标题： 巨偶极子共振光致裂变和光中子反应在$^{238}$U 和$^{232}$Th 中 显示英文标题

标题： Giant Dipole Resonance photofission and photoneutron reactions in $^{238}$U and $^{232}$Th

摘要： 新测量了在巨偶极子共振（GDR）能区的光裂变和光中子反应，针对$^{238}$U 和$^{232}$Th，在新型SUBARU同步辐射设施的激光康普顿散射$\gamma$-射线源上使用高平坦效率的慢化$^3$He 检测阵列。 利用专门的能量依赖、多次触发统计处理方法对高多重性裂变中子符合事件进行了中子多重性排序。 通过考虑由激发裂变碎片顺序中子蒸发理论预测的瞬发裂变中子（PFN）多重性的高斯分布，区分了光中子$(\gamma,\,in)$与$i$~=~1~--~3 和光裂变$(\gamma,\,F)$反应。 我们报告实验得到的$(\gamma,\,n)$、$(\gamma,\,2n)$、$(\gamma,\,3n)$和$(\gamma,\,F)$截面，PFNs 的平均能量和$(\gamma,\,in)$光子中子的平均能量，以及每次裂变事件的 PFNs 平均数量和 PFNs 产额分布的宽度。 基于这些原始实验结果并结合合理的假设，我们还提取了第一机会和第二机会裂变的贡献。 新的实验结果与使用 EMPIRE-3.2 Malta 和 TALYS-1.964 代码对现有数据进行的统计模型计算进行了比较，并与在最可能碎片化方法框架下使用洛斯阿拉莫斯模型获得的瞬发裂变发射计算结果进行了比较，包括有无顺序发射的情况。 显示英文摘要

摘要： New measurements of photofission and photoneutron reactions on $^{238}$U and $^{232}$Th in the Giant Dipole Resonance (GDR) energy region have been performed at the laser Compton-scattering $\gamma$-ray source of the NewSUBARU synchrotron radiation facility using a high-and-flat efficiency moderated $^3$He detection array. The neutron-multiplicity sorting of high-multiplicity fission neutron coincidence events has been performed using a dedicated energy dependent, multiple firing statistical treatment. The photoneutron $(\gamma,\,in)$ with $i$~=~1~--~3 and photofission $(\gamma,\,F)$ reactions have been discriminated by considering a Gaussian distribution of prompt-fission-neutron (PFN) multiplicities predicted by the theory of evaporation in sequential neutron emission from excited fission fragments. We report experimental $(\gamma,\,n)$, $(\gamma,\,2n)$, $(\gamma,\,3n)$ and $(\gamma,\,F)$ cross sections, average energies of PFNs and of $(\gamma,\,in)$ photoneutrons, as well as the mean number of PFNs per fission act and the width of the PFNs multiplicity distribution. Based on these primary experimental results and combined with reasonable assumptions, we extract also the first- and second-chance fission contributions. The new experimental results are compared with statistical-model calculations performed with the EMPIRE-3.2 Malta and TALYS-1.964 codes on the present data and with prompt fission emission calculations obtained with the Los Alamos model in the frame of the most probable fragmentation approach with and without sequential emission.