Development of neutron in-beam Mossbauer spectroscopy

到目前为止，已经报道了许多关于核转变的化学效应的研究，即热原子化学，简称HAC。由于核反冲，热原子处于高激发态。弄清楚核事件发生后固体中立即发生的事情是固相HAC的一个研究目标。然而，人们预计，在溶解和化学分析过程中，在常规固相HAc中测量的放化产物在固体中的分布将受到严重影响。通过发射穆斯堡尔谱，我们可以非破坏性地获得与穆斯堡尔跃迁核衰变有关的化学效应的信息。如果通过核反应测量源系统的发射穆斯堡尔谱，即在束内穆斯堡尔谱工作中，核反应和随后迅速衰变到穆斯堡尔水平的组合的化学效应应该出现在谱中。The co…核反应比穆斯堡尔衰变对HAC效应的贡献要大得多，因为它们的反冲能量。在本项目中，我们对硫化铁等铁化合物进行了中子束内穆斯堡尔谱研究，使我们能够以100 ns的时间尺度非破坏性地获得信息，这比传统的HAC技术要短得多。我们的研究关注和感兴趣的是与^&lt；56&gt；Fe(n，γ)^&lt；57&gt；Fe反应有关的化学效应，如作为热原子效应的化学键断裂和铁氧化态的变化。我们研究的另一个重要目的是在中子装置上建立在束穆斯堡尔谱，通过它我们展示了关于固体中中子诱导热原子的化学行为的实验结果。穆斯堡尔谱测量是在日本原子能研究所JRR-3M反应堆中子束大厅的瞬发γ-射线分析装置上用平行板雪崩计数器进行的。在本工作中制作并改进了PPAC。黄铁矿的在束发射穆斯堡尔谱显示两个双峰。黄铁矿对应的一个组分占总峰面积的1/3，另一个主要组分暂定为黄铁矿间隙部位的Fe~(2+)~(3+)~(2+)。白铁矿的发射光谱也由两个双峰组成：一个对应于白铁矿，另一个双峰。在束内穆斯堡尔谱显示，在两种二硫化铁中，中子俘获反应后的级联γ射线发射迅速产生了一个新的物种，与原始的靶化合物不同。较少

A number of researches have been so far reported on the chemical effects of nuclear transformations, i.e., hot-atom chemistry abbreviated by HAC. Hot atoms are in highly excited states because of nuclear recoil. It is a research goal of solid-phase HAC to make clear as to what happens in solid immediately after the nuclear event. However, it has been expected that the distribution of radiochemical products measured in conventional solid-phaseHAC should be seriously affected in solid during dissolution and chemical analysis. By emission Mossbauer spectroscopy we could obtain information non-destructively on the chemical effects associated with a nuclear decay of Mossbauer transition. If the emission Mossbauer spectrum is measured for the source system fed through a nuclear reaction, that is, in an in-beam Mossbauer spectroscopic work, the chemical effects of the combination of the nuclear reaction and the subsequent prompt decays to Mossbauerr level should appear in the spectrum. The co … More ntribution to HAC effects is assumed to be much greater from the nuclear reaction than from the following Mossbauer decay because of their recoil energies.In the present project, we did the neutron in-beam ^<57>Fe Mossbauer spectroscopic investigations for iron compounds such as iron sulfide, allowing us to obtain non-destructively the information with the time scale of 100 ns, which much shorter than that in the conventional HAC techniques. Our research attention and interest were paid to the chemical effects associated with the ^<56>Fe(n, γ)^<57>Fe reaction, such as chemical-bond rupture and change of iron oxidation-state as the hot-atom effects. Another important aim of our study was to establish the in-beam Mossbauer spectroscopy in neutron facilities, by which we present the experimental results on the chemical behaviors of neutron-induced hot-atoms in solid. Mossbauer measurements were carried out using a parallel plate avalanche counter (PPAC) at the prompt γ-ray analysis setup at the neutron beam hall of the JRR-3M reactor of Japan Atomic Energy Research Institute. The PPACs were fabricated and improved in the present work. The in-beam emission Mossbauer spectrum of pyrite showed two doublets. One component corresponding to pyrite occupied 1/3 of the total peak area, and the other major component was tentatively assumed as Fe^<3+> at the interstitial site of pyrite. The emission spectrum of marcasite was also composed of two doublets : one corresponding to marcasite, and the other doublet. In both iron disulfides, it was revealed that recoil of the cascade γ-ray emission promptly after the neutron capture reaction produced one new species distinguishable from the original target compound by in-beam ^<57>Fe Mossbauer spectroscopy. Less