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ABSTRACTThe flexible waste management (FWM) system has been proposed in order to apply the partitioning and transmutation (P&T) technology for minor actinides (MA) to the current high-level liquid waste (HLLW). This system consists of HLLW calcination to produce easy-to-dissolve granule; its temporary storage is required until the P&T technology deployment and re-dissolution of the granule to remove MA from HLLW after the future P&T technology deployment. The fundamental experiments were conducted to clarify the applicability of FWM system to the current HLLW, and the results indicate the technological validity of the system. The evaluations were carried out for the reduction of storage amount, potential radiotoxicity, and repository area of high-level waste.

The suppression of stochastic effects is the most important issue in the development of resist materials. To suppress the stochastic effects in chemically amplified resists, a high acid generator concentration is required, which, however, likely affects the dissolution kinetics of resist films. In this study, the effects of substituents in the phenyl group of triphenylsulfonium triflate (TPS-TF) on the decomposition and dissolution kinetics of poly(4-hydroxystyrene) (PHS) films dispersed with monosubstituted TPS-TF were investigated using electron pulse radiolysis, γ-radiolysis, electron radiolysis, and quartz crystal microbalance. The phenyl group of TPS-TF was substituted with fluorine, iodine, or methyl groups at the fourth position. The electronegativity of the substituents had little effect on the reaction rate of the methanol-solvated electrons. The dipole moment of the TPS cation affected the C-S bond cleavage. The monosubstitution of the phenyl group of the TPS cation significantly affected the dissolution rate of the PHS films.

Extreme ultraviolet (EUV) lithography is a promising technology for making chips beyond 7 nm technology node; however, it comes with its own challenges. One of them is the need to find a suitable EUV resist. Photoresist performance is gauged by the resolution, LER, and sensitivity trade-off. However, the primary challenge for the photoresist in EUV lithography is the major shift in reaction chemistry relative to that in deep ultraviolet (DUV) lithography. The interaction of the EUV photon (92 eV) with the widely used conventional chemically amplified resist (CAR) is different than that of the DUV photon (5–6 eV). The DUV photon excites only the valence electrons of the photo-acid generator in CAR, which results into acid generation. However, a high-energy EUV photon can ionize the CAR polymer matrix. This leads to the generation of a cascade of secondary electrons. Thus, in addition to acid generation, other chemical reactions like bond scission and cross-linking occur by the interactions between resist and secondary electrons. Apart from chemically amplified reactions, CARs are not very efficient at utilizing the additional pathways offered by secondary electrons. Moreover, stochastics, arising from photon and chemical shot noise, are an additional challenge for an EUV resist. Therefore, there is a need for an alternative photoresist to CAR. Herein, we report a single polymer chain negative tone photoresist. The resist has an acid generator, an organotin moiety, and an acid reactive unit attached to a polymer chain. The resist is designed to use EUV-generated secondary electrons to generate acid and polymer-bound radicals. The polymer-bound radicals and acid amplification reaction can induce cross-linking among polymer chains to create a negative tone solubility switch. In this study, the EUV printability study and reaction mechanism of the resist are elucidated. Electron transfer reactions for radical generation were studied with the help of nanosecond pulse radiolysis and γ-radiolysis. Liquid chromatography and mass spectrometry were used to identify possible acid-amplified reactions.

The development of highly sensitive resists containing tin, which has a large EUV absorption cross section, has recently attracted considerable attention in EUV lithography. The effective utilization of secondary electrons is required for the development of high-performance resists. It is important to design resist materials on the basis of the mechanism of radiation chemical reactions. In this study, the radiation-induced reactions of tetraphenyltin (TPSn), triphenylsulfonium triflate (TPS-Tf), and the copolymer of triphenyl(4-vinylphenyl) stannane (TPSnSt) and 4-methacryloxyphenyldiphenylsulfonium triflate (MAPDPS-Tf) were investigated by electron pulse radiolysis and γ-radiolysis in controlled reaction systems. The decomposed products were analyzed by high-performance liquid chromatography. The G values of decomposed products were determined. For the copolymer, the holes generated by ionizing radiations moved to Sn units and electrons moved to TPS-Tf units. The tin complex side chain decomposed, producing benzene after hole transfer.

Metal oxide nanocluster resists are a promising candidate for enabling the high-volume production of semiconductor devices with high-numerical-aperture extreme ultraviolet exposure tools. In this study, the sensitization mechanism of metal oxide nanocluster resists was investigated by focusing on the radiation-induced reactions of carboxylic acid ligands. Radiolytic products in various solutions of unsaturated carboxylic acids, aromatic carboxylic acids, and saturated carboxylic acids were analyzed by electrospray ionization mass spectrometry, high-performance liquid chromatography, and dynamic light scattering. The conditions of the solutions were selected to control reaction paths of intermediates. The major reaction paths induced by ionizing radiation were clarified. The obtained results suggest that the generation of bridging ligands is essential to the sensitization of metal oxide nanocluster resists. Both low-energy electrons and radical cations can trigger dimerization. The diffusion of small radicals should be suppressed to prevent dimerization at undesired places.

Metal oxide nanocluster resists have recently attracted considerable attention for use in extreme ultraviolet lithography. To obtain sophisticated guidelines for material design, it is necessary to understand well the radiation-induced chemical reaction scheme including the insolubilization mechanism. In this study, the production of CO2, which is considered to be one of the end products of treatment with an ionizing radiation, was investigated for eight types of carboxylic acid under various conditions using γ-rays (60Co) as a radiation source. The amount of CO2produced was measured by gas chromatography. GCO2(/100 eV), which indicates decarboxylation efficiency, was evaluated. CO2was generated through electron addition, hole transfer, and hydroxyl radical addition to the molecular and ionic forms of carboxylic acids. The dependences of GCO2on reaction partners were clarified. The dependences of GCO2on the molecular structure and dissociative state of carboxylic acids were also clarified.

A comparative study using the pulse radiolysis technique was carried out to investigate transient absorption spectra and rate constants for the reactions of (•)OH and N(3)(•) with edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) and its four analogue compounds, 1,3-dimethyl-2-pyrazolin-5-one, 3-methyl-1-(pyridin-2-yl)-2-pyrazolin-5-one, 1-phenyl-3-trifluoromethyl-2-pyrazolin-5-one and 1-(4-chlorophenyl)-3-methyl-2-pyrazolin-5-one. The results showed that, unlike reaction mechanisms previously proposed, the phenyl group of edaravone played an important role in the reaction with (•)OH and OH adducts to the phenyl group were formed. Quantum chemical calculations also strongly supported this attribution and suggested that the most favorable site for attacks by (•)OH is the ortho position of the phenyl group. Moreover, the rate constants for the reactions of edaravone and its analogues towards (•)OH and N(3)(•) were about 8.0 × 10(9), and 4.0 × 10(9) dm(3) mol(-1) s(-1), respectively. Edaravone displayed higher reactivity compared to the others, in contrast to a previous report in which 3-methyl-1-(pyridin-2-yl)-2-pyrazolin-5-one showed the highest reactivity towards (•)OH.

The repair activities of silybin (SLB) and its analogues towards the oxidizing deoxyguanosine monophosphate (dGMP) hydroxyl radical adducts are investigated by pulse radiolytic techniques. On pulse irradiation of nitrous oxide saturated 2.0 mM dGMP aqueous solution containing 0.1 mM silybin at neutral pH, the transient absorption spectrum of the dGMP hydroxyl radical adducts decreases with the formation of the phenoxyl radical of silybin within tens of microseconds, indicating that there is a repair reaction between the dGMP hydroxyl radical adduct and silybin. The rate constant of the repair reaction is calculated to be 1.0 x 10(9) M(-1)s(-1) for silybin. The repair activity of hesperetin (HESP), naringin (NAN) and naringenin (NAR) towards hydroxyl radical adducts of dGMP are also studied.

Hydrogels, which were synthesized by simultaneously occurring processes of radiation-induced polymerization and cross-linked reactions of acryloyl-l-proline methyl ester (APM) at 0 °C in aqueous alcohol solutions, exhibit an ultraslow volume change in response to variations in external temperature. The shrinking speed of the hydrogels prepared in aqueous alcohol is 1000 times slower than that of the hydrogel prepared in pure water; e.g., the hydrogel prepared in aqueous 1-propanol solution shrunk in 6 months. It is revealed that the ultraslow thermoresponse consists of quick- and slow-shrinking periods; the ratio between the two periods depends on the alcohol molecules in the solution. The generation of a hydroxyl group in the polymer network by the coupling reaction between -hydroxyalkyl radical of alcohols and -radical of proline moiety was confirmed by GC/MS analysis of the radiation products. The hydrogen bonding domain containing the hydroxyl groups is proposed to be responsible for the ultraslow response.

Laser flash photolysis with excitation at 248 nm was used to study photochemically derived changes of carboxymethylcellulose (CMC) in aqueous solutions. Transient absorption spectra of solutions after photolysis revealed a broad band with a maximum of approximately 720 nm, which could be ascribed to the signal of the hydrated electron. The interaction of the hydrated electron with CMC was slow (<107 dm3 mol−1 s−1), but the OH radical, formed by the decomposition of H2O2, reacted with CMC at a high rate constant (9.5–11.0 × 108 dm3 mol−1 s−1). The rate constant of the reactions of CMC with hydroxyl radicals depended on the conformation of the macromolecules, which was determined by the pH of the solution. Transient absorption was recorded at a wavelength shorter than 370 nm for CMC solutions photolyzed in the presence of H2O2. As a result of OH attack, long‐lived radicals were formed on CMC. The recombination of macroradicals led to the formation of crosslinking bonds between side‐chain groups, and as a result of it an insoluble gel arose in low‐pH solutions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 505–518, 2005

Time resolved laser photolysis was carried out to study the reaction of NO3 radical toward a series of organic phosphates tributylphosphate TBP and its analogues with different length of side alkyl groups such as CH3, C2H5, C3H7, CHCH32and C4H9in water, acetonitrile, and the mixtures of water and acetonitrile, respectively. For comparison, a similar investigation on SO4−radical was also conducted. The oxidation reaction of NO3 and SO4−radical with the phosphates was attributed to mainly an H-abstract reaction. The kinetics study shows that the rate constants of the reaction between the two radicals and phosphates increase remarkably with increasing of the length of the alkyl groups, e.g.in the case of NO3 radical in acetonitrile, the rate constant increases by almost 4 orders of magnitude from TMP –CH3 to TBP –C4H9. The composition of the solvent also greatly affects the reactivity but it exhibits an opposite effect of the two radicals, the rate constant of NO3 increases with the mole fraction of acetonitrile while that of SO4−decreases. The present study would be helpful for understanding the mechanism of deterioration of TBP in the Purex process.

Pulse radiolysis studies with aqueous benzophenone solutions were performed over the range 25–400 °C, including conditions beyond the critical point of water. The addition of e_aq− to benzophenone forms either ketyl anion in alkaline solutions or neutral ketyl radical in acidic/neutral solutions. Although both have an intense and sharp absorption band in the UV region and a weak but broad band in the visible region, their spectra are clearly different. The peak of the visible band is at 545 nm for the neutral ketyl radical and 610 nm for the anion at room temperature. With increasing temperature, the absorption peak of the ketyl radical shifts to a shorter wavelength while that of the anion shifts to a substantially longer wavelength. The decay of the ketyl radical is not monotonically temperature-dependent: its rate constant (2k/ɛ) increases with temperature up to 100 °C and then decreases at higher temperatures. The rate constant for the addition of e_aq− to benzophenone can be considered to be diffusion controlled and the Arrhenius plot can be fitted with a curved line. The temperature dependence of the rate constant for the reaction of e_aq− with proton was determined up to 400 °C by the competition method using benzophenone as the reference solute. It was also found that the addition of OH&z.rad; radical to benzophenone forms a transient species with a strong absorption band centered at 380 nm and the peak seems to be slightly blue-shifted with temperature. The decay of this species increases rapidly with temperature, indicating the enhanced conversion to stable products at high temperatures.

For sub-picosecond pump-and-probe-type radiation chemistry work, a new synchronized electron linac and laser system was installed in the Nuclear Engineering Research Laboratory (NERL) of University of Tokyo. The new laser system, with a Ti:Sapphire oscillator (795 nm) and amplifiers, generates 300 ps pulses at 10 Hz. The laser is transported through the vacuum chamber and then split into two beams. The first is compressed and converted to the third harmonics (265 nm, <250 μJ, 4–11 ps) so as to drive the photocathode RF-gun and generate a pump-electron beam. The second is compressed to 100 fs and used for the probe light. The high-power RF, which is provided by a new 15 MW klystron, is divided into the gun and the accelerating section. Finally, a time jitter of 330 fs (rms) was achieved between the pump-electron beam and the probe laser, which is equivalent to the design value of 320 fs. A charge of 7 nC/bunch was observed at the exit of the gun from this new laser system. Improvement of the vacuum in the gun (<10-9Torr) is the most effective way to obtain such a high-charge beam. After about three years of operation, the Cu photocathode has shown no degradation of quantum efficiency.

The radiation-induced reactions of ligands play an important role in the sensitization of metal oxide nanocluster resists. However, the details in the radiation chemistry of ligands for metal oxide nanocluster resists are still unknown. In this study, the radiation-induced reactions of carboxylic acid ligands were investigated using a pulse radiolysis method. The rate constants for the reactions of molecular and ionic forms of tiglic, angelic, o-toluic, and p-toluic acids with hydrated electrons were determined. The rate constants for the reactions of tiglic, angelic, benzoic, o-toluic, and p-toluic acids with dodecane radical cations were also determined. The radical ions of tiglic and angelic acids were more unstable than those of benzoic, o-toluic, and p-toluic acids. The results obtained in this study indicate that the molecular structures of ligands affect their reactivity to cationic and anion species and the stability of their radical cations and anions.

Metal oxide nanoparticle resists are promising materials for highly-resolving high-throughput patterning. However, their performance is still inadequate for the application to the production of semiconductor devices. In this study, the dependence of the relationship between chemical gradient and line width roughness (LWR) on the pattern duty, acid generator, and developer was investigated using a zirconia (ZrO2) nanoparticle resist. The line-and-space patterns of ZrO2 nanoparticle resists were analyzed on the basis of the extreme ultraviolet sensitization mechanism. LWR was roughly inversely proportional to the chemical gradient. The proportionality constant decreased with the increase of the ratio of nominal space width to the nominal line width. The proportionality constant for n-butyl acetate was smaller than that for an alternative developer with a high polarity. The proportionality constant decreased by the addition of an acid generator. The improvement of dissolution process and the suppression of secondary electron migration are essential to the suppression of LWR in the ZrO2 nanoparticle resist.

The trade-off relationships between resolution, line width roughness (LWR) and sensitivity is the most serious problem in the development of resist materials. Metal oxide nanoparticle resists are expected to overcome such a trade-off problem. Understanding the sensitization mechanism is important for the efficient development of metal oxide nanoparticle resists. However, the sensitization mechanism of the metal oxide nanoparticle resists is still unknown. In this study, the radiation-induced reactions of methacrylic acid (MAA) ligands for zirconia (ZrO2) nanoparticle resists were investigated using a pulse radiolysis method. Both the reaction paths through MAA radical cation and MAA radical anion are considered to lead to the insolubilization of the zirconia nanoparticle resists. The acid generators suppressed LWR, probably through capturing the thermalized electrons.

Reactions of edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) with deoxyguanosine monophosphate (dGMP) hydroxyl radical adducts were investigated by pulse radiolysis technique. Edaravone was found to reduce the dGMP hydroxyl radical adducts through electron transfer reactions. The rate constants of the reactions were greater than 4 × 108 dm3 mol−1 s−1 and similar to those of the reactions of ascorbic acid, which is a representative antioxidant. Yields of single-strand breaks, base lesions, and abasic sites produced in pUC18 plasmid DNA by gamma ray irradiation in the presence of low concentrations (10–1000 μmol dm−3) of edaravone were also quantified, and the chemical repair activity of edaravone was estimated by a method recently developed by the authors. By comparing suppression efficiencies to the induction of each DNA lesion, it was found that base lesions and abasic sites were suppressed by the chemical repair activity of edaravone, although the suppression of single-strand breaks was not very effective. This phenomenon was attributed to the chemical repair activity of edaravone toward base lesions and abasic sites. However, the chemical repair activity of edaravone for base lesions was lower than that of ascorbic acid.