Comparison of the Empirical Variances and Mean Values of Normally Distributed Populations of Nuclear Counts

This paper discusses the possibility of applying the F-test and double t-test in problems related to the identification of number of radioactive isotopes in a contaminated area by using only counters for radiation detection. The descriptions of the F-test and the double t-test are given along with the corresponding tabular values that enable their implementation. Finally, the experiment is presented via two radioactive samples. The results of the experiment were treated in the manner proposed in the paper and satisfactory results were obtained

Impact of forward emitter current gain and geometry of pnp power transistors on radiation tolerance of voltage regulators

Low-dropout voltage regulators with various geometries and technological realisations of serial pnp power transistors were exposed to ionizing radiation. Although devices with vertical emitters were considered much less susceptible to the influence of radiation on forward emitter current gain than circuits with round emitters, the experiment showed a similar degradation of current gain in both cases. The main reason of high radiation susceptibility of the examined vertical serial pnp transistor is the implementation of an interdigitated emitter, with high perimeter-to-area ratio, causing the great increase of serial transistor’s base current, but a minor influence on the maximum output current. Transistors with round emitters with small perimeter-to-area ratio expressed a moderate current gain degradation, but a rapid fall of the emitter injection efficiency, causing a significant decrease of the maximum output current. Regardless of the similar forward emitter current gain degradation, reliability and operational characteristics of two types of low-dropout voltage regulators were completely different

Power lateral pnp transistor operating with high current density in irradiated voltage regulator

The operation of power lateral pnp transistors in gamma radiation field was examined by detection of the minimum dropout voltage on heavily loaded low-dropout voltage regulators LM2940CT5, clearly demonstrating their low radiation hardness, with unacceptably low values of output voltage and collector-emitter voltage volatility. In conjunction with previous results on base current and forward emitter current gain of serial transistors, it was possible to determine the positive influence of high load current on a slight improvement of voltage regulator LM2940CT5 radiation hardness. The high-current flow through the wide emitter aluminum contact of the serial transistor above the isolation oxide caused intensive annealing of the positive oxide-trapped charge, leading to decrease of the lateral pnp transistor's current gain, but also a more intensive recovery of the small-signal npn transistors in the control circuit. The high current density in the base area of the lateral pnp transistor immediately below the isolation oxide decreased the concentration of negative interface traps. Consequently, the positive influence of the reduced concentration of the oxide-trapped charge on the negative feedback reaction circuit, together with the favourable effect of reduced interface traps concentration, exceeded negative influence of the annealed oxide-trapped charge on the serial pnp transistor's forward emitter current gain

On-line monitoring of base current and forward emitter current gain of the voltage regulator's serial pnp transistor in a radiation environment

A method of on-line monitoring of the low-dropout voltage regulator's operation in a radiation environment is developed in this paper. The method had to enable detection of the circuit's degradation during exploitation, without terminating its operation in an ionizing radiation field. Moreover, it had to enable automatic measurement and data collection, as well as the detection of any considerable degradation, well before the monitored voltage regulator's malfunction. The principal parameters of the voltage regulator's operation that were monitored were the serial pnp transistor's base current and the forward emitter current gain. These parameters were procured indirectly, from the data on the voltage regulator's load and quiescent currents. Since the internal consumption current in moderately and heavily loaded devices was used, the quiescent current of a negligibly loaded voltage regulator of the same type served as a reference. Results acquired by on-line monitoring demonstrated marked agreement with the results acquired from examinations of the voltage regulator's maximum output current and minimum dropout voltage in a radiation environment. The results were particularly consistent in tests with heavily loaded devices. Results obtained for moderately loaded voltage regulators and the risks accompanying the application of the presented method, were also analyzed

The determination of the mean value of the non-homogenous background radiation and the measurement uncertainty using Welch-Satterthwaite equation

In this paper, the procedure for determination of the mean value of non-homogenous background radiation and the expression of measurement uncertainty is considered. The background radiation is described using the Student's distribution, and the measurement uncertainty using the Welch-Satterthwaite equation. The proposed algorithm was experimentally verified under well-controlled laboratory conditions and satisfactory results were obtained. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 171007

Surface-time enlargement law for gas breakdown

This paper investigates, through theory and experiment, the applicability of the results obtained in laboratory tests of relatively short duration performed on model structures, as a part of the process of designing high-voltage equipment intended for lasting exploitation. Possibilities and limititions of applying these results to practical structures are examined using the methods of mathematical statistics. Special attention is devoted to the influence of electrode surface enlargement and pulse load (overvoltage) prolongation on the statistical behaviour of the pulse breakdown voltage random variable, expressed in the form of the enlargement law. In the theoretical part of the paper, the general four-dimensional (space-time) enlargement law is derived, along with its simplified three-dimensional (surface-time) variant. In the part of the paper related to the experiment, performed with the aim of testing the applicability of the derived surface-time enlargement law to SF6 gas-insulated two-electrode systems, a description of the experimental equipment and procedure is provided, along with the details of measurement data processing. Comparison of experimental results with those predicted by the surface-time enlargement law proved its validity for a two-electrode configuration with a homogenous and radial electric field, insulated by SF6 gas under pressure (with gas pressure as a parameter)

Conditions for the Applicability of the Geometrical Similarity Law to Impulse Breakdown in Gases

This paper investigates the conditions for the applicability of the geometrical similarity law to impulse breakdown in gases, using statistical methods necessitated by the stochastic nature of the impulse breakdown voltage. Theoretical analysis in the paper is accompanied by experimental results obtained for geometrically similar systems, i.e. for systems with equal shapes of the macroscopic and microscopic electrical field. The experiments were conducted in controlled laboratory conditions, for a wide range of gas pressure and inter-electrode gap values. Two-electrode systems were used, with both homogeneous and non-homogeneous electrical fields, utilizing SF(6), N(2) and He gases as insulators. Standard lightning and switching voltage impulses were applied, as well as ramp-shaped impulses with different slopes. On the basis of the statistical processing of the obtained experimental results, conclusions regarding the conditions for the applicability of the geometrical similarity law to impulse breakdown in gases are drawn