有源符合中子法测量贫化轴部件质量的方法研究

【作者】 胡根；

【导师】 亢武；

【作者基本信息】 中国工程物理研究院 ， 核技术及应用， 2011， 硕士

【摘要】 在核裁军过程中,核弹头的探测是对核裁军条约执行情况进行核查的重要内容。因为弹芯的结构涉及到核武器的设计机密,在对核武器的类型或拆卸的核材料进行核查时,不允许将其取出进行直接测量,因此如何确定密封容器中核材料的属性就成了军控核查中的重要环节,无损测量技术也就由此发展而来。铀是核武器重要的核材料,但由于其放射性比较弱,自发裂变中子发射率较低,通常来说,被动法难以测量,只能采用主动方法进行探测才更为有效。因此,铀部件及其属性的测量一直是军控核查技术中的一个难点。铀部件的属性虽然目前仍没有明确的定义,但是质量与浓缩度毫无疑问是铀部件最为重要的两个属性,铀部件质量的无损测量技术的研究,在军控核查中有着重要的意义。目前,对铀材料质量的探测方法主要有四种：时间关联符合法、主动缓发中子法、中子多重性测量分析法以及本论文所研究的有源符合中子法。有源符合中子法是通过外源中子诱发可裂变核素发生裂变,测量裂变中子的符合计数,从而确定核材料的含量。本论文的研究是通过有源符合中子法对贫化铀部件进行测量,寻求符合中子计数率与贫化铀部件的质量之间的关系。采用由62根3He计数管构成的井型符合中子探测器,选取Am-Be源作为诱发裂变的外中子源,通过屏蔽体的设计与优化减小了偶然符合计数对真符合计数的影响。实验测得的符合中子计数率与贫化铀部件质量存在着一定的线性关系,在中子源距离贫化铀部件132cm的距离条件下,线性拟合质量与标称质量的最大偏差为7.34%,主要形状影响因素为部件的外径。此外,依靠本实验的探测设备,还成功的进行了被动法测量,且由于消除了外径因素的影响,与主动测量结果相比线性更好,拟合质量最大偏差仅为4.05%,证明了对于贫化铀部件被动法测量同样可行。本论文之后也在同样的条件下进行了高浓铀部件的主动法测量,证明了本论文中搭建的实验系统也兼具了对高浓铀部件质量的测量能力。而对于高浓铀,符合中子计数率与其质量近似成指数关系,拟合质量最大偏差为12.16%,且部件的厚度成为了更大的影响因素。更多还原

【Abstract】 In the process of nuclear disarmament, nuclear warhead detection is an important verification technology of nuclear disarmament treaty. Because the structure of warhead core concerns to the secrets of nuclear weapons’design, it isn’t allowed to take the core out for direct measurement during the verification of the nuclear material. So it becomes an important part of arms control verification that how to certain the attributes of the nuclear material in the sealed containers, the non-destructive measurement technique appears and develops from this.Uranium is an important nuclear weapons material, but because of its weak radioactivity and low emission rate of the spontaneous fission neutrons, the passive method is difficult to measure generally, and active method is more effective. Therefore, the attributes measurement of uranium components is a difficult in arms control verification.The attributes of uranium is still no clear definition, but it is undoubtedly that the mass and the enrichment of uranium components are the most important two attributes. So the research of uranium components non-destructive measurement technique is quite important in arms control verification. At present, there are four methods of the mass measurement of uranium components, they are:time-correlated coincidence, active delayed neutron counting method, neutron multiplicity counting method, and active coincidence neutron counting method which is studied in this thesis. Active coincidence neutron counting method is to induce the fissile nuclides for fission reaction by external neutrons firstly, and then measure the fission neutron coincidence counting to determine the mass of nuclear material.The research of this thesis is through the measurement of the depleted uranium components with the active coincidence neutron counting method to explore the relationship between the coincidence neutron counting rate and the mass of the depleted uranium components. A well neutron coincidence detector including 62 3He counters is used, an Am-Be source is selected as the external neutron source for induced fission, and a shield is optimized to reduce influence of the accidental coincidence counts. As a result of the experiments, there is a linear relationship between the coincidence neutron counting rate and the mass of the depleted uranium components. In the 132cm distance conditions, the maximum deviation of the linear fit mass from the nominal mass of is 7.34%, and the main impact factor is the outer diameter of the depleted uranium components. In addition, relying on the detection equipments used in this experiment, the passive measurement is also finished successfully, and the linear correlation is better than that in the active measurement, because of the elimination of the influence of outer diameter. The maximum deviation of the linear fit mass is only 4.05% and it proves that it is feasible to measure the depleted uranium components with the passive method.The measurement of the highly enriched uranium components with the active coincidence neutron counting method under the same conditions is also carried out, which proves that the high enriched uranium components are also able to be measured in this experimental system. For highly enriched uranium, the relationship between the coincidence neutron counting rate and the mass of the components is exponential, the maximum deviation of the fit mass is 12.16%, and the thickness of the components has become the greater impact factor.更多还原