The efficiency of the measurement setups was calculated from Monte Carlo simulations using MCNP code.  The numerical model of the different studied set-ups, used in MCNP, performed well for the known cases. 
MCNP
Minimum detectable activity concentration of radio-cesium by a LaBr3(Ce) detector for in situ measurements on the ground-surface and in boreholes.A 3.81 × 3.81 cm LaBr3(Ce) detector based portable measurement setup has been developed for in situ gamma spectrometric survey of a contaminated site. 
LaBr3(Ce)