[en] The NSD is a portable Neutron Searching Detector developed at NRCN with a high efficiency for counting fast and thermal neutrons employing improved gamma rejection. In order it to fulfill the latest standards for Detection of Illicit Trafficking of Radioactive Material' the NSD should be optimized using MCNP neutron transport code to establish a 5 kg maximal weight detector configuration required to detect and localize neutron emitting radioactive material. The optimized NSD should detect a slight variation in the range of usual background caused mainly by illicit trafficking or inadvertent movement of radioactive material. It can be used to for pedestrian monitoring in non-canalized configurations or scan larger volume items as a vehicle or a container at check points or critical areas