Annual Report 2009/2010 - JUWEL - Forschungszentrum Jülich

shown in Fig. 96. In both cases the old formulation leads to a strong overestimation of the
count rates up to a factor of about 2 when the source partially illuminates the active detector
surface. In contrast, the count rates based on the new model are in excellent agreement with
the simulated ones. The small discrepancies between the new analytical count rate
calculation and the simulation for increasing source displacements are due to edge
penetration phenomena which are only roughly implemented in the new analytical model.
Fig. 96: Comparison of the count rates obtained for the old and new collimator model for a
source (rS = 10 cm) at different heights to the detector normal.
Next, MCNP5 simulations of angular count rate distributions such as measured in SGS are
performed for Co-60 and Cs-137 point sources in a segment of a drum filled with concrete
( con -3 ). The 0.15 cm thick drum wall consists of stainless steel with a density of
W cm -3 . As an example, the angular dependent count rate distributions simulated
for the E -60 point source located at radial positions of 10 cm
are shown in Fig. 97.
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