Project 6 Enhancement of research methods for material irradiation and defect analysis (R2P6)

概要

OBJECTIVES: Irradiation facilities of high-energy particles for neutrons (Material Controlled irradiation Facility), ions (e.g., Heavy ion irradiation facility) and electrons (Temperature-controlled irradiation facilities of KUR-LINAC) have been extensively developed at the Institute for Integrated Radiation and Nuclear Science. The developed facilities have been in operation and opened for joint research projects. One of the objectives of this project is to further improve or optimize irradiation facilities for advanced irradiation experiments.
　As characterization techniques for irradiated materials, a slow positron-beam system and a focused ion beam system have been developed and introduced, respectively, in addition to previous characterization facilities such as an electron microscope, an electron-spin-resonance spectrometer, a bulk positron annihilation spectrometer and a thermal desorption spectrometer. Another objective is to introduce new techniques or reconsider analytical methods of previously used characterization techniques.
　Based on these two objectives, we expect the enhancement of previous studies and the attraction of new users for the joint research program.
　The allotted research subjects (ARS) and co-researchers are listed below. The titles of research subjects are taken from the individual reports.
ARS-1:
Study to improve transport and measurement performance of a slow positron beamline (A. Kinomura et al.)
ARS-2:
Doping effect of Re, Mo, Ta on electron irradiation induced defects in W (T. Toyama et al.)
ARS-3:
Change in the Positron Annihilation Lifetime of Electron-irradiated F82H by Hydrogen Charging 2 (K. Sato et al.)
ARS-4:
Gamma-ray induced light emission from GaN single crystal wafer (T. Nakamura et al.)
ARS-5:
Irradiation technique for study on corrosion resistance of fusion divertor materials to liquid metal during irradiation (M. Akiyoshi et al.)
ARS-6:
Change of free volume in hydrogenated DLC film by the irradiation of soft X X-rays (K. Kanda et al.)
ARS-7
Positron annihilation spectroscopy on diamond-like carbon films (S. Nakao et al.)

RESULTS:
　In ARS-1, the brightness enhancement system of the KUR slow positron beamline was evaluated and the brightness enhancement values of 5.6 - 8.5 were obtained from phosphor screen images of microchannel plates. The actual samples were measured by positron annihilation lifetime spectroscopy using the KUR slow positron beam.
　In ARS-2, electron-irradiation to W or W-5%Re (in weight %) was performed. After electron irradiation, the average lifetime increased, showing positron trapping to vacancy type defects. In contrast, the average lifetime for W 5%Re remained relatively short compared with the other alloys, suggesting that the formation of irradiation induced defects was suppressed.
　In ARS-3, positron lifetimes of the number of hydrogen atoms trapped at vacancy clusters in electron-irradiated F82H were estimated and compared with the results of positron annihilation lifetime spectroscopy. The decrease in the positron lifetime per additional hydrogen atom is approximately 5 ps for 4 hydrogen atoms or less, and approximately 2 ps for 5 hydrogen atoms or more. However, the positron lifetime is almost constant when V5 contains 7 and 8 hydrogen atoms.
　In ARS-4, as-grown and gamma-ray irradiated GaN single crystal wafers irradiated at room temperature with gamma-rays of a cobalt-60 source. One end of the optical fiber cable was set on the front face of the GaN placed near the Co source and was led to the analysis room with the spectrometer. The emission characteristics of as-grown GaN and gamma-irradiated GaN were compared.
　In ARS-5, irradiation techniques for study on corrosion resistance of fusion divertor materials to liquid metal during irradiation have been developed in this research subject. However, the planned experiments were not performed this year due the limitation of the sample preparation period.
　In ARS-6, The irradiation of soft X-rays to the H H-DLC film was carried out at BL06 of the NewSUBARU synchrotron facility. In Doppeler broadening measurements of the irradiated samples, the W parameter decreased linearly with increasing of the S parameter. This indicate indicated that the same types of positron trapping sites are present.
　In ARS-7, positron annihilation spectroscopy were performed for type-IV (a-C:H) and type-VI (PLC) films deposited by plasma-based ion implantation (PBII). The S-parameters of carbon layer significantly decrease to ~0.47 for both a-C:H and PLC films after annealed at 800oC. However, a-C:H films only indicate the decrease in S-parameters at shallower region of the films.

SUMMARY: Several new irradiation (electron-beam and gamma-rays) and analytical (slow beam and conventional positron measurements) techniques for verious materials have been developed and demonstrated for the objectives of this project. Such studies may enhance developments of new techniques and materials in various scientific fields.

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