摘要:

A new instrument is presented for measurement of the anisotropy energy of thin ferromagnetic films. It permits rapid and simple investigation of the anisotropy over a 360° range. The method is purely electrical; the results are automatically displayed on the oscilloscope screen. The circular film is rotated uniformly in a homogeneous dc field. The magnetization vector oscillates around the direction of this field. Its movement is recorded, and relates directly to the anisotropy energy function. Three examples of results obtained are presented. The resolving power, expressed in terms of magnetic flux inside the sample, is determined by the ambient 60‐cycle field; its value is of the order of 10−11Wb, which corresponds to a thickness of approximately 10 Å for a 80% Ni Permalloy film one cm in diameter. The simplicity and the small cost of the instrument are attractive features. In many cases, both the present analysis and that obtained with a static torquemeter at high field would be complementary.

ISSN:0034-6748    

DOI:10.1063/1.1717878

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The loss of initial polarization of a proton beam during acceleration in a synchrocyclotron is investigated. It is shown that, due to resonance effects, substantial depolarization occurs unless the field inhomogeneities are kept well below 0.01%.

ISSN:0034-6748    

DOI:10.1063/1.1717879

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A single 50‐Mc cavity electron accelerator has been built. When operating in the TM010mode, it is capable of delivering a 29‐amp, 0.2‐&mgr;sec, 8‐Mev, 2‐cm radius beam to a target downstream from the cavity. When focused to a 3‐mm‐diam spot, the beam current is reduced to about 9 amp; the resulting radiation flux is about 1.2 r at one meter for a 0.2‐&mgr;sec pulse length.

ISSN:0034-6748    

DOI:10.1063/1.1717880

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A phase detector system which can be easily adapted to bridge or crossed‐coil NMR spectrometers is described. Modifications to the NMR spectrometer include addition of a constant impedance attenuator for control of the probe excitation voltage, a leakage control system independent of probe balance, and a differential dc amplifier to cancel changes in the leakage from spurious modulation of the transmitter power.

ISSN:0034-6748    

DOI:10.1063/1.1717881

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Radiation damage studies of metal specimens have been achieved by using a Van de Graaff accelerator to supply energetic electrons. The irradiating electrons are magnetically deflected so that the electron beam bombards a well‐defined rectangular area. A method is described which is used to determine the location of the beam with respect to the position of the specimen. A low temperature thermal switch is discussed in terms of its theroetical and and experimental behavior. A practical method for improving the thermal contact between the specimen and its holder by using the helium exchange gas technique is described. Estimates of the degree of thermal contact between specimen and specimen holder are possible because of the particular electrical circuit in the experimental chamber.

ISSN:0034-6748    

DOI:10.1063/1.1717882

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A technique is described for measuring the potential within a plasma by monitoring the time‐of‐flight of a beam of electrons directed through the plasma. The electron beam, intensity modulated at 30 Mc, is accelerated to an initial velocity determined by its cathode potential. The velocity then varies from this initial value as the potential along the flight path varies, changing the arrival time of the 30‐Mc signal at the collector. The phase of the collector signal is continuously compared to that of a reference signal derived from the intensity modulator. The phase comparator has an output which is linearly proportional to the phase difference between the two signals. The sensitivity of the technique depends principally on the energy of the electron beam and the response time of the circuits. Using 900‐v electrons, it is possible to measure a potential of 2 v along a 10‐cm path, or follow changes of this magnitude which occur in a microsecond. The sensitivity can be raised to look at potentials which change more slowly. Under the operating conditions used, 2 v along 10 cm represent a phase change of about 0.1°, or a time change of about 1×10−11sec.

ISSN:0034-6748    

DOI:10.1063/1.1717883

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

It is shown that doped germanium crystals can be used as second sound receivers. Their frequency response, sensitivity, and noise level have been measured for samples of several thicknesses. By comparing the results with the corresponding values found in other types of second sound receivers, it is concluded that germanium receivers are superior to the other types in common use for applications below 10 kc.

ISSN:0034-6748    

DOI:10.1063/1.1717884

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A small, rugged glass Dewar using a liquid nitrogen cooled metal shield is described. This Dewar is relatively inexpensive to construct and to modify, stores helium with only a moderate loss rate, and can be adapted for a wide variety of low temperature experiments. Two other Dewars, in which vapor‐cooled radiation shields replace liquid nitrogen cooled shields, also are described. Helium loss rates show that a liter of liquid helium will keep these Dewars at 4°K for about 5 to 10 hr.

ISSN:0034-6748    

DOI:10.1063/1.1717885

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The heat introduced into a cryogenic system by current‐carrying leads has been investigated experimentally and theoretically. The experimental work consisted of measuring the heat conducted by various cables and wires into a helium Dewar. The experimental results show that the use of long coaxial cables to the helium bath minimizes boil‐off and also that there are optimum wire sizes for the current ranges 0–0.5 amp (#38 AWG) and 0.5–1.0 amp (#34 AWG). The theoretical analysis of the heat input takes into account the varying electrical and thermal conductivities of the leads and also allows for heat exchange with the effluent helium vapor. The results of this analysis indicate the importance of including gas cooling in predicting the boil‐off rate.

ISSN:0034-6748    

DOI:10.1063/1.1717886

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

An apparatus employed for studying light‐modulated changes in the magnetic susceptibility of semiconductors is described. Its chief parts are a flat reed spring from which the specimen is suspended, an electrostatic counter‐balancing system, a frequency modulation phase sensitive motion detector, and a modulated light source. The light modulation operates at the mechanical frequency of reed and specimen, whose forced harmonic motion is proportional to the light‐induced susceptibility changes. The chief advantages of this new method are the elimination of drifts due to changes in the nonmodulated part of the susceptibility, the excellent nonsynchronous noise elimination, and the high detection sensitivity, which was 10−11cgs mass‐susceptibility units at a value ofHgradHof 107gauss2/cm. Another incidental advantage is a simplicity and ruggedness not generally encountered in high sensitivity instruments.

ISSN:0034-6748    

DOI:10.1063/1.1717887

出版商:AIP    

年代:1962

数据来源: AIP