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阐明这些过程是一个前沿领域。损伤过程大致分为两类：一类是由DNA本身的电子跃迁引起的直接损伤过程;另一类是由DNA周围分子（如水）的电子跃迁形成的自由基引起的间接损伤过程。对于直接法，可采用以下三步法，即：例如，核心激发，俄歇过程，和离子解吸（俄歇刺激离子解吸）被认为发挥了重要作用。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谱研究DNA的核激发、俄歇过程和离子脱附，并阐明直接核激发引起的DNA化学键断裂过程，我们测量了DNA巯基在金表面自组装的光电子-光离子符合谱和俄歇-光电子符合谱.但除C-KVV-Auger-C-1 s-光电子符合谱外，大部分符合谱都被偶然符合谱所掩盖。针对现有符合谱仪的信偶比不足的问题，研制了一种改进的符合谱仪。我们改进了PF 713 L11 D型光电子能谱仪。

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.