Radiation Detection at Low Exposure Rates with CdS Crystals, using Pulse Counting or AC or DC Conductivity

We have investigated the dc and ac conduc- tivities of Se75Te20Sn5 glass from 80 to 290 K in the frequency range 40 to 10 6 Hz. The behavior of the ac conductivity with temperature, T, is similar to that observed in many chalcogenide glasses. In this frequency range the ac conductivity r(x) is proportional to x s . The frequency exponent shows a T dependence. The experi- mental data have been analyzed using the modified bi- polaron correlated barrier hopping model, which assumes that the relaxation time should contain a Meyer-Neldel rule term. It is observed that this model is consistent with temperature dependent dc conductivity, rdc, ac conductiv- ity, rac, and s, for activation energies above 0.1 eV. At high frequency, that is, low activation energy, the behavior changes. We suggest that in this regime, the carriers may tunnel rather than hopping. We also present a correlation between the residual ac prefactor r00(x) and the Meyer- Neldel temperature (TMN), similar to that previously reported for dc conductivity. This similarity points strongly to the dc and ac conduction mechanisms being the same.

1. The electric organ discharge (EOD) of wave-type weakly electric fish is generated as an extremely regular series of electric organ pulses. Measurements of pulse duration and EOD frequency were made in the speciesSternopygus andEigenmannia. Pulse duration is highly inversely correlated with EOD frequency in a population of fish, so that the EOD waveform remains quasisinusoidal over the species range of EOD frequencies. This places most of the energy of the EOD within the fundamental harmonic to which the electroreceptors are most sensitive. 2. Treatment with the anesthetic MS-222 transiently lowers EOD frequency, but does not change pulse duration. This demonstrates that pulse duration is independent of immediate EOD frequency and, therefore, of the medullary pacemaker nucleus (PMN). 3. InSternopygus, small monophasic potentials could be recorded outside the tails of curarized fish. These were of constant duration and shape across all fish regardless of the fish's EOD frequency. The location along the body where this potential reversed polarity was close to, although not identical with, the isopotential line for the EOD pulse. These potentials were partially blocked by the curare. They probably represent the summed psps of the synchronously-firing electrocytes. This result supports the hypothesis that differences in EOD waveform, specifically pulse duration, arise from electrocyte membrane events following the psp (postsynaptic potential). 4. Implantation ofSternopygus with 5-α-dihydrotestosterone (DHT) in silastic capsules results in decreased EOD frequencies, as previously reported for this species (Meyer and Zakon 1982; Meyer 1983). In addition, corresponding significant increases in EOD pulse duration occurred (a mean increase of about 1.3 ms or 24%). No changes were measured in controls implanted with empty capsules. The maximum decrease in EOD frequency and increase in pulse duration plateau at different times, suggesting that they are the result of different processes. After removal of the hormone capsules, EOD frequency and pulse duration reverted to baseline levels within a few weeks. 5. These results demonstrate a degree of coordination between the PMN and the electric organ not previously recognized. It is likely that androgens play a role in this process. If, as proposed, the electrocyte membrane properties determine the characteristics of the waveform, then the androgen must act on both the PMN and the electrocytes to keep EOD frequency and pulse duration in register.

Dependence of dc and ac conduction on the pre-sintering temperature in sol–gel derived Ba 0.5Sr 0.5TiO 3 thin films

The complex conductivity in polycrystalline C60 and C70 has been investigated for frequencies 20 Hz≤ν≤106 Hz and temperatures 10 K≤T≤750 K. The high-frequency dielectric constants eα= 2.6±0.1(C60) and e∞= 4.6±0.1 (C70) were deduced from these experiments. The observed low temperature relaxation process in C60 fits well into the relaxation dynamics of the C60 molecules as determined by many other experimental techniques operating on very different time scales. In addition to the study of the dipolar relaxation process, the dc and ac conductivities were determined. From the temperature dependence of the dc conductivities energy barriers of EG=1.75±0.1 eV (C60) and EG=1.7±0.1 eV (C70) were estimated. In C70 we found indications for small polaron tunneling.

Electrical, dielectric, and optical properties of Sb2O3–Li2O–MoO3 glasses

Electrically conductive nanocomposite system based on poly(butyl methacrylate) (PBMA) with different contents of neodymium-doped titanium dioxide (Nd-TiO2) was prepared by in situ free radical polymerization method. The effect of Nd-TiO2 on the morphology and structural properties of the composites was carried out by scanning electron microscope (SEM) and X-ray diffraction analysis (XRD). The temperature-dependent AC conductivity and DC electrical conductivity of PBMA/Nd-TiO2 nanocomposites were studied with respect to the different volume fraction of Nd-TiO2 nanoparticles. SEM and XRD patterns revealed the uniform dispersion and structural regularity of nanoparticles in the polymer matrix. The AC conductivity of PBMA and its composites were found to be increased with an increase in temperatures and frequencies. The activation energy and exponential factor were analyzed from AC conductivity and both results indicate the hopping conduction mechanism present in PBMA/Nd-TiO2 nanocomposite, which is responsible for the variation of conductivity with temperature also. The DC conductivity of nanocomposites was higher than pure PBMA and the conductivity increases with increase in the concentration of Nd-TiO2 nanoparticles. Experimental and theoretical investigations based on McCullough, Bueche, Scarisbrick, and Mamunya modeling were carried out to observe the DC conductivity differences induced by the addition of Nd-TiO2 nanoparticles in PBMA matrix. Among the various modeling studied here, Mamunya model shows better agreement with the experimental conductivity.

Poly (diaminonaphthalene) doped poly (vinyl alcohol) was synthesized by in-situ chemical oxidation polymerization method. The complex conduction mechanism of obtained PDAN doped PVA films were examined by measuring DC and AC conductivity. Non-linear I-V characteristics curve confirming the semiconducting nature of the films at constant temperatures. The DC and AC conductivities of the 0.791g PDAN doped PVA films were (2.041±0.64)×10−5 Scm−1 and (6.28±0.79)×10−6 Scm−1, respectively. The DC conductivity so obtained was six folds larger than earlier reported.

The dc and ac conductivity of polyaniline–polyvinyl alcohol blends

Calibration of thermoluminescent dosimeters for low exposure rates

The ac conductivity of halide based tellurium glasses having composition 70 TeO2-(30-x) BaO-x ZnCl2; x = 5, 10, 15, 20 and 25 has been investigated in the frequency range 10-1 Hz to 105Hz and in the temperature range 453 K to 553 K. The frequency and temperature dependent ac conductivity show mixed behaviour with increase in halide content and found to obey Jonscher’s universal power law. The values of dc conductivity, crossover frequency and frequency exponent have been estimated from the fitting of experimental data of ac conductivity with Jonscher’s universal power law. For determining the conduction mechanism in studied glass system, frequency exponent has been analyzed by various theoretical models. In presently studied glasses, the ac conduction takes place via overlapping large polaron tunneling (OLPT). The values of activation energy for dc conduction (W) and the one associated with relaxation process (E R) are found to increase with increase in x up to glass sample with x = 15 and thereafter it decrease with increase in zinc chloride content. DC conduction takes place via variable range hopping (VRH) as proposed by Mott with some modification suggested by Punia et al. The value of real part of modulus (M') is observed to decrease with increase in temperature. The value of stretched exponent (β) obtained from fitting of M'' reveals the presence of non-Debye type of relaxation in presently studied glass samples. Scaling spectra of ac conductivity and values of electric modulus (M' and M'') collapse into a single master curve for all the compositions and temperatures. The values of relaxation energy (E R) for all the studied glass compositions are almost equal to W, suggesting that polarons have to overcome same barrier while relaxing and conducting. The conduction and relaxation processes in the studied glass samples are composition and temperature independent.

Ac and Dc conductivity in amorphous silicon-hydrogen films

Our research described in the current paper sought to construct poly(methylmethacrylate)/poly vinyl acetate/tetrabutylammonium iodide, PMMA/PVAc/x wt %TBAI, blended polymers as promising materials to develop for energy storage applications. The samples were explored via scanning electron microscopy and X-ray diffraction to establish their structures and morphologies. The incorporation of TBAI into the PMMA/PVAc blend resulted in varying dielectric constant values relative to the pure sample. The effect of TBAI loading percentage and the temperature on the AC conductivity, impedance spectroscopy and complex electric modulus of the undoped sample were examined. The conductivity mechanisms of the various blends were explored. The blends exhibited a non-Debye-type ionic relaxation mechanism. The activation energy value of the host blend was altered by the quantity of TBAI doping. A blend with x = 11wt% exhibited the highest energy density values. Lifting the temperature improved the values of energy densities for the system. In comparison to the undoped sample, the doped samples’ dc conductivities improved. The results indicated that the PMMA/PVAc/TBAI films may serve as viable and desirable blended polymers for application in diverse future electronics and energy storage systems.

Investigations on the electrical and structural properties of polyaniline doped with camphor sulphonic acid

AC conductivity of Au-SiO-Au structures has been investigated between 10-1 to 105 Hz and 77 to 423K. Low frequency measurements confirm, for a large class of specimens, the results obtained previously by Bigorgne et al. (1974); namely the existence of Schottky barriers at the interfaces. The behaviour of the specimens agrees with a model established by Simmons, Nadkarni and Lancaster (1970). Hopping phenomena also occur and become predominant at a relatively high frequency or low temperature. An equivalent circuit derived from the Simmons, Nadkarni and Lancaster model, is proposed; it takes into account the two behaviours which coexist in the entire investigated temperature and frequency ranges. It has been found that activation energies corresponding to AC and DC conductivities are about the same.

Dielectric relaxation in semiconducting oxide glasses