RIKEN Accel. Prog. Rep. 48 (2015)

Ⅲ-4. Radiation Chemistry & Biology

Estimation method of microbeam divergence from glass capillaries forbiological use
R.J. Bereczky,＊1 T. Ikeda,＊1 T. Kobayashi,＊2 M. Utsugi,＊3,＊1 T. Hirano,＊4,＊1 Y. Sakai,＊3 and T. Abe＊1Ion microbeams can be used in various fields such as basic
research, or for many different technical applications suchas in radiobiology. When an ion beam with energy on theorder of megaelectron volts is transmitted through a tapered
glass microcapillary, the extracted beam can be used as aion microbeam for cell irradiation. Moreover, the ions canbe directly guided to the cell using a capillary with athin-end window. At RIKEN, we have developed a unique
technology for mutation breeding using high-energy
heavy-ion beams. Heavy-ion beams at relatively low doses
induce mutations at a high rate without severely inhibiting
growth. Densely ionizing radiation produces clusters ofDNA damage that cannot be repaired by the cell, leading tocell death, or can only be repaired incompletely by the cell,which induces mutations. The effects of heavy-ion beams
on both the lethality and effectiveness of mutation induction
should be investigated in more detail in future studies. Anion microbeam is a useful tool for DNA damage or repair
process research. The regions relevant to mutations in aliving cell are not distributed uniformly, but concentrated
into a small region. A well-defined microbeam is required toirradiate these small regions.
The purpose of our work is the development of
microbeam irradiation for human cells, in which it is easy toobserve DNA damages. Through these investigations, we
provide an estimation method to define the beam
divergence in a tapered glass capillary. Our studies havebeen performed both experimentally and theoretically. In
the case of thinner capillaries, i.e., on the order of 1 micron,the divergence of the transmitted beam has been
investigated, and similar experiments with a 200 μm
diameter capillary without a thin end-window were also
reported1). No study has yet reported on capillaries withoutlet diameters in the 10 μm range and with thin
end-windows, a size at which the application for cellirradiation is not obvious anymore.
The result of our first SRIM simulations2) showeddiscrepancy from the experimental ones (see procedurebelow). When we changed the divergence of the beam
inside the capillary from 0 to a nonzero value, i.e, 2.5°, theresults of the simulation and the experiment were in good
agreement (Fig. 1).
We measured the beam distribution extracted in air as afunction of the distance between the exit of the capillary
and a piece of CR-39, using He ions with the energy of 4.5
MeV produced by the RIKEN pelletron accelerator.
RIKEN Nishina Center
Atomic Physics Laboratory, RIKEN＊3
Toho University, Department of Physics＊4University of Miyazaki, Faculty of Agriculture＊1＊2

The ions were transmitted through a tapered glass capillary(pulled from injection needle), set at the end of the beamline.
The inlet diameter of the capillary was 800 μm, the outlet
diameter was 4 μm, and it had a thin end-window made ofplastic with a thickness of 8 μm3). The length of thecapillary was ~ 65 mm. The profile of the extracted beam
was measured with CR-39 (Fig. 2). The average rate of theions was 14 counts/s during the measurement. To avoid theoverlap of the ion tracks on the CR-39 surface, the numberof transmitted ions was chosen once as 200, and as 600 in
the other cases.
Further systematic studies will be performed in the near
future that will contribute to the development of microbeam
irradiation of human cells.

Fig.1. Comparison of the beam profile of the experiments(black) and SRIM simulations (orange). The horizontal
axis shows the distance of the ion tracks from the center ofthe beam. The values of the beam divergence inside thecapillary are shown in each figures. The distance between
the exit of the capillary and the CR-39 was 6 mm.

Fig.2. Profile of the extracted beam, when the distance
between the exit of the capillary and the CR-39 was 2 mm.
The scale corresponds to 50 μm.
References
1) N. Fujita et al.: NIMB 315, 332-335 (2013).
2) SRIM-2013: http://www.srim.org/.
3) Y. Iwai et al.: Appl. Phys. Lett. 92, 023509 (2008).

- 316 -

完全版2014_本文.indd 316

15/10/16 18:11