An electron-attachment-type negative C₆₀ ion source was developed to intensify the incident negative ion beam current to a tandem accelerator. In this ion source, negative ions are produced by the attachment of low-energy electrons to the sublimated C₆₀. An ion source with a filament and an oven was constructed, and a negative C₆₀ ion beam current of 600 nA was extracted.

We developed novel methods for producing negative C₆₀ ion beams at the accelerator facility Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) to increase the current intensity of swift C₆₀ ion beams accelerated to the MeV energy region using a tandem accelerator. We produced negative C₆₀ ion beams with an intensity of 1.3 µA, which is several tens of thousands of times greater than the intensity of beams produced using conventional methods based on the Cs sputtering process. These beams were obtained by temporarily adding an ionization function based on electron attachment to an existing ion source that is widely used in tandem accelerators. The high-intensity swift C₆₀ ion beams can be made available relatively easily to institutes that have tandem accelerators and ion sources of the type used at TIARA because there is no need to change existing ion sources or install new ones.

Quartz (SiO₂) crystals possess intrinsic columnar pores perpendicular to (0001) surfaces, consisting of three- and six-membered ring (3MR and 6MR) structures of Si and O atoms. The diameters of the larger pores, i.e., 6 MRs, are ~0.49 nm, while the diameters of fullerene (C₆₀) ions are 0.7 nm, i.e., larger than either type of the pores. Transmission electron microscopy observation evidenced approximately two times longer ion tracks in the channeling condition, i.e., 0° incidence to (0001) surface, than an off-channeling condition, i.e., 7° incidence in this case, under 6 MeV C₆₀ ion injection. The track length at the 0° incidence decreases more steeply than that at the 7° incidence with decreasing the energy from 6 MeV to 1 MeV. Finally, the track lengths at the 0° and 7° incidences become comparable, i.e., the channeling-like effect disappears at 1 MeV irradiation. This study experimentally indicates that the channeling-like effect of C₆₀ ions is induced in quartz crystals, while the sizes of the channels are smaller than the C₆₀ ions.

It is known that swift heavy ion (SHI) irradiation induces the shape elongation of metal nanoparticles (NPs) embedded in transparent insulators, which results in anisotropic optical absorption. Here, we report another type of the optical anisotropy induced in CaF₂ crystals without including intentionally embedded metal NPs. The CaF₂ samples were irradiated with 200 MeV Xe¹⁴⁺ ions with an incident angle of 45° from the surface normal. With the increasing fluence, an absorption band at ~550 nm, which is ascribed to Ca aggregates, increases both the intensity and the anisotropy. XTEM observation clarified the formation of the continuous line structures and the discontinuous NP chains parallel to the SHI beam. Numerical simulations of the optical absorption spectra suggested the NP chains but not the continuous line structures as the origin of the anisotropy. The optical anisotropy in CaF₂ irradiated with SHIs is different from the shape elongation of NPs.

Sputtering yields of Si have been measured for C₆₀ ions in the energy range from 10 to 540 keV, where the nuclear stopping is dominant, by measuring thickness change of a pre-amorphized layer with conventional Rutherford-backscattering spectroscopy. The measured sputtering yield shows the maximum, which is approximately 600 Si/C₆₀, around 100 keV. Comparing with the sputtering yields for a monatomic ion calculated both based on the linear-collision-cascade theory of Sigmund and using the SRIM2008 code, nonlinear effect on the sputtering yield has been observed. The nonlinear effect depends on the energy of C₆₀ ions: it is very large around the energies where the sputtering yield has the maximum and hardly observed at 10 keV.

We have developed a system that can irradiate the same position on a target with two laser beams from two laser heads at various specified time intervals in order to generate a double-pulse plasma with a controlled interpulse delay. The horizontally polarized component of one laser beam and the vertically polarized component of the other are collinearly merged using a dielectric polarizer. The direction of polarization of each laser beam is adjusted by means of the rotation angle of a half-wave plate placed after the exit from each laser head. The interpulse delay between the two laser beams is controlled by supplying trigger pulses to drive the flash lamp and the Pockels cell of each laser oscillator. By adjusting the timings of the trigger and the rotation angles of the half-wave plates, the energy and pulse width of each laser beam was adjusted to be the same. Plasma-generation experiments showed that, by controlling the interpulse delay between two laser beams having same energy and pulse width, the system can control the time intervals between the generations of two nearly identical plasma pulses, and the second plasma pulse became unstable from shot to shot in short interpulse delay.