This requires a two-pronged capability of a high-efficiency gamma photon detector and neutron detection capability.  A high efficiency gamma collection detector, i.e. lower cost Sodium Iodide (NaI) is required to maximize the number of photons collected.  The low cost of producing large NaI crystals allows for large detectors which are the current foundation of much of the current technology.  Poor-to-medium energy resolution (dependent on photon energy), make NaI detectors a weak performer for identifying isotopes. 

       Neutron detection capability is critical to countering shielding around nuclear weapons.  The detector has to be large, sensitive, and surrounded with an integrated moderator. Neutron detectors without an integrated moderator or those that depend on moderation from the human body (i.e. water) are not practical since the technique to maximize gamma detection (holding the detector close to the potential radiation source) and the technique to maximize neutron detection (holding the neutron detector close to the body for moderation) is opposite and almost guarantees misuse.