We have measured energy spectra of secondary electrons produced by fast-carbon-cluster $\mathrm{C}_n{}^{+}$ $(n=1–4)$ bombardment of thin carbon foils (3.2, 7.3, 11.9, and $20.3\mu \mathrm{g}∕{\mathrm{cm}}^2$). For clusters of identical velocity, the convoy-electron yield is enhanced with increasing cluster size $n$, while the yield of secondary electrons is reduced. The yield of convoy electrons normalized to the number of injected atoms increases proportionally with cluster size $n$. This proportionality suggests that there is only a weak vicinage effect on the number of primary electrons scattered by the projectile. The vicinage effect observed in low-energy secondary electrons must therefore arise from either transport or transmission through the surface.

We have precisely measured the energy loss of carbon cluster ions Cn+ with a kinetic energy of 0.5 MeV/atom. The measured energies, lost in a thin carbon foil by cluster ions, are lower than that of an atomic ion with the equivalent speed [$\Delta${}E(Cn+)/n<$\Delta${}E(C+)], whereas most existing experimental results show the opposite trend with kinetic energies higher than 2.0 MeV/atom. The experimental values are compared with the calculated ones, which take into account the effect of the Coulomb force, polarization force, and reduction in the cluster average charge on the response of a solid. The agreement between the measured and calculated energy losses indicates that the reduction in the energy loss is due to a structural correlation in electron excitation during the passage of the cluster.

We conducted a retrospective analysis of GRP94 immunohistochemical (IHC) staining, an ER stress protein, on large B-cell lymphoma (LBCL) cells, intracellular p53, and 15 factors involved in the metabolism of the CHOP regimen: AKR1C3 (HO metabolism), CYP3A4 (CHOP metabolism), and HO efflux pumps (MDR1 and MRP1). The study subjects were 42 patients with LBCL at our hospital. The IHC staining used antibodies against the 17 factors. The odds ratios by logistic regression analysis used a dichotomous variable of CR and non-CR/relapse were statistically significant for MDR1, MRP1, and AKR1C3. The overall survival (OS) after R-CHOP was compared by the log-rank test. The four groups showed that Very good (5-year OS, 100%) consisted of four patients who showed negative IHC staining for both GRP94 and CYP3A4. Very poor (1-year OS, 0%) consisted of three patients who showed positive results in IHC for both GRP94 and CYP3A4. The remaining 35 patients comprised two subgroups: Good (5-year OS 60–80%): 15 patients who showed negative staining for both MDR1 and AKR1C3 and Poor (5-year OS, 10–20%): 20 patients who showed positive staining for either MDR, AKR1C3, MRP1, or p53. The Histological Prognostic Index (HPI) (the four groups: Very poor, Poor, Good, and Very good) is a breakthrough method for stratifying patients based on the factors involved in the development of treatment resistance.

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.