Douglas E. Weiss

Dose distributions in tubing irradiated by electron beam : Monte Carlo simulation and measurement

A set of nine tube sleeves was prepared by wrapping polyethylene film around a mandrel. Wall thicknesses ranged from a nominal 0.3 to 0.6 cm and diameters ranged from 2 to 5 cm. The sleeves were irradiated with a scanning 3 MeV electron beam and were dose-mapped by indexing and unwrapping the tube sleeves and measuring the dose by an FTIR spectroscopic technique. A Monte Carlo simulation model is also described which includes all important elements of 3-D geometry necessary to describe this experiment including window foil and beam scan angle. The simulation results were compared with the highly detailed dose distribution measurements in the tubing and the differences were found to be generally within 3 to 6 percent.

Electron beam process validation for sterilization of complex geometries

Abstract The application of low-energy electrons for the disinfection of containers of complex geometries has been limited due to their inability to efficiently penetrate the rigid walls. Most three-dimensional applications have been evaluated using higher energy processors with bulk or through-the-wall treatment. This work has been directed to the validation of electron disinfection of interior surfaces by injecting electrons through the open-mouth of the container. Both direct thin-film dosimetric mapping of the interior and exterior dose distributions for in-line treatment have been conducted and compared with the results of Monte Carlo modeling utilizing 106 or more source electron histories. Sterilizer characterization and model assumptions are described and the advantages of the modeling technique for process parameter optimization discussed.

Pulse radiolysis of vinyl monomers, in the pure state and with added pyrene

Abstract Pulse radiolysis studies have been used to investigate the early phenomena in the radiolysis of acrylic acid, methyl acrylate, butyl vinyl ether, propionic acid, methyl acetate and butyl ether; the latter three solvents were used as model compounds for these vinyl monomers. The triplet state, radical cation, radical anion, and free radical of pyrene (cyclohexadienyl type) were observed to various degrees in the radiolysis of pyrene in these monomers. In acrylic acid, where the free radical and the cation dominate, the monomer polymerizes efficiently, whereas in butyl vinyl ether, where the anion dominates, polymerization does not occur. The behavior of methyl acrylate lies between that of acrylic acid and butyl vinyl ether. However, the high intensity of the electron pulses creates a high concentration of radicals leading to a short lifetime of the radical which in turn leads to a much smaller yield of polymerization. The mechanism of polymerization under high energy radiation is found to be free radical in nature.

Pulsed polymerization of acrylate monomers using electron beam. Conditions for achieving single-phase heterogeneous polymerization

Abstract The heterogeneous nature of energy deposition by ionizing radiation can be used to advantage by pulsing an electron beam at low dose per pulse and high pulse rates. Track overlap is avoided for a short period of time, sufficient to allow an essentially heterogeneous polymerization to take place. High pulse rates appear to maintain this advantage by terminating the incipient homogeneous kinetics while re-initiating the heterogeneous kinetics. Polymerization by this method shortens the residence time necessary for full conversion but beyond 50% conversion, there may no longer be any advantage in a diffusion-limited system. Lower temperature also helps to reduce termination in the early phase of polymerization.