  Due to time and financial restrictions in an educational laboratory, we are
making compromises, using experimental setups in which limitations and
uncertainties are important. In these cases we should pay particular attention
to the role of different factors that affect our experiment, in order to
achieve the best possible educational outcome and to avoid misconceptions. In
this paper problems related to the use of very low activity source 60Co in the
experiment of measuring the linear attenuation coefficient of gamma rays
through matter, will be presented. The role of background radiation in
measurements and in the relative statistical uncertainty as well as the role of
statistical uncertainty in the choice of representative measurements is
discussed. Moreover students' difficulties and misconceptions related mainly to
the statistical uncertainty and its connection to measurements overlapping are
recorded. An explanation for the possible reasons of these misunderstandings is
attempted in order to improve the educational outcome in this experiment.
