Toshiyuki Kijima

Monte Carlo calculations of the behavior of 300 keV electrons from accelerators

Abstract A Monte Carlo method for the passage of electrons based on a single scatterring model has been developed. A code constructed is operable on personal computers, and has been applied to analyze electron behavior in a layered system consisting of Ti (an accelerator window), air, CTA and backing material irradiated by 300 keV electrons, in the static and dynamic irradiation. The energy spectra and the angular distributions of electrons at the CTA surface as well as depth distributions of energy deposition in the CTA layer of 114 μm thickness placed on various backing materials have been obtained. The backscattering coefficients for various backing materials have been calculated. These results indicate that the characteristics of the electrons at the forward surface of CTA in the dynamic irradiation are similar to those of the electrons diffusely incident on the backing material. Some of these results are in good agreement with our experiments.

Electron beam dosimetry for a thin-layer absorber irradiated by 300-keV electrons

Abstract Depth-dose distributions in thin-layer absorbers were measured for 300-keV electrons from a scanning-type irradiation system, the electrons having penetrated through a Ti-window and an air gap. Irradiations of stacks of cellulose triacetate(CTA) film were carried out using either a conveyer (i.e. dynamic irradiation) or fixed (i.e. static) irradiation. The sample was irradiated using various angles of incidence of electrons, in order to examine the effect of obliqueness of electron incidence at low-energy representative of routine radiation curing of thin polymeric or resin layers. Dynamic irradiation gives broader and shallower depth-dose distributions than static irradiation. Greater obliqueness of incident electrons gives results that can be explained in terms of broader and shallower depth—dose distributions. The back-scattering of incident electrons by a metal(Sn) backing material enhances the absorbed dose in a polymeric layer and changes the overall distribution. It is suggested that any theoretical estimations of the absorbed dose in thin layers irradiated in electron beam curing must be accomplished and supported by experimental data such as that provided by this investigation.

Electron beam dosimetry for a multilayer absorber

Abstract Depth dose distributions were measured in a multilayer absorber of Ti-air-cellulose triacetate (CTA)-backing material (Pb, Sn, Fe, Al and CTA) irradiated with 300 and 800-keV electrons. The results are compared with the calculated value using computational code for multilayer absorbers (EDMULT) developed by Tabata et al. (1989, 1990). The absorbed dose in CTA exceeds the calculated value near the surface, while it is smaller than the calculated dose as the penetration depth becomes closer to the range of incident electrons. The measurements and computations show better agreement for the high-energy (800-keV) electrons than for the 300-keV electrons, probably because of the greater obiqueness of incidence at lower energies, which is not taken into account by the computation code.

Formation and quenching of NH fragments in excited states by high energy electron irradiation of helium-ammonia gas mixture

Abstract A gas mixture of helium and ammonia was irradiated with an electron beam from a Van de Graaff accelerator and emission intensities from excited NH fragments were measured as a function of pressure, concentration of ammonia, and the amounts of additives. The energy transfer process is discussed on the basis of the experimental results and kinetic analysis.

Depth-dose distributions in a thin-layer absorber irradiated by 300-keV electrons

Abstract Depth-dose distributions in thin-layers of cellulose triacetate (CTA) film for 300-keV electrons from a scanning-type irradiation system have been estimated by a Monte Carlo radiation transport calculation, and factors for determining the distribution have been investigated. The peak of the typical depth-dose distribution of irradiated CTA film by dynamic irradiation is closer to the surface compared with the case of static irradiation. The main reason for this peak-shift can be the incidence angle of incidence electrons. In the case of electron fluence rate −2 · s −1 , Monte Carlo calculations of 300-keV electron-beam dose distributions in multi-layer CTA film absorber have shown good agreement with the experimental dose measurements, even with backing materials such as Sn, Pb. With fluence rates greater than 0.12 μC · cm −2 · s −1 , a discrepancy between the calculated and the experimental has been observed, mainly due to the effect of charge deposition in the sample at the high dose rates.

Formation and quenching of CO and CO ion in excited states by high energy electron irradiation of heliumcarbon monoxide gas mixture

Abstract Gas mixture of helium and carbon monoxide was irradiated with electron beam from a Van de Graaff accelerator and emission intensities from excited CO and CO ion were measured as a function of pressure, concentration of carbon monoxide in wide ranges. The results are fitted with kinetic analytical formulae derived from simple competition reactions involving energy transfer process assuming steady state concentrations for intermediates, and reasonable agreements were obtained between the experimental results and those predicted in the range of reaction conditions studied in this work.

Photo-emission from excited CF2 radical by high energy electron irradiation of chlorofluorocarbons

Chlorofluorocarbons CCl2F2 (CFC-12) and CHClF2 (HCFC-22) in the gas phase were irradiated with high energy electron beam from a Van de Graaff accelerator and emission intensity of the excited CF2 (A1B1) radical was measured as a function of sample gas. The result shows that a formation path via a precursor exists besides of the direct formation by electron impact. Experiments were also made for mixtures of chlorofluorocarbons and helium or argon.