Energy deposition method for micro-volume in liquid using a tapered glass capillary with a thin end-window

Research and development of ion irradiation of living micro-volume materials, such as cells and cell organelles, has been in progress at RIKEN. Using a tapered glass capillary with an inner diameter of about 1 um at the outlet, we have already succeeded to focus ion beams down to the size of its outlet inner diameter. Recently, we have also developed a thin glass end-window for this type of tapered glass capillary. Inserting this capillary into a liquid target, focused ion irradiation of the target while keeping the beam line under high vacuum has been realized. The volume of the energy deposition region is controllable in three dimensions with about 1 um resolution by adjusting the beam energy and the thickness of the end-window. In order to verify the size of this energy deposition region, the capillary was inserted into a liquid scintillator and scintillation was observed with a microscope. For example, in the case of 3 MeV alpha rays entering a capillary with a end-window thickness of 7 um and outlet inner diameter of 1.5 um, the observed scintillation volume was 6 um in length and 3 um in diameter, consistent with calculations performed by SRIM-2003. Therefore, using a tapered capillary with a thin end-window, we have succeeded in controlling the size of the energy deposition region down to the same order as a typical biological cell.