I and my friends were taking part in a competition(physics and chem expertise needed) and we were having a few doubts about something. I was hoping if anyone of you can help in the clarification of the doubt. We use a positron beam(from the DESY II particle accelerator) directed towards a polymer(eg polythene), which will annihilate a few valence electrons of the atoms in the chain. We’ve not found any source to support our theory that bonds will break although they should as electrons are being annihilated which support bonding. We searched and found nothing because no one else has had a similar experiment before. We also wanted to know if we annihilate an inner core electron then will it lead the de-excitation of the valence electrons further leading to destabilization of bonds. We can’t confirm how the electron donors will react with carbocations/radicals formed, also since there are many possibilities and we are unable to consider all of them. The momentum of the positrons can be set to any value between 0.5 GeV/c and 6 GeV/c. We needed some confirmation to the feasibility of the experiment. All we need is to break the carbon chain, any other ways to do that would be appreciated.

  • $\begingroup$ That's just using ionising radiation, specific kind is largely irrelevant. It does some damage. If you irradiate it enough, you might find some crosslinking, depolymerization and general weakening of material. $\endgroup$ – Mithoron Mar 30 at 18:02

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".

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  • $\begingroup$ In our case, we are working on electron-positron annihilation and not breaking bonds using gamma rays. As the bonds consist of electrons when we annihilate electrons, will it lead to the instability of the carbon chain? And can we then use electron donor groups to break the bonds and form new small carbon chains? $\endgroup$ – Mihir Gupta Mar 30 at 12:22
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    $\begingroup$ Your beam is mostly energy, and only incidentally positrons. The scattering on high energy e-, e+ and gamma rays are all pretty much the same until the energy drops below 1MeV $\endgroup$ – Bob Jacobsen Mar 30 at 13:19
  • $\begingroup$ Right. Since the energy of the positron beam generated in DESY II is about 0.5 GeV , we want to reduce its energy to about 500 keV. We need a suitable material to reduce the kinetic energy of the positron beam , when we pass the beam through it. By online sources we found Al suitable for the task but still we aren’t sure and want to know if it will work. Is there any other way you can think of? $\endgroup$ – Mihir Gupta Mar 30 at 16:24
  • $\begingroup$ @MihirGupta I'm not sure there's a need to complicate it. You can just check how high energy particles are gonna damage it. If you already have access to high energy source, why waste it? $\endgroup$ – Mithoron Mar 30 at 18:13

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