Radiation chemical processes induced by the passage of heavy charged partic
les in organic materials are discussed. An overview of the physics of energ
y loss processes on the subsequent chemical reactions is given. The effects
of the dominant physical parameter, the linear energy transfer, (LET), on
the radical and molecular products from organic compounds are examined. It
is shown how the complex interaction of excited states and radical intermed
iates can sometimes make it difficult to predict the variation of final pro
duct yields with high LET radiation. Molecular hydrogen yields are examined
in detail because of their fundamental and practical aspects. Hydrogen for
mation is especially interesting because it is produced by a variety of rea
ctions with different relative LET dependences. The yield of Hz is found to
be very similar for liquid organic molecules and solid polymers containing
the same molecule as the side group connected to the main carbon-carbon ba
ckbone. Biradical products and cross-linking yields are also found to be co
mparable suggesting very similar chemistry between the liquid and solid com
pounds. (C) 2001 Elsevier Science Ltd. All rights reserved.