Effect of dose on radiation-induced conductivity in polymers

Numerical simulation of radiation-induced conductivity in polymers upon long-term irradiation on the basis of the generalized Rose-Fowler-Vaisberg model, which allows for both dipolar carrier transport and generation of radiation traps during irradiation, was performed. The unusual properties of radiation-induced conductivity, such as the appearance of a maximum on current transients, the absence of a steady state, and a substantial difference between these curves for the first and subsequent irradiation, are rationalized in terms of the formation of free radicals, the major feature of radiolysis in the chemical aspect. This interpretation does not require the involvement of degradation or crosslinking processes, unlike other interpretations that appear in the literature. With the use of low-density polyethylene as an example, it was shown that radiation-induced conductivity both upon pulse and continuous irradiation can satisfactorily be described with the unified set of parameters of the generalized Rose-Fowler-Vaisberg model.     

Escape time of cosmic rays from the galaxy in the anomalous diffusion model

Two versions of the anomalous diffusion model (Lagutin and Uchaikin’s and Lagutin and Tyumentsev’s) based on fractional transport equations are considered within the leaky-box approximation with respect to cosmic ray problems. The distributions of the first passage and escape times are computed via the Monte Carlo method. The observed difference between the results for the two versions is found to be a result of incorrectly choosing the Lagutin-Tyumentsev version’s parameters.     

Effect of thermomechanical processing on the thermal stability of amorphous Fe-B alloys

Results from investigating the effect of thermomechanical processing on the thermal stability of amorphous Fe-B alloys are presented. It is shown that the combined thermomechanical processing of amorphous alloys raises the temperature of intense crystallization onset by 80 K for binary alloys; by 20–50 K, for multicomponent alloys. The greater expansion of the thermal stability interval of binary alloys relative to multicomponent alloys is explained by the presence of alloying dopants such as molybdenum, nickel, and silicon that inhibit the diffusion of boron and thus hinders nucleation and the growth of the crystalline phase. The enhanced thermal stability of amorphous alloys induced by thermomechanical processing is explained by the reduction in size of amorphous-phase frozen crystallization centers and by the formation of a nanostructured state.     

Radiation-Induced Injection Conductivity of Polymers

Steady-state currents flowing through planar polymer layers under irradiation with 15–50 keV electrons were studied experimentally and theoretically. The ultimate range of electrons was somewhat below the layer thickness. The Monte Carlo method was used to determine the basic transport characteristics of fast electrons in polymers (maximum range, depth distribution of absorbed dose and forward current). It was shown that significant steady-state currents (1 to 10% of the electron beam current) were observed only if the thickness of blocking (unirradiated) layer did not exceed 5 m. The magnitude of these currents was almost unaffected by the polymer type (polymers with minimum radiation-induced conductivity and polymers with electron or hole conductivity were examined). It was found that conventional theories of conductivity of dielectrics failed to explain the observed experimental data. Additional arguments in favor of the hypothesis of streamer mechanism of injection currents through an unirradiated polymer layer were obtained. It is emphasized that the radiation-induced heating of polymer samples can play an important role in the phenomenon under study, acting as an undesirable technical factor, that strongly distorts obtainable experimental data.     

The experimental observation of T-layers in a moving plasma interacting with the magnetic field

This paper presents the experimental results of a study of the interaction of plasma bunches injected from an independent source into a parallel plate rail-tube (Hereafter referred to as a railtron) with the magnetic field decelerating their motion. A process of the formation of the stratified plasma structure regular in character has been detected.     

The effect of temperature on carrier transport in molecularly doped polycarbonate

The effect of elevated temperature on the pattern of current transients and the hole mobility in polycarbonate doped with 20 and 30 wt % aromatic hydrazone was studied. With the use of homogeneous carrier generation mode, it was found that the shape of the current transient varies with an increase in the temperature in qualitative agreement with the prediction of the multiple-trapping theory with the exponential trap energy distribution. The apparent activation energy of hole mobility is 0.41 eV in the classical measurement mode and 0.55 eV in the case of homogeneous irradiation.     

The features of hole transport in molecularly doped polystyrene

The hole transport in polystyrene doped with 15 wt % tritolylamine is studied via the time-of-flight technique in both the surface carrier generation mode and the bulk carrier generation mode. The hole transport is shown to be dispersive with a dispersion parameter value of 0.99 ± 0.03 at room temperature. The results contradict the widely held view that hole transport in this molecularly doped polymer is quasi-equilibrium. The hole mobility is found to be almost independent of the electric-field intensity.     

Nonequilibrium transport of charge carriers in terms of the multiple-trapping model with a Gaussian energy distribution of traps

A software package is proposed for the numerical solution of equations in terms of the multipletrapping model with a Gaussian energy distribution of traps for the time-of-flight experiment. The results are compared with the literature data. The calculations are performed not only for the conventional initial condition corresponding to the case of a very thin generation layer but also for a variable thickness of the generation layer.