Experimental determination of the lineal attenuation coefficient of ground

This work reports the measurement of the linear attenuation coefficient of ground in order to elaborate a calculus memory for a nuclear medicine installation. The service is placed in the subsoil and the hot room is surrounded by variable, higher than a meter, thicknesses of ground. Owing to the lack of bibliography about the value of the linear attenuation coefficient of ground, we measured it and compared the result with that obtained by the density correction method relative to concrete, using the linear attenuation coefficient value of this material as derived from experimental measures of this material. Measurements were made using a BaF2 scintillation detector and a 137Cs source, which was selected considering the similitude between its energy and the energy of the radiopharmaceutical used in the service for the PET studies, 22Na. Different increasing thicknesses of ground got from areas located near the service were placed as absorbents. The work involves ten experimental points, interposing cumulatively 1.8cm thicknesses of ground each time, between the detector and the source. The results obtained from both methods do not present a significant difference, however, we have concluded that the measured coefficient is more appropriate that the one estimated by the density correction method. Consequently, for calculating the dose rates at different places of the service, the experimentally determined value μ = 0.0884 cm-1 of the linear attenuation coefficient was used. (author)