[Physics] Physics Digest, Vol 1, Issue 10

[Doug Marett]

Hi Carl,

   Is it possible you are leaving out something? From your description it
sounds like when two photons of sufficient energy constructively interfere
in a magnetic field, an electron-positron pair is generated. It was my
impression that this can only occur in the presence of a nucleus (or a
light-matter interaction, not a photon-photon interaction by itself), for
example see the wikipedia page on pair production where it says:
https://en.wikipedia.org/wiki/Pair_production
"The photon must be near a nucleus in order to satisfy conservation of
momentum, as an electron-positron pair producing in free space cannot both
satisfy conservation of energy and momentum."
Is that actually what you mean? Thanks.

Doug




On Fri, Oct 21, 2016 at 10:59 AM, <cj at mb-soft.com> wrote:

> Footnote:  I also clearly do not understand how I should respond to
> anyone's comments, whether to a person individually, or to your structure,
> where the questioner might find it.  Sorry for beingn so ignorant.
>
> As to "creating electrons and positrons", devious Physics Professors have
> many experiments to abuse students with.  Several are variations of this:
> Total up the required energy of the two intended particles, which tells you
> the needed amount of energy you will need from the source radiation (in an
> accelerator).  Such precisely powered photons are then sent through a
> fairly conventional magnetic field.  Whenever any of the enormous number of
> photons you are sending through your viewing field happens to do a
> Constructive Interference, the result is really obvious.  The electron
> curves one way and the positron curves the opposite way, but exactly the
> same.  The curvature and the strength of the magnetic field allows you to
> do calculations to establish that they actually were an electron and a
> proton.
>
> A similar experimemnt which requires much more patience is to create a
> less powerful photon, to try to get it to create a pion+ and pion-.  That
> experiment does not seem to work as often, although I do not know why, but
> the path curvatures are different, which identifies the new particles as
> pions.  The equipment I was allowed to use was not powerful enough to
> create proton and anti-proton pairs, so I do not think I ever did that
> variation.
>
>
> There are also experimental variants where a photon collides with any of
> several particles, but where the total energy available is correct.
>
> Carl Johnson
>
>
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