Hiromi Sunaga

Accumulated Charge Profile in Polyethylene during Fast Electron Irradiations

Space charge profile and consequent field strength profile were obtained by solving the continuity and Poissons simultaneous equations. Experimental electron deposition curve and radiation-induced conductivity curve were used for calculation. The calculated results explained well the observed replacement current and electrical breakdown phenomena. Dose rate, dose, and temperature effects on charge accumulation were also investigated.

The Effect of Accumulated Charge on Depth Dose Profile in Poly(Methylmethacrylate) Irradiated with Fast Electron Beam

The reduction of the electron penetration length induced by space charge accumulation in solid insulator during exposure of the fast electron beam of the current density below 1 ¿A/cm2 was found by depth-dose measurement in red-dyed poly(methylmethacrylate) plate. The reduction rate depends on charge fluence, the current density and the irradiation temperature. The experimental results are well explained by the calculation of the space charge density and the consequent field strength; these are obtained from a consideration of the deformation of depth-dose profile and the deposition function of thermalized electrons due to the increase of charge accumulation.

On the degradation of 1-MeV electron irradiated Si/sub 1-x/Ge/sub x/ diodes

The degradation of n/sup +/-Si/p/sup +/-Si/sub 1-x/Ge/sub x/ diodes, which are fabricated on strained Si/sub 1-x/Ge/sub x/ epitaxial layers grown on conventional p-type Si substrates, is investigated through the study of the annealing behaviour of forward and reverse diode current and the electrically active defects induced in the Si/sub 1-x/Ge/sub x/ epitaxial layers. The diodes are irradiated at room temperature with 1-MeV electrons with fluences ranging from 10/sup 14/ to 10/sup 15/ e/cm/sup 2/ in a high voltage transmission electron microscope. The germanium fraction of the Si/sub 1-x/Ge/sub x/ epitaxial layer used for the diodes in this study is x=0.12 and 0.16. The degradation of the diode performance and the presence of deep levels are investigated as a function of electron fluence and germanium content. The degradation of the x=0.12 diodes is more remarkable than that of the x=0.16 diodes. In order to examine the recovery process, isochronal thermal anneals are performed in the temperature range between 100 and 350/spl deg/C. From the annealing behaviour, it is pointed out that the electron capture levels, which are related with interstitial boron, are mainly responsible for the increase of reverse and forward current. >

Depth-Dose Distributions in an Aluminum-Blue-Cellophane Stack for a High-Intensity Pulsed Electron Beam in an Atmosphere of Helium

TANAKA, R., SUNAGA, H., AND HOTTA, H. Depth-Dose Distributions in an AluminumBlue-Cellophane Stack for a High-Intensity Pulsed Electron Beam in an Atmosphere of Helium. Radiat. Res. 63, 14-23 (1975). The depth-dose curves of a high-intensity relativistic pulsed electron beam at various distances from a tube face in helium of various pressures were determined by using a stack of aluminum absorbers and blue cellophane sheets. The curves indicate that the beam is self-focused at two pressure regions, i.e., near 10 Torr and above 600 Torr, and that the beam is defocused considerably between these two pinches. The extrapolated ranges decreased rapidly with distance from the tube face at 0.01, 50 and 655 Torr but not at 10 Torr. This decrease is explained in terms of some beam-plasma interactions--especially, in terms of an induced backward electric field and weak focusing of lower-energy electrons.

Degradation and recovery of AlGaAs/GaAs p-HEMT irradiated by high-energy particle

Abstract Results of an extensive study on the irradiation damage and its recovery behavior resulting from thermal annealing in AlGaAs/GaAs pseudomorphic high electron mobility transistors (HEMTs) subjected to a 220-MeV carbon, 1-MeV electrons and 1-MeV fast neutrons are presented. The drain current and effective mobility decrease after irradiation, while the threshold voltage increases in positive direction. The decrease of the drain current and mobility is thought to be due to the scattering of channel electrons with the induced lattice defects and also to the decrease of the electron density in the two dimensional electron gas region. Isochronal thermal annealing shows that the device performance degraded by the irradiation recovers. The decreased drain current for output characteristics recovers by 75% of pre-rad value after 300°C thermal annealing for AlGaAs HEMTs irradiated by carbon particles with a fluence of 1×10 12 cm −2 . The influence of the materials and radiation source on the degradation is also discussed with respect to the nonionizing energy loss. Those are mainly attributed to the difference of particle mass and the probability of nuclear collision for the formation of lattice defect in Si-doped AlGaAs donor layer. A comparison is also made with results obtained on irradiated InGaP/InGaAs p-HEMTs in order to investigate the effect of the constituent atom. The damage coefficient of AlGaAs HEMTs is also about one order greater than that of InGaP HEMTs for the same radiation source. The materials and radiation source dependence of performance degradation is mainly thought to be attributed to the difference of mass and the possibility of nuclear collision for the formation of lattice defects in Si-doped donor layer.

Sterilization of Bacillus spores by converted X rays

Abstract Relative sensitivities of endospores of Bacillus pumilus E601, B. subtilis IAM1069, B. megaterium S31 and B. brevis S5 to gamma rays, converted X rays (bremsstrahlung) and electron beams were examined in order to estimate the conditions in which converted X rays kill Bacillus spores. The radiation sensitivities to gamma rays and electron beams of each strain dried on glass fiber filter without additives were found to be almost equivalent, and D values were obtained as follows: 1.5–1.6 kGy for B. pumilus, 1.4–1.5 kGy for B. subtilis, 1.9–2.0 kGy for B. megaterium and 1.6–2.0 kGy for B. brevis. The radiation sensitivities of endospores of each strain to electron beams were slightly lower than those to gamma rays in the dry condition with additives of 2% peptone + 1 % glycerin on glass fiber filters. The increase of radiation resistance in the presence of additives was also observed with X rays, and it was on an intermediate level between those with gamma rays and electron beams. In the dry condition using cellulose filter paper, only the radiation resistances of B. megaterium and B. brevis in the presence of additives B. megaterium and B. brevis in the presence of additives were increased.

Radiation Dosimeter Using Peroxy Radicals in Irradiated Polytetrafluoroethylene

A new method of radiation dosimetry using peroxy radicals in irradiated polytetrafluoroethylene (PTFE) has been developed. The PTFE used is in powder form. The results show that this dosimeter is useful for both electron and 60Co gamma-ray irradiation. The concentration of the peroxy radicals linearly increases with dose up to 100 Mrads and does not depend on the dose-rate. The peroxy radicals formed by irradiation are stable during prolonged storage, and handling of the sample is easy. The behavior of the peroxy radicals in the irradiated PTFE is discussed.

Dose intercomparison experiment for gamma rays and 3-MeV electrons by mailing dosimetry using free-radical dosimeters

Abstract The high-dose intercomparison experiments between BARC and JAERI for 60 Co-γ-rays and 3-MeV electrons were carried out by mailing alanine (powder and alanine-polymer) and glutamine (powder) dosimeters between the two facilities. Powder dosimeters and alanine-polymer dosimeters were read out by spectrophotometry and EPR spectrometry, respectively. Absorbed dose values at about 1, 10, 33 and 54 kGy estimated by these dosimeters were in good agreement with JAERI nominal doses within ±5% both for γ-rays and electrons. This preliminary result shows that these free-radical dosimeters have useful characteristics as mailing dosimeters for regional transfer dose standardization.

Intercomparative study on low energy electron beam dosimetry

Abstract Studies of dose intercomparison and dose estimation of low energy electron beams from 150 to 300 keV have been conducted to unify and standardize the methods of dosimetry and dose estimation as an activity of Low-Energy Electron-Dose Measurement Committee which started in Japan in 1985. The transfer dosimetry with thin film dosimeters by mail was found to be useful for dose intercomparison between irradiation plants and unification of dose estimation methods. A simple dose calculation formula as a function of basic irradiation parameters, proposed for rough dose estimation, was also checked on the basis of the result of the dose intercomparison.

A simple and accurate measurement method of current density of an electron accelerator for irradiation

Abstract For simple and accurate measurement of the current density distribution in a broad beam from electron accelerators, a method for detecting the charge absorbed in a graphite target exposed to the air has been examined. The present report means to solve several fundamental problems. The effective incidence area of the absorber is strictly defined by the design of the geometrical arrangement of the absorber assembly. Electron backscattering from the absorber is corrected with backscattering coefficients in consideration of oblique incidence on the absorber. The influence of ionic charge produced in air is ascribed to the contact potential between the absorber and the guard, and correction methods are proposed.