Schematic diagram of the HIMAC injector and the MEXP course. Ions are accelerated to by the RFQ linac and to then by the Alvarez linac. The ions were selectively introduced to the MEXP course. The beam intensity was reduced by a solenoid magnet located upstream of the linac and the two mesh attenuators. The beam was defocused by a quadrupole magnet to improve the uniformity of irradiation for the fluence over the area. Just downstream of the SEM, biological samples could be irradiated in vacuum (Ref. 13).
Schematic diagram of a new irradiation system for ions in air near the Bragg peak. Ions with passed through the SEM, a metal foil window, and then went out into the air. The beam monitoring system consisted of a secondary electron monitor (SEM) in vacuum and a flat type ionization chamber (IC) in air. The outputs of the SEM and IC were measured with picoammeters, Keithley 65714A. The Bragg curves were measured by changing the position of the IC moving along the axis of the stage, which was controlled remotely by a PC in the monitoring room. After measurement of the Bragg curve, the IC was replaced with biological samples, and then the samples were irradiated.
Typical Bragg curves measured for five ion species. The vertical axis is the relative ionization yield measured with the IC, the position of which was changed along the axis of the stage, normalized to the output of the SEM, which was proportional to the fluence of ions passing through the SEM. The horizontal axis is depth in air, that is, the distance from the IC to the metal foil window. The datum point of the horizontal axis ( ) was operationally determined, for each experiment, as the downstream position giving the half value of the maximum, the Bragg peak, and the upstream position was defined as being minus.
A typical beam profile of Ar ions measured with a CR-39 track detector. Detectors of were irradiated with Ar ions of , etched for in NaOH at , and then measured with an automatic optical microscope over the central area of area. (a) Typical images of CR-39. (b) The number of etch pits in is shown as a contour graph with a 10 segmented grayscale bar. The beam uniformity (standard deviation∕mean) over the center area of was .
Typical AFM image of area of a CR-39 track detector irradiated with Ar ions and etched in NaOH at for . The black dots are etch pits due to ion traversals; 183 etch pits could be scored.
Fluence as a function of the output of the SEM. The straight lines are regression lines with a zero y-axis intercept. Irradiated fluences to biological samples were calculated using these regression lines.
Example of a survival curve of HeLa cells irradiated with C ions (energy, ; LET, ) at position, which was upstream from the Bragg peak. Since survival fractions () decreased exponentially with the fluences (). The data points were fitted with the equation, , where is a cell inactivation cross section. For this experiment was .
(Color) Typical confocal microscope images of HeLa cells after immunostaining with NBS1 antibody (green), and cell nuclei after counterstaining with propidium iodide (red). (a) Control cell and (b) cell irradiated with C ions and subsequently incubated for at . The irradiated fluence was , which corresponded to 6.2 ions per nucleus, calculated as the product of the fluence and the measured nucleus area, . Bar size, .
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