In the medical diagnostic technique known as positron emission tomography (PET), a positron and an electron annihilate each other and two $\gamma$-ray photons are emitted. What is the angle between the momentum vectors of the two photons?
A)zero degrees
B)45°
C)90°
D)180°
E)Any angle is possible.

Question

Quizplus · Accepted Answer

In PET scans, when a positron and an electron annihilate, they produce two gamma-ray photons that are emitted in opposite directions to conserve momentum, resulting in an angle of 180° between their momentum vectors.

In the Medical Diagnostic Technique Known as Positron Emission Tomography γ\gammaγ

In the Medical Diagnostic Technique Known as Positron Emission Tomography $\gamma$