Breaking of carbon chains due to annihilation of electrons using positron beams
This a problem of radiation chemistry. It has been thoroughly studied in the years 1950 - 1960 - 1970 with gamma rays. When intense source of gamma rays strikes water, electrons are extracted from the water molecule. And some of these electrons are coming from the valence bond O-H. The bond is then weakened, and may even be broken. Usually the electron soon comes back to its original atom. This produces individual H atoms and OH radicals. Usually H and OH soon recombine and produce again H2O a few nanoseconds later. But if the irradiation is intense, they may recombine with similar neighbors. And this produce dissolved H2 and H2O2 molecules. So the water sample contains more and more dissolved H2 and H2O2. Titration of H2O2 in solution is possible, and may be used to determine the doses and the intensity of the radiation absorbed by the sample. 

The same experiments have been done with hydrocarbons. After irradiation, hexane, for example, is partly converted into dodecane, with a lot of different isomers. The distribution of these isomers allows to determine where the initial breaking in hexane happened, in other words which C-H or C-C bond has been initially broken, and in which proportion. Why don't you read the publications by Ausloos or Gäumann or others in this old literature. Today nearly nobody is interested any more in this chemistry, which is considered to be "finished".