摘要:

The conductivity induced by gamma radiation from Co60has been measured for polyethylene and Teflon as functions of temperature, dose rate, and applied voltage. The range of dose rates was from about 103to 105R/h and of the temperature from 190° to 300°K. The value of &Dgr;, which shows the dependence of the induced currention the dose rateR, i.e.,i∝R&Dgr;, varies from 1 (characteristic of the monomolecular recombination) to ½ (characteristic of the bimolecular recombination) with decreasing temperature. In both polymers, below about 240°K the induced current at a thermal equilibrium was independent of temperature, although it was slightly increased with decreasing temperature. From the investigation of temperature and dose‐rate dependences, it is considered that the thermal electrons are dominant as charge carriers above 230°K, but fast electrons at below that temperature.

ISSN:0021-8979    

DOI:10.1063/1.1729541

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The one‐carrier, trap‐free space‐charge‐limited current is calculated and the general solution is given in the form of a computed, normalized voltage‐current curve. Both diffusion and drift currents are considered. The result is then compared with the widely used J ∝V2expression and it is shown that this relation is valid for voltages greater than 100kT/q. The contradictions arising in theJ∝V2derivation are clarified. Finally, the carrier transit time through the space‐charge‐limited region is given.

ISSN:0021-8979    

DOI:10.1063/1.1729542

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

Thin films of several III–V and II–VI zinc‐blende‐type semiconductors were prepared by vacuum evaporation. Germanium thin films were prepared by epitaxial vacuum evaporation onto CaF2substrates. The absorption spectra of these films reveal, besides the fundamental absorption edge and its spin‐orbit splitting, additional structure at higher energies. This structure has been interpreted along the lines followed in the interpretation of the reflection spectra of these materials. The agreement between the values for the various energy gaps derived from absorption and from reflection spectra is excellent.

ISSN:0021-8979    

DOI:10.1063/1.1729543

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The dependence of magnetic anisotropy in Permalloy thin films upon the substrate temperature and angle of incidence is demonstrated, and the critical substrate temperature above which the angle of incidence no longer affects the magnetic anisotropy is discussed. Experiments indicate, also, that the increase in grain size with increased substrate temperature influences the value of the magnetic anisotropy attained. By rigid control of these parameters during the evaporation of thin films, the magnetic anisotropy may be made to have almost any desired value; hence, usable magnetic properties may be achieved.

ISSN:0021-8979    

DOI:10.1063/1.1729544

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

A new technique is offered to determine the quantity of radioactive particles observed by a scintillation or proportional counter when the distribution of the source particles vs particle energy is immersed in the distribution of the background particles.The particle identification problem is interpreted from the point of view of a parameter estimation problem in mathematical statistics in the following way: Assume there areMevents, where an event is the occurrence of a scintillation counter pulse.Mis a known number,Nof these events are associated with the desired source particles and the scintillation counter output is source plus background. The remaining (M‐N) events consist of background alone. The background statistics are assumed known and the source pulse amplitude distribution is assumed known to withinKdistribution parameters. One number, the amplitude of the counter response, is observed for each of theMevents. The problem is to estimateN.There are (K+1) unknown parameters: the numberNand theKunknown parameters of the source pulse distribution. The problem is solved by what is essentially a method of moments technique. The estimation procedure has desirable statistical properties for largeNandMin that the estimate ofNis asymptotically unbiased and that the relative variance of the estimate ofNasymptotically goes to zero.Implementation of this technique supplants the conventional multichannel pulse‐height analyzer with digital recording of the individual pulse count amplitudes and subsequent data processing by a modest size digital computer.

ISSN:0021-8979    

DOI:10.1063/1.1729545

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

When silicon plates were bombarded with protons of energies about 100 kV, the infrared absorption spectrum above 1.1 &mgr; showed chromatic fringes corresponding approximately to the range of the protons. The fringes did not begin to disappear on annealing until the plates were heated to over 1100°C. The effect appears to be caused by a reflecting layer involving trapped hydrogen. After long irradiation, small flatbottomed pits were found of about the depth of the range.The effect could also be produced with helium ions on silicon. No effect was found with germanium.

ISSN:0021-8979    

DOI:10.1063/1.1729546

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The optical mode structure of a Fabry—Perot interferometer‐resonator composed of two infinite strip mirrors is investigated from the point of view of the general theory of nonspectral resonances. It is shown that the classical description of this configuration is inadequate to describe its response to highly monochromatic laser radiation and must be supplemented by a discussion of the transverse resonance behavior. This introduces a fine structure to the classical Fabry—Perot rings and implies a discrete resonance behavior for the Fabry—Perot interferometer. In analogy to the characterization of quantum‐mechanical virtual levels by wavefunctions and complex energies it is convenient to characterize the discrete resonances of a Fabry—Perot by mode functions and complex resonant frequencies. On the basis of a reformulation and asymptotic expansion of a previously given stationary expression, it is shown that in the high‐frequency limit, the open sides of the structure can be replaced by an effective impedance boundary condition. The solution of an elementary resonance problem then yields analytic approximations for the mode shapes, characteristic oscillation frequencies, and modal lifetimes. In the common domain of validity these results are in excellent agreement with previous numerical work on this problem.

ISSN:0021-8979    

DOI:10.1063/1.1729547

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The Hugoniot equation of state of pyrolytic graphite of initial density 2.20 g/cm3has been determined to 300 kb for the ``c'' direction. Various explosive techniques for producing the desired pressures, and the optical techniques employed in measuring shock and free‐surface velocities are briefly described. It is found that shock and particle velocity are not linearly related below 70 kb. Above 100 kb, the material is less dense than is powdered natural graphite, as determined by Alder and Christian. The agreement with static compressibility data is satisfactory.

ISSN:0021-8979    

DOI:10.1063/1.1729548

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The theory of the transition of a macroscopic cylindrical superconductor from the superconducting to the normal state when induced by an external longitudinal magnetic field is considered. Iterative approximate solutions are found, and it is shown that a second‐order solution previously derived by Faber is actually a poorer approximation than the first‐order approximation from which it was obtained.

ISSN:0021-8979    

DOI:10.1063/1.1729549

出版商:AIP    

年代:1963

数据来源: AIP

摘要:

The internal friction of deformed silicon crystals has been measured between 3 and 60 kc/sec, up to 1100°C. The component of internal friction due to dislocations becomes appreciable at 500°C, and rises steadily above this temperature. An Arrhenius plot yields an activation energy of 1.61±0.05 eV for all specimens measured, while the magnitude of the internal friction at any given temperature is approximately proportional to dislocation density and inversely proportional to the frequency. An interpretation of the results is discussed in terms of the kinked‐dislocation theories of Brailsford and of Seeger and Schiller. Suitable augmentation of these theories is shown to bring them into a unified form, which is compatible with the Koehler‐Granato‐Lu¨cke extensible string formulation, at least in the temperature range where thermal kink pair generation is negligible. Reasonable assumptions of kink mobility and density give agreement with the theory; the measured activation energy is then that for kink motion. Comparison with results of Chaudhuriet al.shows that this is less than that for gross dislocation movement.

ISSN:0021-8979    

DOI:10.1063/1.1729550

出版商:AIP    

年代:1963

数据来源: AIP