0
$\begingroup$

what happens to positrons after pair production?

There are two possible outcomes, but which one is true or most probable?

  1. The particle antiparticle pair have enough kinetic energy to overcome the electrostatic attraction between so they will move away indefinitely in opposite directions
  2. They do not have enough energy so they will undergo annihilation such that either a) The pair eventually annihilate, but can be observed before they do so (i.e. they are real or "on-shell"), and b) The pair annihilate essentially immediately after creation, and are not observed separately but rather modify the behavior of another process (i.e. they are virtual or "off-shell"),
Improve this question
$\endgroup$
6
  • $\begingroup$ You might want to divide the second possibility into two parts, because different physics are involved in each: 2a. The electron and positron eventually annihilate, but can be observed before they do so (i.e. they are real or "on-shell"), and 2b. The electron and positron annihilate essentially immediately after creation, and are not observed separately but rather modify the behavior of another process (i.e. they are virtual or "off-shell"). $\endgroup$
    – probably_someone
    Oct 12, 2018 at 19:04
  • $\begingroup$ So annihilation stakes place regardless $\endgroup$
    – Manny
    Oct 12, 2018 at 19:14
  • 1
    $\begingroup$ Annihilation with some electron is virtually guaranteed, eventually. The indistinguishability of electrons makes the distinction between which electron the positron meets a dodgy proposition, at best. $\endgroup$
    – Sean E. Lake
    Oct 12, 2018 at 19:23
  • $\begingroup$ The gist here that in the presence of other electrons it is unlikely that the same positron and electron annihilate each other. The positron can be annihilated by any electron. $\endgroup$
    – MaxW
    Oct 12, 2018 at 19:24
  • $\begingroup$ So the answer to my question would simply be annihilation takes place $\endgroup$
    – Manny
    Oct 12, 2018 at 19:34

1 Answer 1

Reset to default
1
$\begingroup$

The pair production of electron and positron can only be possible if the incident electromagnetic radiation is 1.02 MeV. The gamma ray photon disappears into the coulomb field and a part of it's energy condenses to an electron-positron pair and the rest part of energy appears in the form of kinetic energy.

from the principle of conservation of energy

$hv = 2m0c^2 +E^++E^-$

For pair production to take place if

$hv > 2m0c^2$

The energy is shared equally among the electron and positron pair. The positron which is repelled by the nucleus, however, receives slightly more Kinetic energy than that of the electron. Here is where the tricky part comes in. However this difference in energies disappear when the antiparticle passes near other nucleus. I gets attracted quickly by the nearest electron and when they join annihilation takes place and an electromagnetic radiation of same energy 1.02 MeV releases. The direction of photons are such as to conserve the linear momentum. So I suppose that whenever a positron creates a pair production with an electron, these charges will annihilate and a high-energy photon come into being again. Hope it helped.

Improve this answer
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.