Radiation Physics and Chemistry (1977)最新文献

G-values for crosslinking, G(X) and for chain scissions, G(S), have been determined for the electron beam irradiation at room temperature in vacuum of a polyetherimide called ULTEM by General Electric Co.. In addition, ESR studies of the free radicals produced in ULTEM by γ-irradiation in vacuum at 77K have also been carried out. In the electron beam irradiation experiments the very low G(X) and G(S) values, only 0.014 and 0.005 respectively, demonstrate the high radiation stability of this material. The decay at 70° and 160°C of the free radicals in the electron beam irradiated samples accurately followed the Waite equation. Also the solubility-dose data could be accurately interpreted in terms of the Charlesby-Pinner equation.

Radiation sterilization of ultrahigh molecular weight polyethylene (UHMW-PE) was recently found to cause changes in crystallinity, contradicting earlier observations on linear polyethylene of lower molecular weight. In this study, UHMW-PE (Hercules 1900) was gamma-irradiated up to 21 Mrad. Changes in melting and crystallization temperatures, enthalpies of melting and of crystallization, determined by differential scanning calorimetry, are reported. In particular, the temperature at the onset of crystallization provided a clearer view of the radiation damage to the polymer chains. A mechanism based on chain scission is proposed to explain the observed increase in crystallinity in agreement with recent findings. The crystallization temperature may be useful as an indicator of radiation and/or other damage to the UHMW-PE.

The theoretical model of the electron localized in frozen ionic solutions has been applied to investigate the influence of the trap distortion on the electron energy levels in the trap. It has been found that asymmetric traps are slightly more shallow than the symmetrical trap. The differences between electron absorption spectra obtained by pulse radiolysis and those by γ-radiolysis are then explained in terms of the relaxation of distorted ionic traps.

The rate of the reaction of the radiolytically produced reduced species in acetonitrile with various protic solutes (alcohols and water) was measured by the competition method and by directly following the rate of disappearance of the reduced species in pulse radiolytic experiments. The rate constants thus obtained were correlated with the pK_a of the protic additives. This correlation leads to the conclusion that the reaction occurs via a proton transfer. Temperature effect studies on the rate of this reaction lead to the conclusion that the reactive species is the dimer anion radical (CH₃CN)^-₂.

Irradiation of silicon power rectifiers with electrons of 12 MeV energy has been carried out. Minority carrier lifetime τ, forward voltage V_F, reverse recovered charge Q_RR, reverse recovery time t_RR for the diodes, circuit commutated turn-off time t_q, and on-state voltage V_T for the thyristors are measured as a function of dose. Power diodes and thyristors obtained from 〈111〉 neutron transutation or phosphorus doped float-zone silicon slices having 120Ωcm and 65Ωcm starting resistivity respectively and Ga-diffused are irradiated at room temperature. A linear relationship between carrier lifetime of irradiated diodes and electron dose is found and the calculated damage coefficients are k_τ = 1.1x10^-8 cm²/s and 7.2x10^-9 cm²/s for the low-level and high-level lifetimes respectively at 25°C. For irradiated thyristors the linear relationship between turn-off time and dose yields k_tq = 3x10^-9 cm²/s at 125°C. Electron irradiation also affects the resistivity of the starting n-type silicon, increasing it of ≈ 15Ωcm for radiation doses > 1×10⁴ Gy. A dose rate effect on the electrical characteristics of the devices using pulses of different duration is analyzed. Annealing studies are carried out at 150 °C, 200°C and 360°C to assess the stability of the defects produced by the electron bombardment by monitoring the variation of the electrical characteristics of the irradiated devices in the temperature range of interest. DLTS measurements performed on electron irradiated power rectifiers have revealed a complex defect pattern. The E₁ defect level (E_c-0.17 ev) is the principal recombination center that controls lifetime following room temperature irradiation. The energy levels and capture cross sections of these irradiation induced-defects are reported. This study confirms that lifetime control in silicon power devices is feasible by high energy electrons. The major advantages of this technique over metallic diffusion or ⁶⁰Co γ-irradiation methods are: better quality, lower processing cost and higher device yields. Annealing after irradiation is important to ensure long-term device stability.

In 1981 Kronenberg, McLaughlin, and Siebentritt proposed measurement of radiation dosage using optical waveguides with leuco dye solutions. Based on this work, an opti-chromic system was proposed at the Fourth International Meeting on Radiation Processing. This opti-chromic system has been evaluated by McLaughlin and Radak. The opti-chromic waveguide system may be even more valuable for other applications which involve measurements with special requirements and configurations.

The linearity of the radiation response can be enhanced by proper selection of leuco dye concentration, waveguide materials, organic activator solvents, and trace chemical additives. This paper presents experimental data resulting from an examination of the organic solvents TEP, DMSO, and n-propyl alcohol in relationship to stability, temperature characteristics, and radiation chemistry.

The experimental data indicates that by varying the types and combinations of organic solvents, special opti-chromic waveguides can be fabricated to measure various radiation ranges under a variety of temperature ranges which have stability over time.

This report describes the latest informations of the utilization of electron processing systems in Japan and electron processing systems for cross-linking of wire insulations and curing of plywood coating in Asian countries and the latest features of electron processing systems.

The high-dose gamma ray response (10³ - 5×10⁵ Gy) of radiochromic film dosimeters, with ten kinds of plastic matrices (polychlorostyrene containing 1 or 25% C

The responses and stabilities of the polyhalostyrene and nylon films were only slightly affected by the different atmospheres of irradiation, but there were marked differences of response for the other film types. The dyed cellulose triacetate films and polyvinylchloride films are generally more sensitive in N₂O and O₂-deprived atmospheres than in air or in O₂, but the opposite is true for the dyed polyvinyl butyral and aromatic nylon films. The dyed cellulose triacetate and dyed polychlorostryrene with 1% C

UV and EB curing represent complementary technologies with respective advantages and disadvantages. This paper deals with the design and evaluation of UV curable coatings to optimize cure rate and film properties. Topics included are state-of-the-art photoinitiator systems, light intensity effects, retardation of air-inhibition, adhesion, and amplification of photons for enhanced speed of cure.

Secondary emission sources “Laminar Process” allow the extension of the section of the beam in two directions and to control the density of the dose in any place of the beam.

Consequently the dose rate can be modulated and no beam is applied to the support of the window which allows much higher flux and less cooling problems.

This development has pushed us to develop a new type of inerting chamber with low leakage and automatic adaptation to the thickness of the product to be treated.