Dynamic evolution of gases in the γ‐ and helium‐ion radiolyses of solid polymers

Abstract

The dynamic evolution of gaseous hydrogen, methane, and carbon dioxide in the ␥and 4 He-ion radiolyses of solid polymers was investigated. The polymers used include low-density and high-density polyethylene, polypropylene, polystyrene, poly-(methyl methacrylate), Nylon 11, Nylon 6, and poly(dimer acid-co-alkyl polyamine). An inline quadrupole mass spectrometer was utilized to monitor the dynamic profiles of the gases produced in the radiolysis. One-and two-dimensional numerical diffusion models were developed to simulate and extract optimum diffusion coefficients and gas yields from the experimental dynamic gas profiles. It was found that the dynamic evolution of molecular hydrogen from the bulk polymer is controlled by its diffusion in most cases, such as CO 2 in poly(methyl methacrylate). In the ␥ radiolysis of some polymers such as low-density polyethylene and polypropylene, the dynamic evolution of methane is only partially controlled by the diffusion process, and some other postirradiation process is a factor. It is concluded that the simulation method developed in this article is helpful in understanding and predicting the mechanisms of gas evolution in the radiolysis of solid polymers.

Microelectromechanical Transducer to Monitor High-Doses of Nuclear Irradiation

“…HDPE can be found in many different shapes, such as rods, pellets, powders, films, sheets or fibres [ 74 , 75 ]. Even if the hydrogen emission yield factor seems not to depend on the HDPE thickness and shape [ 76 ], the release of this gas in the surrounding atmosphere depends on its diffusion inside the material (Fick’s law of diffusion). Thin films of PE appear to be the best choice in our application.…”

“…This factor appeared not to be significantly dependent on the film thickness and dose level, at least for doses lower than 24.03 kGy. The maximum duration time (in s) necessary for hydrogen to diffuse outside of the polymer can be estimated from the Fick’s law [ 76 ] as follows: where (in µm) is the film thickness and (in µm 2 ·s −1 ) denotes the hydrogen diffusion coefficient in the polymer. At a film thickness ranging from 10 µm to 1000 µm and a typical diffusion coefficient of 2.2 × 10 6 cm 2 ·s −1 [ 76 ], was between about 2 s and 13 min, that is, a duration shorter than the time between the end of the irradiation and beginning of the gas composition analysis.…”

“…The maximum duration time (in s) necessary for hydrogen to diffuse outside of the polymer can be estimated from the Fick’s law [ 76 ] as follows: where (in µm) is the film thickness and (in µm 2 ·s −1 ) denotes the hydrogen diffusion coefficient in the polymer. At a film thickness ranging from 10 µm to 1000 µm and a typical diffusion coefficient of 2.2 × 10 6 cm 2 ·s −1 [ 76 ], was between about 2 s and 13 min, that is, a duration shorter than the time between the end of the irradiation and beginning of the gas composition analysis. This confirms that there was no residual gas trapped in the HDPE film during our experiment and, consequently, the total quantity of hydrogen produced during the radiolysis was accurately estimated.…”

“…where ℎ (in µm) is the film thickness and (in µm 2 •s −1 ) denotes the hydrogen diffusion coefficient in the polymer. At a film thickness ranging from 10 µm to 1000 µm and a typical diffusion coefficient of 2.2 × 10 6 cm 2 •s −1 [76], ∆ was between about 2 s The emission yield factor G x of gas constituent x can be estimated as follows:…”

The radiolysis of poly(4-vinylpyridine) quaternary salt ion exchange resins

“…The radiolysis of organic polymer materials leads to the production of gases, especially H 2 , depending on the nature of polymers or the type of ionizing radiation [11][12][13][14][15][16][17]. The production of H 2 can be explained from simple radical chemistry (e.g., H atom-H atom combination, H atom abstraction, and disproportionation) following C-H bond breakage due to the energy deposited by the passage of ionizing radiation or from the unimolecular decomposition of excited singlet states [13,16].…”