Final answer:
Un-collided gamma flux from a point source refers to the gamma rays emitted from a source before they have interacted with any matter, which is fundamental in studying the properties of the gamma source itself.
Step-by-step explanation:
Un-collided gamma flux from a point source refers to the gamma flux before any collisions. This means that the gamma rays emitted from a point source, such as a radioactive nucleus, have not yet interacted with any matter. Since gamma rays are a form of high-energy electromagnetic radiation produced by nuclear interactions, they are capable of penetrating deeply into matter. When we talk about un-collided gamma flux, we're considering gamma rays that have not yet been absorbed or scattered by any intervening material. The importance of measuring un-collided gamma flux lies in its application to understanding the inherent properties of the gamma source before its rays undergo interactions that change their paths or energies.