摘要:

Fast neutron bombardment of artificial graphite increases the longitudinal elastic modulus and electrical resistivity and decreases the thermal conductivity. Annealing at temperatures higher than the bombardment temperature reverses the neutron‐induced property changes, but complete recovery does not occur until annealing temperatures approach 2000°C. These effects are considered to be the results of the displacement of carbon atoms from normal positions in graphite crystallites to interstitial positions and the production of lattice vacancies. The displaced atoms are trapped in a variety of metastable interstitial trapping centers and, as a result, increase the internal energy of the graphite. Annealing causes interstitial atoms to move to more stable positions, thus releasing stored energy and causing recovery of other neutron‐induced changes. Hall effect studies indicate that the neutron‐induced disturbances (interstitial atoms and clusters of atoms, and lattice vacancies) are electron traps. Data are presented and the implications of various observations are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1722423

出版商:AIP    

年代:1956

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1722425

出版商:AIP    

年代:1956

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1722427

出版商:AIP    

年代:1956

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1722429

出版商:AIP    

年代:1956

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1722431

出版商:AIP    

年代:1956

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1722433

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Flicker noise with a 1/ffrequency dependence has been observed in the secondary emission process. No flicker noise was observed in multiplier phototubes which means that a possible flicker noise component caused by the photoemission or secondary emission process is small in comparison with the shot noise of the tube. The secondary emission flicker noise resistance, measured for Philips EFP60 tubes, increases with increasing primary current and also increases with increasing primary energy. The results are interpreted in terms of a fluctuating work function.

ISSN:0021-8979    

DOI:10.1063/1.1722434

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

The instability of a high‐speed liquid jet with a velocity which has a transient rise followed by a linear decay with time is studied experimentally and theoretically. The jet is produced experimentally by subjecting a liquid reservoir to a shock‐wave pressure. Using a shadowgraph technique, in an interval of thirty microseconds four successive quarter‐microsecond exposures were taken using jets of water and ethanol in external atmospheres of air and helium. It is found theoretically that a velocity discontinuity is advanced through the jet at a velocity which is the mean of the instantaneous particle velocities immediately in front of and behind the discontinuity. The discontinuity consists of a thin disk of liquid normal to the jet axis. Nodules previously observed on high‐speed liquid jets [J. Appl. Phys.25, 569 (1954)] can be explained by this mechanism.

ISSN:0021-8979    

DOI:10.1063/1.1722435

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

A quantitative theory of damping and modulus changes due to dislocations is developed. It is found that the model used by Koehler of a pinned dislocation loop oscillating under the influence of an applied stress leads to two kinds of loss, one frequency dependent and the other not. The frequency dependent loss is found to have a maximum in the high megacycle range. The second type of loss is a hysteresis loss which proves to be independent of frequency over a wide frequency range which includes the kilocycle range. This loss has a strain‐amplitude dependence of the type observed in the kilocycle range. The theory provides a quantitative interpretation of this loss.

ISSN:0021-8979    

DOI:10.1063/1.1722436

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Contact potential difference measurements in a pressure range from one atmosphere to about 10−8mm Hg have indicated that mechanically induced strain of the order of 1% (beyond elastic limit) in polycrystalline strips of silver produces an increase in work function of between 0.01 and 0.03 ev. Annealing at about 400°C for a period of ten minutes approximately restores the original value of work function. Possible explanations of the effect are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1722437

出版商:AIP    

年代:1956

数据来源: AIP