Radial transport characteristics of fast ions due to energetic-particle modes inside the last closed-flux surface in the compact helical system

The internal behavior of fast ions interacting with magnetohydrodynamic bursts excited by energetic ions has been experimentally investigated in the compact helical system. The resonant convective oscillation of fast ions was identified inside the last closed-flux surface during an energetic-particle mode (EPM) burst. The phase difference between the fast-ion oscillation and the EPM, indicating the coupling strength between them, remains a certain value during the EPM burst and drives an anomalous transport of fast ions.     

One-dimensional atomic and electronic structures of submonolayer potassium deposited on stepped Ni(7 5 5) surface

We deposited 0.01-0.16 ML (monolayer) of potassium on stepped (7 5 5) [=6(1 1 1) × (1 0 0)] surface of nickel in order to fabricate and to understand the growth process of one-dimensional (1D) potassium atomic-chain structure by observing the low-energy-electron-diffraction (LEED) patterns. The LEED patterns from potassium adsorbates exhibit a distinct coverage dependence that 1× streaks first appeared at low coverages up to 0.04 ML and later 2× streaks appeared at around 0.09 ML. The streaks become spotty at the higher coverage. We explained these coverage-dependent changes in LEED patterns in a thorough comparison with kinematically calculated LEED patterns constructing a reasonable growth model.     

Evidence for strong Breit interaction in dielectronic recombination of highly charged heavy ions

Resonant strengths have been measured for dielectronic recombination of Li-like iodine, holmium, and bismuth using an electron beam ion trap. By observing the atomic number dependence of the state-resolved resonant strength, clear experimental evidence has been obtained that the importance of the generalized Breit interaction (GBI) effect on dielectronic recombination increases as the atomic number increases. In particular, it has been shown that the GBI effect is exceptionally strong for the recombination through the resonant state [1s2s(2)2p(1/2)](1).     

Comparison of measured and calculated in-air secondary neutrons in passive carbon-ion radiotherapy

Undesired radiation exposure in normal tissues around a treatment volume in proton and carbon-ion radiotherapies is less than that in the conventional radiotherapies due to physical and/or biological properties of charged particles. Such exposure is always considered in a treatment planning, however, undesired exposure in normal tissues far from the treatment volume cannot be considered in the treatment planning, because it is caused by secondary radiation as well as leakage primary particles. Though this exposure is considerably lower than that near the treatment volume, it may be not negligible to estimate the risk of secondary cancer especially for the young patients. In particular, the assessment of the secondary neutrons that inevitably produced within the patient and beam line devices is very important due to the potency of their biological effect. The distributions of the absorbed dose and the biological effectiveness in phantom/patient are required to assess the risk, and Monte Carlo calculation plays a key role due to a difficulty of the measurements. In this study, comparison of measured and calculated in-air neutrons at the patient position in the Heavy Ion Medical Accelerator in Chiba (HIMAC) treatment room are performed to verify the accuracy of the Monte Carlo code, PHITS. Our calculations underestimated epithermal neutrons measured by Bonner sphere system. This discrepancy may be caused by an insufficiency of the calculational geometry modeling, consequently an underestimation of neutrons scattered and moderated by the beam line devices. However, it is unlikely that the underestimation significantly contribute to the dose estimation in phantom. On the other hand, the calculation reproduced the measured ambient dose equivalents well because they were dominated by neutrons above 0.1 MeV. This result showed that the PHITS code has a potential ability to evaluate the neutron exposure of the patient in passive carbon-ion radiotherapy.