| Nuclear warheads detection is an important verification technology for nuclear disarmament treaty in nuclear disarmament process, and this technology is also concerned to the national security interests. Although the current nuclear reduction process is proceeding mainly between the US and Russia, as the deep cut process goes further, it is possible that China would be involved in the nuclear disarmament process. Because the nuclear disarmament verification technologies are quite complex, particularly the technology for nuclear warhead detection is very difficult, and it concerns to the sensitive issues such as national security and nonproliferation of nuclear weapons, it would be benefitial for China to explore the technology of nuclear warhead detection before participating in the nuclear disarmament process. The study on this is the most important technological preparation for our participating in the further deep nuclear disarmament.In this thesis, the numeral simulation studies are performed on the measurement of neutrons and Gamma rays of some typical hypothetical nuclear warhead models. The feasibility of the measurements is studied, the situations that these measurements possibly can be applied are discussed, and the application conditions of these measurements are explored. In numeral simulation of passive neutron detection, it is proposed to use the iterative calculation in analyzing the neutron multiplication in nuclear warhead. On this basis, the mass of the plutonium pit could be obtained under some conditions. In analyzing the neutron active detection, the neutron multiplication in the nuclear warheads induced by outer neutron source with different neutron energys is studied with numeral simulation, and the feasibility of through counting neutrons to determine the presence of high enrichment uranium(HEU) in nuclear warhead has been proved. The method of detecting the warhead which contains HEU pit by counting the released neutrons whose energy is higher than that of source neutron is studied. The feasibility of this method has been studied. The results of numeral simulation show that the higher-energy neutrons counting rate is quite low, it requires more counting time or much stronger low energy neutron source to detect the reliable signals.Detecting nuclear warhead by counting delayed neutrons induced by neutron source is studied. The 2-step calculation method is proposed to resolve the delayed neutron transportation issue. This method can save computer's calculation time, and is easy to operate. The results show that the method is better than the method of counting prompt neutrons indistinguishing real and fake nuclear warheads. If using the natural uranium to replace the HEU pit in warhead, the delayed neutron counting rate would be about 3 times lower.The coincidence neutron detection is proposed to be used in nuclear warhead detection. With the outer neutron source which can only induce 235U fission, it could possibly prove the presence of HEU in a warhead by counting the coincidence neutrons. This method possibly provides one of necessary attributions in identifying the real nuclear warheads. The method of numeral simulating the coincidence neutron detection is proposed with combining the neutron transportation and probabilistic calculation. The method is introduced and used to simulate the nuclear warhead induced fission by source neutrons with energy below 1 MeV. The results show that coincidence detection method has obvious benefit in detecting nuclear warheads. For the same type warhead, the coincidence counts rates of the model of warhead of HEU pit is 10 times as big as that of fake warhead of natural uranium pit. If we know the nuclear warheads configuration by other methods, the method of coincidence neutron detection could be used to distinguish the fake nuclear warheads from the reals.The feasibility of taking the Gamma ray spectrum as a fingerprint of nuclear warhead is studied. The range of the Gamma ray fingerprint could be applied to and the conditions under...
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