We report the synthesis of silicon nanocones using the rf microplasma discharge at atmospheric pressure. The products formed underneath the tube electrode on Fe-coated crystalline silicon were constituted mainly of silicon and silicon oxide despite the use of a methane-argon mixture. Carbon nanotubes and silicon nanowires were also formed around the silicon nanocones. The number density and average size of silicon nanocones increased with the plasma exposure time accompanied by the enlargement of their surface distribution. The growth mechanism of silicon nanocones is discussed in terms of the catalytic growth via diffusion of silicon with nanocrystalline Si particle through FeSix nanoclusters, and enhanced Si oxidation by the plasma heating.
We have started a project, which is a prototyp of a portable neutron source aiming at on-site use for diagnosing deterioration of social infrastructure, such as concrete structures, by using a first neutron imaging technique. A project is named as RANS-2, and based on experimental results obtained at RIKEN Accelerator-driven compact Neutron Source (RANS). From the compactness point of view, along with accelerator, the target station design is important. We adopted the 7Li(p,n)7Be reaction to produce neutrons and the proton energy of 2.49 MeV from an efficient neutron production point of view. In this paper, firstly we report the target neutron characteristics, such as neutron yield, and angular distribution. Secondly, shielding performances of several commercially available candidate materials, in terms of attenuation of fast neutrons in concrete, were evaluated using a Monte Carlo calculation. It is suggested that the boron-added polyethylene is the most effective material for neutron shielding. The flexibility of boron-added rubber (80 wt%, B4C) is also attractive.
RIKEN accelerator driven compact neutron source II (RANS-II), a neutron source that is designed to serve as a prototype of a next-generation downsized accelerator-based compact system, has been constructed and has successfully generated neutrons. We aim to demonstrate the system's suitability for various applications, such as the on-site degradation diagnosis of concrete infrastructures, analysis of raw materials, and other uses. Based on the 7Li(p,n)7Be reaction for neutron production, the major components of RANS-II include a newly developed ECR ion source, 2.5 MeV RFQ using copper plated steel as a proton accelerator along with a customized solid-state amplifier, and a thin lithium neutron production target deposited on a copper substrate deployed at the end of proton beamline. A movable collimator shielding assembly is placed to shield the neutron and gamma rays produced and extract the neutron beam for experimental purposes. Using this system, we succeeded in transporting a pulsed proton beam onto the Li target and observed neutron production at the target. RANS-II was successfully installed in a dedicated space in the neutronics engineering facility at the RIKEN Wako campus. A preliminary test was conducted to analyze the neutron source characterization using conventional dosimetry for neutrons. Results confirm the validity of the proposed design parameters of the RANS-II prototype.
Single crystal alumina was implanted with 2.6/spl times/10/sup 17/ Fe/sup +//cm/sup 2/ at 380 keV. The specimens were annealed at 1073 K and the change of the iron distribution profile and the charge state were investigated. Furthermore, the electrical property and surface morphology were discussed in connection with the behavior of iron.
To characterize the dose rate distribution in an experimental hall of a RIKEN accelerator-driven compact neutron source (RANS) based on the 9 Be(p, n) reaction with 7 MeV proton injection, systematical measurements and calculations for neutron and gamma-ray dose rates by GEometry ANd Tracking (GEANT), Particle and Heavy Ion Transport code System (PHITS), and Monte Carlo N-Particle (MCNP) codes were performed.Calculations always underestimated measurements when proton beam loss effect was not considered.Relatively good agreements were observed among the different simulation codes.To explain the underestimations, the additional dominant neutron and gamma-ray sources due to proton beam loss were identified at the position around exit of the drift tube linac (DTL), made of copper, and the beam pipe from quadrupole (Q) magnets to steering (ST) magnets, made of aluminum, from measurements with placing collimators along linac.The beam loss fractions of 2%-3% on copper and 1% on aluminum, respectively, were the most appropriate estimation.In addition, we proposed the possible measures to reduce the measured total dose rate of 3.8 µSv/h at the operator position in the control room, with the addition of a wall at the entrance of experimental hall and extension of borated polyethylene (BPE) at the end of the beam.As a result, the dose rate became 2.5 times lower than the current one.
