Hiroki, Akihiro; Yamashita, Shinichi*; Kimura, Atsushi; Nagasawa, Naotsugu; Taguchi, Mitsumasa
Nuclear Instruments and Methods in Physics Research B, 365(Part B), p.583 - 586, 2015/12
Effects of liner energy transfer (LET) and dose rate on the optical property of polymer gel dosimeters were investigated. The dosimeter prepared by using a radiation-crosslinked hydroxypropyl cellulose gel and methacrylate monomers such as 2-hydroxyethyl methacrylate and nonaethylene glycol dimethacrylate showed the color change from colorless to white with the He, C, Fe ions irradiation. Absorbance of the irradiated dosimeters increased with the dose up to 10 Gy. The absorbance of the dosimeters at the same total dose decreased with increasing dose rate in the range of 0.1 to 6.8 Gy/min. The absorbance decreased in order of He, C, Fe ions, which was in agreement with a change of LET. The increase in LET affected the decrease in the number of polymerization initiator such as OH radical and hydrated electron, resulting in the reduction of the absorbance of the dosimeters.
Nagasawa, Naotsugu; Taguchi, Mitsumasa
Isotope News, (736), p.47 - 50, 2015/08
no abstracts in English
Kawahara, Yutaka*; Sekiguchi, Takahiro*; Nishikawa, Yukihiro*; Nagasawa, Naotsugu
Nippon Shiruku Gakkai-Shi, 23, p.67 - 69, 2015/03
Silk aerogel has been prepared from liquid silk, and the influences of the ray-irradiation on its mechanical property have been investigated. The formation of crosslinking structure in the sericin component by the ray-irradiation should induced the hardening of the silk aerogel.
Kimura, Atsushi; Nagasawa, Naotsugu; Taguchi, Mitsumasa
Radiation Physics and Chemistry, 103, p.216 - 221, 2014/10
Large quantities of polysaccharide-based biomass are ubiquitous on Earth, and they possess unique structures, distinctive properties, and offer the advantages of being non-toxic and biodegradable. Ionizing radiation is widely used as a convenient tool for the modification of the polysaccharides via decomposition, grafting, and cross-linking. Until now, radiation cross-linked materials have only been produced either from polysaccharide derivatives or using cross-linking reagents, as certain natural polysaccharides have poor solubility in water and organic solvents as well as low chemical reactivity. These limitations could possibly be circumvented by the use of room temperature ionic liquids (RTILs), which can cleave the hydrogen bonds of the polysaccharides to form solutions. In this study, we focus on the application of RTILs as "specific solvents for the dissolution of polysaccharides," and their use in establishing a "proper reaction field for radiation cross-linking." For the first time in this study, we have demonstrated the possibility of producing cellulose gels by -ray irradiation of cellulose in RTILs under humid conditions. The gel fraction could be controlled by adept regulation of following conditions: initial concentration of cellulose, irradiation temperature, water content, and the absorbed dose. The cellulose gel thus obtained had an electronic conductivity of 3.0 mS cm, showing great potential for applications in optoelectronic and medical devices.
Nakagawa, Seiko*; Taguchi, Mitsumasa; Kimura, Atsushi; Nagasawa, Naotsugu; Hiroki, Akihiro
Nuclear Instruments and Methods in Physics Research B, 334, p.64 - 68, 2014/09
N-saturated 2-propanol solutions containing styrene and maleimide were gelled by the addition of hydroxypropylcellulose and irradiated by proton, He and C-ion beams. The trend in the dose rate and LET effects on the yield and molecular weight distribution of the polymer produced in the gel was almost the same in the solution. On the contrary, the dose rate effect in the gel was higher than that in the solution. This effect was accelerated for irradiations by proton as well as heavier ion with a higher LET value.
Aino, Masataka*; Sato, Katsuya; Narumi, Issey*; Nagasawa, Naotsugu; Yoshii, Fumio; Taguchi, Mitsumasa
JAEA-Review 2013-059, JAEA Takasaki Annual Report 2012, P. 113, 2014/03
Oyama, Tomoko; Hinata, Toru*; Nagasawa, Naotsugu; Oshima, Akihiro*; Washio, Masakazu*; Tagawa, Seiichi*; Taguchi, Mitsumasa
Applied Physics Letters, 103(16), p.163105_1 - 163105_4, 2013/10
Micro/nanofabrication of biocompatible and biodegradable poly(-lactic acid) (PLLA) was evaluated using focused Ga ion beam direct etching. The fabrication performance was determined with different ion fluences and fluxes. It was found that the etching speed and fabrication accuracy were affected by irradiation-induced heat because the resistance of PLLA to thermal deformation is decreased when above its glass transition temperature (approximately 60C). By controlling the irradiation conditions, controlled micro/nanostructures of PLLA were fabricated, such as holes (80 nm) and alphabets (width: 100 nm). Moreover, focused ion beam (FIB)-irradiated surfaces were analyzed using micro-area X-ray photoelectron spectroscopy. Owing to reactions such as the physical sputtering of atoms and radiation-induced decomposition, PLLA was gradually carbonized with increasing C=C bonds expected to have good cell attachment properties.
Hiroki, Akihiro; Sato, Yuichi*; Nagasawa, Naotsugu; Ota, Akio*; Seito, Hajime; Yamabayashi, Hisamichi*; Yamamoto, Takayoshi*; Taguchi, Mitsumasa; Tamada, Masao; Kojima, Takuji
Physics in Medicine & Biology, 58(20), p.7131 - 7141, 2013/10
Hiroki, Akihiro; Yamashita, Shinichi; Sato, Yuichi*; Nagasawa, Naotsugu; Taguchi, Mitsumasa
Journal of Physics; Conference Series, 444, p.012028_1 - 012028_4, 2013/06
Polymer gel dosimeters consisting of less toxic methacrylate-type monomers such as 2-hydroxyethyl methacrylate (HEMA) and polyethylene glycol 400 dimethacrylate (9G) with hydroxypropyl cellulose (HPC) gel were prepared. We investigated the effect of monomer compositions on the dose response of the polymer gel dosimeter. The HPC gels as a matrix for the polymer gel dosimeter were obtained by electron beam irradiation to 20wt% of HPC aqueous solution. The dried HPC gels were immersed into mixed monomer solutions, and then the swollen gels were vacuum-packed to prepare the polymer gel dosimeters. The polymer gel dosimeters showed cloudiness by exposing to Co -ray, in which the cloudiness increased with the dose up to 10 Gy. At the same dose, the increase in the cloudiness appeared with increasing concentration of 9G. It was found that the dose response depended on the composition ratio between HEMA and 9G.
Aino, Masataka*; Matsuura, Katsunari*; Nagasawa, Naotsugu; Yoshii, Fumio; Taguchi, Mitsumasa; Sato, Katsuya; Narumi, Issei
JAEA-Review 2012-046, JAEA Takasaki Annual Report 2011, P. 106, 2013/01
Kawahara, Yutaka*; Washika, Shingo*; Ikeda, Yoshimitsu*; Nagasawa, Naotsugu
Nippon Shiruku Gakkai-Shi, 21, p.11 - 13, 2013/00
Silk fibroin fabrics were irradiated with rays of 25 kGy doses, and the changes in their tensile properties and hue were investigated. Both the breaking tensile strength of the fabrics and their elongation at break were decreased after the irradiation, accompanied by their yellowing. However, the values of their tensile properties after the irradiation has been retained more than 90% of those without the irradiation. The degree of crystallinity was almost unchanged even after the irradiation.
Inoue, Mitsuhiro*; Nagasawa, Naotsugu; Tamada, Masao
Noppon Sakyu Gakkai-Shi, 59(2), p.61 - 70, 2012/11
no abstracts in English
Okubo, Satoshi*; Nagasawa, Naotsugu; Kobayashi, Akinobu*; Oyama, Tomoko*; Taguchi, Mitsumasa; Oshima, Akihiro*; Tagawa, Seiichi*; Washio, Masakazu*
Applied Physics Express, 5(2), p.027303_1 - 027303_3, 2012/02
Electron beam nanoimprint lithography was proposed for fabricating the micro-/nanostructures of cross-linked poly(-lactic acid) (RX-PLLA). PLLA with triallyl isocyanurate (TAIC) solutions were dropped on the Si-molds fabricated by the conventional EB lithography technique. PLLA/TAIC on Si-molds were imprinted and cross-linked with doses from 10 to 500 kGy at room temperature under vacuum. The micro-/nanostructures of RX-PLLA were successfully obtained with high accuracy. Hence, it was found that the imprinted structures of RX-PLLA (100 kGy irradiation) show low line edge roughness and high thermal durability at 120 C.
Tranquilan-Aranilla, C.*; Nagasawa, Naotsugu; Bayquen, A.*; Dela Rosa, A.*
Carbohydrate Polymers, 87(2), p.1810 - 1816, 2012/01
Carboxymethyl derivatives of kappa-carrageenan (KC) with varying degrees of substitution were obtained by multi-step carboxymethylation process. The structural and chemical profiles of the derivatives were determined by FTIR, C NMR, gel permeation chromatography, elemental analysis, potentiometric titration and visual estimation of gelation temperature. The derivatives exhibited high degrees of substitution and acidity. However, sulfur content, molecular weight and gelation temperature were lower compared to the parent KC polymer. FTIR confirmed the presence of carboxymethyl groups in the polymer backbone while C NMR revealed that functionalization occurred at the three hydroxyl groups in KC disaccharide unit.
Abad, L.*; Saiki, Seiichi; Nagasawa, Naotsugu; Kudo, Hisaaki*; Katsumura, Yosuke*; Dela Rosa, A. M.*
Radiation Physics and Chemistry, 80(9), p.977 - 982, 2011/09
The optimum molecular weight of irradiated -carrageenan for the plant growth promoting effect is known to be around 10 kDa, which is obtained by irradiation at doses of 100 kGy in solid and of 2 kGy in 1% aqueous solution. In this study, isolated fraction by membrane filter of irradiated -carrageenan was analyzed by NMR. The chemical shifts of C and H spectra at the range of 3-10 kDa indicated that the basic functional structure of -carrageenan (alternating D-galactose-4-sulfate and 3,6-anhydro-D-galactose dimer) remains intact. No radiolytic product having carbonyl groups was detected at the range of 3-10 kDa, and moved to less than 3 kDa probably. From these results, it is assumed that the plant growth promoting effect of irradiated -carrageenan depends on the molecular weight, its intact structure, and not on the radiolytic products.
Hiroki, Akihiro; Hong, P. T. T.*; Nagasawa, Naotsugu; Tamada, Masao
Transactions of the Materials Research Society of Japan, 36(3), p.397 - 400, 2011/09
Properties such as a degree of swelling (Sw) and biodegradability of blend hydrogels based on carboxymethyl cellulose (CMC) and carboxymethyl starch (CMS) were investigated. The irradiations of 40wt% of CMC/CMS aqueous solution (blend ratio of CMC/CMS: 100/0, 75/25, 50/50, 25/75, 0/100) were carried out using Co -ray source to obtain the blend hydrogels. The gel fraction of CMC/CMS blend hydrogels increased sharply up to 10 kGy and reached a constant value at 30 kGy. Increase in the ratio of CMC increased the gel fraction of blend hydrogel. These hydrogels reached the equilibrium swelling state from initial dried gel in about 2 hours. The blend hydrogels with the maximum Sw of about 800 were obtained at 2 kGy. The Sw decreased significantly with increasing the dose, and leveled off in the range of 20-40 kGy. As a result of the biodegradability test in soil, the discharge of carbon oxide generated by the biodegradation of the blend hydrogels (the Sw of about 100) gradually increased with increasing the ratio of CMS, resulting in the decomposition ratio in the range of 5 to 20% at 30 days. Therefore, the biodegradability of the blend hydrogels was controlled by adjusting the composition of the CMC/CMS and irradiation doses.
Saiki, Seiichi; Nagasawa, Naotsugu; Hiroki, Akihiro; Morishita, Norio; Tamada, Masao; Kudo, Hisaaki*; Katsumura, Yosuke*
Radiation Physics and Chemistry, 80(2), p.149 - 152, 2011/02
Carboxymethyl cellulose (CMC), one of polysaccharide derivatives, at highly concentrated aqueous solution undergoes radiation-crosslinking reactions. In this topic, CMC radical, formed by reaction with OH radical attributed to radiation-induced crosslinking reaction, were studied by ESR method to understand the radiation-induced reaction mechanism of CMC aqueous solution. At first, it was succeeded to observe ESR spectra of the CMC radical using photolysis of hydrogen peroxide as the origin of OH radical. Observed ESR spectra were identified as radicals located on the secondary carbon of carboxymethyl groups. Secondly, NO saturated CMC aqueous solution 6 min after electron beam irradiation was measured by ESR method. The spectra were almost same shape as the case of photolysis of hydrogen peroxide, and were assigned as long-lived radicals located on carboxymethyl groups. Next, in the case of N and O saturation, spectra intensity become half or 0. This means that these long-lived radicals are produced by reaction with OH radical.
Quynh, T. M.*; Yoneyama, Masaru*; Maki, Yasuyuki*; Nagasawa, Naotsugu; Dobashi, Toshiaki*
Key Engineering Materials, 459, p.51 - 56, 2010/12
Different poly(-isopropylacrylamide--hydroxyethyl methacrylate) copolymers [P(NIPAM--HEMA)] were synthesized from -isopropylacrylamide (NIPA) and hydroxyethyl methacrylate (HEMA) monomers by both radical and radiation polymerizations for comparison. PLLA--P(NIPAM--HEMA) graft copolymers were synthesized from L-lactide and respective P(NIPAM--HEMA) copolymers by ring opening polymerization. Both NMR and FTIR analyses demonstrated the PLLA chains have been grafted on to the P(NIPAM--HEMA) backbone. These graft copolymers revealed the cloud point temperature higher than that of PNIPAM homopolymer as determined by optical transmittance. The graft copolymers self-assembled into micelles with regularly spherical structures as observed by atomic force microscopy (AFM). The properties of these graft copolymers are interesting for the drug delivery system.
Okubo, Satoshi*; Takahashi, Tomohiro*; Takasawa, Yuya*; Gowa, Tomoko*; Sasaki, Takashi*; Nagasawa, Naotsugu; Tamada, Masao; Oshima, Akihiro*; Tagawa, Seiichi*; Washio, Masakazu*
Journal of Photopolymer Science and Technology, 23(3), p.393 - 397, 2010/11
Microfabrication of biodegradable polymers such as poly(butylene succinate--adipate) (PBSA) and poly(-caprolactone) (PCL) were demonstrated using focused ion beam (FIB) with maskless direct etching. As the result, the micro structures of PBSA and PCL were obtained. The etching depth of both PBSA and PCL were increased with increasing FIB fluence, and the etching rates were estimated to be about 1.3 10 m/(ions cm) and 1.2 10 m/(ions cm), respectively. Moreover, very thin films of PBSA and PCL were made by spin-coating method. The thicknesses of the spin-coated samples were about 200 nm, and the surface roughness was less than 10 nm (RMS). The fine structures such as micro-gear of PBSA and PCL were obtained without solid debris. The line width of the fabricated structure was about 250 nm.
Takigami, Machiko*; Maehara, Yasunobu*; Nagasawa, Naotsugu
Bio Industry, 27(9), p.50 - 55, 2010/09
no abstracts in English