Photon into matter - antimatter pair production question.

[esmeralda4]

Hi there.

Just a few quick questions:

What causes a photon to become an antimatter / matter pair? Is it just random? Can a photon be influenced to encourage it to change? Also what is the process called? Do we say the photon has decayed? That doesn't seem right to me.

In addition, if the antimatter/matter pair then come back together again do they produce one photon or two?

Many thanks

 

[phyzguy]

Hi there.

Just a few quick questions:

What causes a photon to become an antimatter / matter pair? Is it just random? Can a photon be influenced to encourage it to change? Also what is the process called? Do we say the photon has decayed? That doesn't seem right to me.

It's called "pair production". A free photon can't produce a pair and conserve energy and momentum, so it has to interact with something (usually a nucleus) in order for this to happen. In addition, the photon energy has to be greater than twice the rest mass of the particle. For example, to produce an electron/positron pair, the photon energy needs to be greater than 2x(511 KeV) = 1.022 MeV.

In addition, if the antimatter/matter pair then come back together again do they produce one photon or two?

It produces two photons. Again, producing one photon can't conserve energy and momentum.