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Helium plasma irradiation to various metals leads to peculiar morphology changes as forming fiberform nanostructures called fuzz when a certain set of conditions is satisfied. In this Tutorial, we overview experimental observations about the fuzz growth process, conditions, growth rate, etc. on tungsten (W), and fuzz growth observed on other various metals. The fuzz growth mechanism, open questions about fuzz growth, and current understandings on these issues are discussed based on simulation and theoretical works. Several applications (gas sensors and photocatalytic application) with fuzz are shown. We hope that this Tutorial will help new researchers in this field to perform experiments and simulations to reveal new perspectives of fuzz. [ABSTRACT FROM AUTHOR]

Simple Summary: X-ray microbeams are useful tools for elucidating the mechanisms underlying non-target effects, such as the radiation-induced bystander response (RIBR) that occurs under heterogeneous exposure conditions. The microbeam X-ray cell irradiation system at the Central Research Institute of Electric Power Industry (Tokyo, Japan) has been upgraded to enable irradiation with titanium characteristic X-rays (TiK X-rays), which have a longer penetration distance than aluminum characteristic X-rays. The beam size of the TiK X-rays was elliptical, with a long diameter of 7.5 μm and a short diameter of 6.9 μm. The dose rate at the sample position was approximately 0.8 Gy/min. Using this system, we irradiated the nuclei of HeLa cells with high precision and then analyzed RIBR. The percentage of bystander cells with pan-nuclear induction of phosphorylated histone H2AX on serine 139 (γ-H2AX) was significantly increased in one field of view, including microbeam-irradiated cells 180 and 360 min after TiK X-ray microbeam irradiation. Radiation-induced bystander response (RIBR) is a response induced in non-irradiated cells that receive bystander signals from directly irradiated cells. X-ray microbeams are useful tools for elucidating the mechanisms underlying RIBR. However, previous X-ray microbeams used low-energy soft X-rays with higher biological effects, such as aluminum characteristic X-rays, and the difference from conventional X-rays and γ-rays has often been discussed. The microbeam X-ray cell irradiation system at the Central Research Institute of Electric Power Industry has been upgraded to generate higher energy titanium characteristic X-rays (TiK X-rays), which have a longer penetration distance sufficient to irradiate 3D cultured tissues. Using this system, we irradiated the nuclei of HeLa cells with high precision and found that the pan-nuclear induction of phosphorylated histone H2AX on serine 139 (γ-H2AX) in the non-irradiated cells increased 180 and 360 min after irradiation. We established a new method to quantitatively evaluate bystander cells, using the fluorescence intensity of γ-H2AX as an indicator. The percentage of bystander cells increased significantly to 23.2% ± 3.2% and 29.3% ± 3.5% at 180 and 360 min after irradiation, respectively. Our irradiation system and the obtained results may be useful for studies of cell competition as well as non-targeted effects. [ABSTRACT FROM AUTHOR]

The generation of tungsten fuzzy nanostructure by exposure to helium plasma is one of the important problems for the use of tungsten material as divertor plates in nuclear fusion reactors. In the present paper, the formation mechanisms of the helium bubble and the tungsten fuzzy nanostructure were investigated by using several simulation methods. We proposed the four-step process which is composed of penetration step, diffusion and agglomeration step, helium bubble growth step, and fuzzy nanostructure formation step. As the fourth step, the formation of the tungsten fuzzy nanostructure was successfully reproduced by newly developed hybrid simulation combining between molecular dynamics and Monte-Carlo method. The formation mechanism of tungsten fuzzy nanostructure observed by the hybrid simulation is that concavity and convexity of the surface are enhanced by the bursting of helium bubbles in the region around the concavity. [ABSTRACT FROM AUTHOR]

To estimate the physical dose at the center of spread-out Bragg peaks (SOBP) for various conditions of the irradiation system, a semiempirical approach was applied. The dose at the center of the SOBP depends on the field size because of large-angle scattering particles in the water phantom. For a small field of 5×5 cm2, the dose was reduced to 99.2%, 97.5%, and 96.5% of the dose used for the open field in the case of 290, 350, and 400 MeV/n carbon beams, respectively. Based on the three-Gaussian form of the lateral dose distributions of the carbon pencil beam, which has previously been shown to be effective for describing scattered carbon beams, we reconstructed the dose distributions of the SOBP beam. The reconstructed lateral dose distribution reproduced the measured lateral dose distributions very well. The field-size dependencies calculated using the reconstructed lateral dose distribution of the therapeutic carbon beam agreed with the measured dose dependency very well. The reconstructed beam was also used for irregularly shaped fields. The resultant dose distribution agreed with the measured dose distribution. The reconstructed beams were found to be applicable to the treatment-planning system. [ABSTRACT FROM AUTHOR]

In carbon therapy, doses at center of spread-out Bragg peaks depend on field size. For a small field of 5×5 cm2, the central dose reduces to 96% of the central dose for the open field in case of 400 MeV/n carbon beam. Assuming the broad beam injected to the water phantom is made up of many pencil beams, the transverse dose distribution can be reconstructed by summing the dose distribution of the pencil beams. We estimated dose profiles of this pencil beam through measurements of dose distributions of broad uniform beams blocked half of the irradiation fields. The dose at a distance of a few cm from the edge of the irradiation field reaches up to a few percent of the central dose. From radiation quality measurements of this penumbra, the large-angle scattered particles were found to be secondary fragments which have lower LET than primary carbon beams. Carbon ions break up in beam modifying devices or in water phantom through nuclear interaction with target nuclei. The angular distributions of these fragmented nuclei are much broader than those of primary carbon particles. The transverse dose distribution of the pencil beam can be approximated by a function of the three-Gaussian form. For a simplest case of mono-energetic beam, contributions of the Gaussian components which have large mean deviations become larger as the depth in the water phantom increases. [ABSTRACT FROM AUTHOR]

Abstract: To evaluate the contribution of indirect action mediated by OH radicals in biological effects of high LET radiations, we examined the production of 8-hydroxy-2′-deoxyguanosine (8-OHdG) in 2′-deoxyguanosine aqueous solution using various ion species with an LET range from 20 to 300keV/μm. The 8-OHdG yield decreased with increasing LET. In the hypoxic irradiation condition, the yield showed constant or rather increasing tendency above about 100keV/μm, which is consistent with an oxygen-in-the-track hypothesis to explain the diminishment of oxygen effect. [Copyright &y& Elsevier]

Abstract: The contribution of OH radical-mediated indirect action by particle beams under hypoxic irradiation condition was investigated by using a radical scavenger. V79 cells were irradiated with 150MeV/nucleon helium ions at an LET of 2.2keV/μm in the presence or absence of DMSO, and their colony survivals were determined. The contribution of indirect action to cell killing under hypoxic condition was estimated to be 52±9%. We conclude that OH radical-mediated indirect action still has a half in total contribution on cell killing under hypoxic condition. [Copyright &y& Elsevier]