Development and calibration of a gamma-ray density-meter for sediment-like materials

The core-logger PHAROS was designed at Kernfysisch Versneller Instituut, Groningen, the Netherlands to measure activity concentration of sediment like materials. As the core logger was calibrated for a single material density the variations in the density profile in the scanned core can result in erroneous estimations of activity concentrations. To overcome this, a density-meter was developed and implemented on PHAROS. The density measurement should be non-invasive and should cover a wide range of sediment like materials. The most suitable approach is to deploy gamma-ray transmission technique, where the intensity of non-attenuated photons after traversing the core is directly related to its density. Due to the overall complexity of radiation transport through sediment media, the design of the density-meter was assisted by Monte Carlo simulations. They were deployed to model sophisticated and time-consuming experiments in the process of designing the (137)Cs-based source, to generate the pulse-height response functions of the bismuth-germanate (BGO) scintillator and to estimate the systematic uncertainty induced by the core displacement in the process of the measurement. Moreover, the Monte Carlo simulations have demonstrated as a reliable complementary tool for the generation of PHAROS detector calibration curves. The designed density-meter of PHAROS core-logger indicates to be adequate to estimate densities ranging from approximately 1.6 to approximately 2.7gcm(-3) with the systematic uncertainty within 3%.