Assessment of ambient dose equivalent rate: performance of an automatic survey meter as an instrument to quantify the presence of radiation in soils

Those who work in radiation protection are faced with various quantities that were created to account for the effects of ionizing radiation in the human body. As far as the experimental point of view is concerned, each available equipment is planned to measure a distinct quantity, for a specific radiation protection application, and it is not always clear which one it is. This paper shows a series of tests, planned and applied to a portable gamma ray spectrometer, in order to assure that the monitoring low dose levels of radiation with it is reliable. The equipment is fully automated and does not allow modifications of the conversion factors from counts to ambient dose equivalent. It is therefore necessary to assure that the values provided by the equipment are correct and refer to the actual situation one expects to find in practice. The system is based on an NaI(Tl) scintillation detector, mounted with its electronics in a portable case, suitable for field measurements. It measures ambient dose equivalent rate (Ḣ*(10) in Sv h−1), total counts in the spectrum (from 50 to 1670 keV) and number of counts per channel (128 channels). The tests presented here are: evaluation of the cosmic component, repeatability, check against standard extended sources, and performance with point sources (60Co or 137Cs) on the ground. The results show that the system can be used, with its built-in conversion coefficients, for in situ measurements, whether or not the ground contains only natural radiation or is additionally contaminated.