Abstract
A field gamma ray spectrometer, consisting of a portable high purity germanium detector, portable multichannel analyser, and a notebook computer, was used to conduct in situ rapid scanning of radioactive Ar, Kr, and Xe isotopes in the air around a nuclear facility. The portable gamma ray spectrometer was calibrated using Ar, Kr, and Xe radioisotopes, activated in a research reactor and released in a sealed chamber. The unit was further tested inside the reactor containment to monitor the concentration of 41 Ar. In a typical one hour field measurement, the detection limits for some rare gas radionuclides corresponded to dose rates around 0.1 nSv.h -1 , which is far less than the dose rate induced by derived air concentrations imposed by the authority. The dose rate due to ground level concentrations of gaseous radionuclides dispersed from a source, such as a nuclear facility or a nuclear test, can be monitored in a short period using the portable unit.