基于瞬发γ中子活化分析技术的日遗化武鉴别方法研究

Study on Identification of Chemical Warfare Agents Abandoned by Japanese Army in China Based on PGNAA

日本战败后遗弃在我国境内的数百万枚化学弹亟待销毁处理,而对弹型的准确鉴别是处置和销毁的前提。基于瞬发γ射线中子活化分析(PGNAA)技术,对现有手段难以区分的黄弹、青白弹以及燃烧弹开展鉴别研究,利用Geant4软件分别计算了采用^(252)Cf源、D-D和D-T中子发生器作中子源,聚乙烯或铅材质作反射体的情况下,上述3种弹型的中子诱发特征γ谱,并进行了实验验证。谱分析结果表明,对于燃烧弹中的特征元素P和S,主要检测特征γ射线能量分别为1266 keV和2230 keV,Cl元素的882/1763 keV特征峰与1951/1959 keV特征峰的计数之比可作为鉴别黄弹和青白弹的重要依据。从中子源的选型、反射体的选择、特征元素库的建立以及判别方法等方面,为基于PGNAA技术鉴别日遗化武提供了重要的参考依据。

Tens of thousands of chemical warfare agents were abandoned in China by the Japanese army after their defeat of invasion of China.Most of the chemical warfare agents have been buried in the soil for more than half a century and the risk of chemical toxicants leakage has increased sharply due to corrosion,so the disposal of these weapons is urgent.The effective disposal and destruction of chemical warfare agents are based on the accurate identification.Prompt gamma neutron activation analysis(PGNAA)is a multi-element analysis technology with low invasion,good safety and high accuracy.In this paper,to study the discrimination potentiality of PGNAA technology on the Japanese chemical projectiles abandoned in China,which can’t be identified by the visual inspection and X-ray imaging technology,the discriminant logic tree of the projectiles was established by investigating and analyzing the data of these abandoned chemical warfare agents,and the simulation model of neutron activation analysis of these projectiles was established by the use of Geant4 toolkit.The prompt gamma spectra of incendiary,yellow projectile and blue projectile excited by ^(252)Cf source,D-D neutron generator and D-T neutron generator with neutron yield of 1×10^(7) s-1 were calculated respectively.For the generation of neutrons from ^(252)Cf source,the Watt fission spectrum was used in our simulations.Monoenergetic 2.5 MeV neutrons and 14.1 MeV neutrons were set as D-D neutron generator and D-T neutron generator respectively in our simulations.The reflection effect of neutron reflectors made of lead or polyethylene on neutrons has also been studied in the simulation.To verify the simulation results,an experimental platform was set up with a D-T neutron generator and a N-type HPGe detector with relative efficiency of 55%.The samples under test were made up of non-toxic and harmless chemical agent,the elements composition and mass fraction were closed to the real chemical warfare agents.The results show that for characteristic elements P and S,the main detected prompt gamma ray energies are 1266 keV and 2230 keV,respectively.The analysis of closely-spaced overlapping peaks requires nonlinear least-squares peak fitting,such as the multiple gamma-ray peaks from the hydrogen region.The peak position counts ratio between 882/1763 keV and 1951/1959 keV represent an alternative to the existence of S,which is a key criterion for distinguish yellow projectiles from blue projectiles.This study provides the necessary references from the aspects of neutron source selection,neutron reflector material selection,nuclide library establishment and projectile discrimination method for the chemical warfare agents identification system based on PGNAA technology.