Study of damaging processes induced by direct core-excitations of DNA using electron spectroscopy

辐射诱导DNA损伤过程的研究是辐射生物学的一个重要课题。然而，利用电子能谱在原子水平上解释过程是一个前沿领域。破坏过程大致分为两类；一种是DNA本身的电子跃迁引起的直接破坏过程；另一种是由DNA周围分子（如水）的电跃迁形成的自由基诱导的间接过程。对于直接过程，以下三步过程，即核心激励，俄歇过程和离子解吸（俄歇刺激离子解吸）被认为起重要作用。本研究的目的是利用x射线光电子能谱、离子动能测量和符合光谱学来研究DNA的核心激发、俄歇过程和离子解吸，并阐明DNA直接核心激发引起的化学键断裂过程。我们测量了在金表面自组装DNA硫醇的光电子-光离子符合谱和俄格-光电子符合谱。然而，除了c - kvv - auger - c -1s光电子符合谱外，大部分符合信号都被偶然符合信号所掩盖。由于发现现有符合谱仪的信号/偶然比不够充分，我们研制了一种改进的符合谱仪。我们改进了PF713L11D光电子能谱仪。

Study of radiation-induced damaging processes of DNA is an important topic in radiation biology. The elucidation of the processes in atomic levels using electron spectroscopy, however, is a frontier field. The damaging processes are -roughly classified into two categories; one is the direct damaging processes induced by the electronic transitions of DNA itself; and the other is indirect processes induced by radicals formed by electric transitions of molecules surrounding DNA such as water. For the direct processes, the following three-step process, i. e., core-excitations, Auger processes, and ion desorption (Auger-stimulated ion desorption) is thought to play an important role. The aim of the present study is to investigate core-excitations, Auger processes, and ion desorption of DNA using X-ray photoelectron spectroscopy, ion kinetic energy measurements, and coincidence spectroscopy, and to clarify the processes of chemical bond breaking induced by direct core-excitations of DNA.We measured photoelectron photoion coincidence spectra and Auger-photoelectron coincidence spectra of DNA thiol self-assembled on gold surfaces. However most of the coincidence signals were smeared out by the accidental coincidence signals except for C-KVV-Auger-C-1s-photoelectron coincidence spectra. Since the signal/accidental ratio of the present coincidence spectrometer was found to be not sufficient enough, we have developed an improved apparatus for coincidence spectroscopy. We have improved an apparatus for the photoelectron spectroscopy at PF713L11D.