Kazuya Itoh

The Major DNA Repair Pathway after Both Proton and Carbon-Ion Radiation is NHEJ, but the HR Pathway is More Relevant in Carbon Ions

The purpose of this study was to identify the roles of non-homologous end-joining (NHEJ) or homologous recombination (HR) pathways in repairing DNA double-strand breaks (DSBs) induced by exposure to high-energy protons and carbon ions (C ions) versus gamma rays in Chinese hamster cells. Two Chinese hamster cell lines, ovary AA8 and lung fibroblast V79, as well as various mutant sublines lacking DNA-PKcs (V3), X-ray repair cross-complementing protein-4 [XRCC4 (XR1), XRCC3 (irs1SF) and XRCC2 (irs1)] were exposed to gamma rays (137Cs), protons (200 MeV; 2.2 keV/μm) and C ions (290 MeV; 50 keV/μm). V3 and XR1 cells lack the NHEJ pathway, whereas irs1 and irs1SF cells lack the HR pathway. After each exposure, survival was measured using a clonogenic survival assay, in situ DSB induction was evaluated by immunocytochemical analysis of histone H2AX phosphorylation at serine 139 (γ-H2AX foci) and chromosome aberrations were examined using solid staining. The findings from this study showed that clonogenic survival clearly depended on the NHEJ and HR pathway statuses, and that the DNA-PKcs–/– cells (V3) were the most sensitive to all radiation types. While protons and γ rays yielded almost the same biological effects, C-ion exposure greatly enhanced the sensitivity of wild-type and HR-deficient cells. However, no significant enhancement of sensitivity in cell killing was seen after C-ion irradiation of NHEJ deficient cells. Decreases in the number of γ-H2AX foci after irradiation occurred more slowly in the NHEJ deficient cells. In particular, V3 cells had the highest number of residual γ-H2AX foci at 24 h after C-ion irradiation. Chromosomal aberrations were significantly higher in both the NHEJ- and HR-deficient cell lines than in wild-type cell lines in response to all radiation types. Protons and gamma rays induced the same aberration levels in each cell line, whereas C ions introduced higher but not significantly different aberration levels. Our results suggest that the NHEJ pathway plays an important role in repairing DSBs induced by both clinical proton and C-ion beams. Furthermore, in C ions the HR pathway appears to be involved in the repair of DSBs to a greater extent compared to gamma rays and protons.

Three dimensional constricted electric current near anode and cathode of Faraday MHD generator

The three dimensional phenomena in the weakly ionized plasma near an anode and a cathode of a Faraday type MHD generator are studied by time dependent three dimensional numerical analyses, where the radiation is taken into account. The Navier–Stokes equations are solved with an implicit total variation diminishing scheme with the radiative heat transfer solved by a finite volume method, while the Maxwell equations are solved by using the Galerkin finite element method. The following results are obtained. In the case of the short circuit load (I=160 A), the strong Hall effect induces a strong electrical current concentration at the upstream edge of the anode and the downstream edge of the cathode, resulting in high temperature and high conductivity there. The Lorentz force acting at the spot of electrical current concentration may induce inter-anode breakdown, although the present generator does not suffer from inter-anode breakdown. The Lorentz force working at the electrical current concentration at the cathode, on the other hand, brings the concentration current downstream, resulting in strong inter-cathode breakdown. The radiative heat transfer becomes very high locally, resulting in 700 MW/m3, but the effect can be neglected on the overall generator performance because the plasma is very dense.

A Model for the Reaction at Intermediate Energies

Polarization correlation coefficients have been measured atRIKEN for the \vec 3He(\vec d,p)4He reaction at intermediate energies. We propose a model for the (\vec d, p) reaction mechanism using the pd elastic scattering amplitude which is rigorously determined by a Faddeev calculation and using modern NN forces. Our theoretical predictions for deuteron polarization observables A_y, A_{yy}, A_{xx} and A_{xz} at E_d=140, 200 and 270 MeV agree qualitatively in shape with the experimental data for the reaction 3He(\vec d,p)4He.

Beam-line polarimeter for intermediate-energy deuteron

We have developed a beam-line polarimeter for intermediate energy deuterons at RIKEN Acclearator Research Facility. The d+p elastic scattering is used as polarimetry. Recently, calibration measurement has been carried out at Ed=140 and 200 MeV. The values of Ay(Ayy) are −0.519±0.005 (0.541±0.005) and −0.332±0.005 (0.306±0.006) at 140 MeV and 200 MeV, respectively.

Deuteron polarimeter DPOL and calibration of the system

We have calibrated the effective analyzing powers of the deuteron polarimeter, DPOL, in the deuteron energy region of 210<Ed<270 MeV. The calibration was needed to analyze the polarization transfer measurement for the 12C(d,d′) reaction at 270 MeV whose aim is to search for Double Gamow-Teller resonances in 12C in an excitation energy region of Ex<60 MeV.

Role of deuteron internal variables in the 3He(d,p)4He reaction

Polarization observables for the 3He(d,p)4He reaction have been measured at Ed=140, 200, and 270 MeV. This work aims to investigate the high momentum component of deuteron D-state wave function and the mechanism for the one-nucleon transfer reaction at intermediate energies. Data are compared with impulse approximation calculation based on the three-nucleon scattering amplitudes.

Systematic study of spin-isospin excitations in neutron rich light nuclei via the (d, 2He) reaction at 270 MeV

In order to study the nature of the neutron excess, the Gamow-Teller and spin-isospin dipole transitions have been measured by the (d, 2He) reaction for 6Li, 9Be, and 11B targets at Ed=270 MeV. The experimental B(GT) value is deduced from the measured cross section. In spite of B(SFD), the sum of the measured cross section at θc.m.=4° is compared. In the 11Be nucleus, the effect of the halo due to the large radial component of the halo wave function is observed.