# That the two gamma rays are only one possible decay mode?

by redwraith94
Tags: antimatter, decay, gamma, mode, rays
 P: 166 You don't have to have photons released in multiples of two for momentum conservation - you could quite happily imagine a singular photon flying in the +y direction, and two photons going -y -x and -y +x respectivaly. Assuming this pair are of equal momentum, the angle between these two and the y axis would have to be the same, let's call it $\theta$. Suppose the momentum of the photon in the +y direction has momentum $p_0$ and the momentum of each of the other photons is $p_1$ we then have the conidition (for conservation of momentum in the y axis): $$2p_1\cos{\theta}=p_0$$ It's easy to generalise to any photon momenta.
 P: 685 Hello redwraith94, when a positron and electron collide, a so-called positronium can be generated. Positronium is like a hydrogen atom, but there the electron and and positron move around their common center of mass. http://scienceworld.wolfram.com/phys...sitronium.html There are two different kinds of positronium: (i) para-positronium: the positronium decays to two gamma photons, each photon with an energy of 511keV. And the photons decay into opposite directions. (ii) ortho-positronium: this positronium has a total spin of $1\hbar$, so the two photon decay is forbidden. Instead, ortho-positronium decays to three gamma photons.