Hazardous Gas Production by Alpha Particles in Solid Organic Transuranic Waste Matrices Page: 2 of 3
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Fundamental radiation chemical techniques are used to elucidate the basic
processes occurring in the heavy-ion radiolysis of some of the solid hydrocarbon
matrices such as polymers that are associated with many of the transuranic waste
deposits or the transportation of these radionuclides. The environmental management
of mixed waste containing transuranic radionuclides is difficult because these nuclides
are alpha particle emitters and the energy deposited by the alpha particles causes
chemical transformations in the matrices accompanying the waste. Basic gamma
radiolysis studies have been performed on some organic matrices, however, the
chemical changes induced by alpha particles and other heavy ions are typically very
different and product yields can vary by a large magnitude. The objective of this
research is to measure the production of hazardous gases such as molecular hydrogen
and methane produced in the proton, helium ion, and carbon ion radiolysis of selected
solid organic matrices in order to obtain fundamental mechanistic information on the
radiolytic decomposition of these materials. This knowledge can also be used to
directly give reasonable estimates of explosive or flammability hazards in the storage or
transport of transuranic wastes in order to enhance the safety of DOE sites.
Research Progress and Implications
This report summarizes the work after 21 months of a three-year project on
determining the production of hazardous gases in transuranic waste materials. The first
stage of the project was to design and build an assembly to measure absolute radiolytic
yields in solid organic matrices using accelerated ion beams. The very short range of
ions such as alpha particles and the nature of the products place severe limitations on
the experimental technique. A window assembly was constructed allowing the beam to
pass consecutively through a collimator, a vacuum exit window and into the solid
sample. Two types of sample configurations are necessary. Either a solid sheet of
sample is sealed a short distance from the exit window or small pellets of sample are
confined to a sample holder. A stream of gas, such as nitrogen, flows between the
sample and the beam exit window or between the pellets to flush away gaseous
products that evolve from the sample surface. The gas steam is sampled with a
quadrupole mass spectrometer. By monitoring the desired mass peak with the
spectrometer it is possible to quantitatively determine a number of different products on
The first experiments have focused on the hydrogen evolution in polyethylene
because it is either associated with much of the transuranic waste or it can be used as
a model of such waste. Hydrogen is the main gaseous product formed in polyethylene
and the present work finds a radiation chemical yield of 3.1 molecules/100 eV of energy
absorbed, in agreement with the literature. (1) A gradual increase in hydrogen yield is
found with increasing particle linear energy transfer, LET. The yield of hydrogen with 5
MeV helium ions (LET=97 eV/nm) is 4.5 molecules/100 eV. The highest LET carbon
ions (10 MeV, 840 eV/nm) give yields of hydrogen of up to 5.7 eV/100 eV. The
mechanism for hydrogen formation in particle tracks is not well understood. Increased
radical-radical combination reactions in the particle tracks are probably allowing more
hydrogen atoms to undergo abstraction reactions with the bulk material to form
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LaVerne, Jay A. Hazardous Gas Production by Alpha Particles in Solid Organic Transuranic Waste Matrices, report, June 1, 1999; Notre Dame, Indiana. (digital.library.unt.edu/ark:/67531/metadc788802/m1/2/: accessed April 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.