FAQ - Photons and matter.

[Richard Hull]

A quick rinse in simple photonics for the less fortunate in physics here.

Photons are electromagnetic energy, (radio waves, light, x-rays, gamma rays), and are solely derived from kinetic motion of charged particles at the point of their origin. They have no natural inherent existence.

Photon energy is strictly a function of frequency of the electromagnetic oscillation that defines the energy bundle.

Photons can act as an intermediary, transforming kinetic energy of charged particles into a unique form that can carry that energy over rather large distances relatively intact. Upon interacting with distant mater, the energy can be down-converted back into kinetic energy or used to separate charges in dead or neutral matter. While its existance is but a secondary reaction of primary forces, it serves a very useful function.

Photons are rarely observed in and amongst condensed matter environments to exceed an energy of 1Mev. It is, indeed, very difficult to generate photons over 1 mev in an earth based process. Nature forces photons over 1 mev to degrade in even the most tenuous of matter environments.

The three degrading mechanisms are in order of observed frequency......

1. Photo-electric effect
2. Compton scattering
3. Pair-production

The photoelectric effect is a bulk matter reaction and is the manner in which most observed photons are degraded back into kinetic energy and separation of charge. Here, the photos degrade to virtually zero energy by ejecting outer shell electrons in the case of UV radiation on up to x-rays. Charge is thus separated and the mass of the electron is shot out away from the surface of the material. In most sub UV cases, there might be a mere excitation of electrons and the radiation steps down to an IR photon or a radio wave. There are a lot of possiblities in bulk matter.

If the incoming Photon is energetic enough to interact more with the nucleus or the inner shell electrons sufficiently, an inner shell electron can be ejected and the photon degraded to a low energy x-ray and then this releases more outer shell electrons. This process is Compton scattering and will ultimately continue into bulk matter until the photoelectric effect degrades it to free electrons and excitation of electrons and sub IR radiation.

Finally, should a photon of over about 1.2 mev even approach bulk matter, a reaction can occur where the photon degrades producing a 512Kev electron and a 512kev positron. This state of affairs is very short lived as it violates a thermodynamic arrow directing most universal events.

As a matter of some importance is the observation that mass in virtually all e=mc^2 reactions is a MASS DEFECT exchange and NOT charged matter being permenantly ground up or created. A very significant observation.

The positron, in fractions of a microsecond, finds another electron and annihilates producing two energy degraded photons. Thus, the universe is as it was before the pair production ever occured. (i.e. same number of universal electrons, same amount of energy, and no new mass.

The net effect is one photon of over 1.2 mev was stepped down via pair production to two degraded photons. Again, no new matter was created, no net charge created or destroyed. no net energy created or destroyed and no new particles in the universe.

Again, no ultra high energy photon is ever seen to pair produce in a perfect vacuum. The presence of mater is demanded to force this process.

So you can see that photons can be used in a number of different ways to convert their energy back into motion of mass and separation of charge. Upon doing this, the photon is degraded and at some point has so little energy it is virtually incapable of any recognizable effect on matter. If the universe will ever die it will most likely die by this slow loss of photonic energy in the sub, sub, electron volt level. (heat death).

The photon's primary reason for being is to KEEP THE STEW STIRRED AT GREAT RANGE! The photon can be said to be born to be degraded. The force of charge can only stir and interact at short range. Gravity, per unit atom is also a short range force.

However THE STEW IS SELF STIRRING AT ALL RANGES for it is the alternating, mutually exclusive action of charge and gravity that make the photons in the first place. It is part of the grand beauty of it all. Looking deeper than the simple nuclear particles is not a particularly needed or exciting endeavor. It is not observable and, therefore, any conjecture to a finer structure, no matter how well crafted, will forever remain conjecture.

Richard Hull

[Alex Aitken]

Hope to dont mind me chiming in, but a few things need clarifying.

For clarity, photoelectric effect destroys the photon, you end up with charged particles having inherited the energy as kinetic.

Compton scattering produces charged particles with some of the kinetic energy, and a lower energy photon. There are also conservation of momentum effects that determine allowed directions.

The clarification I think is important to the reading of gamma spectroscopy.

Gamma ray over 1.024 will produce pairs. I know you did the math in your head because I made exactly the same mistake.

Its not really correct to say 512kev electron. As this would imply an electron with 512kev of kinetic energy. In fact it will have very little energy, only what the gamma had left over, 512kev is the energy needed to create the electron and the same for the positron.

There is no problem with the thermodynamic arrow, its only because our bit of the universe happens to have a lot of free electrons in it that the positron doesnt last long. Theres nothing intrinsicaly unstable about the positron. Entropy is satified in its formation because 2 particals have more entropy that the one gamma it was created from. When the positron does hit an electron, what will be produced virtually all the time will be 2 512kev photons in neerly oppasit directions. At this point, no new matter has been created. While the positron was in existance energy has been turned into matter - an electron has positive mass, the positron has positive mass. Overall charge in conserved of course.

[Richard Hull]

I have ammended my original appropriately. Thanks for the corrective suggesstions.

All photons degrade to nothing but kinetic energy of matter particles. All pair production degradation of photons winds up ultimately as compton scattering and all compton scattering winds up as photo electric effect and so on until there is nothing left. They are born "of the mix" to "stir the mix", and stir the mix, they do.

Regarding the positron or any antimatter particles...............

There is no reason to assume any form of universal stability for these particles based on any observation made by man.

Antiparticles are always created out of photon/matter reactions. Therefore, there are always observed extant, matter particles vastly in excess needed to instantly eviscerate an antiparticle.

Photons of high energy MUST be in the presence of matter, as observed, to pair produce. They can't do it on their own.

We have never observed a region of space that heralds stable antimatter. Until we do, speaking of stable antiparticles is a theory.

We might imagine any number of unobserved possibilities..... And we often do. Repeating some of those ideas often enough, by the properly annointed authorities can, sometimes, by fete, give the impression of universal agreement on totally unobserved events or concepts.

I have chosen a path of working with observed and repeatable results in science and letting accepted science and accepted scientific theories take a back seat where they belong.

Richard Hull