Testing Measuring Devices in Well-Defined Pulsed Radiation Fields

Abstract

There is a growing need for research, detector testing and metrological methods to study pulsed radiation fields because many facilities (e.g. high-power laser facilities) and devices produce pulsed ionizing radiation. Although the ELI ALPS laser facility is already operational in Hungary, the operational parameters (frequency of the laser shots, daily operational time of the laser, energy of the laser pulse and the number of the generated particles in the laser-matter interaction) are low, thus the generated pulsed radiation is negligible. Over the following ten years, the operational parameters will be drastically enhanced. In pulsed radiation fields, since the dose rate changes rapidly as a function of time, detectors in commonly used radiation protection measuring devices are not always able to track and accurately measure the dose nor the dose rate above a certain level of exposure. The general goal was to improve our knowledge of and capability to investigate as well as test measuring devices in well-defined pulsed fields to be able to give advice to users and the regulating Authority. The available X- ray source for this type of testing has its limitations, thus the additional goal was to develop a special device that can generate a well-defined pulsed radiation field, which can be adjustable and further developed. Preliminary tests were conducted using an X-ray device and continued with a self-developed Gamma chopper. A STEP OD-02 meter was used as a reference detector and the measurement results compared to the theoretical values. The created pulsed field by the Gamma chopper was known, the dose rate per angle was determined by its mechanical structure, these were the theoretical values. Ionization chambers and TLDs were tested in different pulsed radiation fields. The capabilities and properties of the generated pulsed radiation field as well as the stability of the Gamma chopper were tested. The results were similar to those in the literature, i.e. measuring devices tend to underestimate the dose and dose rate in pulsed radiation fields. The measurements recorded by the STEP OD- 02 meter were in good agreement with the theoretical values. The tests highlighted that selection of the operation mode is crucial in order to accurately measure pulsed radiation fields with ionization chambers. Even though the Gamma chopper can be improved, its heeling effect (swaying, vibration of the rotating disk) was not identified. In the future, the capabilities of the Gamma chopper will be extended to increase its frequency and unshielded to shielded ratio, moreover, measurement procedures will be drawn up to test measuring devices in pulsed radiation fields when using it. Our test campaign was carried out with a precise series of measurements.