[en] Theoretical investigations of neutron fields at the surface of and inside a phantom have been performed on the basis of a three-dimensional Monte-Carlo code assuming a similar incident neutron spectrum. The calculations show that with increasing depth in the phantom the fraction of thermal neutrons increases and the low energy fraction of intermediate and fast neutrons decreases. The knowledge of the neutron spectrum permits to calculate the fluence and the dose absorbed from a detector reading so that it is possible to determine doses in interesting depths of a phantom or of the human body