Shunji Takaki

Strategy for finding new materials for ESR dosimeters

The right strategy for finding a new ESR dosimetric material sensitive to radiation is to follow the orthodox procedures used in the development of thermoluminescence dosimeters (TLD) and phosphorescence studies. Modern procedures used in materials sciences, such as computer calculation of molecular orbitals (MO), should be employed to estimate the ESR and optical properties of prospective materials. Radiation effects in lithium and magnesium sulfates and metal salts of organic acids, such as lithium and magnesium lactates, have been investigated in search for tissue-equivalent dosimeter with a large G value.

Electromagnetic Fault for Earthquake Lightning

A density of bound charges, q, which cancel piezoelectric polarization, appears at a fault zone upon the disappearance of piezoelectricity due to the release of seismic stress, σ. q is described as dq/ dt=-α dσ/ dt-q/eρ, where α, e and ρ are the piezoelectric coefficient, the dielectric constant and the resistivity of the earth, respectively. A model of a fault with length 2a and displacement time τ gives q=[ασ0eρτ(β/a)/(τ-eρ)]( e-t/τ- e-t/eρ) using the velocity of s-waves, β and the stress along the fault plane, σ0. The intensity of earthquake lightning (EQL) and its spatial distribution are calculated based on the excitation of molecules by electrons accelerated under an electric field using the assumed q, taking atmospheric polarization into account.

Satiety function of neurons containing a CCK-like substance in the dorsal parabrachial nucleus.

Abstract Glutaryl-CCK-8 (Glt-CCK-8, 16–160 pmol) suppressed food intake dose dependently when injected into the ventromedial hypothalamus (VMH) bilaterally, but not when injected unilaterally. In contrast, CCK-8 (160 and 320 pmol) did not suppress food intake when injected into the VMH bilaterally. When injected intraperitoneally, Glt-CCK-8 significantly decreased food intake at a dose of 320 pmol, though not at a dose of 160 pmol, whereas CCK-8 significantly reduced food intake even at a dose of 160 pmol. Pretreatment with proglumide, an antagonist of CCK-8, counteracted the effect on food intake of CCK-8 injected intraperitoneally, but did not influence that of Glt-CCK-8 injected either into the VMH or intraperitoneally. However, CCK-8 (800 pmol) prevented the satiety action of Glt-CCK-8 when injected into the VMH before the latter. Since a large dose of CCK-8 injected into the VMH was reported to suppress food intake, these findings suggest that, among the receptors for the satiety action of CCK, intracranial receptor has lower affinity for CCK-8 than for Glt-CCK-8 and peripheral receptor has higher affinity for CCK-8 than for Glt-CCK-8. Furthermore, bilateral lesions of the lateral part of the dorsal parabrachial nucleus (LPBD), from which the neurons containing a CCK-8-like substance extend fibers to the VMH, enhanced the satiety action of Glt-CCK-8 injected into the VMH. These results support the idea that these neurons which project to the VMH are involved in the satiety action.

Pulsed Charge Model of Fault Behavior Producing Seismic Electric Signals (SES)

The electromagnetic (EM) behavior of a geological fault is postulated to follow the mathematical model of a fault in seismology that illustrates seismic EM anomalies EMAs). Charge densities, +q and -q in C/m2 are generated at a fault zone by the change in seismic stress, α as dq/dt = -αdσ/dt - q/∊ρ, where σ,∊ and ρ are the charge generation constants measured in C/N, dielectric constant and reisitivity of bedrocks, respectively. A fault of length, 2a, plane area, A and the displacement or rupture time, τ gives pulsed charge densities, +q(t) and -q(t), or a dipole moment of P(t) = 2aAq(t) = αM0[∊ρ/(τ - ∊ρ) - exp(-t/∊ρ)] using the earthquake moment M0. Maxwells equations for this dipole in a conductive earth give power spectra of EM waves at diferrent distances. Seismic electric signals (SES) including the DC VAN method can be explained as EM waves. Electrons with density n in the atmosphere are accelerated by the electric field and travel a distance l. resulting in the exictation and ionization of atmospheric molecules leading to earthquake lightning (EQL). They also polarize the ionosphere by disturbing the transmission of EM waves prior to an earthquake and artificial electronic noises. The same pulsed field surprised eels and hamsters, suggesting seismic anomalous animal ehavious animal behavior (SAAB) as electro-physiological responses to the stimuli of electric pulses.

Thermoluminescence and Electron Spin Resonance of Atomic Hydrogens in Coesite and Stishovite, High Pressure Phases of SiO2.

Thermoluminescence (TL) of coesite and stishovite has been measured after γ-ray irradiation at room temperature from 60 Co. Analysis of the first TL peaks at 205°C indicates an activation energy, E I =1.20 eV and a pre-exponential frequency factor, s =1.3×10 12 Hz; the second peaks are at 240°C and at 255°C giving E II =1.27 eV and 1.32 eV for coesite and stishovite, respectively. ESR lines at g =2.002 with A ⊥ =46 mT and A ∥ =59 mT show the same isochronal annealing behavior with the same parameters of thermal stability as those of the first TL peaks. Other ESR lines at g =2.002 with A ⊥ =50 mT and A ∥ =53 mT are stable to high temperature. Atomic hydrogens, H 0 , in densified amorphous and in crystalline parts are responsible for the ESR signals and the release of trapped H 0 leads to recombination with a hole center emitting the TL light.

Radiation-induced defects in magnesium lactate as ESR dosimeter

Abstract Magnesium lactate (Mg–lactate: (CH 3 CH(OH)COO) 2 Mg), magnesium lactate doped with lithium lactate (Mg(Li)–lactate) and nominal pure lithium lactate (CH 3 CH(OH)COOLi) doped with Mg–lactate (Li(Mg)–lactate) were irradiated by γ-rays to study radicals for materials of radiation dosimeter with electron spin resonance (ESR). Quartet spectra were ascribed to lactate radicals in Mg–lactate and Li(Mg)–lactate with the spectroscopic splitting factors ( g -factor) of 2.0032±0.004 and 2.0029±0.004 and the intensity ratio of 1:3:3:1 due to the hyperfine coupling constants of ( A / gβ ) of 1.92±0.06 and 1.82±0.06 mT, respectively. The response to γ-ray dose and the thermal stability as well as the effect of UV-illumination have been studied to establish this material as an ESR dosimeter. The number of free radicals per 100 eV (G-value) was obtained to be 1.15±0.32, 1.35±0.35, 0.46±0.14 and 0.78±0.24 for Mg–lactate, Mg(Li)–lactate, Li–lactate and Lie(Mg)–lactate, respectively. Thermoluminescence (TL) curves gave activation energies ( E ) of 0.75, 0.79 and 0.77 eV and frequency factors s (1/ ν 0 ) of 5×10 7 , 4.5×10 7 and 8×10 7 for Mg–lactate, Mg(Li)–lactate and Li(Mg)–lactate, respectively. The lifetimes of radicals in both Mg–lactate and Mg(Li)–lactate were estimated from Arrhenius plots to be approximately 50.7±20 years, while they were 4.9±2.5 and 10±3.5 years for those of Li–lactate and Li(Mg)–lactate, respectively.

A model experiment of electromagnetic wave propagation over long distances using waveguide terminology

Electromagnetic (EM) waves observed by telecommunication engineers ahead of earthquakes are controversial because they should not propagate over long distances from the hypocenter due to dissipation in the conductive Earth. A model of an earth crust dielectric waveguide was proposed and discussed with an earth atmospheric waveguide and tested in a laboratory scaling simulation experiment using a granite slab and an EM generator antenna at the hypocenter for the Kobe Earthquake. The mappings of evanescent and wave-ripple standing waves were obtained by scanning a detector antenna over the Japanese island archipelago model. Theoretical relations of the field intensity ΔV, such as log ΔV =0.375M W + c, where M W and c are the moment magnitude and a constant, respectively have been derived by considering EM waves from an ensemble of dipolar charges at a fault zone. The theoretical scaling law is consistent with the empirical one.

A Dark Discharge Model of Earthquake Lightning

A model of dark discharge in the atmosphere before a large earthquake was proposed to elucidate the mechanism of generation of earthquake lightning and related electroatmospheric phenomena. Change in seismic stress releases piezo-compensating, bound charges due to changes in the piezoelectric polarization of quartz grains in granitic rocks, which produces an intense electric field at the fault zone. The excited or ionized molecules by free electrons accelerated under the electric field produce luminous phenomena in the atmosphere. Both Maxwell and Druyvesteyn distributions of the electron energy under the induced electric field were considered to estimate the rate of ionization and excitation of N2 and O2 molecules. An electric field and spatial distribution of earthquake lightning (EQL) were calculated based on the induced charges in the piezoelectric process which accompanies an earthquake. The intensity of emission from the excitation state, B3Πg of N2 molecule was estimated at 3×1020 photons/m3 close to the fault zone. A nucleus of precipitation might also be formed in a supercooled atmosphere leading to the appearance of earthquake fog and clouds.

Remote TL and OSL for asteroid and meteorite study

Abstract Thermoluminescence (TL) and optically stimulated luminescence (OSL) of the Allende meteorite have been studied using infrared CO 2 laser light as a heat source and HeNe laser light to excite the material, respectively from a long distance. New techniques of remote TL (R-TL) and remote OSL (R-OSL) have been developed for future remote dating from a long distance in a planetary survey. The upper limits of the distance for R-TL and R-OSL were estimated using the laboratory TL signal of the meteorite peaking at 320°C: about 400 photons s −1 for the R-TL and 60 photons s −1 for R-OSL at a distance of 1 km using a laser beam with the divergence of 0.1 mrad at powers of 100 and 1 W, respectively. An age limit of 10 5 or 10 6 years due to the signal saturation and the objects heterogeneity, as expected from previous studies, may make the asteroid survey difficult but would still help to investigate the surface activities of icy planets and satellites in outer planet worlds.

Laser-beam induced remote thermoluminescence (R-TL) image for future planetary material survey

Thermoluminescence (TL) of calcite (CaCO3) irradiated by γ-rays has been measured from a distance by heating with a CO2 infrared laser beam. The diameter of a TL spot at the exposure site increased due to thermal diffusion and became dark. The surrounding area showed TL in the form of a broad ring. TL images obtained after the exposure were compared with those simulated by numerically solving the equation of three-dimensional heat diffusion using the parameters of the TL peaks, i.e., frequency factors ν0 I = ν0 II = 5×1011 s-1 and activation energies E I = 1.28 and E II = 1.58 eV, the thermal conductivity and the specific heat. The remote TL (R-TL) may be used in the future for planetary survey by heating or exciting a ground object from a rover or from a spacecraft.