Fig. 6-1 Schematic drawing of single ion hit system The following three elemental techniques were essential to be required for sharp-shooting by a single ion. (1) Micro beam focusing: An incident beam depressing divergent is shaped finely by a beam slit, and then is focused by a precision magnetic lens (2) Beam positioning: Ion hitting sites are decided by using a X-Y beam scanner and a precision sample stage (3) Single ion hitting: Irradiation is "On" at the electrostatic beam deflecting plate which acts as a high speed beam switch and "Off" by the signal of the secondary electron emitted from irradiated sample

Fig. 6-2 An example of computer-assisted single ion hit pattern The left figure is the pattern, "Takasaki special product DARUMA," inputted into a computer. Based on this pattern, 15 MeV Ni ions were irradiated one by one on CR-39 film detected ion trajectories in solid. The right figure is an optical microscopic image of "DARUMA" developed by etching. This image is constructed of the points made by every hit of a Ni ion (etch-pit).

In the advanced science and technology fields, by using a method of governing one atom or one molecule, a new material is created and a function of material is analyzed. As the size of the memory cells in the newest semiconductor devices are so small (typically around 0.5 x 0.5 micrometer2 ), the memory and the micro-processor devices can easily make an error through only one hit of a heavy, energetic charged particle (heavy ion) when they are mounted on an artificial satellite in the space environment. Since DNA of organisms mutates as the result of a slight alteration of the molecular configuration, the heredity information in the DNA of a biological cell is also hugely affected by the result of one heavy ion hitting. In order to clarify the mechanism of these phenomena in an extremely small area and then develop a positive application (for instance, in cell-processing technology), we have developed in JAERI a system which allows a single heavy ion to sharp-shoot a specific site within an accuracy of 1 micrometer. Development of the following techniques was required to realize this system, i.e., focusing heavy ion beam to 1 micrometer in diameter, beam positioning to a specific site of the sample and a single ion hit to extract just one ion from the ions (Fig. 6-1). Among them development of the single hit technique was the most difficult. For sharp-shooting to multi specific sites for every single ion successively within a short period, an advanced system has been developed, in which the ions are aimed along the hit pattern inputted into a computer and injected at the target automatically.

Reference T. Kamiya et al., An Automated Single Ion Hit at JAERI Heavy Ion Microbeam to Observe Individual Radiation Damage, Nucl. Instrum. Methods, Phys. Res. B, 158, 255 (1999).

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