The spatial distributions of thermal neutrons (as measured by dysprosium detectors) and of resonance neutrons (indium detectors protected by cadmium) have been investigated in several media, consisting of water and heavy elements in a heterogeneous arrangement, with two different neutron sources (Ra-α-Be and Ra-γ-Be). The experimental results are summarized in tables where the values of the mean square distances from the source of neutrons are given, for the various media, detectors, and sources used. It was found that among all the media investigated, a mixture of water and iron is the most efficient shield for neutron generating machines such as piles and cyclotrons.