Development of an irradiation system of monochromatic photons (50-1000 eV) for wet biological samples

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All ionizing radiations dissipate energy mainly to the kinetic energy of low-energy secondary electrons. Since the ionizations and excitations produced by these electrons are believed to induce most biological effects, studies using low-energy electrons are indispensable for a fundamental elucidation of the mechanism of radiation biological effects. However, the irradiation of low-energy electrons on living biological samples is practically impossible because of extreme technical difficulties. Instead of the direct irradiation of low-energy electrons, which are very strongly absorbed by all materials, low-energy electrons produced in samples by monochromatic low-energy photons through the photoelectric effect can be used as a source of low-energy electrons. We thus made a special system for the irradiation of low-energy photons from 250 to 1000 eV,and installed it at BL-12A (Photon Factory) through a differential pumping system. The system consists of a He path, an irradiation chamber, an XZ stage for scanning irradiation and a gas-handling system. We had one-week of machine time in both 1995 and 1996. We measured the basic performances of the system, and carried out two trial experiments for the irradiation of mammalian cells. We have thus obtained basic information concerning the system and know how to handle sufficiently to perform experiments in the next step.