Severely SNIPPED


When a photon imparts its energy to an electron, doesn't that "combine"
the two energies? What am I missing? Also, please describe how a photon
could impart half its energy to an electron. Is the result half a photon?

A photon is modeled as energy as a function of wavelength.

There are high energy photons, gamma rays. [energies at 0.5 MeV and higher]

There are medium energy photons, X rays. [energies at 0.5 KeV to 0.5 MeV]

There are low energy photons, radio [EM] waves. [Energies below 0.05 KeV]

Electrons are bound in their atomic orbits with energies from a few tens
of eVs to about 300 KeV. [My cross section tables were retired when I
was.][And these energy levels are different for all materials.]

Apply conservation of energy, under the poor assumption of a 100%
absorption factor [actually a probability distribution is more
appropriate] and it's easy to see that gamma rays surrender ONLY a
portion of their energy as they interact with electrons. Elementary
Example: 1 MeV photon interacts with and 100% ionizes a H atom releasing
2 electrons totaling about 40 KeV. So, the forward traveling photon's
energy changed from 1 MeV to 960 KeV. [i.e. a change in wavelength
occurred for the photon ... in radio terms it retuned to a lower
frequency band.] Conservation of energy applies to the photon.
Conservation of energy also applies to the ionized electron. When it
recombines with an ionized H atom the energy may be released in various
forms including a 40 KeV photon, or heat, or both.

Medium energy photons also conserve energy. The Absorptions cross
sections for most materials are several orders of magnitude larger than
for gamma rays but the principle is still the same. There is an
additional case where a photon may be absorbed but the energy is
insufficient to fully ionized the atom. In these cases there is a
transient increase to an excited state for the electrons and a
subsequent release of energy, mostly as heat but also a lower energy
photon [EM noise source] is created.

So, Cecil to answer your basic question: "The energy in the photon
changes [decreases] when there is an interaction with an electron."

Corollary: "The energy level in the electron changes [increases] when it
absorbs energy from a photon."

Deacon Dave