摘要:

A diamond anvil high pressure cell made of beryllium, a special goniometer head, and a Buerger‐type precession camera designed for x‐ray diffraction by single crystals at high pressures are described in some detail. The most important problems still to be solved are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1684179

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A microwave reflection technique for measuring both the transient and quiescent electrical conductivity of semiconductors in a temperature range from 4.2 to 450 K is described. This technique eliminates the difficulties due to non‐Ohmic contacts when making electrical measurements on semiconductors, particularly silicon.

ISSN:0034-6748    

DOI:10.1063/1.1684180

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Beams of metastable helium produced by electron bombardment generally contain atoms in both the 21Sand 23Sstates. It is important in many experiments to distinguish between these states, or at least to know the population ratio. A beam of 23Sand ground state helium atoms has been produced by electron bombardment and subsequent resonant quenching of 21Satoms with 21S−21P2 &mgr; radiation. This radiation mixes the 21Sand 21Pstates, the latter decaying primarily to the 11Sstate by emission of 584 Å radiation. The quenching has been studied as a function of beam atom velocity. The results indicate that beams of metastable helium containing less than 1% 21Satoms can be produced.

ISSN:0034-6748    

DOI:10.1063/1.1684181

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A system is described in which a multichannel analyzer is used to repeatedly scan a powder x‐ray diffraction spectrum in discrete intervals. Counts are recorded at a given angle for the required dwell time. A preset indexer actuated by the multichannel analyzer drives a stepping motor the required increment in angle. The channel memory is advanced by one and the above process is repeated until the end of a scan. The indexer then drives the diffractometer back to the starting angle. Scans are repeated until sufficient data are accumulated. All the scans are made in the same direction to avoid backlash errors. The system prints out the contents of the memory at definite intervals (usually every 12 h) so that in the event of a malfunction only the data taken since the last printout are lost. Other advantages and some disadvantages of the system are described.

ISSN:0034-6748    

DOI:10.1063/1.1684182

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Miniature pressure transducers which are suitable for measuring pressures on models placed in rarefied shock tunnel flows are described. Special attention is given to the problems of mechanical vibration, convective heating, and miniaturization. It is shown that by using a matched pair of piezoelectric crystals in conjunction with special first‐stage circuitry a pressure transducer can be built which, for example, is 5.1 mm in diameter and has the following characteristics: (1) a pressure sensitivity of 1.64 mV/Torr, (2) an acceleration sensitivity of less than 0.0425 mV/gat frequencies up to 200 Hz, and (3) a negligible response to heat flux rates up to 1.33 &Dgr;pMW/m2, where &Dgr;pis the measured pressure increment in units of torricelli.

ISSN:0034-6748    

DOI:10.1063/1.1684183

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A technique for carrying out Mo¨ssbauer experiments with monochromatic polarized radiation is described. Mo¨ssbauer spectra of longitudinally magnetized YIG (yttrium iron garnet) employing circularly polarized radiation are given.

ISSN:0034-6748    

DOI:10.1063/1.1684184

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Kirchhoff's equation for the current flow from a capacitor connected in series with an inductance and a resistance that varies with current is solved by an iterative integration scheme. The resistance of the circuit is assumed to increase during the discharge due to Joule heating. The conditions for over‐, under‐, and critical damping are derived such that a circuit can be designed that has a short risetime and a long decay time without current oscillation. The realistic nature of the circuit is verified experimentally.

ISSN:0034-6748    

DOI:10.1063/1.1684185

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Three methods of switching photomultipliers (pulsing of the first dynodes, pulsing of the whole chain, pulsing of the last dynodes) have been tested and compared on the grounds of a good on/off ratio, a low electrical noise, and a short risetime of the gain. In this work we report the measurements and the results of this research and we find that for our needs the best one is the last for which we obtained an on/off ratio of about 300, a risetime of 20 nsec, and a very low electrical noise.

ISSN:0034-6748    

DOI:10.1063/1.1684186

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The design and operation of a miniature x‐ray tube used as a calibration source for a rocket borne x‐ray astronomy experiment are described. The tube utilizes a miniature lamp filament and a 0.05 mm aluminum foil as a transmission target. Anode current of 1 &mgr;A and accelerating potential of 4 kV produce approximately 1000 1.48 keV photons/sec. Shelf life of the tube is greater than three months and the operating life is several hours.

ISSN:0034-6748    

DOI:10.1063/1.1684187

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A technique is described for measuring complex permittivities of low loss dielectric materials with a semiconfocal Fabry‐Perot resonator. Equations are derived for calculation of dielectric constant and loss tangent. Results are presented for slip‐cast fused silica at 94 GHz.

ISSN:0034-6748    

DOI:10.1063/1.1684188

出版商:AIP    

年代:1969

数据来源: AIP