Does annihilation always produce two photons?

Does annihilation always produce two photons?

Annihilation occurs when a particle and a corresponding antiparticle meet and their mass is converted into radiation energy. Two photons are produced in the process (as a single photon only would take away momentum which isn’t allowed, as no outside forces act).

Can a photon decay into two electrons?

To produce two electrons, therefore, the photon energy must be at least 1.02 MeV. Photon energy in excess of this amount, when pair production occurs, is converted into motion of the electron-positron pair. In this way pair production was first detected (1933).

How is positronium produced?

After a radioactive atom in a material undergoes a β+ decay (positron emission), the resulting high-energy positron slows down by colliding with atoms, and eventually annihilates with one of the many electrons in the material. It may however first form positronium before the annihilation event.

What happens if 2 electrons collide?

Colliding two electrons will always produce two scattered electrons, and it may sometimes produce some photons from initial and final state radiation. Rarely some extra particle-antiparticle pair (like electron and positron) can pop up.

What is the binding energy of positronium?

Energy levels The lowest energy level of positronium (n = 1) is −6.8 eV. The next level is −1.7 eV. The negative sign is a convention that implies a bound state.

Is positronium an atom?

positronium, short-lived hydrogen-like atom composed of an electron and a positron (rather than an electron and a proton) arising as a positron is slowed down in matter and captured by an electron. Two forms are known.

Why are two photons produced?

This release most commonly occurs by producing two particles of light called photons or gamma rays. (The reason TWO photons are produced may seem a bit complicated, but two are needed to conserve both momentum and energy. Briefly, since the electron and the positron were at rest, the total system had no momentum.

How many photons does a photon decay from a parapositronium atom?

Para-positronium can decay into any even number of photons (2, 4, 6.), but the probability quickly decreases as the number increases It is called conservation of angular momentum. An even number of photons allow to match the S=0 M_s=0 angular momentum.

What percentage of positrons self decay into gamma rays?

Only ~0.5% of positrons form ortho -positronium that self-decays (usually into three gamma rays). This natural decay rate of ortho -positronium is relatively slow (~140 ns decay lifetime), compared to the aforementioned pick-off process, which is why the three-gamma decay rarely occurs.

What is the lifetime of a para-positronium atom?

It has a mean lifetime of 0.12 ns and decays preferentially into two gamma rays with energy of 511 keV each (in the center-of-mass frame ). Para -positronium can decay into any even number of photons (2, 4, 6.), but the probability quickly decreases with the number: the branching ratio for decay into 4 photons is 1.439 (2) × 10−6.

What is the spin of a photon when it decays?

Para-positronium can decay into any even number of photons (2, 4, 6,…), but the probability quickly decreases as the number increases It is called conservation of angular momentum. An even number of photons allow to match the S=0 M_s=0 angular momentum. Two photons can add up to spin either 0 or 2 as each carries a spin of 1.