Long-lived neutron-induced radioisotopes in OKTAVIAN facility concrete wall after 38 year-operation

An intense 14 MeV neutron source facility named OKTAVIAN was installed in the A15 building,Osaka University in 1981.Along the operation period,new radioisotopes with various half-life have been produced as neutron activation products in its concrete wall shield.In this work,we investigated the concrete wall in the heavy irradiation room of OKTAVIAN using gamma spectrometry method to discover the presence of radioisotope having large half-life value (long-lived radioisotope) as neutron activation products.Computational simulations were performed prior to measurement to predict the presence of long-lived radioisotopes by employing MCNP5 and FISPACT codes.A pre-calibrated Germanium detector with high energy resolution was employed to measure the concrete.Several long-lived activation products have been observed such as ¹⁵²Eu,⁵⁴Mn,⁶⁵Zn,²²Na and ⁶⁰Co.The activity of each radioisotope was derived after estimating the detector efficiency using MCNP5.As a result of the measurement and analysis,the followings are concluded:(1) Though presence of activation products represents radiological risk to everyone who performs an experimental activity in the irradiation room of the OKTAVIAN facility,the present result shows that past experiments were carried out safely without any significant additional exposure dose coming from the wall for the last 38 years.(2) The approximated total fluence of D-T neutrons to the wall was successfully estimated from the produced radioisotope,¹⁵²Eu,because it has the longest half-life of 13.5 years among the observed radioisotopes.(3) From the results of (1) and (2),it could be possible to estimate the total activity of the concrete wall in the OKTAVIAN facility,which is very essential and important information,because this would be very valuable for decommissioning or disposal of the facility in the future.     

Synthesis,characterization, and CO2 permeation properties of acetylene‐terminated polyimide membranes

A novel fluorine‐containing telechelic polyimide end‐capped with acetylene group which derived from 4,4‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 3,4‐diaminodiphenyl ether (DADE), and 4‐(2‐phenylethynyl) phthalic anhydride (PEPA) was synthesized using polycondensation. The physical and CO₂ permeation properties of its crosslinked membranes prepared by the cyclotrimerization reaction of the acetylene groups at the polymer chain end using tantalum (V) chloride (TaCl₅) as a catalyst under thermal treatment was investigated in terms of CO₂‐induced membrane plasticization. The crosslinked membranes showed a gel content in organic solvent, which was good solvent of noncrosslinked membranes, and improved their thermal stability. Based on the measurement of the high‐pressure time dependence on CO₂ permeation, the crosslinked 6FDA–DADE–PEPA membranes exhibited more resistance to CO₂‐induced plasticization than noncrosslinked 6FDA–DADE and thermal treated 6FDA–DADE–PEPA. Furthermore, the increase in TaCl₅ content resulted in more resistance to plasticization. The cyclotrimerization reaction of the acetylene groups at the polymer chain ends using a transition metal catalyst under thermal treatment was found to be more effective than conventional thermal treatments for suppressing membrane plasticization without the membrane densification. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Volatilization of 137Cs and 106Ru from Borosilicate Glass Containing Actual High-Level Waste

Volatility of ¹³⁷ Cs and ¹⁰⁶Ru from borosilicate glass containing actual high-level waste was measured in an almost closed stainless-steel canister. The temperature dependence of the volatility of ¹³⁷Cs was close to that obtained in our previous study using ¹³⁴Cs. The volatility of ¹⁰⁶Ru was about one-fifth that of ¹³⁷Cs at 600° and 800°C. The air contamination by ¹³⁷Cs and ¹⁰⁶Ru in the canister at 400°C was estimated at 1.8 × 10² and 2 × 10 Bq/cm³, respectively, when it was assumed that the glass contained a realistic amount of ¹³⁷Cs and ¹⁰⁶Ru expected in commercial waste glass. These results are useful for predicting safety in a storage facility under operation.     

Properties of Nitrogen-Containing Yttria—Alumina—Silica Melts and Glasses

The viscosity and solubility of nitrogen in Y₂O₃–Al₂O₃–SiO₂ melts have been systematically examined. The effects of nitrogen content on viscosity for Y-Al-Si-O-N melts and on Vickers hardness of oxynitride glasses also have been examined. Although the viscosity of Y₂O₃–Al₂O₃–SiO₂ melts was decreased, the solubility of nitrogen into the melts was increased with increased Y₂O₃ content. These results indicated that the yttrium ion behaved as a network modifier. Therefore, the structural units for viscous flow became small, and the amount of nonbridging oxygen increased in the melts when the Y₂O₃ content increased. The viscosity of Y-Al-Si-O-N melts and Vickers hardness of oxynitride glasses remarkably increased with increased nitrogen content. These results suggested that the substitution of nitrogen for oxygen in the melts may have led to a high average coordination of nonmetal atoms and that the increased cross-linking produced a more rigid glass network.     

In situ study of ionic conductivity for polyether-LiCF3SO3 electrolytes with subcritical and supercritical CO2

In situ measurements of the ionic conductivity were performed on polyethers, poly(ethylene oxide) (PEO) and poly(oligo oxyethylene methacrylate) (PMEO), with lithium triflate (LiCF₃SO₃) as crystalline and amorphous electrolytes, and at CO₂ pressures up to 20 MPa. Both PEO and PMEO systems in subcritical and supercritical CO₂ increased more than five fold in ionic conductivity at 40 °C composed to atmospheric pressure. The pressure dependence of the ionic conductivity for PEO electrolytes was positive under CO₂, and increased by two orders of magnitude under pressurization from 0 to 20 MPa, whereas it decreases with increasing pressure of N₂. The enhancement is caused by the plasticizing effect of CO₂ molecules that penetrate into the electrolytes.     

A study of a jumping one-leg robot with two degrees of freedom

This study aims to improve human jumping capabilities from an engineering perspective by proposing a supportive device, as in a robot suit. The robot expresses a time-oriented optimal torque pattern, which is the most efficient jumping motion and timing, of each joint that can jump the highest using a motor. Then humans learn the most efficient jumping motion. To actualize the most efficient jumping motion, we observe human jumping motions and analytically calculate the most efficient torque patterns based on them. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Preparation of inorganic-organic hybrid films containing particles using electrophoretic deposition method

The composite films of methylsiloxane inorganic-organic hybrid and MoS₂ particles have successfully been fabricated by electrophoretic deposition of MoS₂ particles in a mixed solution of methyl ethyl ketone (MEK) and inorganic-organic hybrid sol. The addition of 20 vol% hybrid sol into a MEK suspension increased the amount of MoS₂ deposition twice as much as that of MoS₂ deposition in MEK alone. The fraction of particles deposited on a substrate in MEK-20 vol% sol was estimated to be much larger than that in MEK. The hydrolyzed methyltriethoxysilane in a hybrid sol modified MoS₂ particles, resulting in lower negative zeta potential, which reduces the repulsion force among particles and makes the incorporation of particles into a deposition film easier. The surface modification also enables the incorporation of particles into a deposit by the interaction of surface modifiers. These factors enhance the incorporation of MoS₂ particles in electrophoretic deposition in MEK-sol.     

VCM design with round coil and axe-shaped magnet for hard disk drive actuator

In this paper, we proposed a novel single-sided magnet voice coil motor (VCM) design that can reduce out-of-plane force. Out-of-plane force of a VCM causes the actuator vibration, which results in settling vibration and acoustic noise. The proposed single-sided magnet VCM consists of a round coil and an axe-shaped magnet. We designed the optimized configuration by using numerical magnetic field simulation and compared its performance with those of a conventional VCM. Torsional moment was reduced by 90% at the worst position of the middle track, and bending moment was reduced by 50% at the worst position of the inner track compared with a conventional VCM. Rotational moment in our VCM was almost the same as that of the conventional one. We manufactured an actuator with the new design VCM and confirmed that the new single-sided magnet VCM shows a good performance as expected, although its magnet volume and coil resistance were almost the same as a conventional design. The measured frequency response of the actuators from the coil current to the head displacement showed that the coil torsional mode vibration of the proposed VCM is reduced remarkably.