Testing of the measuring instruments in non-governmental networks for the purpose of environmental monitoring of ionising radiation

Abstract

Non-governmental networks for environmental monitoring employ a wide range of radiation protection instruments from different manufacturers, which provide the public with often unreliable dosimetric data. These Measuring Instruments in Non-governmental Networks (MINN) are mostly based on Geiger-Muller tube gas detectors, which represent low-cost easily operated instruments. An extensive testing of these devices was performed in order to validate the data acquired with MINN within the 16ENV04 Preparedness EMPIR project. In total, 16 different dosemter types were selected, with a sample size of four dosemeters per dosemeter type. Performance testing included the energy dependence and the linearity tests of the dosemeter response. Additionally, during the Researcher Mobility Grant associated with the 16ENV04 project, two Geiger-Muller based dosemeter types, with a sample size of two dosemeters per type were included in the testing. These instruments were subjected to the angular dependence testing in both horizontal and vertical planes, besides the energy dependence and linearity tests in the reference Cs-137 field at Physikalisch-Technische Bundesanstalt (PTB). For all the dosemeter types, inherent background, response to secondary cosmic radiation and the response to small changes of dose rate were determined at the metrological facilities of PTB. The sensitivity of the measuring instruments used in non-governmental networks to small variations of the ambient dose equivalent rate was examined by exposing the dosemeters to low dose rate Cs-137, Co-60 and Ra-226 radiation sources, in order to estimate the effect of environmental radioactive contamination with artificially produced radionuclides. For the comparison purposes, besides the measuring instruments used in non-governmental networks, a previously characterized CdZnTe-based spectrodosemeter was irradiated with the aforementioned radiation fields. The measured values were compared with a reference Reuter-Stokes ionisation chamber used for low-dose rate level measurements.