Molecular Hydrogen Production in the Radiolysis of High-Density Polyethylene

Abstract

The production of molecular hydrogen in the radiolysis of high-density polyethylene by γ rays and heavy ion beams has been investigated. Only the slightest increase in the radiation chemical yield of 3.1 molecules/100 eV was found from γ rays to protons of 5-15 MeV. A gradual increase in yield was observed on further increasing the linear energy transfer of the incident particles. This increase amounted to almost a doubling in the hydrogen yield from 10 eV/nm protons to about 800 eV/nm carbon ions. The exact reason for the increase in molecular hydrogen yield is uncertain, but it may involve reactions of excited states or enhanced combination reactions of carbon-centered radicals, thereby allowing more hydrogen to escape the particle tracks. Diffusion from the bulk material was found to have a dominant role on the observed dynamic profiles of hydrogen gas. A simple one-dimensional diffusion model was used to estimate the diffusion constant of hydrogen in polyethylene to be 2.2 × 10 -6 cm 2 /s.

Hydrogen production in ?-ray and helium-ion radiolysis of polyethylene, polypropylene, poly(methyl-methacrylate), and polystyrene

“…Companion studies were performed with γ rays on these polymers and high‐density polyethylene (HDPE). These results are combined with previous studies with helium ions on HDPE9 to give an overview of the effects of LET on the production of molecular hydrogen from different types of polymeric materials.…”

“…It was assumed that the stabilizers in the polyethylene and PP were at too low a concentration to significantly affect the yield of molecular hydrogen. All the polymer samples were cut into small pellets with a diameter of about 1 mm to minimize the influence of gas diffusion from the bulk polymer on the observed yields 9. The pellets were surface‐cleaned with water from a Millipore Milli‐Q UV system and dried in a vacuum oven before the irradiations.…”

“…The flow of UHP nitrogen through the sample cell was performed as in the γ radiolysis. Hydrogen detection involving an inline technique similar to that previously described9 was the same for both γ‐ray and helium‐ion radiolysis. A quadrupole mass spectrometer (Blazers QMA140 analyzer) was used to analyze the carrier gas downstream from the sample cell through a capillary tube (ϕ = 50 μm, L = 20 cm).…”

“…Radiation chemical effects on polymeric materials have been extensively studied with γ rays and electron beams 1–3. In recent years, the research interests in this field have begun to include gas production due to irradiation with ion beams of different types and energies 4–9. These studies have determined the radiation‐induced chemical changes in polymers as a function of the linear energy transfer (LET), equal to the stopping power, of the incident particles.…”

“…Another very important and practical problem involved in the production of hydrogen is the radiolysis of the polymer materials mixed with nuclear waste. Hazardous gases such as hydrogen and methane produced in the self‐radiolysis of these polymer matrices cause difficulties in the handling, shipping, and storage of the nuclear waste 9–11. α particles emitted by transuranic radionuclei may lead to product yields completely different than those found with γ rays.…”