Summary of Pair Production
Production of electron-positron pairs from gamma rays.
the post excerpt ===
An exceptionally useful summary of the concept of energy and mass.
Quote from Victor Toth:
If two colliding photons can create an electron-positron pair, does it mean it's an energy to mass conversion?
Do not think in terms of “energy to mass conversion”.
Mass and energy are equivalent. They literally mean the same thing.
Rest mass is one of the many forms in which energy (or mass) can exist.
For photons, all their energy is in the form of kinetic energy.
For an electron or a positron, some of the energy is in the form of rest mass, the rest is in the form of kinetic energy.
So when two photons collide and produce an electron-positron pair in photon-photon scattering, some of the kinetic energy of the two photons is converted into the rest masses of the electron and positron; the rest becomes the kinetic energy of the electron-positron pair.
Interactions do this all the time: convert one form of energy into another. In the broadest sense, we usually talk about potential energy (i.e., the “potential to do work”) and kinetic energy (the energy of motion, i.e., the “result of work”). All forms of energy fall into these two categories. Rest mass, in particular, is just one of many possible forms of potential energy. Under the right circumstances, it can be converted into kinetic energy, e.g., when an electron and a positron collide and produce a pair of photons. But it is no more mysterious than, say, turning the (gravitational) potential energy of a brick on the tenth floor into kinetic energy as it falls toward the ground and accelerates.
This is definitely not a valid explanation of pair production.
There are no photons involved unless you need that word to be comfortable when not in QM.
Photon is just the QM name for a single wavelength of light - or synchronized perpendicular electric and magnetic fields. QM always needs subatomic particles so it imagines one called a photon to describe this single wavelength. Light is not a particle. The propagating fields have a wavelength and light has wave behaviors.
From U of Oregon===
Pair production is a direct conversion of radiant energy to matter. It is one of the principal ways in which high-energy gamma rays are absorbed in matter. For pair production to occur, the electromagnetic energy, in a discrete quantity called a photon [or a single wavelength], must be at least equivalent to the mass of two electrons.
gamma rays don't just spontaneously produce a pair of subatomic particles when two light paths intersect.
An atom must be present to absorb that energy.
When the wavelength is so short below a threshold (in gamma ray range) and when the radiant energy is absorbed by the atom the result is the pair production.
This is somewhat similar to the photoelectric effect where a wavelength is UV or shorter is absorbed by certain atoms the atom will eject an electron from a shell when absorbing that energy; excess energy beyond that needed for the ejection is passed to the electron in its velocity or kinetic energy.
Here, the gamma ray energy is distributed among the two ejected particles where there is an excess over the required threshold to match the energy equivalent of the two particles. An atom is always required to absorb the energy
Hit back to go to previous page in history.
Here is the list of topics in this Cosmology Topic Group .
Ctrl + for zoom in; Ctrl - for zoom out ; Ctrl 0 for no zoom;
triple-tap for zoom to fit; pinch for zoom change; pinched for no zoom