Abstract
Cluster ion beams have unique features in energy deposition, but their biological effects are yet to be examined. In this study, we employed bacterial spores as a model organism, established an irradiation method, and examined the lethal effect of 2 MeV C, 4 MeV C2, and 6 MeV C3 ion beams. The lethal effect per particle (per number of molecular ions) was not significantly different between cluster and monomer ion beams. The relative biological effectiveness and inactivation cross section as a function of linear energy transfer (LET) suggested that the single atoms of 2 MeV C deposited enough energy to kill the spores, and, therefore, there was no significant difference between the cluster and monomer ion beams in the cell killing effect under this experimental condition. We also considered the behavior of the atoms of cluster ions in the spores after the dissociation of cluster ions into monomer ions by losing bonding electrons through inelastic collisions with atoms on the surface. To the best of our knowledge, this is the first report to provide a basis for examining the biological effect of cluster ions.
Highlights
Cluster ion beams are composed of accelerated molecular ion particles consisting of more than two atoms
We compared the lethal effect of 6 MeV C3, 4 MeV C2, and 2 MeV C as a combination of cluster and monomer ion beams having the same energy per atom (2 MeV/atom)
We considered the internuclear distance after the dissociation of cluster ions into monomer ions on the sample surface
Summary
Cluster ion beams are composed of accelerated molecular ion particles consisting of more than two atoms. The nonlinear effects of swift cluster ion beams, for instance, the nonlinear increase of secondary particle emission arising from a very high energy density deposited at the surface of the target, have been of interest in the area of beams interacting with matter [1,2]. Studies on the nonlinear cluster effect in inorganic materials [6], interaction with solids [7,8], and surface analytical techniques have been carried out [9], and recently, the very efficient negative fullerene ion source was successfully developed [10]. At present, the irradiation target of cluster ions has been confined to very thin materials that can be installed in a vacuum chamber
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