摘要:

In previous work the thermoluminescence of golden sapphire (Al2O3containing Ni and Mg), which was &ggr; irradiated under liquid nitrogen, was compared with glow curves of fused borax seeded with Ni and Mg. The emission intensity obeyed, reasonably well, the expressionI=&agr;N0k′ exp−1/(dT/dt)t0tk′dT. In the present paper it is shown that light‐induced glow curves in &ggr;‐irradiated sapphire have the form of a second‐order decay process, namelyI=I0[b/ (b+t)]m. Gamma‐ray induced thermoluminescence in ruby shows dominant emission bands with maxima at about 150°K and 240°K. Light‐induced thermoluminescence in &ggr;‐ray damaged ruby shows an afterglow long after the crystal has reached room temperature.

ISSN:0021-8979    

DOI:10.1063/1.1702418

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The relation between chemical etch pits and dislocations has been studied in thin single‐crystal foils of copper. Both deformed and as‐grown crystals in {111} orientations were employed. A procedure was developed for etching thin foils so that both the etch pits and dislocations were simultaneously revealed by transmission electron microscopy methods. Results are also presented from companion studies of unetched foils and replica studies of etched surfaces. Although a relation was found between etch pits and dislocation emergent points, a one‐to‐one correspondence did not exist. A discussion is presented of other defects which may nucleate etch pits, including some experimental results on deformation‐produced prismatic dislocation loops. The relation of the present results to dislocation studies by etching methods alone is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1702419

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The characteristics of tracks produced by fission fragments have been studied by transmission electron microscopy in the following layer structure materials: molybdenite (MoS2), talc, clinochlore, jefferisite, and various micas including biotite, phlogopite, muscovite, and synthetic fluor‐phlogopite. The measured track widths showed little correlation with the decomposition temperatures and it was concluded that the track formation cannot be described by a simple thermal spike model. The absence of any new rings or spots in the electron diffraction pattern of a heavily irradiated sample led to the conclusion that the tracks themselves consisted of a disordered region and not of a definable new crystalline phase. In many of the materials the tracks faded during observation in the beam. Although this fading could be eliminated by using a cold stage, it was not caused simply by the thermal instability of tracks; some materials which showed rapid track fading retained tracks to higher temperatures in external annealing experiments than did those in which no fading occurred. Annealing experiments also showed that tracks served to nucleate the high temperature decomposition of natural micas in a manner analogous to that previously reported for synthetic mica. The results of experiments in which Al absorbers were placed between a fission source and mica samples were interpreted as indicating that only particles with masses ≳ 30 are capable of forming visible tracks. This conclusion is consistent with the negative results of other irradiations in which mica samples were bombarded with 4‐MeV alpha particles, 150‐MeV oxygen nuclei, and 3‐BeV protons. Experimental observations of the interaction of dislocations with tracks are also presented.

ISSN:0021-8979    

DOI:10.1063/1.1702420

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

When a heavy charged particle such as a fission fragment traverses certain materials it leaves a trail of radiation damage which shows up as a track when a sample is viewed by transmission electron microscopy. If a sample of a silicate mineral containing such tracks is immersed in a suitable reagent such as hydrofluoric acid it has been found that the tracks are very selectively attacked. Fine hollow channels are formed along the particle paths while the rest of the material is untouched. A study of this effect in various silicate minerals is reported as a function of etching reagent, etching temperature, and etching time. The minimum width of the etched channels is considerably less than the apparent widths of the tracks prior to etching. It is concluded that the track images result in large part from elastic strains surrounding a damaged core. The etching effect also serves to ``develop'' and ``fix'' particle tracks and hence increases the usefulness of silicate minerals as particle detectors.

ISSN:0021-8979    

DOI:10.1063/1.1702421

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The ``aquarium technique'' is applied in the experimental determination of the equation of state for water and Lucite. Results for water are compared with similar results obtained by other methods. Measurements of the peak pressures in the detonation waves are presented for explosives of various types and rates of reaction. The peak pressures were found to be the Chapman‐Jouguet or ``detonation'' pressures of the thermohydrodynamic theory. There was no evidence whatever for the ``spike'' of the Zeldovich‐von Neumann model even though conditions were such that this spike would have been detected by the method employed if it were actually present, at least in the large diameter, nonideal explosives of maximum reaction zone length.

ISSN:0021-8979    

DOI:10.1063/1.1702422

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The dielectric constant &egr;′ and dielectric loss &egr;″ have been determined from 30 to 300 000 cps in theaandccrystal directions for nonstoichiometric compositions of rutile with dc resistivities from 104to 1013&OHgr;‐cm. Measurements with asymmetrical electrodes and geometrical variations indicate that the properties are primarily a bulk effect. Quasi‐ferroelectric effects were observed at field gradients greater than 500 V/cm and at frequencies above 0.5 cps. It is suggested that the dielectric properties of rutile can be explained by an artificial dielectric model consisting of conducting needles of heterogeneously distributed oxygen vacancies embedded in an insulating medium.

ISSN:0021-8979    

DOI:10.1063/1.1702423

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Analytic expressions are given for the time spent by a particle tunneling through a potential barrier. The expressions are derived for an incident wave packet which is initially Gaussian, centered about a point an arbitrary distance away from a rectangular potential barrier and moving toward the barrier with constant average velocity. Upon collision with the barrier, the packet splits into a transmitted and a reflected packet. The resultant transmission time is positive, nonzero and in principle measurable. Although the transmission time becomes quite large as the incident kinetic energy becomes very small, in general, for nonzero incident momentum and finite potential barriers which are neither very thick nor very thin, the transmission times are less than the time that would be required for the incident particle to travel a distance equal to the barrier thickness. The transmission times for metal‐insulator‐metal thin film sandwiches, given approximately by&dgr;t3=ℏ/(Ef&phgr;)12, whereEfis the Fermi energy of the metal, and &phgr; the vacuum work function, are of the order of 10−16sec, compared to RC time constants of about 10−13sec.

ISSN:0021-8979    

DOI:10.1063/1.1702424

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The central purpose of this paper is to establish a lower bound on the mean‐square error of linear, noisy, dissipative measurement systems designed to measure a constant quantity. A lower bound on mean‐square error is determined to be (2kTA)/t, wherekis Boltzmann's constant,Tis the absolute system temperature,tis the time consumed by the measurement, andAis a parameter of the measurement system closely related to its driving point immittance. This lower bound shows, among other things, that a nonzero measurement interval is required to obtain a useful estimate of the quantity being measured.The lower bound is arrived at by considering a logical structure for linear noisy measurement systems and mathematical expressions derived for the mean‐square error of such systems. The key step in establishing the lower bound is the consideration of the unavoidable random perturbation at the system input due to the generalized Nyquist noise discussed earlier by Callen and Welton. Use of the general lower bound is illustrated by establishing more specific lower bounds for two classes of systems, namely, current measuring galvanometers and thermal detectors. In these cases the lower bounds are consistent with minimum values for the mean‐square error of such systems as previously reported in the literature by McCombie.

ISSN:0021-8979    

DOI:10.1063/1.1702425

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

An optical‐maser modulator employing a transparent piezoelectric medium is described. The device is based on multiple interference in transmission or reflection, the intensity in the interference pattern being modulated by a change in thickness of the piezoelectric plate. Using barium titanate it is shown that 80% modulation and 20‐Mc bandwidths are readily attainable. A sacrifice of modulation to 10% permits bandwidths ∼200 Mc. A slight modification allows the device to operate purely as a phase modulator.In addition, an optical‐maser modulator employing a grating ruled on a piezoelectric medium is described. Spatial modulation is brought about by a change in grating constant via the piezoelectric effect. As a communication device in conjunction with an optical maser operating at 0.7&mgr;, 10% modulation and a bandwidth ∼10 Mc can be obtained using barium titanate driven near the fundamental resonance frequency.

ISSN:0021-8979    

DOI:10.1063/1.1702426

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A new method, based on second‐order elasticity, has been developed to predict departures from Vegard's law in binary alloy systems in which the end members have similar outer‐electronic structures. This method has been found to be successful in predicting the correct sign and order of magnitude of the deviation in 28 of 44 binary systems. It has also been compared with 7 techniques presented in the literature, and was found to be a significant improvement over the other techniques. The new approach described herein contributes to the understanding of departures from Vegard's law, and its general applicability to all systems has been noted.

ISSN:0021-8979    

DOI:10.1063/1.1702427

出版商:AIP    

年代:1962

数据来源: AIP