Equipment for Environmental Radioactivity Measurement: Calibration and Traceability

Abstract

Radiation level and activity concentration of radioisotopes present in the earth’s environment can be detected and measured by specific instruments based on several detection techniques. The environmental radioactivity monitoring and measurement instruments commonly use gaseous ionization chamber (GM Tube), liquid or solid scintillation medium [LSC, NaI(Tl), ZnS(Ag)], semi-conductor (HPGe, PIPS), or their combination as detection methods. These instruments should be capable of measuring trace levels of radionuclides present in the environmental matrices with utmost accuracy. In the last few decades, organizations like ISO, IAEA, and BIPM have taken several measures to bring conformity in measurement through proper certification and QC mechanisms which are recognized worldwide. It is safely assumed (and often demonstrated) by an instrument manufacturer that a new instrument is calibrated as per established norms. It initially behaves according to the specifications; however, its capabilities gradually vary with time due to mechanical deterioration, dust, moisture, chemicals, etc. present in the operating environment. These deviations from standard specifications depend upon the frequency of usage and the severity of the operating conditions and are expected and acceptable within documented limits. A recalibration of the instrument becomes necessary when these limits are breached and the results are no more acceptable. Calibration of environmental radioactivity detection and measurement instruments, using certified standard radioactive sources or certified reference materials, is of paramount importance, as it has a direct impact on the health of humans, environment, and non-human biota. In addition, these sources must be traceable with an unbroken chain of measurements to the SI (BIPM) via international bodies like NIST, ILAC-MRA, or National Metrological Institutes/Laboratories.