MODEL OF PHYSICAL PROCESSES IN PRIMARY AND SECONDARY CONVERTERS OF THE DETECTOR

Abstract

The level of development and application of radiation technologies is largely determined by the state of nuclear instrumentation. The advent of modern semiconductor sensors for the first time linked nuclear instrumentation and electronics into a single complex - semiconductor detector. It combines semiconductor primary converter of ionizing radiation (sensor), a secondary converter of information from the sensor (electronics) and software for processing this information, interconnected in terms of the problem being solved and parameters. The structural diagram of detector consists of two main parts: a primary converter of ionizing radiation (IR) energy into an electrical signal - a sensor; secondary converter of this electrical signal. The characteristics of detector are mainly determined by the physical properties of the semiconductor crystal as a sensitive element of the primary converter, as well as by the features of the process of recording an electrical signal. The process of registering an IR consists in converting a non-electrical quantity characterizing it into an electrical signal. In other words, this converts one type of energy - the energy of IR - into another, more convenient for processing and accumulating information. A current or voltage pulse arises in the radiation sensor directly as a result of ionization of its active medium - a semiconductor; this pulse carries extensive information. First of all, it is correlated with the moment of time of the nuclear process. In addition, the pulse marks the fact that radiation is emitted within the solid angle at which the sensor is visible from the source. Pulse amplitude is often a measure of the energy loss of radiation in the sensor. The pulse shape is different for different types of radiation, as well as for different areas and angles of radiation hitting the sensor. In this work, a model of a gamma radiation detector has been created as a single system of primary and secondary converters. It contains physical analysis and analytical presentation of the processes occurring in the CdZnTe-sensor and electronic preamplifier. It is shown that the charge collection in the sensor differs in time, which leads to a spread of signal pulses in duration and amplitude. In this regard, model shows the need to use a charge-sensitive preamplifier. The main advantage of the model is solution to problem of optimizing signal-to-noise ratio in detector.