Takeshi Hagihara

Deformation luminescence in gamma-irradiated alkali halides

Abstract The deformation luminescence (DL) at a constant deformation rate in KCl crystal colored by γ-irradiation was studied, focusing on what the luminescence center is that is relevant to the DL phenomenon. It was found from the comparison of the spectra in DL and those in the thermoluminescence that the V2-center as luminescence center as well as the F-center as electron donor play a dominant role in the present process.

Theory of deformation luminescence in KCl crystal

Abstract A theory of deformation luminescence (DL) in KCl crystal colored by γ-irradiation is presented for understanding the characteristics of the DL intensity I . The intensity calculated by simple rate equations describing the change in the numbers of luminescence centers and electrons explains well the deformation rate and temperature dependence of I .

A new interpretation of proportionality between vacancy formation energy and melting point

A simple picture of vacancy formation in pure metals is proposed to account for the empirical law that the vacancy formation energy W is proportional to the melting point Tm. We imagined that surface vacancy is created by making a transition of a surface atom from a solid state to a liquid one. Thus W becomes equivalent to the transition energy of the atom to a liquid state. If one creates the concentrated liquid state atoms by depositing an energy e on a surface spot. W is nearly given by e divided by the number of liquid state atoms n. For large n, this process could be pictured as a melting of the surface spot. Determining n by the thermal spike model for the energy e, we found a constant W/kTm = 3(3/4π)(2πe/3)32 = 9.7, k being Boltzmanns constant. This value is in good agreement with the empirical one.

Theory of statistical dislocation dynamics in photomechanical effects

Abstract A simple theory is proposed for the photoplastic effect in alkali halides containing F-centers based on statistical dislocation dynamics. The present theory depicts well several dependences of flow stress increment on, e.g., defect concentration, strain rate and light intensity.

Dynamic Young’s Modulus and Internal Friction in Composite Materials

The strain amplitude dependence of Dynamic Young’s modulus and internal friction have been studied on variously fatigued glass cloth reinforced epoxies and was compared with laser transmittance. The temperature dependence was also measured in temperature range from 100 to 380 K.

Dislocation motion in photomechanical effects and the lifetime of photochemical products of the F-center in alkali halides

Abstract A simple theory describing photomechanical effects in colored alkali halides was proposed based on statistical dislocation dynamics. From the present theory together with empirical data on photomechanical measurements, the lifetime of the F - -center in KCl is found to be about 2 s at around RT and the relevant activation energy is 0.29 eV.

Thermo-Stimulated Current and Dielectric Loss in Composite Materials

Thermo-stimulated current and dielectric loss measurements have been performed on five kinds of commercially available composite materials in order to study the electric properties of composite materials at low temperatures. Thermo-stimulated current measurements have been made on the composite materials in which the matrix quality was changed intentionally. The changes in the matrices were introduced by gamma irradiation or different curing conditions. Thermo-stimulated current and dielectric loss measurements revealed the number and the molecular weight of dipolar molecules. The different features of thermo-stimulated currents and dielectric losses were determined for different composite materials. The gamma irradiation and the curing conditions especially affect the thermo-stimulated current features. The changes in macroscopic mechanical properties reflect those of thermo-stimulated current. It was found that the change in quality and/or degradation of the composite materials could be detected by means of thermo-stimulated current and/or dielectric loss measurements.

Two kinds of positive holes in YBa2Cu3O7-δ around Tc through the analysis of the hall effect in weak field

Abstract To obtain information about the mechanism of high Tc superconductivity in YBa2Cu3O7-δ (YBCO) the dependence of Hall coefficient RH and electrical resistivity ρ on the temperature were studied in range from 77 to 300K. An inflexion point θ was found to exist around 130K in RH(T) and ρ(T) curves. Both the mobility μ and the concentration of the holes were evaluated above and below θ, separately. The μ of the holes dominant below θ was ten times greater than that above θ. The concentration of the heavy holes above θ was, however, one hundred times larger than that below θ. A discussion will be given in terms of the transport process of the holes drifting through P[sgrave]- and Pσ-orbits on the CuO2 planes in YBCO.

Deformation Luminescence in gamma-irradiated KCl single crystals

Abstract Deformation Luminescence(DL) is studied on KCl crystal colored by γ-irradiation. The spectra analysis of DL and thermoluminescence reveals that F-center plays a role as electron donor through the interaction with moving dislocation and V2-center is a probable luminescence center. A theory is presented for understanding the deformation rate and temperature dependences of DL intensity.

Negative photoplastic effect due to the relaxed excited state of the F-center in alkali halides

Abstract To make clear the mechanism of the photoplastic effect (PPE) in alkali halides containing F-centers, on the basis of the photochemical reaction of the F-center, temperature dependence of the PPE in KC1, and KBr and NaCl was studied from 95 K up to RT. The characteristic critical points θ ts in colored KC1 and KBr were determined to be 110 and 190 K, respectively. Below θ t the sign of the PPE in both crystals was negative, i.e., decrement of the flow stress during light illumination was observed. Moreover, the θ ts were in good agreement with the temperature where the photoconductivities show remarkable increase in the course of the measurements. The negative PPE is explained in terms of the rotation of the principal strain axis of the relaxed state of the F-center having ⟨100⟩ tetragonarity as to relax the stress around the edge dislocation coming closely.