Effect of electron drift and emission on the surface potential of an irradiated dielectric

A mathematical model is proposed for the steady-state charging of dielectrics with an open surface under bombardment with a nonpenetrating electron beam. The model is based on inclusion of the emission and drift mechanisms of the leakage of charge injected into the dielectric. Charge transfer through the unirradiated layer of dielectric adjacent to the grounded substrate is assumed to occur in a space-charge-limited current mode. As a result of this the strength in the unirradiated layer is of sufficient strength to make a certain contribution to the surface potential of the dielectric. The steady-state surface potential on the electron-beam parameters and the characteristics of the sample are studied by analyzing the proposed model. We consider the irradiation conditions under which one of the charge-leakage mechanisms dominates.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 5–10, November, 1990.     

Relationship of neural and otoacoustic emission thresholds during endocochlear potential development in the gerbil

Distortion product otoacoustic emissions and auditory brainstem responses (ABRs) were measured in neonatal gerbils at three ages: at 15-16 days after birth (dab), near the onset of hearing when the endocochlear potential (EP) is known to be still immature; at 22 dab, when the EP first reaches mature levels; and at 30 dab. Comparing individual 15-16 dab animals to the 22 dab group, ABR threshold changes were typically larger than those for cubic distortion tone (CDT, 2f1-f2) emission thresholds which were, in turn, larger than those for the simple difference tone (DT, f2-f1). In contrast, from 22 to 30 dab there were no important changes in CDT or DT emission thresholds. Observed threshold-change relationships were very similar to those found in differential diagnosis investigations, where the EP was experimentally decreased using a chronic furosemide application. Therefore, most of the change in cochlear function over the two week period studied could be attributed to the maturation of EP during the first week. Model calculations further show that relative changes in CDT and DT emission thresholds are compatible with a movement of the operating point of the cochlear amplifier toward its symmetrical "central" point as the EP reaches mature levels.     

Dynamics of fractoluminescence and electromagnetic and acoustic emission upon an impact against the marble surface

The blow of a steel striker against the marble surface induces strain waves and electromagnetic emission. Simultaneously, microcracks appear in the marble single crystal with excited free CO ₂ ^? radicals at the microcrack banks. Relaxation of electronic excitation leads to the emergence of fractoluminescence bursts. The burst intensity is proportional to the area of the microcrack surfaces. Measurements show that the linear size of the microcracks varies from ～2 to ～47 μm.     

Investigation of the polarization of explosives during impact and the influence of an external electric field on the impact sensitivity of superfine PETN

Results of measurements of the polarization of powdered PETN, TNT, and HMX are presented and the influence of an external electric field on the impact sensitivity of superfine PETN is studied. The experiments were conducted on a modified device no. 1.     

Simulation test on charge density and surface potential in an oil tank during filling operation

Explosion accidents in oil tanks took place twice in the last three years in China. The simulation test on charge density and surface potential during filling gasoline into a tank has been conducted. The volume-averaged charge density was found to rise to a maximum about 20 min after the pump was started and then began to decrease. The surface potential rose steadily for about 30 min and then decreased during filling operation. The maximum of surface potential sharply increased when the filling rate rose.     

Dynamics of the peel front and the nature of acoustic emission during peeling of an adhesive tape

We investigate the peel front dynamics and acoustic emission (AE) of an adhesive tape within the context of a recent model by including an additional dissipative energy that mimics bursts of acoustic signals. We find that the nature of the peeling front can vary from a smooth to a stuck-peeled configuration depending on the values of dissipation coefficient, inertia of the roller, and mass of the tape. Interestingly, we find that the distribution of AE bursts shows power law statistics with two scaling regimes with increasing pull velocity as observed in experiments. In these regimes, the stuck-peeled configuration is similar to the "edge of peeling" reminiscent of a system driven to a critical state.     

Photon and electron emission during halogen adsorption on sodium

The adsorption of chlorine, bromine and iodine on UHV evaporated sodium films is accompanied by the emission of photons and electrons. Although the emission probabilities are small (～10^?7 and ～10^?5 per adsorbed molecule respectively), the effect provides a sensitive means of monitoring the adsorption process. For moderate exposures, the photon and electron yields are proportional to the pressure. At high exposures, due to the formation of a halide film on the surface, the photon yield decreases rapidly, eventually becoming proportional to the square root of the pressure. The high sensitivity allows use of the light signal to measure diffusion through the halide layer. The spectral distributions of the observed photons are characterized by wide (～1 eV) emission bands in the range 4000–8000 A. The spectra are influenced by surface composition, as demonstrated most clearly in the Na + I₂ spectrum, where a peak occurs on the high energy side of the main band when the NaI film starts to form. The origin of the spectra, their comparison with gas phase chemiluminesccnce and a model of the reaction kinetics are discussed.     

Hard X-ray emission by clusters in an intense femtosecond laser field during collective recombination

We consider the new mechanism of X-ray generation by clusters under irradiation by femtosecond laser pulses, the so-called collective photorecombination. We develop the theory of the photo-recombination of electrons that pass from atomic clusters at the outer ionization to the ground level of a homogeneously charged cluster. Such a cluster is considered to be a quantum potential well. The dipole approximation is inapplicable for this process. We conclude that X-ray photons in collective photorecombination on a charged cluster as a whole have an energy that is much larger than that for photorecombination on separate atomic ions inside the cluster. For a typical cluster of 2.25 × 10⁶ electrons, with a radius R = 300 Å, and a number density of plasma electrons n _e = 2 × 10²² cm^?3, we find that at a 5% outer ionization of this cluster, the energy of hard X-ray photons is 7.2 keV.     

Point of impact prediction in isotropic and anisotropic plates from the acoustic emission data

It is shown in this paper that the conventional triangulation technique is not very reliable for locating the impact point even in isotropic plates when the sensors are placed close to the point of strike for two reasons: First, it is difficult to pinpoint the exact time of arrival of the signal and, second, the Lamb modes in a plate are dispersive. Dispersive signals attenuate differently at various frequencies and propagate with different speeds causing distortions in the received signals, and thus introduce error in the time of flight measurement. The triangulation technique assumes that wave speeds in all directions are the same, which is not true for anisotropic plates. Here an alternative approach based on an optimization scheme is proposed to locate the point of impact in isotropic and anisotropic plates. A formulation is presented for the general anisotropic case. Experiments are carried out with an aluminum plate by dropping balls on the plate and picking up acoustic signals at different locations. The impact points predicted by the conventional triangulation technique and the proposed modified method are compared for this isotropic plate. Then it is investigated how the prediction would change if the plate is assumed to have some anisotropy.     

Gamow states in a realistic two-center potential and nucleon emission in heavy-ion collisions

For a realistic finite-depth two-center potential with fixed spherical Woods-Saxon wells adiabatic bound and Gamow states have been calculated by representing each potential in a harmonic oscillator basis in momentum representation. Numerical results for the real and complex energy eigenvalues of the single-particle states as a function of the distance between the centers of the wells are presented for a neutron in a ¹⁶O + ¹⁶O potential. Due to the neglect of volume conservation and of any shape degrees of freedom the considerations are restricted to separation regions with a small overlap of the density distributions only. The matrix elements for the coupling of adiabatic states due to non-adiabatic effects in the collective relative motion of the potentials during a heavy-ion collision have been calculated for bound-bound as well as bound-continuum transitions. Neglecting the rotational coupling, from the population of Gamow states a differential neutron emission spectrum has been computed, which for a peripheral ¹⁷O + ¹⁶O reaction shows distinct peaks at the position of low-lying asymptotic adiabatic states and a decreasing high-energy tail connected with emission from quasistationary states, pushed up in energy when the collision partners are coming in contact. An appreciable fraction of the particle emission appears as a sequential decay of the excited fragments after separation.     

A comment on the effects of Cs on photon and secondary ion emission during sputtering

The effect of Cs on photon and negative ion emission is discussed for situations where the sputtered atom interacts either very weakly or very strongly with the target surface. The experimental data seem to favor the strong interaction case.     

Effect of the microstructure of a metal on the emission spectrum excited during destruction of current-carrying conductors by an MHD instability

The spectral characteristics of the radiation emitted during the destruction of copper conductors with different microstructures by a high-density current are investigated experimentally. The proposed mechanisms leading to radiation generation and the experimental results corresponding to these mechanisms are discussed. Zh. Tekh. Fiz. 69, 137–140 (February 1999)     

Light emission during adsorption and desorption of oxygen on magnesium oxide

Chemisorption of oxygen on a previously outgassed MgO sample is accompanied by a luminescence phenomenon which follows an Elovitch kinetic law. Heating the MgO sample in vacuo after O₂ adsorption causes the appearance of strongly correlated thermally stimulated desorption (TSD) and luminescence (TSL) peaks. Analysis by the least-squares method shows that thermostimulated spectra prove to be the superposition of one second-order peak and one (TSL) or two (TSD) first-order peaks. The observed compensation law and the strong correlation between activation energy and preexponential factor are discussed. On the basis of our experiments a tentative mechanism about light emission is also proposed.     

Scaling of the acoustic emission characteristics during plastic deformation and fracture

The scaling of the amplitude and time distributions of acoustic emission pulses, which reflects the self-similarity of defect structures, is revealed. The possibility of separation of independent contributions to the flow of acoustic emission events, which have substantially different scaling exponents, is shown for porous materials. The differences in the scaling exponents are related to the development of plastic deformation and fracture of the materials. The developed approach to an analysis of acoustic emission can be used to describe its predominant mechanisms during deformation.     

Influence of the electric field on the alignment of carbon nanotubes during their growth and emission

The problems of the electric field action on carbon nanotubes (CNTs) during their growth and under the electron field emission conditions are considered. The relations determining the growth rate of an extended structure under the action of the electric field are established. The relation connecting the angle of orientation of a CNT inclined to the substrate surface and the applied electric field is used for computing current-voltage characteristics of the cathode consisting of inclined CNTs. The degree of deviation of these characteristics from the Fowler-Nordheim classic dependence is determined, on the one hand, by the parameters characterizing the CNT spread over the angles of inclination and, on the other hand, by the value of the Young modulus characterizing the bending stiffness of a nanotube. It is shown that in zero external electric field, a certain effect on the CNT orientation can be produced by the CNT potential relative to the substrate, which is due to the effect of the contact potential difference.     

Spontaneous emission of photons and electrons during chemisorption of chlorine on sodium

Photons and electrons are emitted when Cl₂ molecules react on a Na surface prepared by UHV evaporation. The emission yield per reacting molecule is 10^?7-10^?6 for photons and approximately 10^?5 for electrons. The dominating light emission band has a maximum at hv = 2.15 eV (width 0.6 eV). A less intense u.v. band has a maximum at about 4.7 eV. A drastic decrease in the photon and electron emission at a Cl₂ exposure of about 5.10^?3 torr·sec, is attributed to the formation of a continuous NaCl film on the Na surface.