Positrons and positronium in macromolecules; Consequences of different charge states

Kobayashi, Yoshinori*; Sato, Kiminori*; Yamawaki, Masato*; Michishio, Koji*; Oka, Toshitaka; Washio, Masakazu*

Radiation Physics and Chemistry, 202, p.110590_1 - 110590_6, 2023/01

https://doi.org/10.1016/j.radphyschem.2022.110590

Because of their different charge states, positrons and positronium (Ps) behave quite differently in macromolecules. The behavior of positively charged positrons is strongly influenced by electrostatic interactions. In nonpolar macromolecules such as polyethylene, energetic positrons, if not incorporated into Ps, fall into a delocalized state. These positrons are sensitively trapped by polar groups, if any. On the other hand, charge-neutral Ps is localized in a free volume regardless of the macromolecule's chemical structure. In this study, we discuss the behavior and annihilation characteristics of positrons and Ps in various macromolecules, emphasizing their differences.

Structural analysis of high-energy implanted Ni atoms into Si(100) by X-ray absorption fine structure spectroscopy

Entani, Shiro*; Sato, Shinichiro*; Honda, Mitsunori; Suzuki, Chihiro*; Taguchi, Tomitsugu*; Yamamoto, Shunya*; Oshima, Takeshi*

Radiation Physics and Chemistry, 199, p.110369_1 - 110369_7, 2022/10

https://doi.org/10.1016/j.radphyschem.2022.110369

Ni silicide synthesis by Ni ion beam irradiation into Si attracts attention due to its advantages including the ability of formation of local structures, the controllability of ion beams, the formability of silicide without heat treatment and the high reproducibility of the resulting specimen. In this work, we investigate the local atomic structure of Si implanted with 3.0 MeV Ni ions. Analysis of Ni K-edge fluorescent-yield extended X-ray absorption fine structure reveals that Ni atoms have mixed structure of metallic-like face-centered cubic Ni and NiSi phases at the initial stage of the irradiation and the formation of NiSi promotes significantly with the ion fluence above 10 ions cm. With consideration of the agreement between the ion fluence threshold for the structural transition and the critical Si-amorphization fluence, it is concluded that the amorphization of Si plays an important role in the synthesis of the NiSi phase in Ni-irradiated Si.

Dense radical formation in L-alanine-3,3,3-d3 and L-alanine-d4 by 1.5 keV soft X-ray irradiation

Nakagawa, Seiko*; Oka, Toshitaka; Fujii, Kentaro*; Yokoya, Akinari*

Radiation Physics and Chemistry, 192, p.109884_1 - 109884_5, 2022/03

https://doi.org/10.1016/j.radphyschem.2021.109884

Radicals produced in crystalline L-alanine-3,3,3-d3 and L-alanine-d4 were observed by the electron spin resonance (ESR) technique during 1.5 keV soft X-ray irradiation. The line width of the ESR spectra obtained by the soft X-ray irradiation was 1.5 times wider than that of hard X-rays from a previous report, meaning a higher density of radicals. The efficiency of the radical yield by the soft X-ray irradiation was 10 relative to that by -irradiation. For the soft X-ray irradiation, many radicals will be lost by the efficient radical-radical recombination due to the higher density of the radicals, just as the high-LET irradiation by heavy ions. We concluded that the high LET nature of the lower energy photons leads to the dense radical formation in the crystalline alanine powder.

Performance of in situ gamma-ray spectrometry in the assessment of radioactive cesium deposition around the Fukushima Daiichi Nuclear Power Plant

Ji, Y.-Y.*; Ochi, Kotaro; Hong, S. B.*; Nakama, Shigeo; Sanada, Yukihisa; Mikami, Satoshi

Radiation Physics and Chemistry, 179, p.109205_1 - 109205_11, 2021/02

https://doi.org/10.1016/j.radphyschem.2020.109205

In situ gamma-ray spectrometry using diverse survey platforms has been conducted in contaminated areas with several dose rate levels around the Fukushima Daiichi Nuclear Power Plant (FDNPP). Six survey sites, including two evacuation zones around the FDNPP, were selected for ground-based gamma-ray spectrometry using HPGe (high purity Ge) and LaBr(Ce) detectors to assess the radioactive cesium deposition in the ground. The diverse levels of radioactivity of Cs were then distributed to six survey sites from 30 to 3000 kBq m in the measurement period of October 2018. A method to directly calculate the depth profile using in situ measurement was introduced so as to have representation over a wide area, and the results were successfully compared with those of sample analysis at one point in the site.

X-ray absorption study of platinum nanoparticles on an ion-irradiated carbon support

Kakitani, Kenta*; Kimata, Tetsuya*; Yamaki, Tetsuya*; Yamamoto, Shunya*; Matsumura, Daiju; Taguchi, Tomitsugu*; Terai, Takayuki*

Radiation Physics and Chemistry, 153, p.152 - 155, 2018/12

https://doi.org/10.1016/j.radphyschem.2018.09.017

Identification of penetration path and deposition distribution of radionuclides in houses by experiments and numerical model

Hirouchi, Jun; Takahara, Shogo; Iijima, Masashi; Watanabe, Masatoshi; Munakata, Masahiro

Radiation Physics and Chemistry, 140, p.127 - 131, 2017/11

BB2016-0282.pdf:0.39MB

https://doi.org/10.1016/j.radphyschem.2017.02.005

Evaluation of annealing and double ion beam irradiation by a laser-induced and laser-detected surface acoustic wave diagnostic system

Kitazawa, Sin-iti*; Wakai, Eiichi; Aoto, Kazumi

Radiation Physics and Chemistry, 127, p.264 - 268, 2016/10

https://doi.org/10.1016/j.radphyschem.2016.07.009

The effects of annealing and double ion irradiation on nuclear structural materials were investigated using a novel, non-destructive, non-contact diagnostic method. A laser-induced and laser-detected surface acoustic wave (SAW) was adopted as a diagnostic system. The SAWs propagation velocity and the SAWs vibration velocity along the normal direction of the surface were measured to investigate mechanical properties of the substrates. Change of the shear modulus was detected in the annealed substrates. Non-linear effect on amplitude of the excited SAW was observed on the double ion irradiated materials. The potential of the SAW diagnostic system for assessing nuclear structural materials was demonstrated.

Quick measurement of continuous absorption spectrum in ion beam pulse radiolysis; Application of optical multi-channel detector into transient species observation

Iwamatsu, Kazuhiro*; Muroya, Yusa*; Yamashita, Shinichi*; Kimura, Atsushi; Taguchi, Mitsumasa; Katsumura, Yosuke*

Radiation Physics and Chemistry, 119, p.213 - 217, 2016/02

https://doi.org/10.1016/j.radphyschem.2015.10.024

A quick measurement system of a continuous absorption spectrum covering a wide range from 200 to 950 nm was constructed by employing an optical multi-channel detector. Ion beam pulse radiolysis with 12.5 MeV/u He, 18.3 MeV/u C and 17.5 MeV/u Ne ions were performed with the measurement system. Transient absorption spectrum of (SCN) was clearly observed in KSCN aqueous solutions within a few minutes in spite of their very small absorbance, demonstrating high sensitivity of 0.001-0.003 in absorbance in the range from 260 to 660 nm as well as short measurement time of a few minutes. Two different absorption peaks attributed to Br and Br were observed simultaneously in NaBr aqueous solutions, showing powerfulness of the measurement system in overviewing chemical kinetics under ion beam irradiation especially in not well investigated chemical systems.

Fabrication of Pt nanoparticle incorporated polymer nanowires by high energy ion and electron beam irradiation

Tsukuda, Satoshi*; Takahashi, Ryota*; Seki, Shuhei*; Sugimoto, Masaki; Idesaki, Akira; Yoshikawa, Masahito; Tanaka, Shunichiro*

Radiation Physics and Chemistry, 118, p.16 - 20, 2016/01

https://doi.org/10.1016/j.radphyschem.2015.05.029

Polyvinylpyrrolidone (PVP)-Pt nanoparticles (NPs) hybrid nanowires were fabricated by high energy ion beam irradiation to PVP thin films including HPtCl. Single ion hitting caused crosslinking reactions of PVP and reduction of Pt ions within local cylindrical area along an ion trajectory (ion track); therefore, the PVP nanowires including Pt NPs were formed and isolated on Si substrate after wet-development procedure. The number of Pt NPs was easily controlled by the mixed ratio of PVP and HPtCl. However, increasing the amount of HPtCl led to decreasing the radial size and separation of the hybrid nanowires during the wet-development. Additional electron beam irradiation after ion beam improved separation of the nanowires and controlled radial sizes due to an increase in the density of crosslinking points inner the nanowires.

Cross sections, stopping powers, and energy loss rates for rotational and phonon excitation processes in liquid water by electron impact

Kai, Takeshi; Yokoya, Akinari; Ukai, Masatoshi*; Watanabe, Ritsuko

Radiation Physics and Chemistry, 108, p.13 - 17, 2015/03

https://doi.org/10.1016/j.radphyschem.2014.11.008

Role of secondary electrons on DNA damage have not been understood sufficiently because there still exists a lack of cross section of rotational and phonon excitation in the liquid phase for precise simulation of the electron behavior. We calculated cross sections, stopping powers, and energy loss rates for the excitations in liquid water. The values for rotation are less by three orders of magnitude than those in the gas phase, while the values for phonon are close to those reported for amorphous ice. Thermalization process has so far been estimated from an assumption that the energy loss rates do not depend strongly on the energy below 1 eV. However, we found that the energy loss rates depend significantly on the energy. This fact indicates that the thermalization time will be longer than the previously estimated time, and we predict that thermalization process strongly involve in subsequent hydrated and chemical processes. The data set provide here is expected to useful to make the role of the secondary electrons on DNA damage much clear.