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1 Dec 1962

Volume 33, Issue 12, pp. 3389-3599

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Thermoluminescence and the Influence of γ‐Ray Induced Defects In Single‐Crystal α‐Al2O3

A. F. Gabrysh, H. Eyring, V. LeFebre, and M. D. Evans

J. Appl. Phys. 33, 3389 (1962); http://dx.doi.org/10.1063/1.1702418 (3 pages) | Cited 11 times

Online Publication Date: 11 June 2004

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In previous work the thermoluminescence of golden sapphire (Al2O3 containing Ni and Mg), which was γ irradiated under liquid nitrogen, was compared with glow curves of fused borax seeded with Ni and Mg. The emission intensity obeyed, reasonably well, the expression
math
. In the present paper it is shown that light‐induced glow curves in γ‐irradiated sapphire have the form of a second‐order decay process, namely I = 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 γ‐ray damaged ruby shows an afterglow long after the crystal has reached room temperature.

Dislocations and Chemical Etch Pits in Copper

A. W. Ruff

J. Appl. Phys. 33, 3392 (1962); http://dx.doi.org/10.1063/1.1702419 (9 pages) | Cited 9 times

Online Publication Date: 11 June 2004

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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.

Observations of Charged‐Particle Tracks in Solids

P. B. Price and R. M. Walker

J. Appl. Phys. 33, 3400 (1962); http://dx.doi.org/10.1063/1.1702420 (7 pages) | Cited 35 times

Online Publication Date: 11 June 2004

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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.

Chemical Etching of Charged‐Particle Tracks in Solids

P. B. Price and R. M. Walker

J. Appl. Phys. 33, 3407 (1962); http://dx.doi.org/10.1063/1.1702421 (6 pages) | Cited 89 times

Online Publication Date: 11 June 2004

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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.

Measurements of Detonation Pressure

M. A. Cook, R. T. Keyes, and W. O. Ursenbach

J. Appl. Phys. 33, 3413 (1962); http://dx.doi.org/10.1063/1.1702422 (9 pages) | Cited 13 times

Online Publication Date: 11 June 2004

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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.

Dielectric Properties of Single‐Crystal Nonstoichiometric Rutile (TiO2)

Lewis E. Hollander and Patricia L. Castro

J. Appl. Phys. 33, 3421 (1962); http://dx.doi.org/10.1063/1.1702423 (6 pages) | Cited 12 times

Online Publication Date: 11 June 2004

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The dielectric constant ϵ′ and dielectric loss ϵ″ have been determined from 30 to 300 000 cps in the a and c crystal directions for nonstoichiometric compositions of rutile with dc resistivities from 104 to 1013 Ω‐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.

Tunneling of a Wave Packet

Thomas E. Hartman

J. Appl. Phys. 33, 3427 (1962); http://dx.doi.org/10.1063/1.1702424 (7 pages) | Cited 349 times

Online Publication Date: 11 June 2004

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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
math
, where Ef is the Fermi energy of the metal, and ϕ the vacuum work function, are of the order of 10−16 sec, compared to RC time constants of about 10−13 sec.

A Lower Bound and Other Properties of the Mean‐Square Error of Linear Measurement Systems

Joseph L. Hammond

J. Appl. Phys. 33, 3434 (1962); http://dx.doi.org/10.1063/1.1702425 (7 pages)

Online Publication Date: 11 June 2004

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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, where k is Boltzmann's constant, T is the absolute system temperature, t is the time consumed by the measurement, and A is 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.

Piezoelectric Optical‐Maser Modulator

L. F. Johnson and D. Kahng

J. Appl. Phys. 33, 3440 (1962); http://dx.doi.org/10.1063/1.1702426 (4 pages) | Cited 1 time

Online Publication Date: 11 June 2004

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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 0.7μ, 10% modulation and a bandwidth ∼10 Mc can be obtained using barium titanate driven near the fundamental resonance frequency.

Departures from Vegard's Law

K. A. Gschneidner and G. H. Vineyard

J. Appl. Phys. 33, 3444 (1962); http://dx.doi.org/10.1063/1.1702427 (7 pages) | Cited 30 times

Online Publication Date: 11 June 2004

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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.

X‐Ray Diffraction Study of the Effects of Solutes on the Occurrence of Stacking Faults in Silver‐Base Alloys

R. P. I. Adler and C. N. J. Wagner

J. Appl. Phys. 33, 3451 (1962); http://dx.doi.org/10.1063/1.1702428 (8 pages) | Cited 61 times

Online Publication Date: 11 June 2004

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The addition of the solutes cadmium, indium, and tin to silver increases the probability of deformation faults α in filings from 3×10−3 in pure silver to a maximum value of 45×10−3 at the highest concentrations of solute. In addition, the twin fault probability β measured from center of gravity displacements varies from 10×10−3 for pure silver to 30×10−3 for the alloys highest in tin or indium concentration. Lattice parameters ahkl were determined from all available reflections of the cold‐worked and annealed specimens and plotted as a function of cos2θ∕sinθ. By relating the large scatter of the individual ahkl to the occurrence of deformation faults in the deformed material, the true lattice parameter, a0(CW), and the deformation fault probabilities α of cold‐worked materials could be determined. There was an apparent decrease in lattice parameter of the deformed Ag‐Sn alloys which was largest (∼0.1%) for the greatest tin concentration (Ag‐9%Sn). Using Fourier analysis of line profiles, the effective particle sizes (De)hkl and root mean square strains [〈ϵL2〉av]hkl☒ were determined. The measured effective particle sizes were anisotropic [(De)111∕(De)200=1.7] and are primarily a consequence of deformation and twin faulting. The values for the compound fault probability (1.5α+β) from peak shift and asymmetry and from anisotropic particle sizes, i.e., from peak broadening, agreed rather well.

Formation Conditions and Structure of Thin Epitaxial Germanium Films on Single‐Crystal Substrates

Billy W. Sloope and Calvin O. Tiller

J. Appl. Phys. 33, 3458 (1962); http://dx.doi.org/10.1063/1.1702429 (6 pages) | Cited 26 times

Online Publication Date: 11 June 2004

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An experimental investigation of the effects of formation conditions on the structural characteristics of thin Ge films vacuum deposited onto synthetic single crystals of CaF2, NaCl, NaF, and MgO is reported. Formation conditions include substrate temperature during deposition, rate of deposition, and heat treatment. The amorphous to crystalline transformation of Ge was found to occur in the 300–350°C substrate temperature range. It is shown that single‐crystal films, 1500 Å thick, can be formed on CaF2 substrates at temperatures between 450° and 700°C by proper choice of rate of deposition. Crystalline structure, porosity, complexity of imperfections, and film adhesion are dependent on the rate of deposition and deposition temperature.

Power Density of Optimally Focused Space‐Charge‐Limited Electron Beams

Helmut Schwarz

J. Appl. Phys. 33, 3464 (1962); http://dx.doi.org/10.1063/1.1702430 (7 pages) | Cited 4 times

Online Publication Date: 11 June 2004

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Factors affecting the power density of optimally bundled electron beams used for the welding, cutting, and machining of solid material are described. The power density and spot size of these beams are expressed as a function of acceleration voltage, beam current, and electron optical characteristics of the system. Assuming that the spherical aberration of the beam‐focusing lens system limits the spot size of the space‐charge‐limited beam, the power density under optimum conditions increases approximately with the fifth power of the acceleration voltage, and decreases with the 7∕4 power of the beam current.
A criterion is also given which enables one to determine whether the electron beam at its impact on the workpiece is space‐charge‐limited or not. Some considerations are given to the neutralization of the electron space charge by ions originating from the background pressure of the vacuum system.

Theories of Birefringence Induced in Liquids by Ultrasonic Waves

N. C. Hilyard and H. G. Jerrard

J. Appl. Phys. 33, 3470 (1962); http://dx.doi.org/10.1063/1.1702431 (10 pages) | Cited 16 times

Online Publication Date: 11 June 2004

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Some liquids and solutions become doubly refracting and behave as uniaxial crystals when traversed by acoustic waves of high frequency. In many aspects the induced birefringence is analogous to birefringence due to flow. Theories for this behavior are presented and discussed in detail. For liquids and solutions of flexible macromolecules the birefringence is proportional to the square root of the acoustic intensity and to the frequency of the wave, but for colloidal solutions it varies directly as the intensity and is independent of frequency. It is shown that from measurements of the birefringence, values of relaxation times and diffusion constants can be obtained. The method has a number of advantages over flow birefringence studies and in common with the latter does not depend on the possession of a permanent dipole moment by the molecules.

Color Centers and the Flow Stress of LiF Single Crystals

John S. Nadeau

J. Appl. Phys. 33, 3480 (1962); http://dx.doi.org/10.1063/1.1702432 (7 pages) | Cited 50 times

Online Publication Date: 11 June 2004

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Lithium fluoride crystals were exposed to cobalt‐60 gamma radiation at 300° and 78°K. Changes of the flow stress and of the optical absorption were measured in an effort to relate the hardening to identifiable color centers.
In crystals irradiated at 300°K there was found to be a good correlation between the flow stress and the concentration of F centers. The magnitude of the hardening, however, suggested that it was caused by interstitial defects. Comparison of the hardening produced by additive coloring with that produced by irradiation indicated that the hardening defects were interstitial fluorines. This direct relation between interstitials and F centers supports a Varley type of mechanism for F‐center production in the bulk crystal. Some limited experiments with NaCl and KCl showed qualitatively the same behavior and suggest that the same F‐center production mechanism may occur in them.
Irradiation of LiF at 78°K produced stable trapped‐hole centers and pulse annealing experiments showed that the Vk center (self‐trapped hole) contributed to the hardness at low temperatures. A sharp decrease of flow stress was observed at about 110°K where the paramagnetic resonance experiments of Kanzig and the optical measurements of Wiegand and Smoluchowski indicate disappearance of the Vk center.

Thickness Dependence of BaTiO3 Switching Time

H. L. Stadler

J. Appl. Phys. 33, 3487 (1962); http://dx.doi.org/10.1063/1.1702433 (4 pages) | Cited 29 times

Online Publication Date: 11 June 2004

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The ferroelectric switching time of barium titanate single crystals has been measured at room temperature as a function of electric field and crystal thickness. The switching time was found to be independent of crystal thickness at high fields in disagreement with earlier work by Merz, who found the switching time proportional to thickness at the same high fields. At low fields the results are in substantial agreement with Merz and other previous work. At fields E greater than a threshold field of 1.4 (1+0.007 cm∕d) kV∕cm, where d is the crystal thickness, the switching time ts is given by 9E−1.4±0.1 (kV∕cm)1.4 sec. Below this threshold the switching time is adequately represented by ts=0.8 exp[3.5(1+0.007 cm∕d) kV∕cm∕E] μsec for d≳0.007 cm, but for d«.007 cm, the data are fitted better by ts=1.5×103 (Ed)−10.3±0.5 sec (V)10.3. Thus the data do not agree with the predictions of any known surface layer model of BaTiO3 switching.

Optimization of Efficiency of a Cesium‐Diode Converter

C. K. Sanathanan

J. Appl. Phys. 33, 3491 (1962); http://dx.doi.org/10.1063/1.1702434 (3 pages)

Online Publication Date: 11 June 2004

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When the inter‐electrode spacing is very small in an alkali‐metal vapor diode, plasma heat transfer cannot be neglected. An efficiency analysis very similar to that of Schock includes this effect and compares it to that due to radiation loss. In the analysis the heat‐transfer coefficient h[W∕(cm)2(°K)] is given values 0, 0.005, and 0.01. This range is based on the experimental values of h obtained in potassium and cesium diodes. The greatest effect of h on efficiency is found theoretically to occur when the electron‐emitter work function or output voltage is larger than the optimum value for a particular temperature.

Dislocation Damping in Magnesium Oxide Crystals at Low Frequencies

Philip Dahlberg, R. D. Carnahan, and J. O. Brittain

J. Appl. Phys. 33, 3493 (1962); http://dx.doi.org/10.1063/1.1702435 (6 pages) | Cited 5 times

Online Publication Date: 11 June 2004

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Amplitude dependent internal friction measurements have been made on MgO crystals over the temperature range 0° to 300°C at frequencies of ∼5 cps. Analysis of the temperature dependency of the critical breakaway strain, delineating the transition from amplitude independent to amplitude dependent internal friction, permits an evaluation of the relative pinning strengths of the Fe2+ and Fe3+ ions, determined on specimens from bulk sources. The Fe3+ ion exhibits a binding energy of 0.035 eV, whereas the Fe2+ ion has either a lower binding energy and∕or a lower mobility which precludes the development of an equilibrium atmosphere. Optical absorption measurements confirm the presence of the Fe3+ ion in one bulk crystal and its absence in the other.

A Variable Composition, High Field Superconducting Solenoid

H. Riemersma, J. K. Hulm, A. J. Venturino, and B. S. Chandrasekhar

J. Appl. Phys. 33, 3499 (1962); http://dx.doi.org/10.1063/1.1702436 (6 pages) | Cited 4 times

Online Publication Date: 11 June 2004

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In previous work we described the fabrication of cold‐worked niobium plus 25% zirconium wire and the use of such wire to construct a solenoid in which a field of 58±1 kG was achieved under loss‐free superconducting conditions. We have continued these experiments with other compositions and find that the critical current in short samples at 21 000 G and 4.2°K decreases with increasing zirconium content for the compositions investigated, namely, Nb+25% Zr, Nb+33% Zr, and Nb+50% Zr. Kunzler observed that the magnetic field required to destroy the supercurrent in these alloys increased with increasing zirconium concentration in the same range of compositions. This behavior led us to build a new solenoid composed of several concentric sections with the lowest composition (25% Zr) on the outside and the highest composition (50% Zr) on the inside. Experiments with this coil are discussed.

Rapid Solution Hardening, Dislocation Mobility, and the Flow Stress of Crystals

Robert L. Fleischer

J. Appl. Phys. 33, 3504 (1962); http://dx.doi.org/10.1063/1.1702437 (5 pages) | Cited 190 times

Online Publication Date: 11 June 2004

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A theory is derived for impurity‐controlled dislocation mobility and the resultant temperature variation of the flow stress of lithium fluoride. The theory is suitable to crystals in which the hardening is primarily due to tetragonal lattice distortions such as result from the introduction of magnesium into lithium fluoride, these being defects whose interactions with dislocations have been calculated previously. Dislocation motion is envisioned as a series of thermally activated dislocation jumps through the stress fields produced by individual solute atoms. The theory predicts the observed temperature variation of the flow stress within 25%, approximate values of the slopes of the velocity‐stress relations, and the activation energy for dislocation motion.

Reactor Damage in Pure Metals

R. R. Coltman, C. E. Klabunde, D. L. McDonald, and J. K. Redman

J. Appl. Phys. 33, 3509 (1962); http://dx.doi.org/10.1063/1.1702438 (14 pages) | Cited 58 times

Online Publication Date: 11 June 2004

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By relocating the fuel in the vicinity of a liquid helium cryostat located in the Oak Ridge Graphite Reactor it has been possible to separate the thermal and fast components of the reactor neutron flux. Studies of the radiation damage effects arising from each type of flux have been made. It has been found that an appreciable fraction of the reactor damage in several metals arises from thermal neutrons. The effect results from the recoil of an atom from the (n,γ) reaction at the time of thermal neutron capture. The low temperature recovery of thermal neutron damage is greater and shows more annealing peak structure than the recovery of fast neutron damage. Thermal neutron damage concentration studies have been made on cadmium, and pronounced suppression of the annealing is found as the concentration is increased. The mean primary recoil energy from a thermal neutron capture event has been calculated for several elements. Values range from about 50 eV for the heavier elements to several hundred eV for the lighter elements. The relative effects of atomic recoils from decay events and decay beta‐atom collisions are estimated and found to be small compared to (n,γ) recoil effects. Damage from fission neutrons has been studied in copper, and it was found that the recovery of this damage is suppressed compared to that obtained from reactor fast neutrons.

Emission of Negative Ions from Metal Surfaces Bombarded by Positive Cesium Ions

Victor E. Krohn

J. Appl. Phys. 33, 3523 (1962); http://dx.doi.org/10.1063/1.1702439 (3 pages) | Cited 49 times

Online Publication Date: 11 June 2004

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High yields (>1%) of negative metal ions, usually including clusters of metal atoms and oxides, have been observed from targets of Cu, Ag, Au, Be, Cd, Al, Sn, Ta, W, and Ni bombarded by a beam of positive cesium ions. The increase observed in the negative‐ion yields when an auxiliary beam of neutral cesium was directed at a copper target indicates that the presence of cesium on the target was an important factor in the production of large numbers of negative ions. From targets of aluminum and tin, respectively, the Al2− and Sn2− yields were an order of magnitude greater than the corresponding single‐atom yields.

Relaxation Oscillation near the Threshold of Instability in Yttrium Iron Garnet

S. Wang and G. E. Bodway

J. Appl. Phys. 33, 3526 (1962); http://dx.doi.org/10.1063/1.1702440 (3 pages) | Cited 3 times

Online Publication Date: 11 June 2004

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Coherent low‐frequency relaxation oscillation in the amplitude of the z component of magnetization and the imaginary part of susceptibility has been observed in YIG at a microwave power level slightly above the threshold of instability. The relaxation time associated with the uniform mode has also been measured. The condition for coherent relaxation oscillation depends critically on the magnitude of the dc magnetic field. The low‐frequency oscillation is interpreted to be the beat of two high‐frequency components due to a split in the frequency of the k spin wave ωk±Δωk. It is also believed that the period of oscillation is controlled by the relaxation time associated with the uniform mode.

X‐Ray Fluorescent Yields from Several Light Elements

F. D. Davidson and Ralph W. G. Wyckoff

J. Appl. Phys. 33, 3528 (1962); http://dx.doi.org/10.1063/1.1702441 (2 pages) | Cited 4 times

Online Publication Date: 11 June 2004

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Relative emissions and relative fluorescent efficiencies of excitation of K x rays have been measured for various elements in the range between iron and oxygen. Agreement with theory is generally satisfactory.

Direct Observation of Crystal Imperfections in KCl Single Crystal by Electron Microscope

Tadatosi Hibi and Keiji Yada

J. Appl. Phys. 33, 3530 (1962); http://dx.doi.org/10.1063/1.1702442 (7 pages) | Cited 7 times

Online Publication Date: 11 June 2004

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The processes of change of a thin KCl single crystal due to electron irradiation were observed by means of an electron microscope and electron diffraction. It was found that under weak electron irradiation loop structures first appeared and then disappeared showing a lot of small bright specks over the whole crystal. In this stage, each diffraction spot had streaks in 〈100〉 directions. Under intense electron irradiation bright squares appeared initially without the appearance of loop structures. In this stage, the diffraction pattern was a perfect net‐like pattern. It was found that by using the replica technique, loop structures and large squares appeared in the crystal, and also that by using the dark‐field image method the contrast of loop structures and bright squares was due to Bragg reflection, which had resulted from the formation of voids and cubic cavities in the crystal, respectively. From the experimental results, the mechanism of coagulation of vacancies in KCl crystal with electron irradiation is discussed.
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