摘要:

An absolute method of standardization and measurement of the magnetic susceptibility of small samples is presented which can be applied to most techniques based on the Faraday method. The fact that the susceptibility is a function of the area under the curve of sample displacementversusdistance of the magnet from the sample, offers a simple method of measuring the susceptibility without recourse to a standard sample. Typical results on a few substances are compared with reported values, and an error of less than 2% can be achieved.

ISSN:0034-6748    

DOI:10.1063/1.1716404

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

At low‐voltage levels a diode ring forms an extremely simple four‐quadrant passive analog multiplier characterized by reliability, stability, and wide band width. Operation is analyzed theoretically, and experimental tests are described. These show that with care in selecting diodes and adjusting circuit values, 1% accuracy is obtainable at input levels up to 150 mv.

ISSN:0034-6748    

DOI:10.1063/1.1716405

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

An electromechanical analog integrator for obtaining a continuous time integral of varying voltage is described. It is suited for applications where integrating times of greater than one minute are encountered. Particular consideration is given to its applicability to magnetic resonance data reduction.

ISSN:0034-6748    

DOI:10.1063/1.1716406

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

A dosimeter for electron beams has been constructed which utilizes the luminescence of plastic phosphors under electron bombardment. A phosphor, in sheet form, was placed in a Lucite medium and the luminescence of a small volume of the phosphor was focused on a photomultiplier. By scanning the phosphor, the three‐dimensional dose distribution within the medium was determined. Special attention was paid to obtaining the dose close to the surface of the medium by which the electron beam entered.

ISSN:0034-6748    

DOI:10.1063/1.1716407

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

A device is described for obtaining powder diffraction patterns of thin sheets pressed between opposing diamond pistons. The pressure, initially applied by a small auxiliary laboratory press, is clamped onto the sample by a lock‐nut. The whole unit is designed to replace the sample mount of a standard x‐ray diffraction unit. Sample patterns taken on two of the high pressure modifications of bismuth are exhibited.

ISSN:0034-6748    

DOI:10.1063/1.1716408

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

An electronic coulometer is described which has 15‐ohms input impedance, precision of 0.003 coulomb per minute, and long time stability of 0.1% of full scale value. Its calibration and testing are described, and means of adapting it to other operating conditions are given.

ISSN:0034-6748    

DOI:10.1063/1.1716409

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

A high‐precision capacitor divider method for measuring the voltage on the terminal of a 2‐Mv Van de Graaff accelerator is described. Calibration of the system was done using the Be(&ggr;,n) threshold reaction. Linearity was tested using a total beam calorimeter and a beam current integrator.

ISSN:0034-6748    

DOI:10.1063/1.1716410

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The effect of temperature on the stability of the Varian V‐4300–2 NMR spectrometer has been investigated. The spectrometer was most sensitive to changes in room‐air temperature. A change of 0.3°C per minute caused a spectrometer drift of about 20 cps per minute. A change of 0.1°C per minute in temperature of magnet cooling water caused a spectrometer drift of 1 cps per minute. Enclosing the magnet served to minimize effects of air temperature changes but amplified the effects of water temperature changes. Satisfactory control was attained by running the refrigeration units continuously and regulating the temperatures by controlling the suction pressure on the evaporators. Under these conditions spectra were reproducible to within ½ cps.

ISSN:0034-6748    

DOI:10.1063/1.1716411

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

A grinder which can be used for sectioning diffusion specimens in which the average diffusion distance is a very few microns is described. Three fixed steel balls are used to determine the grinding plane of the instrument, and the specimen is held with constant orientation at the center of the triangle formed by the balls. The orientation of the grinding plane with respect to the specimen surface can be changed to make the two parallel by adjusting the lengths of the legs to which the steel balls are attached. These lengths can be adjusted over several centimeters, permitting a large variation in specimen thickness and orientation. A differential screw arrangement on each leg makes it possible to orient the grinding plane and crystal surface to within 5×10−6radian with respect to one another. The shaft on which the specimen remains mounted during the entire grinding procedure can be moved in a line perpendicular to the grinding plane so that the specimen surface protrudes beyond the grinding plane. A solid grinding plate is then used to grind the specimen away until the surface lies in the plane. Since no loose grinding compound is used, the material removed from the specimen can easily be collected for preparing a radioactive slide. It is also possible to assay the radioactivity of the specimen itself. The motion of the shaft, and, consequently, the thickness ground away, is measured directly using an electronic indicator and is checked every 10 &mgr; against gauge blocks. It is estimated that sections parallel to within 10−5radian and with the thickness known to the order of a few hundredths of a micron can be removed with the device, the lower limit on the thickness of the slice being about 1 &mgr;.

ISSN:0034-6748    

DOI:10.1063/1.1716412

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

A circuit technique is described which reduces the rise times of high‐power pulses by means of exploding wires. This circuit is a nonlinear lumped parameter transmission line. The magnetic energy is stored in the interstage lead inductances and rapidly transferred into (or more correctly, shared with) succeeding stages by the vaporization of exploding wire resistive fuse elements connected in shunt between the leads. In our case, each of three resistive fuse elements consisted of 20 to 50 parallel 0.001‐in. diam copper wires held in place across a 2‐in. gap with pressure sensitive tape. An empirically determined arrangement is described wherein we have increased the maximum rate of current rise from 300 000 amp/&mgr;sec to 800 000 amp/&mgr;sec. Using this technique, a magnetic field of 10 000 gauss is built up in 0.15 &mgr;sec throughout a volume 4 cm in length and 10 cm in diameter.It will be shown that the best results are obtained with high conductivity fuse materials such as copper or aluminum. Similarity theorems are presented for the design of pulse steepening elements for use with circuits having similar pulse shapes but different energies and characteristic impedances.

ISSN:0034-6748    

DOI:10.1063/1.1716413

出版商:AIP    

年代:1959

数据来源: AIP