Why can you never create a single electron but you can easily create electron positron pairs?

A single electron sitting motionless in space cannot give off a photon and recoil otherwise we get energy for nothing. In another frame this electron is moving with momentum and energy even so it still cannot shoot off a single photon because the physics of the original centre of mass frame.

Why pair production is not possible in free space?

Then it has energy E=pc. Now imagine you want to produce a particle-antiparticle pair of non-zero mass m (assume without loss of generality that the momentum is so that py1=py2=0). Then, according to momentum conservation, their momenta have to be pz1+pz2=p, px1+px2=0.

How do you make an electron positron pair?

In the pair production process, an incident gamma ray of sufficiently high energy is annihilated in the Coulomb field of a nearby charged particle, resulting in the creation of an electron–positron pair.

Why must a positron be created when an electron is created?

The photon must be near a nucleus in order to satisfy conservation of momentum, as an electron–positron pair produced in free space cannot satisfy conservation of both energy and momentum. Because of this, when pair production occurs, the atomic nucleus receives some recoil.

Why can’t electron positron pair production process occur in vacuum?

Originally Answered: why does pair production cannot occur in vacuum? Because the pair production is a concept of conservation of energy and momentum. But in vacuum we can’t conserv it . In vaccum we don’t want any any type of KE energy to move in the absent of the air.

What happens to positron after pair production?

For pair production to occur, the electromagnetic energy, in a discrete quantity called a photon, must be at least equivalent to the mass of two electrons. The positron that is formed quickly disappears by reconversion into photons in the process of annihilation with another electron in matter.

Why can’t electron-positron pair production process occur in vacuum?

What happens when a positron and electron come together?

When they meet, the positron and the electron, which are Antiparticles of each other, destroy themselves mutually, they annihilate. Two annihilation gamma with equal energy are also emitted back to back.

Why the pair production process does not take place in vacuum short answer?

Reason: The pair production can not take place in a vacuum or space. The pair production can happen only in the presence of an external object like an atomic nucleus which can experience some recoil during the collision process to conserve the energy and the momentum at the same time.

What is produced when a positron collides with an ordinary electron?

The most common annihilation on Earth occurs between an electron and its antiparticle, a positron. A positron, which may originate in radioactive decay or, more commonly, in the interactions of cosmic rays in matter, usually combines briefly with an electron to form a quasi-atom called positronium.