When a positron collides with an electron, they annihilate each other, resulting in the emission of two gamma rays.

Here's why:

* Annihilation: Positrons and electrons are antiparticles of each other. When they collide, their masses are converted entirely into energy.

* Conservation of Momentum: To conserve momentum, the energy cannot be released in a single direction. Instead, it is released as two photons (gamma rays) traveling in opposite directions.

* Energy Calculation: The energy of each gamma ray is equal to the rest mass energy of the electron (or positron), which is 511 keV (kilo-electron volts).

This process is called pair annihilation, and it's a fundamental phenomenon in particle physics.