In-situ gamma-ray mapping of environmental radioactivity at iThemba LABS and associated risk assessment

In-situ and ex-situ measurements of environmental radioactivity were made on the iThemba LABS (iTL) grounds in South Africa. The MEDUSA and HPGe detector systems were used to make insitu and ex-situ measurements, respectively. The MEDUSA was mounted ∼0.5m above the ground on a 4× 4 vehicle to traverse [at ∼2m · s−1] the accessible portions of the iTL grounds. Spatial data (via a GPS receiver) were acquired every 1 s, and -ray spectra every 2 s. MEDUSA count rate maps were produced to show the spatial distribution of radioactivity on the grounds. The HPGe was used to measure the radioactivity in soil (and also in some grass) samples collected at particular spots on the iTL grounds. The sampled spots include six identified high activity spots (“hot spots”) and two “calibration spots”. The activity concentrations were determined for both the natural and anthropogenic radionuclides. The absorbed and effective doses (from external -ray irradiation) were also determined for the natural and anthropogenic radionuclides. The maximum effective dose to humans on the iTL grounds as a result of external exposure to natural and anthropogenic radionuclides was found to be well below the regulatory 1mSv per year per member of public.