Question

Explain what we mean by the 6MeV spectrum being harder than the 6MV spectrum, also explain why the 6MV photon beam is more penetrating.

Answer 1

A 6 MeV spectrum indicates a beam of electrons with energy 6 MeV( MeV=mega electron volts).

But a 6 MV (MV= mega volts) spectrum generally indicates a beam of electromagnetic waves which will produce photons of maximum energy 6 MeV, not more than that. The mean energy of the electromagnetic wave in this case is about 1/3rd of the maximum.

This implies the effective energy of the 6MV beam is less than that of 6MeV beam, and hard beam is the one with higher energy. so, 6MeV beam is harder.

Penetration of the beam depends on the speed of beam in the medium, the faster it travels, the more it can penetrate . Photons travel faster than any other particles in a medium, given the same energy, so a photon beam would always be more penetrating.