Transmutation of nuclear wastes using photonuclear reactions triggered by Compton backscattering photons at the Shanghai laser electron gamma source

Based on the facility of the Shanghai Laser Electron Gamma Source (SLEGS), the transmutation for nuclear wastes such as ¹³⁷Cs and ¹²⁹I is investigated. It is found that nuclear waste can be transmuted efficiently via photonuclear reaction triggered by gamma photons generated from Compton backscattering between CO₂ laser photons and 3.5 GeV electrons. The nuclear activities of ¹³⁷Cs and ¹²⁹I are evaluated and compared with the results of transmutation triggered by bremsstrahlung gamma photons driven by ultra intense laser. Due to the better character of gamma photon spectrum as well as the high brightness of gamma photons, the transmutation rate of Compton backscattering method is much higher than that of the bremsstrahlung method.     

Structure study of light unbound nuclei near drip line

Some experimental techniques and theoretical analysis on unbound nuclei structure study are briefly introduced in this article. The unbound nuclei structure investigation can inspect the reliability of theoretical calculation, and is also important to extend the modern nuclear structure model to exotic nuclear regions. With the recent development of radioactive Ion Beam (RIB) facility and some new experimental methods, the structure of unbound nuclei near drip line can be studied in experiment.     

原子核高K同质异能态的诱发γ辐射

介绍了原子核高K同质异能态潜在的应用价值及国内外研究的进展。 总结了形成同质异能态的3种主要物理机制。 说明了高K同质异能态的应用原理是将其激发到更高的不稳定的K混合态上, 再发生诱发退激, 形成γ瀑, 释放其存储的能量。 同时又介绍了K混合态的3种主要产生机制。 最后分析了178Hfm2诱发退变的实验, 讨论了这些实验的区别和与角动量投影壳模型计算结果的差异。The nuclear isomer states have great potential value of application. The important experimental and theoretical researches are presented here. There are three kinds of physics mechanism for the formation of the isomer states. The principle of releasing the energy stored in the isomer is to excite it to higher states, K mixing states, which can spontaneously decay to the ground state forming the γ cascade. After introducting the three ways to form the K mixing states, we analyzed experiments on the most prospective isomer 178Hfm2, discussed the key differences between these experiments and suggested that the Projected Shell Model (PSM) can be helpful to confirm the occurrence of the  K mixing states and would work out characteristics of the induced decay.     

TMSR白光中子源本底屏蔽设计

为了满足钍基熔盐堆对核数据的需求，中国科学院上海应用物理研究所自行设计并建造了紧凑型的15 MeV电子加速器驱动的白光中子源。电子直线加速器、中子产生靶以及探测器系统处于同一个实验大厅，中子/伽马射线本底较高，原有屏蔽并不能满足在低能区进行热中子物理实验测量的低中子本底需求。为了降低热中子本底，提高在热区的测量能力，需要对中子源进行局部屏蔽。根据调试运行经验以及模拟计算结果，分析了中子伽马射线本底的来源，利用MCNP5模拟计算了混凝土、铅、含硼聚乙烯对中子/伽马射线的屏蔽效果，优化设计了局部屏蔽方案。模拟计算结果显示，该屏蔽方案可将热中子本底降低三个量级，伽马本底降低两个量级。屏蔽后的实验测量结果表明，探测器处的有效热中子与本底热中子的比值达到约100:1，屏蔽效果显著，为后续在热中子能区顺利开展中子物理测量实验奠定了基础。     

17N破裂反应产物的测量

利用RIBLL提供的丰中子放射性束测量了17N在197Au和9Be靶上的破裂反应.用1?4单元阵列探测器测量得到了前角带电粒子产额和关联粒子对的破裂截面,得到了17N在197Au和9Be靶上的带电粒子破裂截面比为4—5倍,结果表明对重靶核除了核破裂机制外还要考虑库仑破裂的贡献.     

高激发213Fr核的形变研究

对132MeV ¹⁶O+¹⁹⁷Au反应产生的裂变碎片和巨偶极共振γ射线进行了符合测量,得到了E=92MeV的高激发²¹³Fr的γ衰变谱和γ角关联谱.观测到复合核巨偶极共振γ角关联谱存在很大的各向异性.利用改进的统计模型程序分析了实验数据,不考虑裂变延迟时,统计模型计算可以很好拟合地实验结果.通过对γ角关联谱的理论计算与实验结果的比较,可以得出高激发²¹³Fr核(E=92MeV)的形状从集体长椭球向非集体扁椭球变化.     

30MeV/u40Ar+112,124Sn反应中的同位素产额比与核温度

系统研究了30MeV/u ⁴⁰Ar+^112,124Sn反应中的轻粒子同位素产额比随角度和初始激发能的变化关系.对于两个反应体系,均观察到³He/⁴He和⁶Li/⁷Li的产额比随角度的增加而增加,⁶He/⁴He和⁸Li/⁷Li随角度的增加而减小.统计发射的运动学效应不能完全符合实验结果.各种单同位素产额比与靶核的N/Z比有关,表现出同位旋效应,而由双同位素比提取的核温度几乎没有靶核相关性.     

高激发213Fr核的形变研究

对132MeV^16O ^197Au反应产生的断变碎片和巨偶极共振γ射线进行了符合测量,得到了E^*=92MeV的高发^213Fr的γ衰变谱和γ角关联谱,观测到复合核巨偶极共振γ角关联谱存在很大的各向异性,利用改进的统计模型程序分析了实验数据,不考虑裂变延迟时,统计模型计算可以很好拟合地实验结果,通过对γ角关联谱的理论计算与实验结果的比较,可以得出高激发^213Fr核（E^*=92MeV)的形状从长集体长椭球向非集体扁椭球变化。     

17N破裂反应产物的测量

利用RIBLL提供的丰中子放射性束测量了^17N在^197Au和^9Be靶上的破裂反应,用14单元阵列探测器测量得到了前角带电粒子产额和关联粒子对的破裂截面,得到了^17N在^197Au和^9Be靶上的带电粒子破裂截面比为4－5倍,结果表明对重靶核除了核破裂机制外还要考虑库仑破裂的贡献。     

Measurement of 232Th (n,γ) cross section at the CSNS Back-n facility in the unresolved resonance region from 4 keV to 100 keV

The neutron capture cross section of ²³²Th was measured at the neutron time-of-flight facility Back-n of China Spallation Neutron Source (CSNS) for the first time. The measurement was performed with 4 hydrogen-free deuterated benzene C₆D₆ liquid scintillation detectors, in the ES#2 experiment station on the beam line, at a distance of about 76 m from the neutron-production assembly. The total energy detection principle in combination with the pulse height weighting technique (PHWT) was applied to analyze the measured data. Results of the ²³²Th (n,γ) reaction cross section in the unresolved resonance region from 4 keV to 100 keV were obtained, which shows a good agreement with the existing experimental data from EXFOR, as well as with the evaluated data from the ENDF/B-VIII.0 and CENDL-3.1. In addition, the excitation function of ²³²Th (n,γ)²³³Th reaction in the unresolved resonance region was theoretically calculated by using the code TALYS-1.95. By fitting the experimental cross section and theoretical data, the average parameters in the unresolved resonance region were extracted. The datasets are openly available at http://dx.doi.org/10.11922/sciencedb.j00113.00015.