Hideki Namba

Radical formation in the radiolysis of solid alanine by heavy ions

Abstract Radical formation in solid α-alanine irradiated with 175-MeV Ar8+ and 460-MeV Ar13+, 220-MeV C5+, and 350-MeV Ne8+ ions were studied by the ESR method. The radical yield (number of radicals per incident ion) is constant below the critical fluence of about 1010 ions cm−2 for the Ar ions, 1011 ions cm−2 for the C ion, and 5 × 1011ions cm−2 for the Ne ion. Above the critical fluence, the yield decreases with increasing ion fluence. G-value of the radical formation was obtained from the constant yield at the low fluences. The G-value is not a simple function of LET. This is ascribed to the difference in lateral dose distribution of ion tracks. Assuming a simple cylindrical shape of the ion tracks, the average dose in and the radius of the ion tracks were estimated from the G-values. The radius is 8–25 nm, which is larger than the radius of 2–5 nm for 0.5–3 MeV H+ and He+ ion-irradiations. The fluence-yield curves were simulated with the cylindrical tracks and with the dose-yield relationship for the radical formation in γ-irradiated alanine. The simulated curves agree well with the experimental ones. With the cylindrical model of ion tracks, the variation of the radical yield at the high fluences can be estimated for solid alanine irradiated with several hundreds of MeV heavy ions.

Oxygen gas dosimeter for flow systems

Abstract Oxygen was used as a high dose gas phase dosimeter by measuring the concentration of ozone formed with electron beam irradiation in a flow system. The formed ozone was measured by an ultraviolet absorption ozone detector. A part of the formed ozone was decomposed during irradiation. The decomposition of ozone is mainly caused by radical reactions of OH and HO 2 with ozone, and the rate of decomposition can be estimated easily by computer calculations. It is therefore possible to use this method as a gas phase dosimeter with a correction for the decomposition. The dose rate obtained by this method was in good agreement with that of the nitrous oxide dosimeter.

Enhancement of removal of SO2 and NOx by powdery materials in radiation treatment of exhaust gases

Abstract We studied the effect of powdery silica on radiation removal of SO 2 and NOx from mixtures of SO 2 , NOx, water vapour, oxygen and nitrogen under irradiation by electron beams of 1.5 MeV at 120°C. The SO 2 and NOx concentrations decreased when powdery silica was fed without irradiation. Decrements of SO 2 and NOx concentrations were markedly enhanced when powdery silica was fed together with the irradiation. The enhancement of SO 2 - and NOx-removal is attributed to the adsorption of SO 2 and NO on the water-covered surface of powdery silica, and the effective removal of NO 2 due to the reaction with water adsorbed on the surface of powdery silica. The results obtained show that the addition of powdery silica under irradiation is an effective method of enhancing the removal of SO 2 and NOx.

Kinetics of SO2 removal from flue gas by electron beam technique

Abstract Laboratory scale experiments were carried out in order to get more information about the oxidation of SO 2 by OH radicals (homogeneous reaction) and the oxidation of SO 2 at aerosol surfaces (heterogeneous reaction). For the experiment of homogeneous reaction, SO 2 was added to synthetic flue gas without initial NO and without ammonia and the mixture was irradiated with electron beam. The SO 2 removal was measured as a function of temperature and water vapour concentration at constant dose. For the experiment of heterogeneous reaction, SO 2 was added to nucleating sulfuric acid aerosol. No SO 2 removal was observed in this case. So, it can be concluded that the heterogeneous oxidation of SO 2 is negligible in the absence of ammonia. Therefore, the oxidation of SO 2 must be interpreted merely by homogeneous gas phase chemistry. The gas phase kinetics are derived from comparison of experimental results and computer modelling.

Material balance of nitrogen and sulfur components in simulated flue gas treated by an electron beam

Abstract The material balance of nitrogen and sulfur components in simulated flue gas (NOSO 2 H 2 OO 2 NH 3 N 2 ) treated by an electron beam was measured using 15 N labeled NO (250 ppm). Combinations of chemical analysis, instrumental analysis and mass analysis were used to identify and quantify the nitrogen-containing products as well as to determine the ratio of 15 N in each product. The products 15 N 14 N, 15 NO 3 − , 15 NO 2 , 15 N 14 NO and 15 N 15 NO were detected after electron beam treatment of the gas. Perfect material balance of 15 N (103%) was obtained. The material balance of the sulfur components was measured using two different chemical analysis methods. All the removed SO 2 was converted to SO 4 2− by electron beam treatment, and both methods yielded a satisfactory balance (103 and 105%).

FAST FLUORESCENCE DECAY OF NAPHTHALENE INDUCED BY AR ION IRRADIATION

Abstract A single photon counting system was constructed for a time resolved fluorescence measurement with pulsed heavy ions from the AVF cyclotron in Takasaki Ion Accelerators for Advanced Radiation Application (TIARA). Fluorescence spectra and decay of naphthalene in poly(vinyl butylal) (PVB) film were observed from the irradiation with Ar ions. Though fluorescence spectra were assigned to the first singlet excited state of naphthalene, the decay with Ar ion irradiation were faster than that excited by UV light. This faster decay results from quenching by the transient species produced. The relative initial concentration of the excited state of naphthalene to that of the radicals increases with increasing energy deposited along the incident ions trajectory.

Chemical effects of heavy ion beams on organic materials

Abstract Effects of ion beam irradiation on α-alanine, adipic acid and polydimethylsiloxane were examined. Stable radicals were generated in the radiolysis of solids of α-alanine and adipic acid by γ-ray, 220 MeV C ions, 350 MeV Ne ions and 175 MeV Ar ions. The G -value decreases in this order. The G -value for adipic acid decreases more than that for α-alanine. The decreases in the G -value are ascribed to high local dose in the ion tracks. Effective G -value of the radicals for γ-irradiations decreases at high doses. The local dose in the ion tracks exceeds those doses, and the G -values for the ion irradiation are hence smaller than the G -value for γ-irradiations. The difference in the dependence of the G -values for α-alanine and adipic acid on the ion beams is due to difference in the dose–yield relationship for radical formation. The high local dose in the ion tracks exceeds the gelation dose of some of polymers. Formation of gel strings of polydimethylsiloxanes generated in heavy ion tracks was observed by atomic force microscopy.

Effect of specific energy of heavy ions for 1,2,4,5-tetracyanobenzene radical anion formation

Abstract The absorption spectrum of poly(vinyl alcohol) (PVA) film doped with 1,2,4,5-tetracyanobenzene (TCNB) was measured after the irradiation with several hundred MeV of C, Ne and Ar ions. The absorbance due to the TCNB radical anion increased and then decreased with increasing the fluence for all ions. The fluence dependence of the absorbance was analyzed by use of the “chemical” track model with a cylindrical structure. As a result, the estimated radius of the chemical track decreases for C and Ne ions with increasing specific energy (ion energy per atomic mass unit). Furthermore, at the same specific energy, the radius increases with increasing ion mass. The formation yield (G-value) of the TCNB radical anion estimated by optical absorbance and ESR measurements was smaller than that by γ -ray irradiation.

Radical formation in the radiolysis of solid adipic acid by γ-rays and heavy ions

Radical formation in solid adipic acid irradiated with γ-rays, 175 MeV Ar8+, 220 MeV C5+, and 350 MeV Ne8+ ions was studied by ESR method. The radical yield for the ion irradiations (number of radicals per incident ion) is constant below a critical fluence of about 5 × 1010ions cm−2 for the Ar ions, 1011 ions cm−2 for the C and the Ne ions. Above the critical fluence, the yield decreases with increasing ion fluence. The G-value of the radical formation was obtained from the constant yield at the low fluences: 5.6 for the C ion, 2.3 for the Ne ion, and 0.65 for the Ar ion. The G-value for the Ar ion is about 110 of the value of 6.3 for γ-irradiation. The larger effect of radiation quality for adipic acid than the effect for alanine is ascribed to the difference in the dose-yield relationship of the radical formations.

Energy distribution around 175 MeV Ar ion path in argon at the density of water

The ionization distribution in Ar gas by 175 MeV Ar ion was measured, and reduced to the energy density as a function of the radial distance in water. The energy density within the radial distance smaller than 294 nm decreased proportionally to the inverse of the square of the distance. Beyond this distance, however, the energy density decreased more steeply. The deposited energy except in the core region of the track amounts to 89% of linear energy transfer (LET).