【作者】 赵良勇；

【导师】 孔祥忠；

【作者基本信息】 兰州大学 ， 粒子物理与原子核物理， 2009， 博士

【摘要】 核数据的准确测量关系着核工业和国防工业的诸多方面。在实际的应用中,高精度的核数据将会给工业仪器与设备的设计和核武器的小型化提供可靠的理论和实验支撑。14 MeV核反应截面是核物理的重要研究课题之一,它能揭示入射粒子和靶核的相互作用机制,有利于深化对核力、核结构的认识,是检验核理论的基本依据。此外,核截面数据也是核技术和核能利用的基础。特别是对核反应理论模型的建立和完善,聚变反应堆的设计、核数据库的建立以及核天体物理有着重要的意义。在中子导致的核反应中,俘获截面是很重要的一个核参数,用它可以了解核反应的产生机制,研究原子核在高激发态的运动规律;中子裂变截面则是核反应堆、核武器设计的重要数据;而中子微分截面的测定可以更细致地反映核反应的特征,有助于对核反应机制的进一步研究。我国规划将核电作为未来主要的能源,使核电站的发展形势愈来愈好。在反应堆的物理设计方面需要大量的核数据,特别是中子截面数据,如各种裂变燃料的中子裂变截面,慢化材料的中子弹性散射截面以及控制材料和屏蔽材料的中子吸收截面数据。随着核设计、核测试和计算机数字模拟的深入开展,要求我国的核数据具有精度高、能量宽、核素全和种类全的特点。核数据应用方面相继提出了很多核素的测量要求,大部分集中在可裂变核素、重核、串级反应核和一些裂变产物核。当今世界各国对煤、石油等有限资源需求的日益增加,促使人们致力于寻求新的能源。核聚变能的开发和利用是解决能源问题的重要途径之一。为了估计在聚变堆中产生的放射性废物和恰当的选用低放射性水平的结构和屏蔽材料,也需要知道许多核素的中子反应截面。14 MeV中子截面还直接关系到聚变堆的安全运行、周围环境的剂量水平、旧材料的再利用和废料的处理处置等。在我国,随着国防事业的发展以及国际上对核查与反核查工作的开展,也需要大批核素的反应截面。核反应截面还可以用作阈探测器测量中子注量和能谱,用于活化分析、放射性同位素生成、核医学、核粒子辐照、地球科学（石油测井、探矿等）、天体核物理等方面。裂变产物产额数据在核科学技术和核工程中也有着重要的应用,如在衰变热、屏蔽、剂量、燃耗、燃料处理、核废物处理和安全等方面的计算中都需要裂变产物产额数据。在核测试中,裂变产额数据用于测定核爆威力。由于核爆产生很宽能量范围的连续谱中子,需要足够精度的产额随不同入射中子能量变化关系的数据。此外由于大量基础研究对放射性束的需求,其中丰中子放射性束流主要利用强流质子束轰击可裂变材料,对产生的裂变产物进行分离加速,这也要求提供较高精度的裂变产额数据。本工作对²³⁸U的14 MeV中子诱发的裂变产额的测量工作进行了前期的研究,如实验方案的调研,实验仪器的调试,实验室的规划等。研究了拟采用直接γ能谱法测量快中子诱发²³⁸U裂变产物产额的初步方案。直接γ能谱法是利用双裂变电离室定出²³⁸U样品在加速器中子场辐照时间段内的平均裂变率,然后采用快速直接γ能谱法测定目标核的放射性强度得到产物核的生成率,从而得到目标核素的累积产额数据。同时本文介绍了14 MeV中子导致的核反应截面的测量系统,各个修正量的确定方法,测定了天然锇（Osmium）和溴化钠样品中的溴（Bromine）的14 MeV中子反应截面。实验样品在中国工程物理研究院（CEAP）的强流中子发生器K-400上进行照射的,中子能量是用⁹⁰Zr（n,2n）^89m+gZr与⁹³Nb（n,2n）^92mNb反应截面比来测定的;利用^93Nb（n,2n）^92mNb反应作为标准截面来监督中子注量;产物核的γ放射性利用ORTEC公司生产的高纯锗探测器GEM-60P进行测量。更多还原

【Abstract】 The accurate mesurements of the nuclear data are relative to many fields of the Nuclear and Defense industries. The high accurate data will provide reliable support of theory and experimental for the designs of the industral equippments and the miniaturization of the nuclear weapons. The study of the cross sections of nuclear reactions induced by 14MeV neutrons is one of the important tasks in the Nuclear Physics fields. It can provide the evidences of the interactions between the incident particles and the nucleus in the target. It is helpful to make human beings to understand the nuclear force and the nuclear structure as well. It is the basal part to check the nuclear theory out. Furthermore, the nuclear cross section data are also the foundation of the nuclear technology and the applications of nuclear energy. Especially it plays an important role in the following fields: the establishing and improving of the nuclear reaction models, the design of the fusion reactor, the building of the nuclear data base and the nuclear astrophysics.The capture cross section is a more important parameter in the nuclear reactions induced by neutrons. It is used to make the principle of the nuclear reactions clear, to study the rules of the high excited states of the atomic nucleus; fission cross section provide more significant data of the nuclear powers and the nuclear weapons. The measurement of differential cross section could be helpful to indicate the characteristic of nuclear reactions in detail and to perform more further study of the nuclear reaction.The nuclear power will be the major energy source in our country. This situation indicates that the development of nuclear power will be more quickly. There are many nuclear data specially the cross section data are needed in the design of nuclear reactors, such as fission cross sections of the fission substances, elastic scattering cross sections of the moderating materials, absorption cross sections of the control and shielding materials.With the farther development of the design and test of the nuclear fields and the computer digital simulations, it needs the nuclear data base with the characteristic of high accuracy, wide energy boundary, more nuclides and species. More requests are submitted to measure the nuclear data for the applications of nuclear technology, focusing on fissionable nucleus, heavy nucleus, cascade reaction nucleus and some fission product nucleus.The more demand of the limited energy sources such as coal and petroleum in the world nowadays, the more work is needed to be done in developing new energy sources. The better way to solve the energy source problem is to develop and to utilize the fusion power. More cross sections induced by neutrons are needed to evaluate the radioactive wastes in the fusion reactor and to adopt proper structure and shielding materials in the fusion reactor. The cross sections induced by 14 MeV neutrons are relative to the safe operation, the dose levels of the surrounding environment, the reuse, treatment and disposal of the radioactive wastes, etc. With the development of our national defense and the work of verification and anti-verification of nuclear weapons, a number of nuclear cross sections are needed. The nuclear cross sections could be widely used in measuring the neutron flux and spectroscopy, activation analysis, producing radioisotope, nuclear medicine, irradiations, geoscience （petroleum logging, mine explorations etc.） and nuclear astrophysics.The fission product yield is also more important in the nuclear science, technology and engineering, such as the calculations in decay heat, shieldings, doses, fuel burnup, fuel processing, the treatment of radioactive wastes and nuclear security, etc. The fission product yields are applied for evaluating the level of nuclear explosion in the field of nuclear test. The fission product yields related to the energies of incident neutrons must be more accurate because there are continuum spectra neutrons with broad energy ranges generated in the nuclear explosion. Furthermore, radioactive beam is required in many foundational research,including neutron-rich beam which can be generated by bombarding the fissionable materials with high intensity proton beam and separated from the fission product by the technology of accelerating particles. Thus this needs more accurate fission product yields provided as well.The primary work were performed in seeking for likely experimental plan, the adjustments of laboratory apparatus and the design of our laboratory. The direct Y -spectroscopy method will be adopted to measure the fission product yields of U-238 induced by fast neutrons in future work. First dual fission ionization chamber is used to determine the fission rate during the U-238 sample irradiated in the accelerator’s neutron field; second HpGe Y -spectroscopy is used to measure the radioactivity and to obtain the generation rate of the product nucleus; finally the cumulative yields of the product nucleus can be given. The measurement system of the cross section induced by 14 MeV neutrons and the determinations of corrective value were introduced in this paper. The cross sections of Osmium and Bromine induced by 14 MeV neutrons were presented. Our samples were irradiated at the K-400 Neutron Generator at Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics（CAEP）; the neutron energies in the measurements were determined by the cross section ratios for ⁹³Nb（n, 2n）^92mNb and ⁹⁰Zr（n, 2n）^89m+gZr reactions; the neutron flux was monitored by the standard cross section of ⁹³Nb（n, 2n）^92mNb reaction; the y radioactivities were measured with GEM-60P coaxial high-purity germanium （HPGe） detector （ORTEC, made in USA）.更多还原