摘要:

A new superconducting circuit has been used in a sensitive magnetic susceptibility apparatus to detect changes in magnetic susceptibility as small as 10−10cgs/g in a 104Oe field, and in a low field magnetometer with which magnetic fields as low as 5×10−7Oe have been measured. A low field superconducting shield for testing sensitive magnetometers has been developed and used to provide stable magnetic fields of less than 10−6Oe, maintained stably for as long as six days. The measured attenuation of externally applied axial field changes is shown to be a factor of about 31 per shield radius. The stability of the persistent field of a Nb‐25% Zr superconducting solenoid, observed over an 8 h period, indicated an average drift in the persistent solenoid field of less than one part in 1010/sec. Also, the attenuation of various high field magnetic shields of Nb‐25% Zr foil was measured.

ISSN:0034-6748    

DOI:10.1063/1.1720694

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A carbon bolometer, used as a high speed thermometer for observing heat pulses in solids at low temperatures, is described. In conjunction with a KCl substrate, the carbon bolometer was compared with a thin film superconducting bolometer. The carbon bolometer was found to have a frequency response flat to at least 2.5 kHz.

ISSN:0034-6748    

DOI:10.1063/1.1720695

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A constant amplitude, reverse bend stress fatigue testing device is described which permits simultaneous testing of up to eight specimens at extremely low pressure levels below 10−10Torr. The vibratory force was provided by an electromagnetic exciter with vibration frequencies in the range of 50–200 cps. Fatigue tests with 1100‐H14 aluminum showed that a substantial increase in the cyclic fracture life was obtained in high vacuum as compared to the fatigue behavior in unit atmosphere of air. The fatigue life improvement increased proportionally with the cyclic stress frequency.

ISSN:0034-6748    

DOI:10.1063/1.1720696

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A method is discussed for producing and measuring the electric charge on single droplets pulsed out of a main stream of droplets which were produced by periodic mechanical excitation of a jet of liquid. With this method, charges on the order of 100 electrons can be measured on the single droplets.

ISSN:0034-6748    

DOI:10.1063/1.1720697

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A load cell employing foil strain gauges is described for measuring small uniaxial loads (5×104to 2×106dynes) applied magnetically to develop bending stresses in crystals under hydrostatic pressures up to 15 kbar. Two calibration methods of direct loading at pressure were used—a magnetically operated plunger and dead weight loading. It was established that the change in gauge output (the ``pressure effect'') during increase of pressure at no‐load is in keeping with previous work. However, the gauge factor, as determined by the load cell response after balancing at pressure, decreases with increasing pressure. For the strain gauges used here, the decrease is approximately linear and at 10 kbar is as much as 20%.

ISSN:0034-6748    

DOI:10.1063/1.1720698

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A method of measuring beam divergence is reported that provides simultaneous variable intensity multiple exposures of the laser output on Polaroid film, and does not require densitometer tracings of the exposures to establish the beam divergence. Using this technique, beam divergence as a function of power output of 12 ``Q‐switched'' ruby rods is reported. Inference is made that the active divergence of a ruby rod is the sum of the passive beam divergence of that rod plus the divergence due to radial mode structure. Thermal distortion probably contributes very little to the beam divergence.

ISSN:0034-6748    

DOI:10.1063/1.1720699

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A simple plane horizontal layer type apparatus is described for measuring thermal conductivities of gases over a wide pressure range. Experimental results obtained with argon, nitrogen, and air indicate that thermal conductivities and thermal accommodation coefficients can be determined with the apparatus within about 2% accuracies at pressures ranging from free molecule to continuum conditions.

ISSN:0034-6748    

DOI:10.1063/1.1720700

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A 35 GHz, reflection‐cavity type microwave spectrometer is described. We use a 35 GHz ferrite modulator in the signal arm to produce a double sideband (±100 kHz) suppressed carrier signal to reduce the 1/fmicrowave crystal noise. Solid metal cavities and low frequency modulation of the externally applied magnetic field are used to reduce leakage from the cavity, thereby reducing susceptibility to microphonics and allowing more freedom in the choice of cavity modes suitable for a wide variety of experiments with metallic or dielectric samples. This instrument employs a 35 GHz ferrite phase shifter to phase lock the microwave signal in the reference arm of the bridge for observation of absorption signals An analogous scheme for phase‐locking at dispersion signals is also suggested. A narrow passband, low noise, active filter, with a Q factor of approximately 106, is used as part of a feedback loop around the 100 kHz receiver. This minimizes the possibility of saturation of the receiver due to less than critical coupling to the microwave cavity. Practical advantages of the present unit in low temperature spectroscopy, particularly with regard to helium bubbling and helium level change, are stressed. Comparative sensitivity tests of this unit with the standard 200 Hz magnetic field modulation systems show that, at cavity power levels smaller than 5 mW, a factor of ten improvement can be attained. At higher microwave power levels the improvement available is hampered by microphonics in the bridge. The theoretical analysis of the microwave bridge operation, of various key components, and of the electronic system is presented in the text and in the appendices.

ISSN:0034-6748    

DOI:10.1063/1.1720701

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A theoretical analysis has been carried out to determine the trajectories of charged particles incident upon a pair of concentric spherical grids, where the inner grid is maintained at a large accelerating potential with respect to the outer grid. The results show that under certain conditions a beam of charged particles incident on the outer grid is sharply focused inside the inner grid. These results were confirmed experimentally using hemispherical grids and electron beams.

ISSN:0034-6748    

DOI:10.1063/1.1720702

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The following describes a Lecher system with finlines for providing the transition to waveguides which is suitable for incorporation in microwave interferometers. This device gives a spatial resolution perpendicular to the wires which is smaller than the wire separation, even for 4 mm waves, i.e. smaller than &lgr;/2.

ISSN:0034-6748    

DOI:10.1063/1.1720703

出版商:AIP    

年代:1967

数据来源: AIP