants. Here the presence of a large initial ringing transient makes it necessary to consider possible modifications in the design of the receiver system. The analysis indicates that an untuned transformer coupled input circuit is potentially superior to the traditional parallel resonant circuit in this case.

ISSN:0034-6748    

DOI:10.1063/1.1720155

出版商:AIP    

年代:1966

数据来源: AIP

摘要:

A sample holder is described that considerably facilitates the measurement of specific resistivity on small, irregularly shaped single crystals over a large range of temperature. Utilizing the van der Pauw technique, accurate values of this electrical transport parameter have been obtained without loss of contact at temperatures as low as 4.2°K. The essential advantage of this holder is its simplicity which eliminates the necessity of specialized techniques for accurate measurements on irregular crystals as small as 1 mm.

ISSN:0034-6748    

DOI:10.1063/1.1720156

出版商:AIP    

年代:1966

数据来源: AIP

摘要:

A simple, contact free, ultrasensitive distance and displacement measuring instrument has been investigated. Experiments demonstrate that the instrument is capable of operating at spacings as small as a few hundred angstroms. Calculations indicate that distances of 10−3to 10−6cm and less can be reproduced to within about one part in 105. With suitable calibration, distance measurements in the 10−3to 10−6cm range can be expected to have accuracies limited only by available calibration techniques. The instrument would be most useful as a null or differential distance measuring device. It has the unusual property that resolution improves over several orders of magnitude as the null or measurement point is approached. Since the instrument contains no optical or mechanical lever systems, or delicately balanced bridges, it has inherent long term stability. Proposed applications include: (1) measurement of ball and hole diameters (contact free), (2) differential thermal expansion cell, (3) mechanical vibration sensor, (4) surface profile delineator (contact free), and (5) surface contour delineator (contact free).

ISSN:0034-6748    

DOI:10.1063/1.1720157

出版商:AIP    

年代:1966

数据来源: AIP

摘要:

Six hundred power transistors on water‐cooled heatsinks are connected in a Kerns actuator circuit to modulate the power line feeding the Berkeley 88‐Inch Cyclotron. The regulator senses the rectified three phase line voltage and attenuates the frequency components between 0.001 and 200 Hz to 0.03% of the average value. Elimination of these components from the main power line removes the need for expensive wide band regulators for each of the many critical high power loads in the building. The paper discusses the design considerations and construction techniques of this regulator.

ISSN:0034-6748    

DOI:10.1063/1.1720158

出版商:AIP    

年代:1966

数据来源: AIP

摘要:

The application of a small general purpose computer as an ``on line'' data acquisition device for Mo¨ssbauer effect experiments is described. A method of conversion from analog to digital information and an outline of the computer program are given. The performance of the system is demonstrated by a Mo¨ssbauer spectrum of iron sulphide (pyrite). The extension of these techniques to other experiments is briefly considered.

ISSN:0034-6748    

DOI:10.1063/1.1720159

出版商:AIP    

年代:1966

数据来源: AIP

摘要:

A method is described which allows making photoextinction measurements with a sensitivity of 0.01%. The procedure involves inserting test media directly into the cavity of a 6328 Å He‐Ne gas laser and detecting transmission losses by measuring laser output changes with a photomultiplier. Calibration is accomplished by using a very thin variable Brewster angle flat within the cavity.

ISSN:0034-6748    

DOI:10.1063/1.1720160

出版商:AIP    

年代:1966

数据来源: AIP

摘要:

A method using a high pressure vessel of piston‐cylinder type is introduced which is capable of the measurement of the ferromagnetic Curie points of fragile materials such as a sintered ferrite under high pressures. Since a sample is fixed in silicon grease inside the vessel, it is compressed hydrostatically and is protected from breaking by the application of solid pressures. Measurements on Mn‐Zn and Ni‐Zn ferrites show that their Curie points rise with the increase of applied pressures, the rate being nearly +1°C/kbar in both cases.

ISSN:0034-6748    

DOI:10.1063/1.1720161

出版商:AIP    

年代:1966

数据来源: AIP