【作者】 乔录成；

【导师】 徐家云；

【作者基本信息】 四川大学 ， 粒子与原子核物理， 2003， 硕士

【摘要】 对于提供核能源或中子源的核裂变反应系统，需从理论上给出它的临界安全性和中子能谱，通常通过k本征值问题的计算来实现。由于蒙特卡罗方法（简称MC方法）被认为是处理粒子输运问题的精确计算方法，国外已发展出了计算k本征值问题的蒙特卡罗程序，例如KENO、MCNP等，但这些程序都不能计算除k本征值问题以外的其它诸如λ、α等本征值问题，而对于特定的核裂变系统，采用这些本征值比用k本征值问题更为重要，比如采用λ本征值问题可以得到比用k本征值问题更接近实际的中子能谱。为此，我们从对λ本征值问题计算模型的研究出发，在原有KENO程序的基础上，研制出了计算λ本征值问题的蒙特卡罗程序。 环境中放射性对健康的影响日益成为人们关心的问题。在放射性测量中，采用高纯锗γ谱仪可以方便地分析环境样品中放射性核素的种类和含量，但要准确地分析核素含量，需要准确知道各样品中的各种能量γ射线的探测效率，通常由一定密度和样品量的标准样品来得到这一效率。但由于待测环境样品的来源不同，其介质成份、密度和体积量可能相差很大，实验上又难以制作各种各样的标准样品，采用蒙特卡罗方法可以比较容易地解决这些问题，对此，我们采用蒙特卡罗方法，研究了高纯锗γ谱仪对不同环境样品的探测效率，解决了实验上制作各种标准样品的难题。 针对上述问题取得了如下创新结果： 1．在蒙特卡罗程序KENO-Ⅳ的基础上，建立了λ-k_eff迭代计算模型，从原理和方法上解决了λ本征值问题的计算。该模型把λ本征值问题的计算转化成带参数λ的一系列k本征值问题的计算，其参数λ值的调节通过上一次迭代计算的k_eff来实现。 2．研制出了计算入本征值问题的蒙特卡罗程序，并用该程序进行了入本征值问题的计算。计算所得入本征值、入本征值能谱与理论预言吻合。为反应堆等核裂变系统的核临界安全分析和中子核反应率的计算提供了有意义的结果。 3．利用蒙特卡罗程序MCmp－4B模拟计算了高纯锗Y谱仪对环境样品的探测效率，并与标准样品的实验结果比较，检验了计算结果的正确性。 4．模拟计算了探测效率随环境样品成份、密度及样品体积的变化规律，得出了具有实际意义的结果，解决了实验中制作各种标准样品的烦琐问题。更多还原

【Abstract】 The nuclear fissile reaction system, which provides nuclear energy or neutrons, theoretically demands its criticality safety and neutron energy spectrum to be predicated. Generally, those are realized by calculating the k-eigenvalue problem. Because Monte Carlo Method, for short MC method, has been known as accurate numerical methods for calculating particle transport, a number of general Monte Carlo Code have been developed abroad, for example KENO and MCNP are MC code. But these code only can calculate the k eigenvalue problem, and not calculate such as the λ. and a eigenvalue problem. However, for some special nuclear fissile systems, those eigenvalue problem are more important comparing to the k eigenvalue problem, for instance, using λ -eignevalue problem may obtain more accurate neutron spectrum than using k-eigenvalue problem. Therefore, we have constructed the calculations model of λ -eignevalue problem, and on the basis ofKENO code, developed the MC code of λ -eigenvalue problem.The unhealthful radioactivity in environment has increasingly been an interest problem. In the radioactivity measure of the environment samples, HPGe γ -spectrometer can expediently analyze the species and content of the radionuclide in the environment samples. Those demands the detection efficiency corresponding to the different energy y -ray in the various environment samples. We are used to gain the detection efficiency by making the standard samples, because of the different source of the environment samples, the component and density and volume of the samples can’t entirely match those of the standard samples, so it is very difficult to make the standard samples, thereby, in order to conquered experiment difficulty, this article has calculated the detection efficiency of HPGe γ -spectrometer by existing Monte Carlo code.Aim at the above problem, this article obtained following creative results:1.Base on the KENO-IV code, λ-keff iteration model has been constructed in this thesis. By this model, the λ-eigenvalue problem can be treated as a series of k eigenvalue problems with a certain λ number which is adjusted by keff. The Monte Carlo code for calculating λ eigenvalue problem has been developed in this thesis. This code has been used to calculate the λ-eigenvalue problem and the calculation results of λ-eigenvalue, correspond spectra and correspond reaction rates are consistent with the predication of the theory, and gained the practical results.2.Using the MCNP-4B code, this article has calculated the efficiency calibration curves of the HPGe -spectrometer ,compared with the results of experiment. The results have shown that the Monte Carlo simulation calculation has been a convenient and reliable method for the efficiency calibration of the HPGe γ, -spectrometer. We have calculated the variety rules of detection efficiency with the samples of various components and densities and sizes on different energy points, gained the factual results, and resolved the difficulty of the experiment.更多还原